LTC3526L/LTC3526LB 550mA 1MHz Synchronous Step-Up DC/DC Converters in 2mm × 2mm DFN Description Features n n n n n n n n n n n n n n 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 1MHz Fixed Frequency Operation VIN > VOUT Operation Integrated Soft-Start Current Mode Control with Internal Compensation Burst Mode® Operation with 9µA IQ (LTC3526L) Low Noise PWM Operation (LT3526LB) Internal Synchronous Rectifier Logic Controlled Shutdown (IQ < 1µA) Anti-Ring Control Low Profile (2mm × 2mm × 0.75mm) DFN-6 Package Applications n n n n The LTC®3526L/LTC3526LB 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 a 680mV start-up voltage and operation down to 500mV once started. A switching frequency of 1MHz 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 features Burst Mode operation at light load conditions allowing it to maintain high efficiency over a wide range of load. The LTC3526LB 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 1µA and thermal shutdown. The LTC3526L/LTC3526LB are housed in a 2mm × 2mm × 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. Typical Application Efficiency and Power Loss vs Load Current 100 4.7µH 90 EFFICIENCY VIN 4.7µF OFF ON VOUT LTC3526L SHDN GND 1.78M VOUT 3.3V 200mA 4.7µF FB 1M 3526l TA01a 100 70 60 10 50 POWER LOSS 40 1 30 20 POWER LOSS (mW) VIN 1.6V TO 3.2V SW 1000 VIN = 2.4V 80 EFFICIENCY (%) n 0.1 10 0 0.01 0.1 1 10 100 0.01 1000 LOAD CURRENT (mA) 3526l TA01b 3526lfc LTC3526L/LTC3526LB 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)...............................................–40°C to 85°C Storage Temperature Range................... –65°C to 150°C 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 = 125°C, θJA = 102°C/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#PBF LTC3526LEDC#TRPBF LCSS 6-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C LTC3526LBEDC#PBF LTC3526LBEDC#TRPBF LCST 6-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C 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 –40°C to 85°C, otherwise specifications are at TA = 25°C. 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 Feedback Pin Input Current VFB = 1.30V 1.195 1.225 V 1 50 nA Quiescent Current—Shutdown VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V 0.01 1 µA Quiescent Current—Active Measured on VOUT, Nonswitching 250 500 µA Quiescent Current—Burst Measured on VOUT, FB > 1.230V (LTC3526L Only) N-Channel MOSFET Switch Leakage Current VSW = 5V 9 18 µA 0.1 5 µA 10 µA 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 N-Channel MOSFET Current Limit l Current Limit Delay to Output (Note 3) Maximum Duty Cycle VFB = 1.15V l Minimum Duty Cycle VFB = 1.3V l Switching Frequency SHDN Pin Input High Voltage SHDN Pin Input Low Voltage l 550 87 Ω 0.6 Ω 750 mA 60 ns 90 % 0 0.75 1 1.25 0.8 % MHz V 0.3 V 3526lfc LTC3526L/LTC3526LB 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/LTC3526LBE are 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 102°C/W. Typical Performance Characteristics 1000 100 100 80 10 50 1 40 30 PLOSS AT VIN = 1.0V PLOSS AT VIN = 1.2V PLOSS AT VIN = 1.5V 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) EFFICIENCY (%) 60 VIN = 1.2V VIN = 1.8V VIN = 2.4V VIN = 3.0V 70 60 50 1 40 30 10 0.01 1000 0 0.01 3526l G01 3526l G02 Efficiency vs Load Current and VIN for VOUT = 5V (LTC3526L) Maximum Output Current vs VIN 1000 400 90 80 100 50 40 30 20 10 0 0.01 10 VIN = 1.2V VIN = 2.4V VIN = 3.6V 1 VIN = 4.2V 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) 3526l G03 300 IOUT (mA) 60 POWER LOSS (mW) 70 VOUT = 3.3V 60 VOUT = 2.5V 50 VOUT = 1.8V 40 30 20 10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VIN (V) 3526l G04 Minimum Load Resistance During Start-Up vs VIN 10000 VOUT = 3.3V 350 VOUT = 5V 70 PLOSS AT VIN = 1.2V 0.1 PLOSS AT VIN = 1.8V PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.0V 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 20 0.1 10 POWER LOSS (mW) VIN = 1.0V