LTC3526EDC-2-TRPBF

LTC3526-2/LTC3526B-2 500mA 2MHz Synchronous Step-Up DC/DC Converters in 2mm × 2mm DFN FEATURES n n n n n n n n n n n n n n n n DESCRIPTION The LTC®3526-2/LTC3526B-2 are synchronous, fixed frequency step-up DC/DC converters with output disconnect. Synchronous rectification enables high efficiency in the low profile 2mm × 2mm DFN package. Battery life in single AA/AAA powered products is extended further with an 850mV start-up voltage and operation down to 500mV once started. A switching frequency of 2MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The current mode PWM design is internally compensated, reducing external parts count. The LTC3526-2 features Burst Mode operation at light load conditions, while the LTC3526B-2 features continuous switching. Anti-ring circuitry eliminates EMI concerns by damping the inductor in discontinuous mode. Additional features include a low shutdown current of under 1μA and thermal shutdown. The LTC3526-2/LTC3526B-2 are housed in a 6-pin 2mm × 2mm × 0.75mm DFN package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents pending. Delivers 3.3V at 100mA from a Single Alkaline/ NiMH Cell or 3.3V at 200mA from Two Cells VIN Start-Up Voltage: 850mV VIN Operating Range: 0.5V to 5V 1.6V to 5.25V VOUT Range Up to 94% Efficiency Output Disconnect 2MHz Fixed Frequency Operation VIN > VOUT Operation Integrated Soft-Start Current Mode Control with Internal Compensation Burst Mode® Operation with 9μA Quiescent Current (LTC3526-2) Low Noise PWM Operation (LTC3526B-2) Internal Synchronous Rectifier Logic Controlled Shutdown (IQ < 1μA) Anti-Ringing Control Low Profile (2mm × 2mm × 0.75mm) DFN-6 Package APPLICATIONS n n n n n Medical Instruments Flash-Based MP3 Players Noise Canceling Headphones Wireless Mice Bluetooth Headsets TYPICAL APPLICATION 2.2μH SW VIN 1.6V TO 3.2V 1μF OFF ON VIN VOUT 1.78M 4.7μF 1M 35262b2fA01a LTC3526-2 Efficiency and Power Loss vs Load Current 100 90 80 EFFICIENCY (%) VIN = 2.4V EFFICIENCY 100 POWER LOSS (mW) 1000 VOUT 3.3V 200mA 70 60 50 40 30 20 10 0 0.01 0.1 1 10 100 0.01 1000 35262b2f TA01b 10 POWER LOSS LTC3526-2 SHDN GND FB 1 0.1 LOAD CURRENT (mA) 35262b2fa 1 LTC3526-2/LTC3526B-2 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW SW 1 GND 2 VIN 3 7 6 VOUT 5 FB 4 SHDN VIN Voltage ................................................... –0.3V to 6V SW Voltage DC............................................................ –0.3V to 6V Pulsed 1.230V (LTC3526-2 Only) VSW = 5V VSW = 5V, VOUT = 0V VOUT = 3.3V VOUT = 3.3V l 500 85 1.8 0.9 700 60 90 0 2 2.4 0.3 1 2 % MHz V V μA μA 35262b2fa 2 LTC3526-2/LTC3526B-2 ELECTRICAL CHARACTERISTICS Note 1: 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 LTC3526E-2 is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Specification is guaranteed by design and not 100% tested in production. Note 4: Current measurements are made when the output is not switching. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 6: Failure to solder the exposed backside of the package to the PC board ground plane will result in a thermal resistance much higher than 60°C/W. TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current and VIN for VOUT = 1.8V (LTC3526-2) 100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 PLOSS AT VIN = 1.0V PLOSS AT VIN = 1.2V PLOSS AT VIN = 1.5V 1 10 100 LOAD CURRENT (mA) 0.1 1 VIN = 1.0V VIN = 1.2V VIN = 1.5V 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 90 80 70 60 50 40 30 20 10 0 0.01 0.1 PLOSS AT VIN = 1.2V 0.1 PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.0V 1 10 