LTC1515 Series Step-Up/Step-Down Switched Capacitor DC/DC Converters with Reset DESCRIPTION FEATURES APPLICATIONS TYPICAL APPLICATION

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Nicholas Richard
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1 LTC Series Step-p/Step-Down Switched Capacitor DC/DC Converters with Reset FEATRES Adjustable/Selectable 3V, 3.3V or V Output Voltages V to V Input Voltage Range p to ma Output Current Only Three External Capacitors Required Soft Start Limits Inrush Current at Turn-On Low Operating Current: 6µA Very Low Shutdown Current: < µa Shutdown Disconnects Load from Programmable to 3V/V or 3.3V/V Short-Circuit and Overtemperature Protected 6kHz Switching Frequency Open-Drain Power-On Reset Output Available in SO- Package Daisy-Chained Control Outputs APPLICATIONS SIM Interface in GSM Cellular Telephones Smart Card Readers Local Power Supplies DESCRIPTION The LTC, LTC-3/ and LTC-3.3/ are micropower switched capacitor DC/DC converters that produce a regulated output voltage by either stepping up or stepping down the input voltage. Output voltage is adjustable using an external resistor divider (LTC) or programmable to either 3V/V (LTC-3/) or 3.3V/V (LTC-3.3/) using a logic pin. A unique architecture allows the parts to accommodate a wide input voltage range (V to V) while maintaining ±% regulation. Additional circuitry prevents excessive inrush current and output voltage ripple when large to differentials are present. An internal power-on reset circuit forces the pin low on initial power-up. The output remains low until ms (typ) after is in regulation. The parts are short-circuit and overtemperature protected. Battery life is maximized by very low operating currents (I CC = 6µA typ, I CC < µa in shutdown). All three parts are available in an SO- package. Portable Equipment, LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATION ON OFF RESET V 3.3V Programmable 3.3V/V Power Supply with Power-On Reset k 3 LTC-3.3/ /3 C 6 GND C.µF = 3.3V OR V I OT = ma µf µf -CELL NiCd LTC TA OTPT VOLTAGE (V) LTC-X V Output vs Input Voltage....9 I OT = ma /3 = 3V LT TA

2 LTC Series ABSOLTE MAXIMM RATINGS W W W (Note ) to GND....3V to V to GND....3V to V, /3, FB to GND....3V to V Short-Circuit Duration... Indefinite Operating Temperature Range Commercial... C to C Industrial... C to C Storage Temperature Range... 6 C to C Lead Temperature (Soldering, sec)... 3 C PACKAGE/ORDER I FOR FB 3 GND TOP VIEW 6 S PACKAGE -LEAD PLASTIC SO T JMAX = C, θ JA = C/W C C Consult factory for Military grade parts. W ATIO ORDER PART NMBER LTCCS LTCIS S PART MARKING I /3 3 GND TOP VIEW 6 S PACKAGE -LEAD PLASTIC SO T JMAX = C, θ JA = C/W C C ORDER PART NMBER LTCCS-3/ LTCCS-3.3/ LTCIS-3/ LTCIS-3.3/ S PART MARKING 3 33 I3 I33 ELECTRICAL CHARACTERISTICS = V to V, = 3V, C =.µf, C IN = C OT = µf unless otherwise noted (Note ). PARAMETER CONDITIONS MIN TYP MAX NITS Operating Voltage = V. V = 3V/3.3V. V = ADJ. V = 3V (LTC-3/) V V, I OT ma V 3V V, I OT ma V = 3.3V (LTC-3.3/) V V, I OT ma V 3V V, I OT ma V = V (LTC-3/, LTC-3.3/).V V, I OT ma... V 3.3V V, I OT ma... V V FB Feedback Voltage LTC, V FB Ramping Negative.9.3. V V FB Feedback Hysteresis LTC % Effective Output Resistance LTC, = 3V, Step-p Mode 3 Ω Operating Current V, I OT =, = 3V 6 µa > V, I OT =, = 3V 3 µa Shutdown Current = V, V µa = V, > V µa Output Ripple Full Load (Note ) mv P-P Switching Frequency Full Load 6 khz /3, Input Threshold V IL.. V V IH..6 V /3, Input Current /3, = µa /3, = V µa FB Input Current FB =.3V na Output Low Voltage I SINK = µa, = 3V.. V