VIN = 1.2V VIN = 1.5V 70 POWER LOSS (mW) EFFICIENCY (%) 100 90 80 100 20 EFFICIENCY (%) 1000 90 80 100 No-Load Input Current vs VIN (LTC3526L) IIN (µA) 90 Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3526L) VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V 1000 250 200 LOAD (Ω) 100 Efficiency vs Load Current and VIN for VOUT = 1.8V (LTC3526L) VOUT = 5V 150 100 100 50 0 0.5 L = 4.7µH 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VIN (V) 3526l G05 10 0.65 0.75 0.85 0.95 VIN (V) 1.05 1.15 3526l G06 3526lfc LTC3526L/LTC3526LB TYPICAL PERFORMANCE CHARACTERISTICS VOUT = 1.8V COUT = 10µF 25 L = 4.7µH 80 LOAD CURRENT (mA) 70 DELAY (µs) 30 30 90 60 50 40 30 20 20 ENTER BURST 15 10 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 0 4.5 1.0 1.25 VIN (V) 40 25 20 15 ENTER BURST 10 1.5 2.0 VIN (V) 3 VOUT = 5V COUT = 10µF L = 4.7µH 20 ENTER BURST 10 0.85 8 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 RDS(ON) (Ω) PMOS 0.55 0.50 0.45 NMOS 0.40 –1 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 3526l G09 RDS(ON) Change vs Temperature 1.3 NORMALIZED TO 25°C NORMALIZED TO 25°C 1.2 6 4 2 0 –2 –4 –6 1.1 1.0 0.9 0.8 –8 0.35 0.30 0 –3 1.5 4.5 NORMALIZED RDS(ON) FREQUECNY CHANGE (%) 0.80 0.60 NORMALIZED TO VOUT = 3.3V 1 Oscillator Frequency Change vs Temperature 0.90 0.65 2.0 Oscillator Frequency Change vs VOUT 3526l G08d RDS(ON) vs VOUT 0.70 1.75 –2 3526l G08c 0.75 1.5 2 LEAVE BURST 30 0 1.0 3.0 2.5 1.25 3526l G08b Burst Mode Threshold Current vs VIN (LTC3526L) 10 1.0 10 VIN (V) 5 0 ENTER BURST 15 0 1.0 1.5 FREQUENCY CHANGE (%) LEAVE BURST LOAD CURRENT (mA) LOAD CURRENT (mA) 50 30 20 3526l G08a Burst Mode Threshold Current vs VIN (LTC3526L) VOUT = 3.3V 35 COUT = 10µF L = 4.7µH LEAVE BURST 5 3526l G07 40 VOUT = 2.5V COUT = 10µF 25 L = 4.7µH LEAVE BURST 5 10 0 Burst Mode Threshold Current vs VIN (LTC3526L) LOAD CURRENT (mA) 100 Burst Mode Threshold Current vs VIN (LTC3526L) Start-Up Delay Time vs VIN 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 3526l G10 –10 –50 –30 –10 10 30 50 TEMPERATURE (°C) 70 90 3526l G11 0.7 –50 –30 –10 10 30 50 TEMPERATURE (°C) 70 90 3526l G12 3526lfc LTC3526L/LTC3526LB TYPICAL PERFORMANCE CHARACTERISTICS VFB vs Temperature 0.80 10.0 0.25 0.75 9.5 0 0.70 1mA LOAD –0.25 0.65 9.0 IQ (µA) NORMALIZED TO 25°C VIN (V) 0.50 CHANGE IN VFB (%) Burst Mode Quiesent Current vs VOUT (LTC3526L) Start-Up Voltage vs Temperature 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) 80 100 0.50 –50 25 0 25 50 TEMPERATURE (°C) 3526l G13 100 7.0 1.5 VOUT 10mV/DIV AC-COUPLED 3526l G16 2.5 3.0 3.5 VOUT (V) 4.0 4.5 SW PIN 2V/DIV VOUT 20mV/DIV AC-COUPLED INDUCTOR CURRENT 0.2A/DIV 5.0 3526l G15 Burst Mode Waveforms (LTC3526L) SW PIN 2V/DIV 2.0 3526l G14 Fixed Frequency Switching Waveform and VOUT Ripple VIN = 1.2V 500ns/DIV VOUT = 3.3V AT 100mA COUT = 10µF 75 VOUT and IIN During Soft-Start VOUT 1V/DIV INPUT CURRENT 0.2A/DIV SHDN PIN 1V/DIV VIN = 1.2V VOUT = 3.3V COUT = 10µF 10µs/DIV 3526l G17 Load Step Response (from Burst Mode Operation) (LTC3526L) VOUT 100mV/DIV AC-COUPLED VOUT = 3.3V COUT = 10µF 200µs/DIV 3526l G18 Load Step Response (Fixed Frequency) VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 50mA/DIV LOAD CURRENT 50mA/DIV VIN = 3.6V 100µs/DIV VOUT = 5V 20mA TO 170mA STEP COUT = 10µF 3526l G19 VIN = 3.6V 100µs/DIV VOUT = 5V 50mA TO 150mA STEP COUT = 10µF 3526l G20 3526lfc LTC3526L/LTC3526LB TYPICAL PERFORMANCE CHARACTERISTICS Load Step Response (Fixed Frequency) Load Step Response (from Burst Mode Operation) (LTC3526L) VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 50mA/DIV LOAD CURRENT 50mA/DIV VIN = 1.2V 100µs/DIV VOUT = 3.3V 50mA TO 100mA STEP COUT = 10µF 3526l G21 VIN = 1.2V 50µs/DIV VOUT = 3.3V 5mA TO 100mA STEP COUT = 10µF 3526l 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 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 1.5V 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 (4.7µF minimum) should be as short and 3526lfc LTC3526L/LTC3526LB Block Diagram VIN 0.8V TO 5V L1 4.7µH CIN 2.2µF 3 1 VIN VOUT SW VSEL VBEST WELL SWITCH VB VOUT VOUT 1.5V TO 5.25V 6 ANTI-RING 4 SHDN SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION – + 4M IPK COMP VREF IPK UVLO IZERO IZERO COMP 1MHz OSC CLK COUT 4.7µF R1 ERROR AMP SLEEP COMP START-UP LOGIC R2 5 SLOPE COMP + – VREF FB + – MODE CONTROL VREF CLAMP THERMAL SHUTDOWN Operation TSD WAKE CSS EXPOSED PAD GND 7 2 3526l BD (Refer to Block Diagram) The LTC3526L/LTC3526LB are 1MHz synchronous boost converters housed in a 6-lead 2mm × 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. With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3526L achieves high efficiency over a wide range of load currents. 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 LTC3526L/LTC3526LB include an independent startup 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. When either VIN or VOUT exceeds 1.3V typical, the IC enters normal operating mode. When the output voltage 3526lfc LTC3526L/LTC3526LB 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/LTC3526LB 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 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 1MHz. 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/LTC3526LB 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/LTC3526LB 4M ±30% VCNTRL R LTC3526L/LTC3526LB VIN 4M ±30% SHDN 1M ZETEX ZC2811E VCNTRL R > (VCNTRL/(VIN + 0.4) – 1)MΩ SHDN 1M 3526l 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. Zero Current Comparator The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier 3526lfc LTC3526L/LTC3526LB OPERATION (Refer to Block Diagram) 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-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/LTC3526LB 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 160°C, the LTC3526L/LTC3526LB 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 LTC3526L 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. In Burst Mode operation, the LTC3526L still switches at a fixed frequency of 1MHz, 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 transitions to sleep mode where the outputs are off and the LTC3526L 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 LTC3526L will automatically leave Burst Mode operation. Note that larger output capacitor values may cause this transition to occur at lighter loads. Once the LTC3526L 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 features continuous PWM operation at 1MHz. At very light loads, the LTC3526LB will exhibit pulse-skip operation. 3526lfc LTC3526L/LTC3526LB Applications Information VIN > VOUT Operation COMPONENT SELECTION The LTC3526L/LTC3526LB 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/LTC3526LB 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/LTC3526LB can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor values between 3.3µH and 6.8µH 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 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) 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/LTC3526LB 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 LTC3526L SW 1 GND 2 VIN + VIN 3 6 VOUT 5 FB MINIMIZE TRACE ON FB AND SW 4 SHDN MULTIPLE VIAS TO GROUND PLANE 3526l F02 Figure 2. Recommended Component Placement for Single Layer Board 3526lfc 10 LTC3526L/LTC3526LB APPLICATIONS INFORMATION losses, and must be able to support the peak 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/LTC3526LB. 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, LPS4018 MSS5131 MSS4020 MOS6020 ME3220 DS1605, DO1608 Coiltronics www.cooperet.com SD10, SD12, SD14, SD18, SD20, SD52, SD3114, SD3118 FDK (408) 432-8331 www.fdk.com MIP3226D4R7M, MIP3226D3R3M MIPF2520D4R7 MIPWT3226D3R0 Murata (714) 852-2001 www.murata.com LQH43C LQH32C (-53 series) 301015 Sumida (847) 956-0666 www.sumida.com CDRH5D18 CDRH2D14 CDRH3D16 CDRH3D11 CR43 CMD4D06-4R7MC CMD4D06-3R3MC Taiyo-Yuden www.t-yuden.com NP03SB NR3015T NR3012T TDK (847) 803-6100 www.component.tdk.com VLP VLF, VLCF Toko (408) 432-8282 www.tokoam.com D412C D518LC D52LC D62LCB Wurth (201) 785-8800 www.we-online.com 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 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/LTC3526LB are 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 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 3526lfc 11 LTC3526L/LTC3526LB Typical Applications 1-Cell to 1.8V Converter with <1mm Maximum Height 100 4.7µH* 90 VOUT = 1.8V 80 SW 1µF LTC3526L SHDN OFF ON VOUT 1.8V 150mA VOUT VIN 511k EFFICIENCY (%) VIN 0.8V TO 1.6V 10µF** FB GND 1M 70 60 50 40 30 20 3526l TA02a VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *FDK MIP3226D4R7M **MURATA GRM219R60J106KE19D 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA02b 1-Cell to 2.85V Converter 100 90 4.7µH* VOUT = 2.85V 80 VIN 0.8V TO 1.6V VOUT VIN 1µF LTC3526L SHDN OFF ON 1.4M VOUT 2.85V 100mA EFFICIENCY (%) SW 10µF FB GND 1M 70 60 50 40 30 20 3526l TA03a VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 0 0.01 *SUMIDA CDRH3D16-4R7 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA03b 1-Cell to 3.3V 100 4.7µH* 90 VOUT = 3.3V VIN 0.8V TO 1.6V VOUT VIN 1µF OFF ON LTC3526L SHDN 1.78M 10µF FB GND 22pF VOUT 3.3V 75mA 1M 3526l TA04a EFFICIENCY (%) 80 SW 70 60 50 40 30 20 VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *TAIYO-YUDEN NP03SB4R7M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA04b 3526lfc 12 LTC3526L/LTC3526LB TYPICAL APPLICATIONS 2-Cell to 3.3V 100 90 4.7µH* VOUT = 3.3V 80 SW 1µF LTC3526L SHDN OFF ON VOUT 3.3V 200mA VOUT VIN 1.78M 4.7µF FB GND EFFICIENCY (%) VIN 1.6V TO 3.2V 1M 70 60 50 40 30 20 3526l TA05a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 0 0.01 *TAIYO-YUDEN NP03SB4R7M 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA05b 2-Cell to 5V 100 90 6.8µH* VOUT = 5V VIN 1.6V TO 3.2V VOUT VIN 1µF OFF ON LTC3526L SHDN 3.24M 22pF 10µF FB GND VOUT 5V 150mA EFFICIENCY (%) 80 SW 1.02M 70 60 50 40 30 20 3526l TA06a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 0 0.01 *TAIYO-YUDEN NP03SB6R8M 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA06b Li-Ion to 5V 100 6.8µH* 90 VOUT = 5V VIN 2.7V TO 4.3V VOUT VIN 1µF OFF ON LTC3526L SHDN 3.24M 10µF FB GND 22pF VOUT 5V 200mA 1.02M 3526l TA08a EFFICIENCY (%) 80 SW 70 60 50 40 30 20 VIN = 4.2V VIN = 3.6V VIN = 3.0V 10 *TAIYO-YUDEN NP03SB6R8M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 3526l TA08b 3526lfc 13 LTC3526L/LTC3526LB Package Description DC Package 6-Lead Plastic DFN (2mm × 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 3526lfc 14 LTC3526L/LTC3526LB Revision History (Revision history begins at Rev C) REV DATE DESCRIPTION PAGE NUMBER C 9/10 Updated θJA on Pin Configuration 2 Updated Note 6 3 Updated Shutdown section 8 Updated Related Parts 16 3526lfc 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/LTC3526LB Typical Application 3.3V Converter with Output OR’d with 5V USB Input MBR120ESFT 5V USB 4.7µH VOUT 3.3V/5V USB SW VBATT 1.8V TO 3.2V VOUT VIN 1µF OFF ON LTC3526L SHDN 1.78M 10µF FB GND LDO DC/DC 1M 3526l TA07a Related Parts PART NUMBER DESCRIPTION COMMENTS LTC3526/LTC3526B 500mA, 1MHz/2.2MHz, Synchronous Step-Up DC/DC LTC3526-2/LTC3526B-2 Converters with Output Disconnect LTC3526L-2/LTC3526LB-2 94% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9µA, ISD < 1µA, 2mm × 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 = 7µA, ISD < 1µA, 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 = 7µA, ISD < 1µA, 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 × 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 = 19µA/300µA, ISD < 1µA, ThinSOT™ 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 = 12µA, Step-Up DC/DC Converters ISD < 1µA, 3mm × 3mm QFN-16 Package 3526lfc 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT 0910 REV C • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2007