LTC3553 Micropower USB Power Manager With Li-Ion Charger, LDO and Buck Regulator DESCRIPTION FEATURES

Transcription

1 FEATURES n 2μA Standby Mode Quiescent Current (All Outputs On) n Seamless Transition Between Input Power Sources: Li-Ion/Polymer Battery and USB n 24mΩ Internal Ideal Diode Provides Low Loss PowerPath n High Effi ciency 2mA Buck Regulator n 5mA Low Dropout (LDO) Linear Regulator n Pushbutton On/Off Control With System Reset n Full Featured Li-Ion/Polymer Battery Charger n Programmable Charge Current With Thermal Limiting n Instant-On Operation With Discharged Battery n 3mm 3mm.75mm 2-Pin QFN Package APPLICATIONS n USB-Based Handheld Products n Portable Li-Ion/Polymer Based Electronic Devices n Wearable Electronics n Low Power Medical Devices Micropower USB Power Manager With Li-Ion Charger, LDO and Buck Regulator DESCRIPTION The LTC 3553 is a micropower, highly integrated power management and battery charger IC for single-cell Li-Ion/Polymer battery applications. It includes a PowerPath manager with automatic load prioritization, a battery charger, an ideal diode and numerous internal protection features. Designed specifically for USB applications, the power manager automatically limits input current to a maximum of either ma or 5mA. Battery charge current is automatically reduced such that the sum of the load current and the charge current does not exceed the selected input current limit. The also includes a synchronous buck regulator, a low dropout linear regulator (LDO), and a pushbutton controller. With all supplies enabled in standby mode, the quiescent current drawn from the battery is only 2μA. The is available in a 3mm 3mm.75mm 2-pin QFN package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and PowerPath, Hot Swap and Bat-Track are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 65228, 67364, 54878, 63466, , , 7539 and other patents pending. TYPICAL APPLICATION 4.35V TO 5.5V USB INPUT k k T μf.87k DIGITAL CONTROL V BUS NTC PROG SEQ HPWR SUSP LDO_ON BUCK_ON STBY PBSTAT V OUT CHRG BAT BVIN V INLDO LDO LDO_FB SW + μh μf Li-Ion BATTERY pf 2.2μF 2.5M 649k 332k 3.3V 5mA 4.7μF SYSTEM LOAD.2V 2mA μf BATTERY DRAIN CURRENT (μa) Battery Drain Current vs Temperature V BAT = 3.8V STBY = 3.8V REGULATORS LOAD = ma BUCK AND LDO ON ONLY LDO ON ONLY BUCK ON BUCK AND LDO OFF 2 HARD RESET TEMPERATURE ( C) 3553 TAb ON/OFF ON BUCK_FB 3553 TAa 649k

2 ABSOLUTE MAXIMUM RATINGS (Notes, 2, 3) V BUS, V OUT t < ms and Duty Cycle < %....3V to 7V Steady State....3V to 6V BAT, NTC, CHRG, SUSP, PBSTAT, ON, BUCK_FB, LDO_FB....3V to 6V BUCK_ON, LDO_ON, STBY, SEQ, HPWR, BVIN, V INLDO, LDO (Note 4)....3V to V CC +.3V I BAT...A I SW (Continuous)...3mA I LDO (Continuous)...75mA I CHRG, I PBSTAT...75mA Operating Temperature Range... 4 C to 85 C Junction Temperature... C Storage Temperature Range C to 25 C PIN CONFIGURATION HPWR SEQ PBSTAT ON LDO_ON TOP VIEW V BUS SUSP VOUT BAT PROG NTC 2 4 CHRG 3 2 GND 3 SW 4 2 BVIN 5 V INLDO STBY BUCK_ON BUCK_FB LDO_FB LDO UD PACKAGE 2-LEAD (3mm 3mm) PLASTIC QFN T JMAX = C, θ JA = 7 C/W EXPOSED PAD (PIN 2) IS GND, AND MUST BE SOLDERED TO PCB GND ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE EUD#PBF EUD#TRPBF LFYB 2-Lead (3mm 3mm) Plastic QFN 4 C to 85 C EPD#PBF EPD#TRPBF FHST 2-Lead (3mm 3mm) Plastic UTQFN 4 C to 85 C (OBSOLETE) Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: POWER MANAGER ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2), V BUS = 5V, V BAT = 3.8V, HPWR = SUSP = BUCK_ON = LDO_ON = V, R PROG =.87k, STBY = high, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS No-Load Quiescent Currents I BATQ Battery Drain Current (Note 5) Buck and LDO Shutdown, Hard Reset Buck and LDO Shutdown Buck and LDO Enabled, Standby Mode Buck and LDO Enabled Buck Enabled, LDO Shutdown LDO Enabled, Buck Shutdown I OUT = I SW = I LDO = V BUS = V, Hard Reset V BUS = V V BUS = V, BUCK_ON = LDO_ON = STBY = 3.8V V BUS = V, BUCK_ON = LDO_ON = 3.8V, STBY = V V BUS = V, BUCK_ON = 3.8V, LDO_ON = V STBY = V V BUS = V, LDO_ON = 3.8V, BUCK_ON = V, STBY = V I BATQC Battery Drain Current, V BUS Available V BAT = V FLOAT, Timer Timed Out 5 8 μa I BUSQ V BUS Input Current ma, 5mA Modes Charger On Timer Timed Out SUSP = 5V (Suspend Mode) μa μa μa μa μa μa μa μa μa 2

3 POWER MANAGER ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2), V BUS = 5V, V BAT = 3.8V, HPWR = SUSP = BUCK_ON = LDO_ON = V, R PROG =.87k, STBY = high, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I BVINQ BVIN Input Current Buck Shutdown Buck Enabled, Standby Mode Buck Enabled V BUS = V, V BVIN = 3.8V, I SW = (Note 8) BUCK_ON = V BUCK_ON = STBY = 3.8V BUCK_ON = 3.8V, STBY = V μa μa μa I VINLDOQ V INLDO Input Current LDO Shutdown LDO Enabled, Standby Mode LDO Enabled Input Power Supply V BUS = V, V INLDO = 3.8V, I LDO = (Note ) LDO_ON = V LDO_ON = STBY = 3.8V LDO_ON = 3.8V, STBY = V V BUS Input Supply Voltage V I BUS(LIM) Total Input Current HPWR = V (ma) HPWR = 5V (5mA) V UVLO V BUS Undervoltage Lockout Rising Threshold Falling Threshold 3.5 V DUVLO V BUS to BAT Differential Undervoltage Lockout R ON_ILIM Input Current Limit Power FET On-Resistance (Between V BUS and V OUT ) Battery Charger V FLOAT V BAT Regulated Output Voltage l l 8 4 Rising Threshold Falling Threshold μa μa μa ma ma 3.9 V mv 3 mv mv 35 mω V T A 85 C V I CHG Constant-Current Mode Charge Current R PROG =.87k, T A 85 C ma V PROG V PROG,TRKL PROG Pin Servo Voltage PROG Pin Servo Voltage in Trickle Charge V BAT < V TRKL. h PROG Ratio of I BAT to PROG Pin Current 75 ma/ma I TRKL Trickle Charge Current V BAT < V TRKL ma V TRKL Trickle Charge Threshold Voltage V BAT Rising V BAT Falling V V 3 V V ΔV RECHRG Recharge Battery Threshold Voltage Threshold Voltage Relative to V FLOAT mv t TERM Safety Timer Termination Period Timer Starts when V BAT = V FLOAT 5mV Hour t BADBAT Bad Battery Termination Time V BAT < V TRKL Hour h C/ End-of-Charge Indication Current Ratio (Note 6) ma/ma R ON_CHG Battery Charger Power FET I BAT = 2mA 22 mω On-Resistance (Between V OUT and BAT) T LIM Junction Temperature in Constant C Temperature Mode NTC V COLD Cold Temperature Fault Threshold Voltage Rising NTC Voltage Hysteresis %V BUS %V BUS V HOT Hot Temperature Fault Threshold Voltage Falling NTC Voltage Hysteresis V DIS NTC Disable Threshold Voltage Falling NTC Voltage Hysteresis l %V BUS %V BUS 2.2 %V BUS mv I NTC NTC Leakage Current V NTC = V BUS = 5V 5 5 na 3

