AME. 3A, 300KHz ~ 2MHz Synchronous Rectified Step-Down Converter AME5287. General Description. Typical Application. Features.

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1 587 General Description Typical Application The 587 is a Synchronous Rectified Step-Down Converter with internal power MOSFETs. It achieves 3A continuous output current over a wide switching frequency range with excellent load and line regulation. Current mode operation provides fast transient response and eases of loop stabilization. Internal soft-start minimizes the inrush supply current at startup. The circuit protection includes cycle-by-cycle current limiting, output short circuit frequency protection and thermal shutdown. In shutdown mode, the regulator reduces the current less than µa of supply current. V IN 5V C IN 0µF C Optional OFF C 680pF R 3 5KΩ ON IN EN 587 COMP GND SW FB FREQ R FREQ 8KΩ L.µH R 75KΩ R 4KΩ V OUT 3.3V C OUT µf This device is available in SOP-8/PP,DFN-8 package with exposed pad for low thermal resistance. Figure. 3.3V at 3A Step-Down Regulators. Features 3A Output Current Stable with Low ESR Output Ceramic Capacitors Pre-Regulator for Linear Regulators Up to 95% Efficiency Less than µa Shutdown Current Wide Switching Frequency Range from 300KHz~MHz Thermal Protection Cycle-by-Cycle Over Current Protection Output Adjustable from 0.8V to V IN Short Circuit Protection Green Products Meet RoHS Standards V IN 3V~5V C IN 0µF C Optional OFF C 680pF R 3 8.KΩ ON IN EN 587 COMP GND SW FB FREQ R FREQ 8KΩ L.5µH R 6KΩ R 4KΩ V OUT V C OUT µf Figure. V at 3A Step-Down Regulators. Applications TV Distributed Power Systems Pre-Regulator for Linear Regulators Digital Cameras Rev. A.0

2 587 Functional Block Diagram IN CURRENT SENSE EN ENABLE UVLO CURRENT LIMIT FREQ OSC SW COMP GND 0.8V VREF + - EA SLOPE SOFT START PWM OTP LOGIC DRIVER IRCMP SW FB Short circuit - + PGND Pin Configuration SOP-8/PP Top View DFN-8C (3mmx3mmx0.75mm) Top View AZAADJ. COMP. GND 3. EN 4. IN 5. SW 6. SW 7. FREQ 8. FB 9. GND (Exposed Pad) AVAADJ. COMP. GND 3. EN 4. IN 5. SW 6. SW 7. FREQ 8. FB 9. GND (Exposed Pad) * Die Attach: Conductive Epoxy * Die Attach: Conductive Epoxy Note. Connect exposed pad (heat sink on the back) to GND. Rev. A.0

3 587 Pin Description Pin No. Pin Name Pin Description COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. GND Ground. Connect the exposed pad to GND. 3 EN Enable. Pull EN below 0.4V to shut down the regulator. 4 IN 5, 6 SW 7 FREQ 8 FB Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Bypass IN to GND with a suitable large capacitor to eliminate noise on the input to the IC. Power Switching Output. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Frequency Adjust Pin. Add a resistor from this pin to ground determines the switching frequency. Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback reference voltage is 0.8V. 9 GND Ground. Connect the exposed pad to GND. Rev. A.0 3

4 587 Ordering Information x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration Package Type Number of Pins Output Voltage A. COMP Z: SOP/PP A: 8 ADJ: Adjustable (SOP-8/PP). GND V: DFN (DFN-8C) 3. EN 4. IN 5. SW 6. SW 7. FREQ 8. FB 9. GND 4 Rev. A.0

5 587 Absolute Maximum Ratings Parameter Symbol Maximum Unit Supply Voltage V IN 6 V Switch Voltage V SW -.5V to V IN +0.7V V EN, FB, COMP, FREQ to GND -0.3V to VIN+0.3V V ESD Classification HBM kv MM 00 V Recommended Operating Conditions Parameter Symbol Rating Unit Ambient Temperature Range T A -40 to +85 Junction Temperature Range T J -40 to +5 o C Storage Temperature Range T STG -65 to +50 Thermal Information Parameter Package Die Attach Symbol Maximum Unit Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) Internal Power Dissipation SOP-8/PP 5 θ JC DFN-8C 8. SOP-8/PP Conductive Epoxy θ JA 75 DFN-8C 70 SOP-8/PP.333 DFN-8C.49 P D o C / W W Maximum Junction Temperature 50 o C Lead Temperature (soldering 0 sec)** 60 o C * Measure θ JC on backside center of Exposed Pad. ** MIL-STD-0G 0F Rev. A.0 5