3 ELECTRICAL CHARACTERISTICS = V to V, = 3V, C =.µf, C IN = C OT = µf unless otherwise noted (Note ). LTC Series PARAMETER CONDITIONS MIN TYP MAX NITS Leakage Current V = V µa Trip Point (With Respect to ) Ramping Negative. % Trip Point Hysteresis % I OT Short-Circuit Current = V ma t ON Soft Start Turn-On Time ms Delay After Above Threshold ms The denotes specifications which apply over the full operating temperature range. Note : Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note : For V, C OT = µf. TYPICAL PERFORMANCE CHARACTERISTICS W OTPT VOLTAGE RIPPLE (mv P-P ) 6 LTC-X 3.3V Efficiency vs Output Current = 3.3V T A = C = V I OT = ma T A = C C OT = µf = V =.V =.V = 6V.. OTPT CRRENT (ma) LTC-X V Output Voltage Ripple vs Input Voltage C OT = µf G C OT = µf OTPT VOLTAGE (V) 6 LTC-X V Efficiency vs Output Current =.V = 6V = 3.3V = V = V T A = C.. OTPT CRRENT (ma) LTC-X 3.3V Output Voltage vs Input Voltage = 3.3V I OT = ma C OT = µf T A = C G OTPT VOLTAGE RIPPLE (mv P-P ) OPERATING CRRENT (µa) 6 LTC-X 3.3V Output Voltage Ripple vs Input Voltage = 3.3V I OT = ma T A = C 6 LTC-X Operating Current vs Input Voltage = V I OT = ma C C OT = µf C OT = µf C OT = µf C C G G G G6 3

Step-p Mode V Load Transient Response POSITIVE SPPLY CRRENT (µa) C C C 6 G AC COPLED mv/div I OT ma/div = V, = V, C OT = µf, T A = C G ma ma AC COPLED mv/div I OT ma/div = 3.

4 LTC Series TYPICAL PERFORMANCE CHARACTERISTICS LTC-X 3V Efficiency vs Input Voltage W = 3V I OT = ma T A = C LTC-X 3.3V Efficiency vs Input Voltage = 3.3V I OT = ma TA = C LTC-X V Efficiency vs Input Voltage = V I OT = ma TA = C G9 G G LTC-X Shutdown Supply Current vs Input Voltage = V LTC-X Step-Down Mode V Load Transient Response LTC-X Step-p Mode V Load Transient Response POSITIVE SPPLY CRRENT (µa) C C C 6 G AC COPLED mv/div I OT ma/div = V, = V, C OT = µf, T A = C G ma ma AC COPLED mv/div I OT ma/div = 3.3V, = V, C OT = µf, T A = C G PIN FNCTIONS (Pin ): Shutdown Input. A logic low on the pin puts the part into shutdown mode. A logic high (V.6V) enables the part. At high voltages, the pin may still be controlled with 3V logic without causing a large rise in quiescent current. The pin may not float; connect to if unused. (Pin ): Open-Drain Power-On Reset Output. This pin will pull low upon initial power-up, during shutdown or until has been within 6.% of its regulated value for more than ms typ. /3 (LTC-X) (Pin 3): Output Voltage Select. A logic high on the /3 pin will force to regulate to V. A logic low will force to 3V (LTC-3/) or 3.3V (LTC- 3.3/). As with the pin, the /3 pin may be driven with 3V logic over the entire range. The /3 pin may not float. FB (LTC) (Pin 3): Feedback Input. The voltage on this pin is compared to the internal reference voltage (.3V) to keep the output in regulation. An external resistor divider is required between and FB to adjust the output voltage. Total divider resistance should not exceed M. GND (Pin ): Ground. Should be tied to a ground plane for best performance. C (Pin ): Charge Pump Flying Capacitor, Negative Terminal.

5 LTC Series PIN FNCTIONS C (Pin 6): Charge Pump Flying Capacitor, Positive Terminal. (Pin ): Charge Pump Input Voltage. May be between V and V. should be bypassed with a µf low ESR capacitor as close as possible to the pin for best performance. (Pin ): Regulated Output Voltage. Pin selectable to either 3V/V, 3.3V/V or adjustable using an external resistor divider (LTC). should be bypassed with a µf low ESR capacitor as close as possible to the pin for best performance. SI PLIFIED W BLOCK DIGRAM W C C STEP-P/STEP-DOWN CHARGE PMP (LTC-X) (LTC-X) 6kHz OSCILLATOR EN RESET CONTER EN V OS FB (LTC).3V V REF /3 (LTC-X) GND LTC BD APPLICATIONS INFORMATION Regulator Operation W The regulator section of the LTC, LTC-3/ and LTC-3.3/ consists of a charge pump, reference, comparator and some logic. The divided down output voltage is compared to the internal reference voltage. When the divided output drops below the reference voltage, the charge pump is enabled, which boosts the output back into regulation. Hysteresis in the comparator forces the regulator to burst on and off and causes approximately mv of peak-to-peak ripple to appear at the output. By enabling the charge pump only when needed, the parts achieve high efficiencies with low output load currents. Each part s charge pump has a unique architecture that allows the input voltage to be either stepped up or stepped down to produce a regulated output. Internal circuitry senses the to differential voltage and controls the charge pump operating mode. In addition, the effective output impedance of the charge pump is internally adjusted to prevent large inrush currents and allow for a wide input voltage range. When the input voltage is lower than the output voltage, the charge pump operates as a step-up voltage doubler. When the input voltage is greater than the output, the charge pump operates as a step-down gated switch.