4 POWER MANAGER ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2), V BUS = 5V, V BAT = 3.8V, HPWR = SUSP = BUCK_ON = LDO_ON = V, R PROG =.87k, STBY = high, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Ideal Diode V FWD Forward Voltage Detection (Note 2) 5 mv R DROPOUT Diode On-Resistance, Dropout I OUT = 2mA, V BUS = V 24 mω I MAX Diode Current Limit (Note 7) A Logic Inputs (HPWR, SUSP) V IL Input Low Voltage.4 V V IH Input High Voltage.2 V R PD Internal Pull-Down Resistance 4 MΩ Logic Output (CHRG) V OL Output Low Voltage I CHRG = 5mA mv I CHRG Output Hi-Z Leakage Current V BAT = 4.5V, V CHRG = 5V μa BUCK REGULATOR ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2). BUCK_ON = V OUT = BVIN = 3.8V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS BVIN Input Supply Voltage (Note 9) l V V OUT UVLO V OUT Undervoltage Lockout V OUT Falling V OUT Rising f OSC Oscillator Frequency MHz I BUCK_FB BUCK_FB Input Current (Note 8).5.5 μa R SW_PD SW Pull-Down in Shutdown BUCK_ON = V kω Logic Input Pin (STBY) Input High Voltage.2 V Input Low Voltage.4 V Input Current μa Buck Regulator in Normal Operation (STBY Low) I LIM Peak PMOS Current Limit BUCK_ON = 3.8V (Note 7) ma V BUCK_FB Regulated Feedback Voltage BUCK_ON = 3.8V l mv D MAX Max Duty Cycle % R P R DS(ON) of PMOS I SW = ma. Ω R N R DS(ON) of NMOS I SW = ma.7 Ω Buck Regulator in Standby Mode (STBY High) Feedback Voltage Threshold BUCK_ON = 3.8V, V BUCK_FB Falling l mv Short-Circuit Current 3 5 ma Standby Mode Dropout Voltage BUCK_ON = 2.9V, I SW = ma, V BUCK_FB =.76V, V OUT = 2.9V, BVIN = 2.9V 5 mv V V 4

5 LDO REGULATOR ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2). LDO_ON = V OUT = V INLDO = 3.8V, STBY = V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V INLDO Input Voltage Range (Note 9) l V V OUT UVLO V OUT Undervoltage Lockout V OUT Falling V OUT Rising V LDO_FB Regulated Feedback Voltage I LDO = ma, STBY High or Low (Note ) l mv V LDO_FB Line Regulation I LDO = ma, V INLDO =.65V to 5.5V (Note ).7 mv/v V LDO_FB Load Regulation I LDO = ma to 5mA (Note ).25 mv/ma I LDO_FB Feedback Pin Input Current 5 5 na I LDO_OC Available Output Current l 5 ma I LDO_SC Short-Circuit Output Current (Note 7) 3 ma V DROP Dropout Voltage (Note 3) I LDO = 5mA, V INLDO = 3.8V I LDO = 5mA, V INLDO = 2.5V I LDO = 75mA, V INLDO =.8V t LDO_SS Soft-Start Time.2 ms R LDO_PD Output Pull-Down Resistance in Shutdown LDO_ON = V kω V V mv mv mv PUSHBUTTON INTERFACE ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2). V BAT = 3.8V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Pushbutton Pin (ON) V CC_PB Pushbutton Operating Supply Range (Notes 4, 9) l V V ON_TH ON Threshold Rising ON Threshold Falling.4.2 V V I ON ON Input Current V ON = V CC (Note 4) μa R PB_PU Pushbutton Pull-Up Resistance Pull-Up to V CC (Note 4) kω Logic Input Pins (BUCK_ON, LDO_ON, SEQ) Input High Voltage.2 V Input Low Voltage.4 V Input Current μa Status Output Pin (PBSTAT) I PBSTAT PBSTAT Output High Leakage Current V PBSTAT = 3V μa V PBSTAT PBSTAT Output Low Voltage I PBSTAT = 3mA..4 V 5

6 PUSHBUTTON INTERFACE ELECTRICAL CHARACTERISTICS The l denotes specifi cations that apply over the full operating temperature range, otherwise specifi cations are at T A = 25 C (Note 2). V BAT = 3.8V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Pushbutton Timing Parameters (Note ) t ON_PBSTATL Minimum ON Low Time to Cause ON Brought Low During Power-On (PON) or 5 ms PBSTAT Low Power-Up (PUP, PUP2) States t ON_PBSTATH Delay from ON High to PBSTAT High Power-On (PON) State, After PBSTAT Has Been Low for at Least t PBSTAT_PW 9 μs t ON_PUP Minimum ON Low Time to Enter Power-Up (PUP or PUP2) State Starting in the Hard Reset (HR) or Power-Off (POFF) States t ON_HR Minimum ON Low Time to Hard Reset ON Brought Low During the Power-On (PON) or Power-Up (PUP, PUP2) States t PBSTAT_PW PBSTAT Minimum Pulse Width Power-On (PON) or Power-Up (PUP, PUP2) States t EXTPWR t PON_UP Power-Up from USB Present to Power-Up (PUP or PUP2) State BUCK_ON or LDO_ON High to Power-On State Starting in the Hard Reset (HR) or Power-Off (POFF) States Starting with Both BUCK_ON and LDO_ON Low in the Power-Off (POFF) State 4 ms s 4 5 ms ms 9 μs t PON_DIS_BUCK BUCK_ON Low to Buck Disabled μs t PON_DIS_LDO LDO_ON Low to LDO Disabled μs t PUP Power-Up (PUP or PUP2) State Duration 5 s t PDN Power-Down (PDN or PDN2) State Duration s Note : Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The E is tested under pulsed load conditions such that T J T A. The E is guaranteed to meet specifi cations from C to 85 C junction temperature. Specifi cations over the 4 C to 85 C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The junction temperature (T J, in C) is calculated from the ambient temperature (T A, in C) and power dissipation (P D, in Watts) according to the formula: T J = T A + (P D θ JA ), where θ JA (in C/W) is the package thermal impedance. Note that the maximum ambient temperature consistent with these specifi cations is determined by specifi c operating conditions in conjunction with board layout, the rated package thermal impedance and other environmental factors. Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperatures will exceed C when overtemperature protection is active. Continuous operation above the specifi ed maximum operating junction temperature may result in device degradation or failure. Note 4: V CC is the greater of V BUS or BAT. Note 5: Total battery drain current represents the load a battery will see in application due to quiescent currents drawn by the BAT pin (I BATQ ) plus any current drawn from the V OUT pin. In applications where the buck input (BVIN pin) and LDO input (V INLDO pin) are connected to the PowerPath output (V OUT pin), the quiescent currents on BVIN and V INLDO must be added to I BATQ to get the actual battery drain current that will be seen in application. Note 6: h C/ is expressed as a fraction of programmed full charge current with specifi ed PROG resistor. Note 7: The current limit features of this part are intended to protect the IC from short term or intermittent fault conditions. Continuous operation above the absolute maximum specifi ed pin current rating may result in device degradation or failure. Note 8: BUCK_FB High, Not Switching Note 9: V OUT not in UVLO. Note : Measured with the LDO operating in unity-gain, with its output and feedback pins tied together. Note : See the Operation section of this data sheet for detailed explanation of the pushbutton state machine and the effects of each state on regulator and power manager operation. Note 2: If V BUS < V UVLO then V FWD = and the forward voltage across the ideal diode is equal to its current times R DROPOUT. Note 3: Dropout voltage is the minimum input to output voltage differential needed for the LDO to maintain regulation at a specifi ed output current. When the LDO is in dropout, its output voltage will be equal to: V INLDO V DROP. 6