100 LOAD CURRENT (mA) 0.01 1000 1 VIN = 1.2V VIN = 2.4V VIN = 3.0V 100 POWER LOSS (mW) Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3526-2) 1000 100 90 80 70 IIN (μA) 60 50 40 30 20 No-Load Input Current vs VIN VOUT = 5V VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 10 10 0.01 1000 10 0.5 1.0 1.5 2.0 2.5 VIN (V) 3.0 3.5 4.0 4.5 35262b2f G01 35262b2f G02 35262b2f G04 Efficiency vs Load Current and VIN for VOUT = 5V (LTC3526-2) 100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 10 VIN = 1.2V VIN = 2.4V VIN = 3.6V 1 VIN = 4.2V 100 300 IOUT (mA) 250 200 POWER LOSS (mW) 1000 400 350 Maximum Output Current vs VIN VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V LOAD (Ω) 1000 Minimum Load Resistance During Start-Up vs VIN 100 VOUT = 5V 150 100 50 0 0.5 L = 2.2μH 1.0 1.5 2.0 2.5 VIN (V) 35262b2f G05 PLOSS AT VIN = 1.2V 0.1 PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.6V PLOSS AT VIN = 4.2V 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 35262b2f 3.0 3.5 4.0 4.5 10 0.85 0.95 1.05 VIN (V) 1.15 1.25 35262b2f 35262b2fa 3 LTC3526-2/LTC3526B-2 TYPICAL PERFORMANCE CHARACTERISTICS Start-Up Delay Time vs VIN 100 90 80 70 DELAY (μs) 60 50 40 30 20 10 0 1.0 1.5 2.0 0 2.5 3.0 VIN (V) 3.5 4.0 4.5 1 1.25 VIN (V) 1.5 35262b2f G08a Burst Mode Threshold Current vs VIN 30 VOUT = 1.8V COUT = 10μF 25 L = 2.2μH LOAD CURRENT (mA) 20 LEAVE BURST 15 ENTER BURST 10 5 LOAD CURRENT (mA) 40 Burst Mode Threshold Current vs VIN VOUT = 2.5V 35 COUT = 10μF L = 2.2μH 30 25 LEAVE BURST 20 15 ENTER BURST 10 5 0 1 1.25 VIN (V) 35262b2f 1.5 1.75 35262b2f Burst Mode Threshold Current vs VIN 50 VOUT = 3.3V 45 COUT = 10μF L = 2.2μH 40 LOAD CURRENT (mA) 35 30 25 20 15 10 5 0 1.0 1.5 2.0 VIN (V) 2.5 3.0 35262b2f Burst Mode Threshold Current vs VIN 60 50 LOAD CURRENT (mA) 40 LEAVE BURST 30 20 ENTER BURST 10 0 1.0 VOUT = 5V COUT = 10μF L = 2.2μH FREQUENCY CHANGE (%) 2 1 0 –1 –2 –3 –4 –5 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 4.5 Oscillator Frequency Change vs VOUT NORMALIZED TO 3.3V LEAVE BURST ENTER BURST –6 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 35262b2f G08d 35262b2f RDS(ON) vs VOUT 0.90 0.85 0.80 0.75 0.70 RDS(ON) (Ω) 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 NMOS PMOS FREQUENCY CHANGE (%) 10 8 6 4 2 0 –2 –4 –6 –8 Oscillator Frequency Change vs Temperature 1.3 NORMALIZED TO 25˚C 1.2 NORMALIZED RDS(ON) 1.1 1.0 0.9 0.8 RDS(ON) Change vs Temperature NORMALIZED TO 25˚C –10 –50 –30 –10 10 30 50 TEMPERATURE (˚C) 70 90 0.7 –50 –30 –10 10 30 50 TEMPERATURE (˚C) 70 90 35262b2f 35262b2f G11 35262b2f G12 35262b2fa 4 LTC3526-2/LTC3526B-2 TYPICAL PERFORMANCE CHARACTERISTICS VFB vs Temperature 0.50 0.25 CHANGE IN VFB (%) 0 VIN (V) –0.25 –0.50 –0.75 –1.00 20 40 60 –60 –40 –20 0 TEMPERATURE (˚C) 1.00 NORMALIZED TO 25˚C 0.95 0.90 IQ (μA) 0.85 0.80 0.75 0.70 –50 Start-Up Voltage vs Temperature LOAD = 1mA 10.0 9.5 9.0 8.5 8.0 7.5 7.0 1.5 Burst Mode Quiescent Current vs VOUT 80 100 –30 –10 10 30 –50 TEMPERATURE (°C) 70 90 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 35262b2f 35262b2f G14 35262b2f Fixed Frequency Switching Waveform and VOUT Ripple Burst Mode Waveforms VOUT 1V/DIV INPUT CURRENT 0.2A/DIV SHDN PIN 1V/DIV 20μs/DIV VIN = 1.2V VOUT = 3.3V AT 5mA COUT = 10μF 35262b2 VOUT and IIN During Soft-Start SW PIN 2V/DIV VOUT 10mV/DIV AC COUPLED 200ns/DIV VIN = 1.2V VOUT = 3.3V AT 50mA COUT = 4.7μF 35262b2f SW PIN 2V/DIV VOUT 50mV/DIV AC COUPLED VOUT = 3.3V COUT = 10μF 200μs/DIV 35262b2f Load Step Response (from Burst Mode Operation) VOUT 100mV/DIV AC COUPLED LOAD CURRENT 50mA/DIV VIN = 3.6V 100μs/DIV VOUT = 5V 20mA TO 170mA STEP COUT = 10μF 35262b2f Load Step Response (Fixed Frequency) VOUT 100mV/DIV AC COUPLED LOAD CURRENT 50mA/DIV VIN = 3.6V 100μs/DIV VOUT = 5V 50mA TO 150mA STEP COUT = 10μF 35262b2f 35262b2fa 5 LTC3526-2/LTC3526B-2 TYPICAL PERFORMANCE CHARACTERISTICS Load Step Response (Fixed Frequency) VOUT 100mV/DIV AC COUPLED LOAD CURRENT 50mA/DIV VIN = 1.2V 100μs/DIV VOUT = 3.3V 50mA TO 100mA STEP COUT = 10μF 35262b2f Load Step Response (from Burst Mode Operation) VOUT 100mV/DIV AC COUPLED LOAD CURRENT 50mA/DIV VIN = 1.2V 50μs/DIV VOUT = 3.3V 5mA TO 100mA STEP COUT = 10μF 35262b2f PIN FUNCTIONS SW (Pin 1): Switch Pin. Connect inductor between SW and VIN. Keep PCB trace lengths as short and wide as possible to reduce EMI. If the inductor current falls to zero or SHDN is low, an internal anti-ringing switch is connected from SW to VIN to minimize EMI. GND (Pin 2): Signal and Power Ground. Provide a short direct PCB path between GND and the (–) side of the input and output capacitors. VIN (Pin 3): Input Supply Pin. Connect a minimum of 1μF ceramic decoupling capacitor from this pin to ground using short direct PCB traces. SHDN (Pin 4): Logic Controlled Shutdown Input. There is an internal 4MΩ pull-down on this pin. • SHDN = High: Normal operation • SHDN = Low: Shutdown, quiescent current < 1μA FB (Pin 5): Feedback Input to the gm Error Amplifier. Connect resistor divider tap to this pin. The top of the divider connects to the output capacitor, the bottom of the divider connects to GND. Referring to the Block Diagram, the output voltage can be adjusted from 1.6V to 5.25V by: VOUT = 1.195V • 1+ R2 R1 VOUT (Pin 6): Output voltage sense and drain of the internal synchronous rectifier. PCB trace from VOUT to the output filter capacitor (4.7μF minimum) should be as short and wide as possible. Exposed Pad (Pin 7): The Exposed Pad must be soldered to the PCB ground plane. It serves as an additional ground connection and as a means of conducting heat away from the package. 35262b2fa 6 LTC3526-2/LTC3526B-2 BLOCK DIAGRAM VIN 0.85V TO 5V L1 2.2μH CIN 2.2μF VOUT 3 VIN VSEL VBEST VB 1 SW WELL SWITCH VOUT 1.6V TO 5.25V R2 VOUT ANTI-RING GATE DRIVERS AND ANTI-CROSS CONDUCTION 6 4 SHDN 4M SHUTDOWN SHUTDOWN –+ Σ IPK IZERO IPK COMP SLOPE COMP FB IZERO COMP 5 R1 COUT 4.7μF UVLO START-UP LOGIC 2MHz OSC CLK MODE CONTROL CLAMP THERMAL SHUTDOWN TSD WAKE CSS EXPOSED PAD 7 GND 2 + – VREF 1.195V ERROR AMP SLEEP COMP + – VREF 35262b2f 35262b2fa 7 LTC3526-2/LTC3526B-2 OPERATION (Refer to Block Diagram) The LTC3526-2/LTC3526B-2 are 2MHz synchronous boost converters housed in a 6-lead 2mm × 2mm DFN package. With the ability to start up and operate from inputs less than 1V, these devices feature fixed frequency, current mode PWM control for exceptional line and load regulation. The current mode architecture with adaptive slope compensation provides excellent transient load response, requiring minimal output filtering. Internal soft-start and internal loop compensation simplifies the design process while minimizing the number of external components. With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3526-2 achieves high efficiency over a wide range of load currents. Automatic Burst Mode operation maintains high efficiency at very light loads, reducing the quiescent current to just 9μA. Operation can be best understood by referring to the Block Diagram. LOW VOLTAGE START-UP The LTC3526-2/LTC3526B-2 include an independent startup oscillator designed to start up at an input voltage of 0.85V (typical). Soft-start and inrush current limiting are provided during start-up, as well as normal mode. When either VIN or VOUT exceeds 1.4V typical, the IC enters normal operating mode. When the output voltage exceeds the input by 0.24V, the IC powers itself from VOUT instead of VIN. At this point the internal circuitry has no dependency on the VIN input voltage, eliminating the requirement for a large input capacitor. The input voltage can drop as low as 0.5V. The limiting factor for the application becomes the availability of the power source to supply sufficient energy to the output at low voltages, and maximum duty cycle, which is clamped at 90% typical. Note that at low input voltages, small voltage drops due to series resistance become critical, and greatly limit the power delivery capability of the converter. LOW NOISE FIXED FREQUENCY OPERATION Soft-Start The LTC3526-2/LTC3526B-2 contain internal circuitry to provide soft-start operation. The soft-start circuitry slowly ramps the peak inductor current from zero to its peak value of 700mA (typical) in approximately 0.5ms, allowing startup into heavy loads. The soft-start circuitry is reset in the event of a shutdown command or a thermal shutdown. Oscillator An internal oscillator sets the switching frequency to 2MHz. Shutdown Shutdown is accomplished by pulling the SHDN pin below 0.3V and enabled by pulling the SHDN pin above 0.8V typical. Note that SHDN can be driven above VIN or VOUT, as long as it is limited to less than the absolute maximum rating. Error Amplifier The positive input of the transconductance error amplifier is internally connected to the 1.195V reference and the negative input is connected to FB. Clamps limit the minimum and maximum error amp output voltage for improved large-signal transient response. Power converter control loop compensation is provided internally. An external resistive voltage divider from VOUT to ground programs the output voltage via FB from 1.6V to 5.25V. VOUT = 1.195V • 1+ Current Sensing Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage that is summed with the internal slope compensation. The summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. Current Limit The current limit comparator shuts off the N-channel MOSFET switch once its threshold is reached. The current limit comparator delay to output is typically 60ns. Peak switch current is limited to approximately 700mA, independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. 35262b2fa R2 R1 8 LTC3526-2/LTC3526B-2 OPERATION (Refer to Block Diagram) Zero Current Comparator The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier when this current reduces to approximately 30mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. Synchronous Rectifier To control inrush current and to prevent the inductor current from running away when VOUT is close to VIN, the P-channel MOSFET synchronous rectifier is only enabled when VOUT > (VIN + 0.24V). Anti-Ringing Control The anti-ringing control connects a resistor across the inductor to prevent high frequency ringing on the SW pin during discontinuous current mode operation. Although the ringing of the resonant circuit formed by L and CSW (capacitance on SW pin) is low energy, it can cause EMI radiation. Output Disconnect The LTC3526-2/LTC3526B-2 are designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows for VOUT to go to zero volts during shutdown, drawing no current from the input source. It also allows for inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must not be an external Schottky diode connected between the SW pin and VOUT. The output