6 587 Electrical Specifications V IN =5V, T A =5 o C, unless otherwise noted. Parameter Symbol Test Condition Min Typ Max Units Input Voltage V IN V Input UVLO V UVLO.3 V Quiescent Current I Q V EN =5V, V FB =0.7V (No Switching) 600 µa Shutdown Current I SHDN V EN =0V µa Feedback Voltage V FB V Feedback Current I FB na Load Regulation REG LOAD 0A<I OUT <A 0.5 % Line Regulation REG LINE.7V<V IN <5.5V 0.5 %/V EN Voltage High.4 V V EN EN Voltage Low 0.4 V EN Leakage Current I ENLK V EN =3V 0. µa R FREQ =NC KHz Switching Frequency F SW R FREQ =0KΩ KHz R FREQ =47KΩ 0.8. MHz R FREQ =8KΩ.6 MHz High-side Switch Current Limit 3.7 A Error Amp Transconductance G EA 400 µa/v Switch Leakage Current I SWLK V SW =0V, V EN =0V 0. 0 µa High-side Switch On Resistance R DSON,HI 30 mω Low-side Switch On Resistance R DSON,LO 90 mω Thermal Shutdown Protection OTP Rising 60 OTH Hysteresis 0 o C o C 6 Rev. A.0

7 587 Detailed Description Normal Operation The 587 uses a user adjustable frequency, current mode step-down architecture with internal MOSFET switch. During normal operation, the internal high-side (PMOS) switch is turned on each cycle when the oscillator sets the SR latch, and turned off when the comparator resets the SR latch. The peak inductor current at which comparator resets the SR latch is controlled by the output of error amplifier EA. While the high-side switch is off, the low-side switch turns on until either the inductor current starts to reverse or the beginning of the next switching cycle. Dropout Operation The output voltage is dropped from the input supply for the voltage which across the high-side switch. As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the high-side switch to remain on for more than one cycle until it reaches 00% duty cycle. Soft-Start The 587 has a built-in digital soft-start to control the output voltage rise and limit the current surge at the start-up. When the internal soft-start begins, and count 896 switching cycles, soft start is complete, the converter enters steady state operation. Under Voltage Protection Under Voltage Protection will activate once the feedback voltage falls below 0.4V, the operating frequency is switched to /0 of normal switching frequency and after four-times hiccup mode counted, the internal high-side power switch will be turned off,and latched. Unless Restart the power supply. Over Temperature Protection In most applications the 587 does not dissipate much heat due to high efficiency. But, in applications where the 587 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 60 o C, the internal high-side power switch will be turned off and the SW switch will become high impedance. Inductor Selection For most applications, the value of the inductor will fall in the range of.µh to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increase the ripple current I L : I V = L VOUT f L V OUT IN Hiccup Mode During hiccup mode, the 587 disables the highside MOSFET and begins a cool down period of 830 switching cycles. At the conclusion of this cool down period, the regulator performs an internal 896 cycle soft start identical to the soft start at turn-on. Rev. A.0 7

8 587 A reasonable inductor current ripple is usually set as / 3 to /5 of maximum out current. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. For better efficiency, choose a low DCR inductor. Output Voltage Programming The output voltage of the 587 is set by a resistive divider according to the following formula: V OUT R 0.8 = + Volt. R Capacitor Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V OUT /V IN. To prevent large voltage transients, a low ESR input capacitor sized for maximum RMS current must be used. The maximum RMS capacitor current is given by: C IN requires I RMS I OMAX This formula has a maximum at V IN =V OUT, wherei RMS =I OUT /. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. The selection of C OUT is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the I RIPPLE(P-P) requirement. The output ripple V OUT is determined by: V OUT ( V V ) V IN IN OUT Loop Compensation The 587 employs peak current mode control for easy use and fast transient response. Peak current mode control eliminates the double pole effect of the output LC filter. It greatly simplifies the compensation loop design. With peak current mode control, the buck power stagecan be simplified to be a one-pole and one-zero system in frequency domain. The pole can be calculated by: f P = π C OUT R L The zero is a ESR zero due to output capacitor and its ESR. It can be calculated by: f Z = π C ESR OUT COUT V OUT I L ESR+ 8 fc OUT For a fixed output voltage, the output ripple is highestat maximum input voltage since I L increases with input voltage. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for given value and size. 8 Rev. A.0