7 TYPICAL PERFORMANCE CHARACTERISTICS T A = 25 C, unless otherwise specifi ed. I BUS (μa) V BUS Supply Current vs Temperature V BUS = 5V HPWR = L TEMPERATURE ( C) I BUS (μa) V BUS Supply Current vs Temperature (Suspend Mode) 75 V BUS = 5V TEMPERATURE ( C) BATTERY DRAIN CURRENT (μa) Battery Drain Current vs Temperature V BAT = 3.8V STBY = 3.8V REGULATORS LOAD = ma BUCK AND LDO ON ONLY LDO ON ONLY BUCK ON BUCK AND LDO OFF 2 HARD RESET TEMPERATURE ( C) 3553 G 3553 G G3 I BAT (μa) Battery Drain Current vs Temperature (Suspend Mode) 75 V BUS = 5V V BAT = 3.8V TEMPERATURE ( C) I VBUS (ma) V BUS Current Limit vs Temperature V BUS = 5V HPWR = H HPWR = L TEMPERATURE ( C) CURRENT (ma) V BUS and Battery Current vs Load Current R PROG =.87k I VBUS I LOAD I BAT (CHARGING) I BAT (DISCHARGING) LOAD CURRENT (ma) 3553 G G G R ON from V BUS to V OUT vs Temperature I OUT = 2mA 48 4 Charge Current vs Temperature (Thermal Regulation) 6 5 Battery Charge Current and Voltage vs Time 92mAhr CELL V BUS = 5V R PROG =.87k CHRG 6 5 R ON (Ω) I BAT (ma) BATTERY CURRENT (ma) V BAT SAFETY TIMER TERMINATION VOLTAGE (V) TEMPERATURE ( C) 8 V BUS = 5V HPWR = H R PROG =.87k TEMPERATURE ( C) C/ I BAT TIME (hour) 3553 G G G9 7

8 TYPICAL PERFORMANCE CHARACTERISTICS T A = 25 C, unless otherwise specifi ed. V FLOAT (V) V FLOAT Load Regulation V BUS = 5V HPWR = H V FLOAT (V) Battery Regulation (Float) Voltage vs Temperature V BUS = 5V I BAT = 2mA I BAT (ma) Battery Charge Current vs Battery Voltage V BUS = 5V HPWR = H R PROG =.87k I BAT (ma) TEMPERATURE ( C) V BAT (V) G 3553 G 3553 G2 3 Forward Voltage vs Ideal Diode Current V BUS Connect Waveform V BUS Disconnect Waveform V FWD (mv) V BUS = 5V V BUS = V 5V 3.8V V V BUS V OUT LDO (3.3V) BUCK (.2V) 5V 3.8V V V BUS V OUT VOUT LDO (3.3V) BUCK (.2V) V BUS I BAT (ma) G3 V BAT = 3.8V I LDO = ma I BUCK = ma HPWR = HIGH SUSP = LOW STBY = LOW 2μs/DIV 3553 G4 V BAT = 3.8V I LDO = ma I BUCK = ma HPWR = HIGH SUSP = LOW STBY = LOW μs/div 3553 G5 5V HPWR I BUS.5A/DIV A I BAT.5A/DIV A Switching from ma Mode to 5mA Mode V BAT = 3.75V I OUT = 5mA R PROG = 2k SUSP = LOW ms/div 3553 G6 5V SUSP 5V V OUT I BUS A.5A/DIV I BAT A.5A/DIV Switching from Suspend Mode to 5mA Mode V BAT = 3.75V I OUT = 5mA R PROG = 2k HPWR = HIGH ms/div 3553 G7 OSCILLATOR FREQUENCY (MHz) Oscillator Frequency vs Temperature 2.7V 3.8V 5.5V TEMPERATURE ( C) 3553 G8 8

9 TYPICAL PERFORMANCE CHARACTERISTICS T A = 25 C, unless otherwise specifi ed. EFFICIENCY (%) Buck Regulator 3.3V Output Effi ciency vs Load STBY = L.. 3.8V 5V BUCK LOAD (ma) 3553 G9 EFFICIENCY (%) Buck Switching Regulator 2.5V Output Effi ciency vs Load STBY = L 2 3.8V 5V.. BUCK LOAD (ma) 3553 G2 EFFICIENCY (%) Buck Switching Regulator.8V Output Effi ciency vs Load STBY = L 2 3.8V 5V.. BUCK LOAD (ma) 3553 G2 EFFICIENCY (%) Buck Regulator.2V Output Effi ciency vs I LOAD STBY = L.. 3.8V 5V BUCK LOAD (ma) BVIN SUPPLY CURRENT (μa) Buck Regulator Burst Mode Operation BVIN Supply Current NO LOAD STBY = L 45 C 25 C 9 C BVIN SUPPLY VOLTAGE (V) BVIN SUPPLY CURRENT (μa) Buck Regulator Standby Mode BVIN Supply Current NO LOAD STBY = H 45 C 25 C 9 C BVIN SUPPLY VOLTAGE (V) 3553 G G G24 SHORT CIRCUIT CURRENT (ma) Buck Regulator Short-Circuit Current vs Temperature STBY = L TEMPERATURE ( C) 3553 G25 V OUT 5mV/DIV (AC) BUCK (.2V) mv/div (AC) 5mA I BUCK μa Buck Regulator Output Transient (STBY = High) V BUS = V V BAT = 3.8V STBY = HIGH 5μs/DIV 3553 G26 V OUT 5mV/DIV (AC) BUCK (.2V) 5mV/DIV (AC) ma I BUCK ma Buck Regulator Output Transient (STBY = Low) V BUS = V V BAT = 3.8V STBY = LOW μs/div 3553 G27 Burst Mode is a registered trademark of Linear Technology Corporation. 9