6 LTC Series APPLICATIONS INFORMATION W Output Voltage Selection The LTC-X versions have internal resistor networks which set the output voltage. The /3 pin controls an internal switch that shorts out a portion of the resistor network to change the output voltage. A logic high on this pin produces a V output and a low produces either a 3V output or a 3.3V output. The output voltage of the LTC is selected using an external resistor divider (see Figure ). The output voltage is determined using the following formula: = (.3V)[ (R/R)] The total resistance of R and R should not exceed M, otherwise excess ripple may appear at. R OT COT I OT LT F Figure. Step-p Mode Equivalent Circuit OTPT RESISTANCE (Ω) 3 I OT = ma I OT = ma 6 R R 3 LTC FB C 6 GND C Figure. LTC Output Voltage Selection LTC F Maximum and I OT Calculations for the LTC The maximum output voltage and current available with the LTC can be calculated based on the effective output resistance of the charge pump and the open circuit output voltage. In step-up mode, the open circuit output voltage is approximately (see Figure ). In step-down mode, the open circuit output voltage equals. The relationship between R OT and in step-up mode is shown in Figure 3. The following formulas can be used to find the maximum output voltage that may be programmed using the LTC for a given minimum input voltage and output current load. Step-p Mode: Max = ()(Min ) (I OT )(R OT ) Step-Down Mode: Max = (Min ) (I OT )(R OT ) When (I OT )(R OT ) is less than the programmed, the part will automatically switch from step-down mode to step-up mode. In both step-up mode and step- 3 LT F3 Figure 3. Step-p Mode R OT vs Input Voltage down mode, R OT is internally adjusted to ensure that the maximum output current rating can be met. Capacitor Selection For best performance, low ESR capacitors are recommended for both C IN and C OT to reduce noise and ripple. The C IN and C OT capacitors should be either ceramic or tantalum and should be µf or greater. If the input source impedance is very low (<.Ω) C IN may not be needed. Increasing the size of C OT to µf or greater will reduce output voltage ripple particularly with high voltages (V or greater). A ceramic capacitor is recommended for the flying capacitor C with a value of.µf or.µf. Smaller values may be used in low output current applications. Output Ripple Normal LTC series operation produces voltage ripple on the pin. Output voltage ripple is required for the parts to regulate. Low frequency ripple exists due to the hysteresis in the sense comparator and propagation delays in the charge pump enable/disable circuits. High frequency ripple is also present mainly from the ESR

7 APPLICATIONS INFORMATION W (equivalent series resistance) in the output capacitor. Typical output ripple ( < V) under maximum load is mv peak-to-peak with a low ESR, µf output capacitor. For applications requiring to exceed V, a µf or larger C OT capacitor is recommended to maintain maximum ripple in the mv range. The magnitude of the ripple voltage depends on several factors. High input voltages increase the output ripple since more charge is delivered to C OT per charging cycle. A large C flying capacitor (>.µf) also increases ripple in step-up mode for the same reason. Large output current load and/or a small output capacitor (<µf) results in higher ripple due to higher output voltage dv/dt. High ESR capacitors (ESR >.Ω) on the output pin cause high frequency voltage spikes on with every clock cycle. There are several ways to reduce the output voltage ripple. A large C OT capacitor (µf or greater) will reduce both the low and high frequency ripple due to the lower C OT charging and discharging dv/dt and the lower ESR typically found with higher value (larger case size) capacitors. A low ESR (<.Ω) ceramic output capacitor will minimize the high frequency ripple, but will not reduce the low frequency ripple unless a high capacitance value is chosen. A reasonable compromise is to use a µf to µf tantalum capacitor in parallel with a µf to 3.3µF ceramic capacitor on to reduce both the low and high frequency ripple. An RC or LC filter may also be used to reduce high frequency voltage spikes (see Figure ). LTC/ LTC-X LTC/ LTC-X µf TANTALM µf TANTALM µf CERAMIC LT F Inrush Currents A common problem with switched capacitor regulators is inrush current particularly during power-up and com- Ω µf TANTALM Figure. Output Ripple Reduction Techniques Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC Series ing out of shutdown mode. Whenever large (or boosted ) to voltage differentials are present, most charge pumps will pull large current spikes from the input supply. Only the effective charge pump output impedance limits the current while the charge pump is enabled. This may disrupt input supply regulation, especially if the input supply is a low power DC/DC converter or linear regulator. The LTC family minimizes inrush currents both at start-up and under high to operation. Internal soft start circuitry controls the rate at which may be charged from V to its final regulated value. The typical start-up time from = V to V is ms. This corresponds to an effective charging current of only.ma for a µf output capacitor (.ma for µf, etc.). Note that any output current load present during start-up will add directly to the charging currents mentioned above. The soft start circuitry limits start-up current both at initial power-up and when coming out of shutdown. As the (or boosted ) to voltage differential grows, the effective output impedance of the charge pump is automatically increased by internal voltage sensing circuitry. This feature minimizes the current spikes pulled from whenever the charge pump is enabled and helps to reduce both input and output ripple. Power-On Reset The pin is an open-drain output that pulls low when the output voltage is out of regulation. When the rises to within 6.% of regulation, an internal timer is started which releases after ms (typ). In shutdown, the output is pulled low. In normal operation, an external pull-up resistor is generally used between the pin and. Protection Features All of the parts contain thermal shutdown and shortcircuit protection features. The parts will shut down when the junction temperature reaches approximately C and will resume operation once the junction temperature has dropped back to approximately C. The parts will limit output current to ma (typ) when a short circuit condition ( < mv) exists. The parts can survive an indefinite short to GND.