9 587 Where C OUT is the output capacitor, R L is load resistance; ESR COUT is the equivalent series resistance of output capacitor. The compensation design is to shape the converter close loop transfer function to get desired gain and phase. For most cases, a series capacitor and resistor network connected to the COMP pin sets the pole-zero and is adequate for a stable high-bandwidth control loop. In the 587, FB pin and COMP pin are the inverting input and the output of internal transconductance error amplifier (EA). A series R 3 and C compensation network connected to COMP pin provides one pole and one zero: for R 3 <<A EA /GEA, f P = A π C R3 + G f Z = π C where G EA is the error amplifier transconductance EA EA A EA is the error amplifier voltage gain R R 3 is the compensation resistor C is the compensation capacitor 3 GEA π C A The desired crossover frequency f c of the system is defined to be the frequency where the control loop has unity gain. It is also called the bandwidth of the converter. In general, a higher bandwidth means faster response to load transient. However, the bandwidth should not be too high because of system stability concern. When designing the compensation loop, converter stability under all line and load condition must be considered. Usually, it is recommended to set the bandwidth to be less than /0 of switching frequency. Using selected crossover frequency, f C, to calculate R 3 : R 3 = f C V V OUT FB π C G G EA OUT CS EA Where G CS is the current sense circuit transconductance. The compensation capacitor C and resistor R 3 together make zero. This zero is put somewhere close to the pole f P of selected frequency. C is selected by: C C = OUT R Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, V OUT immediately shifts by an amount equal to ( I LOAD X ESR), where ESR is the effective series resistance of C OUT. I LOAD also begins to charge or discharge C OUT, which generates a feedback error signal. The regulator loop then acts to return V OUT to its steadystate value. During this recovery time V OUT can be monitored for overshoot or ringing that would indicate a stability problem. Efficiency Considerations 3 R L Although all dissipative elements in the circuit produce losses, one major source usually account for most of the losses in 587 circuits: I R losses. The I R loss dominates the efficiency loss at medium to high load currents. The I R losses are calculated from the resistances of the internal switches, R SW, and external inductor R L. In continuous mode, the average output current flowing through inductor L is "chopped" between the main switch and the synchronous switch. Thus the series resistance looking into the SW pin is a function of both top and bottom MOSFET R DS(ON) and the duty cycle (D) as follows: R SW = (R DS(ON)TOP )(D) + (R DS(ON)BOTTOM )(-D) The R DS(ON) for both the top and bottom MOSFETs can be obtained from Electrical Characteristics table. Thus, to obtained I R losses, simply add R SW to R L and multiply the result by the square of the average output current. Rev. A.0 9

10 587 Other losses including C IN and C OUT ESR dissipative losses and inductor core losses generally account for less than % total additional loss. Thermal Considerations In most application the 587 does not dissipate much heat due to its high efficiency. But, in applications where the 587 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 60 o C, both power switches will be turned off and the SW switch will become high impedance. 0 Rev. A.0

11 587 Typical Operating Circuit V IN.5V to 5V C IN 0µF Chip Enable C Optional C R 3 L 4 IN SW 5, 6 3 EN 587 COMP FB 8 FREQ 7 GND 9 (Exposed pad) GND R FREQ R R V OUT C OUT V OUT (V) C IN (µf) R(KΩ R(KΩ R3(KΩ C pf L(µH) C OUT µf Table. Recommended Components Selectin for fsw = MHz R 3 C The ground area must provide adequate heat dissipating area to the thermal pad andusing multiple vias to help thermal dissipation. COMP 8 FB R Connect the FB pin directly to feedback resistors. R V OUT V IN GND EN V IN C IN must be placed between V INand GND as close as possible 3 CIN GND 4 5 Place the input and output capacitors as close to the IC as possible 7 6 FREQ SW SW SW C OUT R FREQ V OUT GND SW pad should be connected together to Inductor by wide and short trace, keep sensitive components away from this trace. L Figure Regulators Layout Diagram Rev. A.0