10 TYPICAL PERFORMANCE CHARACTERISTICS T A = 25 C, unless otherwise specifi ed. SWITCH IMPEDANCE (Ω) Buck Regulator Switch Impedance vs Temperature BVIN = 3.2V STBY = L PMOS NMOS FEEDBACK VOLTAGE (V) Buck Regulator Feedback Voltage vs Output Current 3.8V 5V STBY = L BUCK OUTPUT.5V/DIV V LDO OUTPUT V/DIV V Power-Up Sequencing with SEQ Low μs/div 3553 G TEMPERATURE ( C).78. OUTPUT CURRENT (ma) FRONT PAGE APPLICATION CIRCUIT 3553 G G29 BUCK OUTPUT.2V AT ma 2mV/DIV (AC) LDO OUTPUT 3.3V AT ma 5mV/DIV (AC) HIGH STBY LOW Regulator Output Transient During STBY Transition V BUS = V V BAT = 3.8V 5μs/DIV 3553 G3 DROPOUT VOLTAGE (mv) Buck Regulator Dropout Voltage in Standby Mode vs Load Current BVIN = 2.9V 45 C 25 C 9 C LOAD CURRENT (ma) BUCK OUTPUT.5V/DIV V LDO OUTPUT V/DIV V Power-Up Sequencing with SEQ High μs/div FRONT PAGE APPLICATION CIRCUIT 3553 G G32 FEEDBACK VOLTAGE (mv) Regulated LDO Feedback Voltage vs Temperature LDO Load Regulation LDO Short-Circuit Current μa LDO LOAD V INLDO = 2.9V V INLDO = 3.8V V INLDO = 5V LDO OUTPUT VOLTAGE (mv) LDO IN UNITY GAIN V INLDO = 3.8V V OUT = V BAT = 3.8V V BUS = V STBY = LOW LDO SHORT-CIRCUIT CURRENT (ma) TEMPERATURE ( C) LDO LOAD (ma) V INLDO (V) 3553 G G G36

11 TYPICAL PERFORMANCE CHARACTERISTICS T A = 25 C, unless otherwise specifi ed. LDO DROPOUT VOLTAGE (mv) LDO Dropout Voltage at V INLDO = 3.8V 45 C 25 C 9 C LDO DROPOUT VOLTAGE (mv) LDO Dropout Voltage at V INLDO = 2.5V 45 C 25 C 9 C LDO DROPOUT VOLTAGE (mv) LDO Dropout Voltage at V INLDO =.8V 45 C 25 C 9 C LDO LOAD (ma) LDO LOAD (ma) LDO LOAD (ma) 3553 G G G39 LDO Output Transient (STBY = Low) LDO Output Transient (STBY = High) LDO Rejection of Buck Output Ripple V OUT 5mV/DIV (AC) LDO (3.3V) 5mV/DIV (AC) V OUT 5mV/DIV (AC) LDO (3.3V) mv/div (AC) BUCK OUTPUT.8V mv/div (AC) ma I LDO ma V BUS = V V BAT = 3.8V STBY = LOW 5μs/DIV 3553 G4 ma I LDO ma V BUS = V V BAT = 3.8V STBY = HIGH 5μs/DIV 3553 G4 LDO OUTPUT.2V mv/div (AC) μs/div BUCK OUTPUT CONNECTED TO V INLDO 5mA LDO LOAD 4.7μF LDO OUTPUT CAPACITOR V BAT = 3.8V, V BUS = V 3553 G42

12 PIN FUNCTIONS HPWR (Pin ): High Power Logic Input. When this pin is low the input current limit is set to ma and when this pin is driven high it is set to 5mA. The SUSP pin needs to be low for the input current limit circuit to be enabled. This pin has a conditional internal pull-down resistor when power is applied to the V BUS pin. SEQ (Pin 2): Regulator Power-Up Sequence Select. While in the power off or hard reset states, a button press or application of USB bus power causes the pushbutton interface to temporarily enable both regulators. The state of the SEQ pin determines which regulator is enabled before the other. If SEQ is low, the buck regulator is enabled fi rst. If SEQ is high, the LDO regulator is enabled first. The second regulator is enabled once the feedback voltage of the first regulator nears regulation. The SEQ pin must be tied to either V OUT or ground. PBSTAT (Pin 3): Pushbutton Status. This open-drain output is a debounced and buffered version of the ON pushbutton input. It may be used to interrupt a microprocessor. ON (Pin 4): Pushbutton Input. Weak internal pull-up forces a high state if ON is left floating. A normally open pushbutton is connected from ON to ground to force a low state on this pin. LDO_ON (Pin 5): Logic Input Enables the Low Dropout (LDO) Regulator. This pin must be driven to a valid logic level. Do not float this pin. STBY (Pin 6): Standby Mode. When this pin is driven high, the buck and LDO regulator quiescent current is reduced to very low levels, while still maintaining output voltage regulation. In this mode, the buck regulator is limited to ma maximum load current, and the LDO regulator s response to line and load transients is slower. This pin must be driven to a valid logic level. Do not float this pin. BUCK_ON (Pin 7): Logic Input Enables the Buck Regulator. This pin must be driven to a valid logic level. Do not float this pin. BUCK_FB (Pin 8): Feedback Input for the Buck Regulator. This pin servos to a fi xed voltage of.8v when the control loop is complete. 2 LDO_FB (Pin 9): Feedback Input for the Low Dropout Regulator. This pin servos to a fi xed voltage of.8v when the control loop is complete. LDO (Pin ): Low Dropout (LDO) Linear Regulator Output. This pin should be bypassed with a low impedance multilayer ceramic capacitor. V INLDO (Pin ): Power Input Pin for the LDO Regulator. This pin is to be connected to V OUT or any supply voltage below V OUT, such as the buck regulator output. This pin should be bypassed with a low impedance multilayer ceramic capacitor. BVIN (Pin 2): Power Input for the Buck Regulator. It is recommended that this pin be connected to the V OUT pin. It should be bypassed with a low impedance multilayer ceramic capacitor. SW (Pin 3): Power Transmission (Switch) Pin for the Buck Regulator. CHRG (Pin 4): Open-Drain Charge Status Output. This pin indicates the status of the battery charger. It is internally pulled low while charging. Once the battery charge current reduces to less than one-tenth of the programmed charge current, this pin goes into a high impedance state. An external pull-up resistor and/or LED is required to provide indication. NTC (Pin 5): The NTC pin connects to a battery s thermistor to determine if the battery is too hot or too cold to charge. If the battery s temperature is out of range, charging is paused until it drops back into range. A low drift bias resistor is required from V BUS to NTC and a thermistor is required from NTC to ground. If the NTC function is not desired, the NTC pin should be grounded. PROG (Pin 6): Charge Current Program and Charge Current Monitor Pin. Connecting a resistor from PROG to ground programs the charge current as given by: I CHG (A)= 75V R PROG If suffi cient input power is available in constant-current mode, this pin servos to V. The voltage on this pin always represents the actual charge current.

13 PIN FUNCTIONS BAT (Pin 7): Single-Cell Li-Ion Battery Pin. Depending on available power and load, a Li-Ion battery on BAT will either deliver system power to V OUT through the ideal diode or be charged from the battery charger. V OUT (Pin 8): Output Voltage of the PowerPath Controller and Input Voltage of the Battery Charger. The majority of the portable products should be powered from V OUT. The will partition the available power between the external load on V OUT and the internal battery charger. Priority is given to the external load and any extra power is used to charge the battery. An ideal diode from BAT to V OUT ensures that V OUT is powered even if the load exceeds the allotted input current from V BUS or if the V BUS power source is removed. V OUT should be bypassed with a low impedance multilayer ceramic capacitor. SUSP (Pin 9): Suspend Mode Logic Input. If this pin is driven high the input current limit path is disabled. In this state the circuit draws negligible power from the V BUS pin. Any load at the V OUT pin is provided by the battery through the internal ideal diode. When this input is grounded, the input current limit will be set to desired value as determined by the state of the HPWR pin. This pin has a conditional internal pull-down resistor when power is applied to the V BUS pin. V BUS (Pin 2): USB Input Voltage. V BUS will usually be connected to the USB port of a computer or a DC output wall adapter. V BUS should be bypassed with a low impedance multilayer ceramic capacitor. GND (Exposed Pad Pin 2): Ground. The exposed package pad is ground and must be soldered to the PC board for proper functionality and for maximum heat transfer. 3

14 BLOCK DIAGRAM V BUS 2 8 V OUT HPWR SUSP 9 INPUT CURRENT LIMIT CC/CV CHARGER 7 BAT EXTPWR UVLO 6 PROG 2 BVIN NTC CHRG 5 4 BATTERY TEMP MONITOR CHARGE STATUS.25MHz OSCILLATOR 248 OSC.8V EN 3 SW STBY 8 BUCK_FB 2mA BUCK DC/DC V INLDO.8V EN LDO STBY 6 STBY 9 LDO_FB BUCK_ON 7 5mA LDO LDO_ON PBSTAT ON PUSHBUTTON INTERFACE AND SEQUENCE LOGIC SEQ 2 2 GND 3553 BD 4

15 OPERATION Introduction The is a highly integrated power management IC that includes the following features: PowerPath controller Battery charger Ideal diode Pushbutton controller 2mA buck regulator 5mA low dropout (LDO) linear regulator Designed specifi cally for USB applications, the PowerPath controller incorporates a precision input current limit which communicates with the battery charger to ensure that input current never violates the USB specifi cations. The ideal diode from BAT to V OUT guarantees that ample power is always available to V OUT even if there is insufficient or absent power at V BUS. The also includes a pushbutton input to control the two regulators and system reset. The constant-frequency current mode step-down switching regulator provides 2mA and supports % duty cycle operation as well as Burst Mode operation for high effi ciency at light load. No external compensation components are required for the switching regulator. The LDO can deliver up to 5mA, and is stable with a ceramic output capacitor of at least μf. For application fl exibility, the LDO s power input pin, V INLDO, is independent of the buck s BVIN pin. The LDO can be powered by the buck output or be driven by the PowerPath V OUT. Either regulator can be programmed for a minimum output voltage of.8v and can be used to power a microcontroller core, microcontroller I/O, memory or other logic circuitry. V BUS 2 Simplifi ed PowerPath Block Diagram ma/5ma INPUT CURRENT LIMIT CC/CV CHARGER + IDEAL 5mV 8 V OUT 7 BAT The buck regulator operates at.25mhz. Both regulators include a low power standby mode which can be used to power essential keep-alive circuitry while draining ultralow current from the battery for extended battery life. USB PowerPath Controller The input current limit and charger control circuits of the are designed to limit input current as well as control battery charge current as a function of I VOUT. V OUT drives the combination of the external load, the buck and LDO regulators and the battery charger. If the combined load does not exceed the programmed input current limit, V OUT will be connected to V BUS through an internal 35mΩ P-channel MOSFET. If the combined load at V OUT exceeds the programmed input current limit, the battery charger will reduce its charge current by the amount necessary to enable the external load to be satisfied while maintaining the programmed input current. Even if the battery charge current is set to exceed the allowable USB current, the average input current USB specifi cation will not be violated. Furthermore, load current at V OUT will always be prioritized and only excess available current will be used to charge the battery. The input current limit is programmed by the HPWR and SUSP pins. If SUSP pin set high, the input current limit is disabled. If SUSP pin is low, the input current limit is enabled. HPWR pin selects between ma input current limit when it is low and 5mA input current limit when it is high. Ideal Diode From BAT to V OUT The has an internal ideal diode from BAT to V OUT designed to respond quickly whenever V OUT drops below BAT. If the load increases beyond the input current limit, additional current will be pulled from the battery via the ideal diode. Furthermore, if power to V BUS (USB) is removed, then all of the application power will be provided by the battery via the ideal diode. The ideal diode is fast enough to keep V OUT from dropping signifi cantly with just the recommended output capacitor. The ideal diode consists of a precision amplifi er that enables an on-chip P-channel 3553 Fa 5

16 OPERATION MOSFET whenever the voltage at V OUT is approximately 5mV (V FWD ) below the voltage at BAT. The resistance of the internal ideal diode is approximately 24mΩ. Suspend Mode When the SUSP pin is pulled high the enters suspend mode to comply with the USB specifi cation. In this mode, the power path between V BUS and V OUT is put in a high impedance state to reduce the V BUS input current to 5μA. The system load connected to V OUT is supplied through the ideal diode connected to BAT. V BUS Undervoltage Lockout (UVLO) and Undervoltage Current Limit (UVCL) An internal undervoltage lockout circuit monitors V BUS and keeps the input current limit circuitry off until V BUS rises above the rising UVLO threshold (3.8V) and at least 2mV above V BAT. Hysteresis on the UVLO turns off the input current limit circuitry if V BUS drops below 3.6V or within 5mV of V BAT. When this happens, system power at V OUT will be drawn from the battery via the ideal diode. To minimize the possibility of oscillation in and out of UVLO when using resistive input supplies, the input current limit is reduced as V BUS falls below 4.45V typical. Battery Charger The includes a constant-current/constant-voltage battery charger with automatic recharge, automatic termination by safety timer, low voltage trickle charging, bad cell detection and thermistor sensor input for out of temperature charge pausing. When a battery charge cycle begins, the battery charger first determines if the battery is deeply discharged. If the battery voltage is below V TRKL, typically 2.9V, an automatic trickle charge feature sets the battery charge current to % of the programmed value. If the low voltage persists for more than /2 hour, the battery charger automatically terminates. Once the battery voltage is above 2.9V, the battery charger begins charging in full power constant current mode. The current delivered to the battery will try to reach 75V/R PROG. Depending on available input power and external load conditions, the battery charger may or may not be able to charge at the full programmed current. The external load will always be 6 prioritized over the battery charge current. The USB current limit programming will always be observed and only additional current will be available to charge the battery. When system loads are light, battery charge current will be maximized. Charge Termination The battery charger has a built-in safety timer. When the battery voltage approaches the float voltage, the charge current begins to decrease as the enters constantvoltage mode. Once the battery charger detects that it has entered constant-voltage mode, the four hour safety timer is started. After the safety timer expires, charging of the battery will terminate and no more current will be delivered to the battery. Automatic Recharge After the battery charger terminates, it will remain off drawing only microamperes of current from the battery. If the portable product remains in this state long enough, the battery will eventually self discharge. To ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below V RECHRG (typically 4.V). In the event that the safety timer is running when the battery voltage falls below V RECHRG, the timer will reset back to zero. To prevent brief excursions below V RECHRG from resetting the safety timer, the battery voltage must be below V RECHRG for approximately 2ms. The charge cycle and safety timer will also restart if the V BUS UVLO cycles low and then high (e.g., V BUS, is removed and then replaced). Charge Current The charge current is programmed using a single resistor from PROG to ground. /75th of the battery charge current is delivered to PROG which will attempt to servo to.v. Thus, the battery charge current will try to reach 75 times the current in the PROG pin. The program resistor and the charge current are calculated using the following equations: R PROG = 75V I CHG,I CHG = 75V R PROG

17 OPERATION In either the constant-current or constant-voltage charging modes, the PROG pin voltage will be proportional to the actual charge current delivered to the battery. Therefore, the actual charge current can be determined at any time by monitoring the PROG pin voltage and using the following equation: I BAT = V PROG R PROG 75 In many cases, the actual battery charge current, I BAT, will be lower than I CHG due to limited input current available and prioritization with the system load drawn from V OUT. Thermal Regulation To prevent thermal damage to the IC or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to approximately C. Thermal regulation protects the from excessive temperature due to high power operation or high ambient thermal conditions and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the or external components. The benefi t of the thermal regulation loop is that charge current can be set according to the desired charge rate rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions. Charge Status Indication The CHRG pin indicates the status of the battery charger. An open-drain output, the CHRG pin can drive an indicator LED through a current limiting resistor for human interfacing or simply a pull-up resistor for microprocessor interfacing. When charging begins, CHRG is pulled low and remains low for the duration of a normal charge cycle. When charging is complete, i.e., the charger enters constant-voltage mode and the charge current has dropped to one-tenth of the programmed value, the CHRG pin is released (high impedance). The CHRG pin does not respond to the C/ threshold if the reduces the charge current due to excess load on the V OUT pin. This prevents false end of charge indications due to insuffi cient power available to the battery charger. Even though charging is stopped during an NTC fault the CHRG pin will stay low indicating that charging is not complete. Battery Charger Stability Considerations The s battery charger contains both a constantvoltage and a constant-current control loop. The constantvoltage loop is stable without any compensation when a battery is connected with low impedance leads. Excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least μf from BAT to GND. Furthermore, a μf 2 ceramic capacitor in series with a.3ω resistor from BAT to GND is required to keep ripple voltage low if operation with the battery disconnected is allowed. High value, low ESR multilayer ceramic chip capacitors reduce the constant-voltage loop phase margin, possibly resulting in instability. Ceramic capacitors up to 22μF may be used in parallel with a battery, but larger ceramics should be decoupled with.2ω to Ω of series resistance. In constant-current mode, the PROG pin is in the feedback loop rather than the battery voltage. Because of the additional pole created by any PROG pin capacitance, capacitance on this pin must be kept to a minimum. With no additional capacitance on the PROG pin, the battery charger is stable with program resistor values as high as 25k. However, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above khz. Therefore, if the PROG pin has a parasitic capacitance, C PROG, the following equation should be used to calculate the maximum resistance value for R PROG : R PROG 2π khz C PROG 7

18 OPERATION NTC Thermistor The battery temperature is measured by placing a negative temperature coeffi cient (NTC) thermistor close to the battery pack. To use this feature connect the NTC thermistor, R NTC, between the NTC pin and ground and a bias resistor, R NOM, from V BUS to NTC, as shown in Figure. R NOM should be a % resistor with a value equal to the value of the chosen NTC thermistor at 25 C (R25). The will pause charging when the resistance of the NTC thermistor drops to.54 times the value of R25 or approximately 54k (for a Vishay curve thermistor, this corresponds to approximately 4 C). If the battery charger is in constant-voltage mode, the safety timer also pauses until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The is also designed to pause charging when the value of the NTC thermistor increases to 3.7 times the value of R25. For a Vishay curve thermistor this resistance, 37k, corresponds to approximately C. The hot and cold comparators each have approximately 3 C of hysteresis to prevent oscillation about the trip point. R NOM k R NTC k 2 5 V BUS NTC.76 V BUS (NTC RISING).35 V BUS (NTC FALLING).7 V BUS (NTC FALLING) NTC BLOCK TOO_COLD TOO_HOT NTC_ENABLE 3553 F Alternate NTC Thermistors and Biasing The provides temperature qualifi ed charging if a grounded thermistor and a bias resistor are connected to NTC. By using a bias resistor whose value is equal to the room temperature resistance of the thermistor (R25) the upper and lower temperatures are preprogrammed to approximately 4 C and C, respectively (assuming a Vishay curve thermistor). The upper and lower temperature thresholds can be adjusted by either a modifi cation of the bias resistor value or by adding a second adjustment resistor to the circuit. If only the bias resistor is adjusted, then either the upper or the lower threshold can be modifi ed but not both. The other trip point will be determined by the characteristics of the thermistor. Using the bias resistor in addition to an adjustment resistor, both the upper and the lower temperature trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. Examples of each technique are given below. NTC thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. The Vishay-Dale thermistor NTHS63N-N3F, used in the following examples, has a nominal value of k and follows the Vishay curve resistance-temperature characteristic. In the explanation below, the following notation is used. R25 = Value of the thermistor at 25 C R NTC COLD = Value of thermistor at the cold trip point R NTC HOT = Value of the thermistor at the hot trip point r COLD = Ratio of R NTC COLD to R25 r HOT = Ratio of R NTC HOT to R25 R NOM = Primary thermistor bias resistor (see Figure 2) R = Optional temperature range adjustment resistor (see Figure 2) Figure. Typical NTC Thermistor Circuit 8

19 OPERATION R NOM 5k 2 5 V BUS NTC.76 V BUS (NTC RISING) + TOO_COLD By using a bias resistor, R NOM, different in value from R25, the hot and cold trip points can be moved in either direction. The temperature span will change somewhat due to the nonlinear behavior of the thermistor. The following equations can be used to easily calculate a new value for the bias resistor: R 2.7k R NTC k.35 V BUS (NTC FALLING).7 V BUS (NTC FALLING) Figure 2. NTC Thermistor Circuit With Additional Bias Resistor + + TOO_HOT NTC_ENABLE 3553 F2 The trip points for the s temperature qualifi cation are internally programmed at.35 V BUS for the hot threshold and.76 V BUS for the cold threshold. Therefore, the hot trip point is set when: R NTC HOT R NOM +R NTC HOT V BUS =.35 V BUS and the cold trip point is set when: R NTC COLD R NOM +R NTC COLD V BUS =.76 V BUS Solving these equations for R NTC COLD and R NTC HOT results in the following: R NTC HOT =.538 R NOM and R NTC COLD = 3.7 R NOM By setting R NOM equal to R25, the above equations result in r HOT =.538 and r COLD = 3.7. Referencing these ratios to the Vishay Resistance-Temperature Curve chart gives a hot trip point of about 4 C and a cold trip point of about C. The difference between the hot and cold trip points is approximately 4 C. R NOM = r HOT.538 R25 R NOM = r COLD 3.7 R25 where r HOT and r COLD are the resistance ratios at the desired hot and cold trip points. Note that these equations are linked. Therefore, only one of the two trip points can be independently set, the other is determined by the default ratios designed in the IC. Consider an example where a 6 C hot trip point is desired. From the Vishay curve R-T characteristics, r HOT is.2488 at 6 C. Using the above equation, R NOM should be set to 46.4k. With this value of R NOM, the cold trip point is about 6 C. Notice that the span is now 44 C rather than the previous 4 C. This is due to the decrease in temperature gain of the thermistor as absolute temperature increases. The upper and lower temperature trip points can be independently programmed by using an additional bias resistor as shown in Figure 2. The following formulas can be used to compute the values of R NOM and R: R NOM = r COLD r HOT 2.74 R25 R=.536 R NOM r HOT R25 For example, to set the trip points to C and 45 C with a Vishay curve thermistor choose: R NOM = k =4.2k the nearest % value is 5k: R =.536 5k.4368 k = 2.6k The nearest % value is 2.7k. The final solution is shown in Figure 2 and results in an upper trip point of 45 C and a lower trip point of C. 9

20 OPERATION BUCK REGULATOR Introduction The includes a constant-frequency currentmode 2mA buck regulator. At light loads, the regulator automatically enters Burst Mode operation to maintain high effi ciency. Applications with a near-zero-current sleep or memory keep-alive mode can command the buck regulator into a standby mode that maintains output regulation while drawing only.5μa quiescent current. Load capability drops to ma in this mode. The buck regulator is enabled, disabled and sequenced through the pushbutton interface (see the Pushbutton Interface section for more information). It is recommended that the buck regulator input supply (BVIN) be connected to the system supply pin (V OUT ). This is recommended because the undervoltage lockout circuit on the V OUT pin (V OUT UVLO) disables the buck regulator when the V OUT voltage drops below the V OUT UVLO threshold. If driving the buck regulator input supply from a voltage other than V OUT, the regulator should not be operated outside its specifi ed operating voltage range as operation is not guaranteed beyond this range. Output Voltage Programming Figure 3 shows the buck regulator application circuit. The output voltage for the buck regulator is programmed using a resistor divider from the buck regulator output connected to the feedback pin (BUCK_FB) such that: V BUCK =.8V R R2 + Typical values for R can be as high as 2.2MΩ. (R + R2) can be as high as 3MΩ. The capacitor C FB cancels the pole created by feedback resistors and the input capacitance of the BUCK_FB pin and also helps to improve transient response for output voltages much greater than.8v. A variety of capacitor sizes can be used EN STBY PWM CONTROL GND V IN MP MN.8V SW BUCK_FB Figure 3. Buck Regulator Application Circuit 3553 F3 for C FB but a value of pf is recommended for most applications. Experimentation with capacitor sizes between 2pF and 22pF may yield improved transient response. Normal Buck Operating Mode (STBY Pin Low) In normal mode (STBY pin low), the buck regulator performs as a traditional constant-frequency current mode switching regulator. Switching frequency is determined by an internal oscillator which operates at.25mhz. An internal latch is set at the start of every oscillator cycle, turning on the main P-channel MOSFET switch. During each cycle, a current comparator compares the inductor current to the output of an error amplifi er. The output of the current comparator resets the internal latch, which causes the main P-channel MOSFET switch to turn off and the N-channel MOSFET synchronous rectifi er to turn on. The N-channel MOSFET synchronous rectifi er turns off at the end of the clock cycle, or when the current through the N-channel MOSFET synchronous rectifi er drops to zero, whichever happens first. Via this mechanism, the error amplifi er adjusts the peak inductor current to deliver the required output power. All necessary compensation is internal to the buck regulator requiring only a single ceramic output capacitor for stability. At light load and no-load conditions, the buck automatically switches to a power-saving hysteretic control algorithm that operates the switches intermittently to minimize switching losses. Known as Burst Mode operation, the buck cycles L C FB R R2 C OUT V BUCK 2

21 OPERATION the power switches enough times to charge the output capacitor to a voltage slightly higher than the regulation point. The buck then goes into a reduced quiescent current sleep mode. In this state, power loss is minimized while the load current is supplied by the output capacitor. Whenever the output voltage drops below a predetermined value, the buck wakes from sleep and cycles the switches again until the output capacitor voltage is once again slightly above the regulation point. Sleep time thus depends on load current, since the load current determines the discharge rate of the output capacitor. Standby Mode Buck Operation (STBY Pin High) There are situations where even the low quiescent current of Burst Mode operation is not low enough. For instance, in a static memory keep alive situation, load current may fall well below μa. In this case, the 22μA typical BVIN quiescent current in Burst Mode operation becomes the main factor determining battery run time. Standby mode cuts BVIN quiescent current down to just.5μa, greatly extending battery run time in this essentially no-load region of operation. The application circuit commands the into and out of standby mode via the STBY pin logic input. Bringing the STBY pin high places the regulator into standby mode, while bringing it low returns it to Burst Mode operation. In standby mode, buck load capability drops to ma. In standby mode, the buck regulator operates hysteretically. When the BUCK_FB pin voltage falls below the internal.8v reference, a current source from BVIN to SW turns on, delivering current through the inductor to the switching regulator output capacitor and load. When the FB pin voltage rises above the reference plus a small hysteresis voltage, that current is shut off. In this way, output regulation is maintained. Since the power transfer from BVIN to SW is through a high impedance current source rather than through a low impedance MOSFET switch, power loss scales with load current as in a linear low dropout (LDO) regulator, rather than as in a switching regulator. For near-zero load conditions where regulator quiescent current is the dominant power loss, standby mode is ideal. But at any appreciable load current, Burst Mode operation yields the best overall conversion effi ciency. Shutdown The buck regulator is shut down and enabled via the pushbutton interface. In shutdown, it draws only a few nanoamps of leakage current from the BVIN pin. It also pulls down on its output with a k resistor from its switch pin to ground. Dropout Operation It is possible for the buck regulator s input voltage to fall near or below its programmed output voltage (e.g., a battery voltage of 3.4V with a programmed output voltage of 3.3V). When this happens, the PMOS switch duty cycle increases to %, keeping the switch on continuously. Known as dropout operation, the output voltage equals the regulator s input voltage minus the voltage drops across the internal P-channel MOSFET and the inductor. Soft-Start Operation In normal operating mode, soft-start works by gradually increasing the maximum allowed peak inductor current for the buck regulator over a 5μs period. This allows the output to rise slowly, helping minimize the inrush current needed to charge up the output capacitor. A soft-start cycle occurs whenever the buck is enabled. Soft-start occurs only in normal operation, but not in standby mode. Standby mode operation is already inherently current-limited, since the regulator works by intermittently turning on a current source from BVIN to SW. Changing the state of the STBY pin while the regulators are operating doesn t trigger a new soft-start cycle, to avoid glitching the outputs. Inductor Selection Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. 2

22 OPERATION Inductor value should be chosen based on the desired output voltage. See Table. Table 3 shows several inductors that work well with the step-down switching buck regulator. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors. Larger value inductors reduce ripple current, which improves output ripple voltage. Lower value inductors result in higher ripple current and improved transient response time, but will reduce the available output current. To maximize effi ciency, choose an inductor with a low DC resistance. Choose an inductor with a DC current rating at least.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current specifi ed for the buck converter. Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher core and DCR losses, and will not give the best effi ciency. The choice of which style inductor to use often depends more on the price versus size, performance and any radiated EMI requirements than on what the buck requires to operate. The inductor value also has an effect on Burst Mode operation. Lower inductor values will cause Burst Mode switching frequency to increase. Input/Output Capacitor Selection Low ESR (equivalent series resistance) ceramic capacitors should be used at the buck output as well as at the buck input supply. Only X5R or X7R ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. For good transient response and stability the output capacitor should retain at least 4μF of capacitance over operating temperature and bias voltage. Generally, a good starting point is to use a μf output capacitor. Table. Choosing the Inductor Value DESIRED OUTPUT VOLTAGE RECOMMENDED INDUCTOR VALUE.8V or Less μh.8v to 2.5V 6.8μH 2.5V to 3.3V 4.7μH Table 2. Ceramic Capacitor Manufacturers AVX Murata Taiyo Yuden Vishay Siliconix TDK Table 3. Recommended Inductors for the Buck Regulator INDUCTOR PART NO. L (μh) MAX I DC (A) MAX DCR (Ω) SIZE (L W H) (mm) MANUFACTURER 7AS-4R7M 7AS-6R8M 7AS-M CDRH2DBNP-4R7N CDRH2DBNP-6R8N CDRH2DBNP-N SD32-4R7-R SD32-6R8-R SD32--R EPL24-472ML_ EPL24-682ML_ EPL24-3ML_ * = Typical DCR *.25*.38* *.29*.446* Toko Sumida Cooper Coilcraft 22

23 OPERATION The switching regulator input supply should be bypassed with a 2.2μF capacitor. Consult with capacitor manufacturers for detailed information on their selection and specifi cations of ceramic capacitors. Many manufacturers now offer very thin (<mm tall) ceramic capacitors ideal for use in height-restricted designs. Table 2 shows a list of several ceramic capacitor manufacturers. LOW DROPOUT LINEAR REGULATOR (LDO) The LDO regulator supports a load of up to 5mA. The LDO takes power from the V INLDO pin and drives the LDO output pin with the goal of bringing the LDO_FB feedback pin voltage to.8v. Usually, a resistor divider is connected between the LDO s output pin, feedback pin and ground, in order to close the control loop and program the output voltage. For stability, the LDO output must be bypassed to ground with at least a μf ceramic capacitor. The LDO is enabled or disabled via the pushbutton interface. In cases where the LDO is disabled and the PowerPath is actively driving V OUT, an internal pull-down resistor is switched in to help bring the output to ground. When the LDO is enabled, a soft-start circuit ramps its regulation point from zero to final value over a period of roughly.2ms, reducing the required V INLDO inrush current. The LDO has two input voltage requirements. The LDO s quiescent bias current is supplied through an internal connection to the USB PowerPath V OUT pin. The LDO s power input is taken from the V INLDO pin. For proper LDO operation, the V INLDO pin must be connected to a voltage no greater than V OUT. For example, V INLDO can be connected to V OUT, or to the buck regulator output. Connecting V INLDO to a voltage exceeding V OUT may result in loss of regulation. Output Voltage Programming Figure 4 shows the LDO regulator application circuit. Program the LDO output voltage, V LDO, by choosing R and R2 such that: V LDO =.8V R R2 + LDO ENABLE GND V INLDO MP LDO_FB LDO OUTPUT C OUT Standby Mode LDO Operation (STBY Pin High) To reduce battery drain current in applications with a static memory keep-alive or other ultralow quiescent current state, the LDO may be placed into standby mode (together with the buck regulator). When the STBY pin is brought high, LDO bias current is reduced. Unlike the buck LDO R.8V R F4 Figure 4. LDO Application Circuit 23

24 OPERATION regulator, the LDO s load capability remains unchanged. However, the LDO s transient response is slowed, as illustrated in Figure 5 and Figure 6. LDO OUTPUT VOLTAGE AC-COUPLED.V/DIV 5mA I LDO 5mA 5μs/DIV LDO REGULATING 3.3V 4.7μF OUTPUT CAPACITOR STBY LOW 3553 F5 Figure 5. LDO Load Step Response in Normal Operation measures should be taken to ensure that the buck is not operated outside the specifi ed BVIN input supply range, as operation beyond this range is not guaranteed. LDO Regulator UVLO Considerations The LDO regulator s bias current is supplied via an internal connection to the USB PowerPath V OUT pin. The V OUT UVLO shuts down the LDO when V OUT drops below about 2.6V in order to prevent the LDO from operating incorrectly due to too low a bias supply voltage. The LDO power input pin, V INLDO, can be driven with as little as.65v. There is, however, no UVLO to enforce this requirement. It is thus recommended that V INLDO be tied to either the buck regulator output (programmed to regulate at least.65v), or to the USB PowerPath V OUT pin, to ensure proper operation. PUSHBUTTON INTERFACE 24 LDO OUTPUT VOLTAGE AC-COUPLED.V/DIV 5mA I LDO 5mA 5μs/DIV LDO REGULATING 3.3V 4.7μF OUTPUT CAPACITOR STBY HIGH 3553 F6 Figure 6. LDO Load Step Response in Standby Mode V OUT UNDERVOLTAGE LOCKOUT (V OUT UVLO) An undervoltage lockout circuit on the USB PowerPath V OUT pin shuts down and prevents both the buck and the LDO from enabling when the V OUT pin voltage drops below about 2.6V. Buck Regulator UVLO Considerations It is recommended that the buck regulator input supply (BVIN pin) be connected directly to the USB PowerPath output (V OUT pin). With this connection, the V OUT UVLO prevents the buck regulator from operating at low input supply voltages where loss of regulation or other undesirable operation may occur. In applications where the buck input is supplied from other than the V OUT pin, other State Diagram/Operation Figure 7 shows the pushbutton state diagram. The pushbutton state machine has a clock with a.82ms period. Upon first application of power, V BUS or BAT, an internal power on reset (POR) signal places the pushbutton circuitry into the power-down (PDN) state. One second EXTPWR OR PB4MS SEC PUP2 POFF PDN2 UVLO AND EITHER BUCK_ON OR LDO_ON HRST 5SEC UVLO OR BOTH BUCK_ON AND LDO_ON HRST EXTPWR OR PB4MS HR PUP PON PDN 5SEC HRST POR Figure 7. Pushbutton State Diagram BUCK_ON OR LDO_ON 3553 F7 SEC