disconnect feature also allows VOUT to be pulled high, without any reverse current into a battery connected to VIN. Thermal Shutdown If the die temperature exceeds 160°C, the LTC3526-2/ LTC3526B-2 will go into thermal shutdown. All switches will be off and the soft-start capacitor will be discharged. The device will be enabled again when the die temperature drops by about 15°C. Burst Mode OPERATION The LTC3526-2 will automatically enter Burst Mode operation at light load and return to fixed frequency PWM mode when the load increases. Refer to the Typical Performance Characteristics to see the output load Burst Mode threshold current vs VIN. The load current at which Burst Mode operation is entered can be changed by adjusting the inductor value. Raising the inductor value will lower the load current at which Burst Mode operation is entered. In Burst Mode operation, the LTC3526-2 still switches at a fixed frequency of 2MHz, using the same error amplifier and loop compensation for peak current mode control. This control method eliminates any output transient when switching between modes. In Burst Mode operation, energy is delivered to the output until it reaches the nominal regulation value, then the LTC3526-2 transitions to sleep mode where the outputs are off and the LTC3526-2 consumes only 9μA of quiescent current from VOUT. When the output voltage droops slightly, switching resumes. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Burst Mode output voltage ripple, which is typically 1% peak-to-peak, can be reduced by using more output capacitance (10μF or greater), or with a small capacitor (10pF to 50pF) connected between VOUT and FB. As the load current increases, the LTC3526-2 will automatically leave Burst Mode operation. Note that larger output capacitor values may cause this transition to occur at lighter loads. Once the LTC3526-2 has left Burst Mode operation and returned to normal operation, it will remain there until the output load is reduced below the burst threshold. Burst Mode operation is inhibited during start-up and softstart and until VOUT is at least 0.24V greater than VIN. The LTC3526B-2 features continuous PWM operation at 2MHz. At very light loads, the LTC3526B-2 will exhibit pulse-skip operation. 35262b2fa 9 LTC3526-2/LTC3526B-2 APPLICATIONS INFORMATION VIN > VOUT OPERATION The LTC3526-2/LTC3526B-2 will maintain voltage regulation even when the input voltage is above the desired output voltage. Note that the efficiency is much lower in this mode, and the maximum output current capability will be less. Refer to the Typical Performance Characteristics. SHORT-CIRCUIT PROTECTION The LTC3526-2/LTC3526B-2 output disconnect feature allows output short circuit while maintaining a maximum internally set current limit. To reduce power dissipation under short-circuit conditions, the peak switch current limit is reduced to 400mA (typical). SCHOTTKY DIODE Although it is not required, adding a Schottky diode from SW to VOUT will improve efficiency by about 2%. Note that this defeats the output disconnect and short-circuit protection features. PCB LAYOUT GUIDELINES The high speed operation of the LTC3526-2/LTC3526B-2 demands careful attention to board layout. A careless layout will result in reduced performance. Figure 1 shows the recommended component placement. A large ground pin copper area will help to lower the die temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. COMPONENT SELECTION Inductor Selection The LTC3526-2/LTC3526B-2 can utilize small surface mount chip inductors due to their fast 2MHz switching frequency. Inductor values between 1.5μH and 3.3μH are suitable for most applications. Larger values of inductance will allow slightly greater output current capability (and lower the Burst Mode threshold) by reducing the inductor ripple current. Increasing the inductance above 10μH will increase size while providing little improvement in output current capability. The minimum inductance value is given by: L> where: VIN(MIN) • VOUT(MAX) VIN(MIN) 2 • RIPPLE • VOUT(MAX ) ( ) Ripple = Allowable inductor current ripple (amps peakpeak) VIN(MIN) = Minimum input voltage VOUT(MAX) = Maximum output voltage The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to support the peak LTC3526-2 SW 1 6 VOUT GND 2 5 FB MINIMIZE TRACE ON FB AND SW + VIN VIN 3 4 SHDN MULTIPLE VIAS TO GROUND PLANE 35262b2f Figure 1. Recommended Component Placement for Single Layer Board 35262b2fa 10 LTC3526-2/LTC3526B-2 APPLICATIONS INFORMATION inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core area to support the peak inductor currents of 700mA seen on the LTC3526-2/LTC3526B-2. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested components and suppliers. Table 1. Recommended Inductors VENDOR Coilcraft (847) 639-6400 www.coilcraft.com PART/STYLE LPO4815 LPS4012, LPS4018 MSS5131 MSS4020 MOS6020 ME3220 DS1605, DO1608 SD10, SD12, SD14, SD18, SD20, SD52, SD3114, SD3118 MIP3226D4R7M, MIP3226D3R3M MIPF2520D4R7 MIPWT3226D3R0 LQH43C LQH32C (-53 series) 301015 CDRH5D18 CDRH2D14 CDRH3D16 CDRH3D11 CR43 CMD4D06-4R7MC CMD4D06-3R3MC NP03SB NR3015T NR3012T VLP VLF VLCF , D412C D518LC D52LC D62LCB WE-TPC type S, M Output and Input Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. A 4.7μF to 10μF output capacitor is sufficient for most applications. Larger values up to 22μF may be used to obtain extremely low output voltage ripple and improve transient response. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Y5V types should not be used. The internal loop compensation of the LTC3526-2 is designed to be stable with output capacitor values of 4.7μF or greater (without the need for any external series resistor). Although ceramic capacitors are recommended, low ESR tantalum capacitors may be used as well. A small ceramic capacitor in parallel with a larger tantalum capacitor may be used in demanding applications that have large load transients. Another method of improving the transient response is to add a small feed-forward capacitor across the top resistor of the feedback divider (from VOUT to FB). A typical value of 22pF will generally suffice. Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It follows that ceramic capacitors are also a good choice for input decoupling and should be located as close as possible to the device. A 2.2μF input capacitor is sufficient for most applications, although larger values may be used without limitations. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their selection of ceramic capacitors. Table 2. Capacitor Vendor Information SUPPLIER AVX Murata Taiyo-Yuden TDK Samsung PHONE (803) 448-9411 (714) 852-2001 (408) 573-4150 (847) 803-6100 (408) 544-5200 WEBSITE www.avxcorp.com www.murata.com www.t-yuden.com www.component.tdk.com www.sem.samsung.com Coiltronics www.cooperet.com FDK (408) 432-8331 www.fdk.com Murata (714) 852-2001 www.murata.com Sumida (847) 956-0666 www.sumida.com Taiyo-Yuden www.t-yuden.com TDK (847) 803-6100 www.component.tdk.com Toko (408) 432-8282 www.tokoam.com Wurth (201) 785-8800 www.we-online.com 35262b2fa 11 LTC3526-2/LTC3526B-2 TYPICAL APPLICATIONS 1-Cell to 1.8V Converter with