12 587 Characterization Curve Efficiency vs. Output Current Efficiency vs. Output Current Efficiency (%) VOUT=3.3V V OUT =.5V VOUT=.8V VOUT=.V VOUT =.0V Efficiency (%) VOUT=3.3V VOUT=.5V V OUT =.8V VOUT =.V V OUT=.0V 0 0 V IN = 5V RFREQ = 8K 0 0 V IN = 5V RFREQ = 30K Output Current (ma) Output Current (ma) Efficiency (%) V OUT =3.3V Efficiency vs. Output Current VOUT=.5V V OUT =.8V V OUT=.V VOUT=.0V V IN = 5V RFREQ = 47K Output Current (ma) Efficiency (%) Efficiency vs. Output Current V OUT=3.3V VOUT=.5V VOUT=.8V V OUT=.V VOUT=.0V VIN = 5V RFREQ = NC Output Current (ma) Rev. A.0

13 587 Characterization Curve (Contd.) Load Step Load Step VIN= 3.3V VOUT=.0V IOUT= A to 3A VIN= 3.3V V OUT =.8V IOUT= A to 3A ) V OUT = 00mV/div ) I L = A/div Time (00mSec/DIV) Time (00mSec/DIV) ) V OUT = 00mV/div ) I L = A/div Load Step Load Step VIN= 5.0V VOUT=.0V IOUT= A to 3A VIN= 5.0V VOUT= 3.3V I OUT = A to 3A ) V OUT = 00mV/div ) I L = A/div Time (00mSec/DIV) ) V OUT = 00mV/div ) I L = A/div Time (00mSec/DIV) Rev. A.0 3

14 587 Characterization Curve (Contd.) Power ON from V IN Power off from V IN ) V IN = 5V/div ) Vsw= 5V/div 3) V OUT = V/div 4) I L = A/div.0mS / div ) V IN = 5V/div ) Vsw= 5V/div 3) V OUT = V/div 4) I L = 5A/div.0mS / div Start-Up from EN Power Off from EN mS / div.0ms / div ) EN= 5V/div ) V SW = 5V/div 3) V OUT = V/div 4) I L = A/div ) EN= 5V/div ) V SW = 5V/div 3) V OUT = V/div 4) I L = 5A/div 4 Rev. A.0

15 587 Characterization Curve (Contd.) Steady State Test Steady State Test VIN= 5V VOUT=.V IOUT= 3A V IN = 5V VOUT= 3.3V IOUT= 3A ) V OUT = 0mV/div ) V SW = V/div 400nS / DIV ) V OUT = 0mV/div ) V SW = V/div 400nS / DIV V FB vs. Temperature Frequency vs. Temperature VFB (V) Frequency (KHz) V IN = 5V 00 V IN = 5V Temperature ( C) Temperature ( C) Rev. A.0 5

16 587 Characterization Curve (Contd.) Frequency vs. Supply Voltage Frequency vs. Output Current Frequency (KHz) V OUT = 3.3V Input Voltage (V) Frequency (KHz) V IN =5.0V V OUT = 3.3V Iout (ma) Short Circuit Test Short Circuit Test VIN=5V VOUT=V VIN=5V VOUT=3.3V Time (00ms/DIV) Time (00ms/DIV) ) V OUT = V/div ) I OUT = A/div ) V OUT = V/div ) I OUT = A/div 6 Rev. A.0

17 587 Tape and Reel Dimension SOP-8/PP P PIN W Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOP-8/PP.0±0. mm 4.0±0. mm 500pcs 330± mm DFN-8C (3mmx3mmx0.75mm) P PIN W Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size DFN-8C (3x3x0.75mm).0±0. mm 4.0±0. mm 3000pcs 330± mm Rev. A.0 7

18 587 Package Dimension SOP-8/PP TOP VIEW D SIDE VIEW? SYMBOLS MILLIMETERS INCHES MIN MAX MIN MAX A E E E L A A C PIN D C E E L b b e FRONT VIEW A A A D e.70 BSC BSC q 0 o 8 o 0 o 8 o E D Rev. A.0

19 587 Package Dimension (Contd.) DFN-8C (3mmx3mmx0.75mm) D b e L E E PIN IDENTIFICATION TOP VIEW D BOTTOM VIEW A G G REAR VIEW SYMBOLS MILLIMETERS INCHES MIN MAX MIN MAX A D E e D E b L G G Rev. A.0 9

20 Life Support Policy: These products of, Inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of, Inc., Inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information., Inc., October 0 Document: TU003-DS587-A.0 Corporate Headquarter, Inc. 8F,, WenHu St., Nei-Hu Taipei 4, Taiwan. Tel: Fax: