LTC3526L-2/LTC3526LB-2 550mA 2MHz Synchronous Step-Up DC/DC Converters in 2mm x 2mm DFN Features n n n n n n n n n n n n n n n Description Delivers 3.3V at 100mA from a Single Alkaline/ NiMH Cell or 3.3V at 200mA from Two Cells VIN Start-Up Voltage: 680mV 1.5V 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(R) Operation with 9A IQ (LTC3526L-2) Low Noise PWM Operation (LTC3526LB-2) Internal Synchronous Rectifier Logic Controlled Shutdown (IQ < 1A) Anti-Ring Control Low Profile (2mm x 2mm x 0.75mm) 6-Lead DFN Package The LTC(R)3526L-2/LTC3526LB-2 are synchronous, fixed frequency step-up DC/DC converters with output disconnect. Synchronous rectification enables high efficiency in the low profile 2mm x 2mm DFN package. Battery life in single AA/AAA powered products is extended further with a 680mV 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 LTC3526L-2 features Burst Mode operation at light load conditions allowing it to maintain high efficiency over a wide range of load. The LTC3526LB-2 features fixed frequency operation for low noise applications. Anti-ring circuitry reduces EMI by damping the inductor in discontinuous mode. Additional features include a low shutdown current of under 1A and thermal shutdown. Applications n n n n The LTC3526L-2/LTC3526LB-2 are housed in a 2mm x 2mm x 0.75mm DFN package. Medical Instruments Noise Canceling Headphones Wireless Mice Bluetooth Headsets L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents pending. Typical Application Efficiency and Power Loss vs Load Current 100 2.2H 90 EFFICIENCY VIN 4.7F OFF ON VOUT LTC3526L-2 SHDN GND 1.78M 33pF 4.7F FB 1M 3526lb2 TA01a 100 70 60 10 50 POWER LOSS 40 1 30 20 POWER LOSS (mW) VIN 1.6V TO 3.2V VOUT 3.3V 200mA EFFICIENCY (%) 80 SW 1000 VIN = 2.4V 0.1 10 0 0.01 0.1 1 10 LOAD CURRENT (mA) 100 0.01 1000 3526lb2 TA01b 3526lb2fa LTC3526L-2/LTC3526LB-2 Absolute Maximum Ratings (Note 1) Pin Configuration VIN Voltage.................................................... -0.3V to 6V SW Voltage DC............................................................. -0.3V to 6V Pulsed <100ns.......................................... -0.3V to 7V SHDN, FB Voltage......................................... -0.3V to 6V VOUT. ............................................................ -0.3V to 6V Operating Temperature Range (Notes 2, 5)...............................................-40C to 85C Storage Temperature Range................... -65C to 150C TOP VIEW SW 1 GND 2 6 VOUT 7 VIN 3 5 FB 4 SHDN DC PACKAGE 6-LEAD (2mm s 2mm) PLASTIC DFN TJMAX = 125C, JA = 102C/W (NOTE 6) EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PC BOARD Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3526LEDC-2#PBF LTC3526LEDC-2#TRPBF LFFC 6-Lead (2mm x 2mm) Plastic DFN -40C to 85C LTC3526LBEDC-2#PBF LTC3526LBEDC-2#TRPBF LFFD 6-Lead (2mm x 2mm) Plastic DFN -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ Electrical Characteristics The l denotes the specifications which apply over the specified operating temperature range of -40C to 85C, otherwise specifications are at TA = 25C. VIN = 1.2V, VOUT = 3.3V unless otherwise noted. PARAMETER CONDITIONS Minimum Start-Up Input Voltage ILOAD = 1mA Input Voltage Range After Start-Up. (Minimum Voltage is Load Dependent) MIN TYP MAX 0.68 0.8 UNITS V l 0.5 5 V Output Voltage Adjust Range l 1.5 5.25 V Feedback Pin Voltage l 1.165 1.195 1.225 V Feedback Pin Input Current VFB = 1.30V 1 50 nA Quiescent Current--Shutdown VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V 0.01 1 A 250 500 A 9 18 A Quiescent Current--Active Measured on VOUT, Nonswitching Quiescent Current--Burst Measured on VOUT, FB > 1.230V (LTC3526L-2 Only) N-Channel MOSFET Switch Leakage Current VSW = 5V 0.1 5 A 10 A P-Channel MOSFET Switch Leakage Current VSW = 5V, VOUT = 0V 0.1 N-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.4 P-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.6 750 mA 60 ns 87 90 % 1.8 2 N-Channel MOSFET Current Limit l Current Limit Delay to Output (Note 3) Maximum Duty Cycle VFB = 1.15V, VOUT = 5V l Minimum Duty Cycle VFB = 1.3V l Switching Frequency SHDN Pin Input High Voltage SHDN Pin Input Low Voltage l 550 0 2.4 0.8 % MHz V 0.3 V 3526lb2fa LTC3526L-2/LTC3526LB-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 LTC3526LE-2/LTC3526LBE-2 are guaranteed to meet performance specifications from 0C to 85C. Specifications over -40C to 85C 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 125C 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 102C/W. Typical Performance Characteristics Efficiency vs Load Current and VIN for VOUT = 1.8V (LTC3526L-2) 100 1000 100 100 80 100 1000 50 10 1 40 30 20 PLOSS AT VIN = 0.9V PLOSS AT VIN = 1.2V PLOSS AT VIN = 1.5V 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 60 10 50 VIN = 1.2V VIN = 1.8V 1 VIN = 2.4V VIN = 3.0V 40 30 10 0.01 1000 0 0.01 0.1 3526lb2 G01 Efficiency vs Load Current and VIN for VOUT = 5V (LTC3526L-2) 100 1000 400 100 50 10 40 30 1 20 300 IOUT (mA) 60 POWER LOSS (mW) 70 VOUT = 2.5V VOUT = 1.8V 50 40 30 0.1 20 10 0.5 0.01 1000 1.0 1.5 2.0 2.5 3.0 3.5 VIN (V) 3526lb2 G02 4.5 4.0 3526lb2 G03 Minimum Load Resistance During Start-Up vs VIN 10000 VOUT = 3.3V 350 80 1 10 100 LOAD CURRENT (mA) VOUT = 3.3V 60 Maximum Output Current vs VIN 90 VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 1000 250 200 VOUT = 5V 150 100 100 50 10 0 0.01 PLOSS AT VIN = 1.2V PLOSS AT VIN = 1.8V PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.0V 20 0.1 80 70 IIN (A) 60 70 LOAD () VIN = 0.9V VIN = 1.2V VIN = 1.5V VOUT = 5V 90 100 POWER LOSS (mW) 70 EFFICIENCY (%) 90 POWER LOSS (mW) EFFICIENCY (%) No-Load Input Current vs VIN (LTC3526L-2) Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3526L-2) 90 80 EFFICIENCY (%) TA = 25C, unless otherwise noted. 0.1 1 10 100 LOAD CURRENT (mA) PLOSS AT VIN = 1.2V PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.6V PLOSS AT VIN = 4.2V 0.1 1000 0 0.5 L = 2.2H 1.0 1.5 2.0 2.5 VIN (V) VIN = 1.2V VIN = 2.4V VIN = 3.6V VIN = 4.2V 3.0 3.5 4.0 4.5 3526lb2 G05 10 0.65 0.75 0.85 0.95 VIN (V) 1.05 1.15 3526lb2 G06 3526lb2 G04 3526lb2fa LTC3526L-2/LTC3526LB-2 Typical Performance Characteristics Burst Mode Threshold Current vs VIN (LTC3526L-2) Start-Up Delay Time vs VIN 35 VOUT = 1.8V COUT = 10F 30 L = 2.2H 90 LOAD CURRENT (mA) 80 60 50 40 30 20 25 ENTER BURST 20 15 10 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 0 4.5 Burst Mode Threshold Current vs VIN (LTC3526L-2) 70 60 LOAD CURRENT (mA) LOAD CURRENT (mA) VOUT = 3.3V COUT = 10F 50 L = 2.2H 40 LEAVE BURST 30 20 ENTER BURST 10 1.0 1.1 1.2 1.3 VIN (V) 1.4 1.5 1.0 ENTER BURST 20 10 8 FREQUECNY CHANGE (%) 0.75 0.70 PMOS 0.55 0.50 NMOS 1.6 VIN (V) 1.8 2.0 2.2 3526lb2 G08b NORMALIZED TO VOUT = 3.3V 1 0 -1 -2 -3 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 -4 1.5 4.5 2.0 3526lb2 G08d 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 3526lb2 G09 RDS(ON) Change vs Temperature 1.3 NORMALIZED TO 25C NORMALIZED TO 25C 1.2 6 NORMALIZED RDS(ON) 0.80 1.4 2 Oscillator Frequency Change vs Temperature 0.85 1.2 3 30 0.90 4 2 0 -2 -4 -6 1.1 1.0 0.9 0.8 -8 0.35 0.30 10 4 LEAVE BURST 40 RDS(ON) vs VOUT 0.40 15 Oscillator Frequency Change vs VOUT 50 3526lb2 G08c 0.45 ENTER BURST 20 3526lb2 G08a VOUT = 5V COUT = 10F L = 2.2H 0 1.0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 VIN (V) 0.60 25 0 1.6 10 0.65 30 Burst Mode Threshold Current vs VIN (LTC3526L-2) 60 LEAVE BURST 5 3526lb2 G07 RDS(ON) () VOUT = 2.5V 35 COUT = 10F L = 2.2H 5 10 0 40 LEAVE BURST FREQUENCY CHANGE (%) DELAY (s) 70 Burst Mode Threshold Current vs VIN (LTC3526L-2) LOAD CURRENT (mA) 100 0 TA = 25C, unless otherwise noted. 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 3526lb2 G10 -10 -50 -30 -10 10 30 50 TEMPERATURE (C) 70 90 3526lb2 G11 0.7 -50 -30 -10 10 30 50 TEMPERATURE (C) 70 90 3526lb2 G12 3526lb2fa LTC3526L-2/LTC3526LB-2 Typical Performance Characteristics VFB vs Temperature Start-Up Voltage vs Temperature 0.80 10.0 0.25 0.75 9.5 0 0.70 1mA LOAD -0.25 0.65 NO LOAD 8.5 -0.50 0.60 8.0 -0.75 0.55 7.5 -1.00 20 40 60 -60 -40 -20 0 TEMPERATURE (C) 80 0.50 -50 100 25 0 25 50 TEMPERATURE (C) 75 3526lb2 G13 Load Regulation 0.5 VOUT = 1.8V 0.4 VOUT = 3.3V 0.4 0.3 0.2 0.2 0 -0.1 -0.2 -0.3 VIN = 0.9V VIN = 1.2V VIN = 1.5V -0.4 -0.5 0.01 0.1 1 10 LOAD (mA) 100 1000 CHANGE IN VOUT (%) 0.3 0.2 0.1 0.1 0 -0.1 -0.2 -0.3 VIN = 1.2V VIN = 1.8V VIN = 2.4V -0.4 -0.5 0.01 3526lb2 G23 Fixed Frequency Switching Waveform and VOUT Ripple 0.1 1 10 LOAD (mA) 100 1000 3526lb2 G16 4.0 5.0 4.5 3526lb2 G15 VOUT = 5V 0 -0.1 -0.2 VIN = 1.2V VIN = 2.4V VIN = 3.6V VIN = 4.2V -0.3 -0.4 -0.5 0.01 0.1 1 10 LOAD (mA) 100 1000 3526lb2 G25 VOUT and IIN During Soft-Start VOUT 1V/DIV INPUT CURRENT 0.2A/DIV SHDN PIN 1V/DIV VOUT 20mV/DIV AC-COUPLED VIN = 1.2V 200ns/DIV VOUT = 3.3V AT 100mA COUT = 4.7F 3.0 3.5 VOUT (V) 3526lb2 G24 SW PIN 2V/DIV VOUT 20mV/DIV AC-COUPLED 2.5 0.1 Burst Mode Waveforms (LTC3526L-2) SW PIN 2V/DIV 2.0 Load Regulation 0.5 0.3 CHANGE IN VOUT (%) CHANGE IN VOUT (%) 0.4 7.0 1.5 100 3526lb2 G14 Load Regulation 0.5 Burst Mode Quiesent Current vs VOUT (LTC3526L-2) 9.0 IQ (A) NORMALIZED TO 25C VIN (V) 0.50 CHANGE IN VFB (%) TA = 25C, unless otherwise noted. VIN = 1.2V 20s/DIV VOUT = 3.3V AT 5mA COUT = 10F 3526lb2 G17 VOUT = 3.3V COUT = 4.7F 200s/DIV 3526lb2 G18 3526lb2fa LTC3526L-2/LTC3526LB-2 Typical Performance Characteristics TA = 25C, unless otherwise noted. Load Step Response (from Burst Mode Operation) (LTC3526L-2) Load Step Response (Fixed Frequency) VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 50mA/DIV LOAD CURRENT 50mA/DIV VIN = 3.6V 100s/DIV VOUT = 5V 20mA TO 170mA STEP COUT = 10F 3526lb2 G19 VIN = 3.6V 100s/DIV VOUT = 5V 50mA TO 150mA STEP COUT = 4.7F Load Step Response (Fixed Frequency) 3526lb2 G20 Load Step Response (from Burst Mode Operation) (LTC3526L-2) VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 50mA/DIV LOAD CURRENT 50mA/DIV VIN = 1.2V 100s/DIV VOUT = 3.3V 50mA TO 100mA STEP COUT = 4.7F 3526lb2 G21 VIN = 1.2V 50s/DIV VOUT = 3.3V 5mA TO 100mA STEP COUT = 10F 3526lb2 G22 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, Exposed Pad Pin 7): Signal and Power Ground. Provide a short direct PCB path between GND and the (-) side of the input and output capacitors. 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. VIN (Pin 3): Input Supply Pin. Connect a minimum of 1F ceramic decoupling capacitor from this pin to ground using short direct PCB traces. SHDN (Pin 4): Logic Controlled Shutdown Input. There is an internal 4M pull-down on this pin. * SHDN = High: Normal operation * SHDN = Low: Shutdown, quiescent current < 1A 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 1.5V to 5.25V by: R2 VOUT = 1.195V * 1+ R1 VOUT (Pin 6): Output voltage sense and drain of the internal synchronous rectifier. PCB trace from VOUT to the output filter capacitor (4.7F minimum) should be as short and wide as possible. 3526lb2fa LTC3526L-2/LTC3526LB-2 Block Diagram VIN 0.8V TO 5V L1 2.2H CIN 2.2F 3 1 VIN VOUT SW VSEL VBEST WELL SWITCH VB VOUT ANTI-RING 4 SHDN SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION - + 4M 3 IPK COMP VREF IPK UVLO IZERO IZERO COMP 2MHz OSC CLK COUT 4.7F R1 ERROR AMP SLEEP COMP START-UP LOGIC R2 5 SLOPE COMP + - VREF FB VOUT 1.5V TO 5.25V 6 + - MODE CONTROL VREF CLAMP THERMAL SHUTDOWN Operation TSD WAKE CSS EXPOSED PAD GND 7 2 3526lb2 BD (Refer to Block Diagram) The LTC3526L-2/LTC3526LB-2 are 2MHz synchronous boost converters housed in a 6-lead 2mm x 2mm DFN package. With a guaranteed ability to start up and operate from inputs less than 0.8V, this device features 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. range of load currents. Burst Mode operation maintains high efficiency at very light loads, reducing the quiescent current to just 9A. Operation can be best understood by referring to the Block Diagram. With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3526L-2 achieves high efficiency over a wide When either VIN or VOUT exceeds 1.3V typical, the IC enters normal operating mode. When the output voltage Low Voltage Start-Up The LTC3526L-2/LTC3526LB-2 include an independent start-up oscillator designed to start up at an input voltage of 0.68V (typical). Soft-start and inrush current limiting are provided during start-up, as well as normal mode. 3526lb2fa LTC3526L-2/LTC3526LB-2 Operation (Refer to Block Diagram) 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 LTC3526L-2/LTC3526LB-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 750mA (typical) in approximately 0.5ms, allowing start-up 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. Although SHDN can be driven above VIN or VOUT (up to the absolute maximum rating) without damage, the LTC3526L-2/LTC3526LB-2 have a proprietary test mode that may be engaged if SHDN is held in the range of 0.5V to 1V higher than the greater of VIN or VOUT. If the test mode is engaged, normal PWM switching action is interrupted, which can cause undesirable operation in some applications. Therefore, in applications where SHDN may be driven above VIN, a resistor divider or other means must be employed to keep the SHDN voltage below (VIN + 0.4V) to prevent the possibility of the test mode being engaged. Please refer to Figure 1 for two possible implementations. LTC3526L-2/LTC3526LB-2 4M 30% VCNTRL R LTC3526L-2/LTC3526LB-2 VIN 4M 30% SHDN 1M ZETEX ZC2811E VCNTRL R > (VCNTRL/(VIN + 0.4) - 1)M SHDN 1M 3526lb2 F01 Figure 1. Recommended Shutdown Circuits when Driving SHDN above VIN 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 1.5V to 5.25V. R2 VOUT = 1.195V * 1+ R1 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 750mA, independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. 3526lb2fa LTC3526L-2/LTC3526LB-2 Operation (Refer to Block Diagram) Zero Current Comparator Burst Mode OPERATION 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. The LTC3526L-2 will enter Burst Mode operation at light load current 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. 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-ring circuit 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 LTC3526L-2/LTC3526LB-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 SW 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 160C, the LTC3526L-2/ LTC3526LB-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 15C. In Burst Mode operation, the LTC3526L-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 LTC3526L-2 transitions to sleep mode where the outputs are off and the LTC3526L-2 consumes only 9A 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 (10F or greater), or with a small capacitor (10pF to 50pF) connected between VOUT and FB. As the load current increases, the LTC3526L-2 will automatically leave Burst Mode operation. Note that larger output capacitor values may cause this transition to occur at lighter loads. Once the LTC3526L-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 current. Burst Mode operation is inhibited during start-up and softstart and until VOUT is at least 0.24V greater than VIN. The LTC3526LB-2 features continuous PWM operation at 2MHz. At very light loads, the LTC3526LB-2 will exhibit pulse-skipping operation. 3526lb2fa LTC3526L-2/LTC3526LB-2 Applications Information VIN > VOUT Operation COMPONENT SELECTION The LTC3526L-2/LTC3526LB-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. Inductor Selection Short-Circuit Protection The LTC3526L-2/LTC3526LB-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). The LTC3526L-2/LTC3526LB-2 can utilize small surface mount chip inductors due to their fast 2MHz switching frequency. Inductor values between 1.5H and 4.7H 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 6.8H will increase component size while providing little improvement in output current capability. The minimum inductance value is given by: L> Schottky Diode Although not recommended, 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. ( VIN(MIN) * VOUT(MAX ) - VIN(MIN) 2 * Ripple * VOUT(MAX ) ) where: Ripple = Allowable inductor current ripple (amps peakpeak) VIN(MIN) = Minimum input voltage PCB layout guidelines The high speed operation of the LTC3526L-2/LTC3526LB2 demands careful attention to board layout. A careless layout will result in reduced performance. Figure 2 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. 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 LTC3526L-2 SW 1 GND 2 VIN + VIN 3 6 VOUT 5 FB MINIMIZE TRACE ON FB AND SW 4 SHDN MULTIPLE VIAS TO GROUND PLANE 3526lb2 F02 Figure 2. Recommended Component Placement for Single Layer Board 3526lb2fa 10 LTC3526L-2/LTC3526LB-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 current of 750mA seen on the LTC3526L-2/LTC3526LB-2. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested components and suppliers. Table 1. Recommended Inductors VENDOR PART/STYLE Coilcraft (847) 639-6400 www.coilcraft.com LPO4815 LPS4012, LPS3314 MSS4020 ME3220 Coiltronics www.cooperet.com SD10, SD12, SD3114, SD3118 FDK (408) 432-8331 www.fdk.com MIP3226D MIPF2520D MIPWT3226D MIPSZ2012D MIPS2520D Murata (714) 852-2001 www.murata.com LQH3NP LQH32P LQM2MPN Sumida (847) 956-0666 www.sumida.com CDRH2D14 CDRH2D11 CDRH3D11 Taiyo-Yuden www.t-yuden.com NR3010T NR3015T NR3012T TDK (847) 803-6100 www.component.tdk.com VLP VLF, VLCF Toko (408) 432-8282 www.tokoam.com D412C Wurth (201) 785-8800 www.we-online.com WE-TPC type S, M, TH, XS 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 4.7F to 10F output capacitor is sufficient for most applications. Larger values 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 LTC3526L-2/ LTC3526LB-2 are designed to be stable with output capacitor values of 4.7F 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 2.2F 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 PHONE WEBSITE AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Taiyo-Yuden (408) 573-4150 www.t-yuden.com TDK (847) 803-6100 www.component.tdk.com Samsung (408) 544-5200 www.sem.samsung.com 3526lb2fa 11 LTC3526L-2/LTC3526LB-2 Typical Applications 1-Cell to 1.8V Converter with <1mm Maximum Height 100 2.2H* 90 VOUT = 1.8V VIN 0.8V TO 1.6V VOUT VIN 1F LTC3526L-2 SHDN OFF ON VOUT 1.8V 150mA 511k 68pF 10F** FB GND 1M EFFICIENCY (%) 80 SW 3526lb2 TA02a 70 60 50 40 30 20 VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *FDK MIPWT3226D2R2 **MURATA GRM219R60J106KE19D 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA02b Fixed Frequency 1-Cell to 2.85V Low Noise Converter 100 90 2.2H* VOUT = 2.85V SW VIN 0.8V TO 1.6V VOUT VIN 1F LTC3526LB-2 SHDN OFF ON VOUT 2.85V 100mA 1.4M 4.7F FB GND EFFICIENCY (%) 80 1M 70 60 50 40 30 20 3526lb2 TA03a VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *SUMIDA CDRH2D11NP-2R2N 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA03b 1-Cell to 3.3V 100 90 2.2H* VOUT = 3.3V VIN 0.8V TO 1.6V SW VOUT VIN 1F OFF ON LTC3526L-2 SHDN 1.78M 10F FB GND 33pF VOUT 3.3V 75mA 1M 3526lb2 TA04a EFFICIENCY (%) 80 70 60 50 40 30 20 VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *TAIYO-YUDEN NR3015T2R2M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA04b 3526lb2fa 12 LTC3526L-2/LTC3526LB-2 Typical Applications 2-Cell to 3.3V 100 90 2.2H* VOUT = 3.3V VIN 1.6V TO 3.2V VOUT VIN 1F OFF ON LTC3526L-2 SHDN 1.78M 33pF 4.7F FB GND VOUT 3.3V 200mA EFFICIENCY (%) 80 SW 1M 70 60 50 40 30 20 3526lb2 TA05a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 *COILCRAFT LPS3314-222ML 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA05b 2-Cell to 5V 100 90 3.3H* VOUT = 5V VIN 1.6V TO 3.2V SW VOUT VIN 1F OFF ON LTC3526L-2 SHDN 3.24M 33pF 10F FB GND VOUT 5V 150mA EFFICIENCY (%) 80 1.02M 70 60 50 40 30 20 3526lb2 TA06a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 0 0.01 *COILCRAFT LPS4018-332ML 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA06b Li-Ion to 5V 100 3.6H* 90 VOUT = 5V VIN 2.7V TO 4.3V VOUT VIN 1F OFF ON LTC3526L-2 SHDN GND 3.24M 22pF VOUT 5V 200mA 10F FB 1.02M 3526lb2 TA08a *WURTH 744031003 EFFICIENCY (%) 80 SW 70 60 50 40 30 20 VIN = 4.2V VIN = 3.6V VIN = 3.0V 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526lb2 TA08b 3526lb2fa 13 LTC3526L-2/LTC3526LB-2 Package Description DC Package 6-Lead Plastic DFN (2mm x 2mm) (Reference LTC DWG # 05-08-1703 Rev B) 0.70 p0.05 2.55 p0.05 1.15 p0.05 0.61 p0.05 (2 SIDES) PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 1.42 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.125 TYP 0.56 p 0.05 (2 SIDES) 0.40 p 0.10 4 6 2.00 p0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) PIN 1 NOTCH R = 0.20 OR 0.25 s 45o CHAMFER R = 0.05 TYP 0.200 REF 0.75 p0.05 3 (DC6) DFN REV B 1309 1 0.25 p 0.05 0.50 BSC 1.37 p0.05 (2 SIDES) 0.00 - 0.05 BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3526lb2fa 14 LTC3526L-2/LTC3526LB-2 Revision History REV DATE DESCRIPTION PAGE NUMBER A 9/10 Changed 60C/W to 102C/W in Note 6 3 Updated Pin 2 text in Pin Functions 6 Updated Shutdown section 8 Updated Related Parts 16 3526lb2fa 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. 15 LTC3526L-2/LTC3526LB-2 Typical Application 3.3V Converter with Output OR'd with 5V USB Input MBR120ESFT 5V USB 2.2H* VOUT 3.3V/5V USB SW VBATT 1.8V TO 3.2V VOUT VIN 1F OFF ON LTC3526L-2 SHDN 1.78M 33pF 10F FB GND LDO DC/DC 1M 3526lb2 TA07a *MURATA LQH3NPN2R2NM0 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC3526/LTC3526B LTC3526-2/LTC3526B-2 LTC3526L/LTC3526LB 500mA, 1MHz/2.2MHz, Synchronous Step-Up DC/DC Converters with Output Disconnect 94% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9A, ISD < 1A, 2mm x 2mm DFN-6 Package LTC3525L-3 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect 93% Efficiency VIN: 0.88V to 4.5V, VOUT = 3V, IQ = 7A, ISD < 1A, SC-70 Package LTC3525-3 LTC3525-3.3 LTC3525-5 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect 95% Efficiency VIN: 1V to 4.5V, VOUT(MAX) = 3.3V or 5V, IQ = 7A, ISD < 1A, SC-70 Package LTC3427 500mA ISW, 1.2MHZ, Synchronous Step-Up DC/DC Converter with Output Disconnect 93% Efficiency VIN: 1.8V to 4.5V, VOUT(MAX) = 5V, 2mm x 2mm DFN Package LTC3400/LTC3400B 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converters 92% Efficiency VIN: 1V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD < 1A, ThinSOTTM Package LTC3527/LTC3527-1 Dual 600mA/400mA ISW, 1.2MHz/2.2MHz Synchronous 94% Efficiency VIN: 0.7V to 5V, VOUT(MAX) = 5.25V, IQ = 12A, Step-Up DC/DC Converters ISD < 1A, 3mm x 3mm QFN-16 Package 3526lb2fa 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com LT 0910 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2009