8 LTC Series TYPICAL APPLICATIONS Low Power, Low Noise Step-p/Step-Down V Supply with Reset ON OFF V 3V ON OFF RESET.M k Programmable 3V/V GSM SIM Card Power Supply NC 3 LTC-3/ /3 C 6 GND C.µF k 3 FB GND LTC C C = 3V OR V I OT = ma µf µf Li-Ion LTC TA 6.µF µf µf.v Ω IN LT- OT GND 3 = 3V TO V µf µf = V I OT = ma V RIPPLE < mv P-P LTC TA3 Positive and Negative Supply ON OFF NC 3 LTC-3/ /3 C 6 GND C.µF * CENTRAL SEMICONDCTOR CMPSH-3 DAL SCHOTTKY ** OPTIONAL CIRCITRY FOR MAINTAINING WITH LOW LOADS Q, Q: N39.µF µf * µf Q ** Ω.k Q.k µf = V I OT = ma,.v.v I OT = ma, 3.3V.V =.V TO.V = V TO 3.V I OT = ma LTC TA PACKAGE DESCRIPTION.. (.3.).. (..) RELATED PARTS TYP.3.69 (.36.)..9 (.3.3) *DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED.6" (.mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED." (.mm) PER SIDE Dimensions in inches (millimeters) unless otherwise noted. S Package -Lead Plastic Small Outline (Narrow.) (LTC DWG # --6).. (..).. (.9 6.9).9.9* (..) 6 3..** (3. 3.9) PART NMBER DESCRIPTION COMMENTS LTC Series Step-p/Step-Down Switched Capacitor DC/DC Converters V to V, 3.3V and V Versions, I OT to ma LTC6 Micropower, Regulated V Charge Pump DC/DC Converter I OT = ma ( V), I OT = ma ( 3V) LTC- Micropower, Regulated V Charge Pump DC/DC Converter LTC Without Shutdown and Packaged in SOT-3 LTC Micropower, Regulated V Charge Pump DC/DC Converter Available in -Pin MSOP, 6µA Quiescent Current, I OT = ma LTC/LTC6 SIM Power Supply and Level Translators Step-p/Step-Down SIM Power Supply and Level Translators LTC66 ma CMOS Voltage Converter V to V Conversion with Low Voltage Loss. (.) TYP SO 996 Linear Technology Corporation 63 McCarthy Blvd., Milpitas, CA 93- () 3-9 FAX: () 3- TELEX: f LT/TP 9 K PRINTED IN SA LINEAR TECHNOLOGY CORATION 99

DESCRIPTION FEATURES. LTC1550/LTC1551 Low Noise, Switched Capacitor Regulated Voltage Inverters APPLICATIONS TYPICAL APPLICATION

DESCRIPTION FEATURES. LTC1550/LTC1551 Low Noise, Switched Capacitor Regulated Voltage Inverters APPLICATIONS TYPICAL APPLICATION LTC55/LTC55 Low Noise, Switched Capacitor Regulated Voltage Inverters FEATRES Regulated Negative Voltage from a Single Positive Supply Low Output Ripple: Less Than mv P-P Typ High Charge Pump Frequency: