LTC3526-2/LTC3526B-2 500mA 2MHz Synchronous Step-Up DC/DC Converters in 2mm × 2mm DFN FEATURES DESCRIPTION n 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. n n n n n n n n n n n n n n APPLICATIONS n n n n n 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. Medical Instruments Flash-Based MP3 Players Noise Canceling Headphones Wireless Mice Bluetooth Headsets TYPICAL APPLICATION LTC3526-2 Efficiency and Power Loss vs Load Current 100 2.2μH 90 VIN 1μF OFF ON EFFICIENCY VOUT 3.3V 200mA VOUT LTC3526-2 SHDN GND 1.78M 4.7μF FB 100 70 60 10 50 POWER LOSS 40 1 30 1M 35262b2fA01a 20 POWER LOSS (mW) SW VIN 1.6V TO 3.2V 1000 VIN = 2.4V 80 EFFICIENCY (%) n 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 0.1 10 0 0.01 0.1 1 10 100 0.01 1000 LOAD CURRENT (mA) 35262b2f TA01b 35262b2fa 1 LTC3526-2/LTC3526B-2 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) 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 (Note 2).... –40°C to 85°C Storage Temperature Range................... –65°C to 150°C TOP VIEW SW 1 GND 2 6 VOUT 7 5 FB 4 SHDN VIN 3 DC PACKAGE 6-LEAD (2mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 60°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 LTC3526EDC-2#PBF LTC3526EDC-2#TRPBF LCNM 6-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C LTC3526BEDC-2#PBF LTC3526BEDC-2#TRPBF LCNP 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 Output Voltage Adjust Range MIN l 1.7 1.6 l 1.165 0°C to 85°C Feedback Pin Voltage Feedback Pin Input Current VFB = 1.30V TYP MAX 0.85 1 UNITS V 5.25 5.25 V V 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 (LTC3526-2 Only) 9 18 μA N-Channel MOSFET Switch Leakage Current VSW = 5V 0.1 5 μA P-Channel MOSFET Switch Leakage Current VSW = 5V, VOUT = 0V 0.1 10 μA N-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.4 Ω P-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.6 Ω 700 mA 60 ns l N-Channel MOSFET Current Limit Current Limit Delay to Output 500 (Note 3) Maximum Duty Cycle VFB = 1.15V, VOUT = 5V l Minimum Duty Cycle VFB = 1.3V l l Switching Frequency SHDN Pin Input High Voltage 85 90 1.8 2 2.4 0.9 VSHDN = 1.2V VSHDN = 3.3V % MHz V SHDN Pin Input Low Voltage SHDN Pin Input Current % 0 0.3 1 0.3 V 1 2 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 Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3526-2) 100 1000 80 50 1 40 30 20 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) 60 10 50 1 40 30 10 0 0.01 0.01 1000 0.1 Efficiency vs Load Current and VIN for VOUT = 5V (LTC3526-2) 1000 400 30 20 10 0 0.01 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) 35262b2f 300 IOUT (mA) 40 10 POWER LOSS (mW) 70 50 20 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VIN (V) 35262b2f G04 Minimum Load Resistance During Start-Up vs VIN 1000 VOUT = 3.3V 350 100 60 VOUT = 1.8V 10 0.5 Maximum Output Current vs VIN 90 80 VOUT = 2.5V 50 35262b2f G02 35262b2f G01 100 VOUT = 3.3V 60 30 0.01 1000 1 10 100 LOAD CURRENT (mA) VOUT = 5V 40 PLOSS AT VIN = 1.2V 0.1 PLOSS AT VIN = 2.4V PLOSS AT VIN = 3.0V 20 0.1 80 70 IIN (μA) 10 100 VIN = 1.2V VIN = 2.4V VIN = 3.0V 70 POWER LOSS (mW) 60 POWER LOSS (mW) VIN = 1.0V VIN = 1.2V VIN = 1.5V EFFICIENCY (%) 100 70 VOUT = 2.5V VOUT = 1.8V 250 LOAD (Ω) 80 EFFICIENCY (%) 90 90 90 EFFICIENCY (%) No-Load Input Current vs VIN 100 1000 200 VOUT = 5V 150 100 100 50 0 0.5 L = 2.2μH 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VIN (V) 35262b2f G05 10 0.85 0.95 1.05 VIN (V) 1.15 1.25 35262b2f 35262b2fa 3 LTC3526-2/LTC3526B-2 TYPICAL PERFORMANCE CHARACTERISTICS Burst Mode Threshold Current vs VIN Start-Up Delay Time vs VIN 40 30 100 VOUT = 2.5V 35 COUT = 10μF L = 2.2μH LOAD CURRENT (mA) 80 70 60 50 40 30 20 LOAD CURRENT (mA) VOUT = 1.8V COUT = 10μF 25 L = 2.2μH 90 DELAY (μs) Burst Mode Threshold Current vs VIN 20 LEAVE BURST 15 ENTER BURST 10 5 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 1.25 VIN (V) 1.5 LOAD CURRENT (mA) LOAD CURRENT (mA) 50 25 20 15 2 NORMALIZED TO 3.3V 1 40 LEAVE BURST 30 20 ENTER BURST 10 1.5 2.0 VIN (V) 0 1.0 3.0 2.5 1.5 2.0 2.5 3.0 VIN (V) 3.5 0.90 10 0.85 8 0.75 RDS(ON) (Ω) 0.70 PMOS 0.55 0.50 NMOS 0.40 4.0 –3 –4 –6 1.5 4.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 35262b2f RDS(ON) Change vs Temperature 1.3 NORMALIZED TO 25˚C NORMALIZED TO 25˚C 1.2 6 NORMALIZED RDS(ON) FREQUENCY CHANGE (%) 0.80 0.45 –2 Oscillator Frequency Change vs Temperature RDS(ON) vs VOUT 0.60 –1 35262b2f G08d 35262b2f 0.65 0 –5 5 1.0 1.75 Oscillator Frequency Change vs VOUT VOUT = 5V COUT = 10μF L = 2.2μH ENTER BURST 0 1.5 35262b2f FREQUENCY CHANGE (%) 60 VOUT = 3.3V 45 COUT = 10μF L = 2.2μH 40 LEAVE BURST 1.25 1 VIN (V) Burst Mode Threshold Current vs VIN 50 10 ENTER BURST 35262b2f G08a Burst Mode Threshold Current vs VIN 30 15 0 1 4.5 35262b2f 35 LEAVE BURST 20 5 0 1.0 25 10 10 0 30 4 2 0 –2 –4 –6 1.1 1.0 0.9 0.8 –8 0.35 0.30 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 35262b2f –10 –50 –30 –10 10 30 50 TEMPERATURE (˚C) 70 90 35262b2f G11 0.7 –50 –30 –10 10 30 50 TEMPERATURE (˚C) 70 90 35262b2f G12 35262b2fa 4 LTC3526-2/LTC3526B-2 TYPICAL PERFORMANCE CHARACTERISTICS VFB vs Temperature 1.00 10.0 LOAD = 1mA NORMALIZED TO 25˚C 0.95 9.5 0 0.90 9.0 –0.25 IQ (μA) 0.25 VIN (V) CHANGE IN VFB (%) 0.50 Burst Mode Quiescent Current vs VOUT Start-Up Voltage vs Temperature 0.85 8.5 –0.50 0.80 8.0 –0.75 0.75 7.5 –1.00 20 40 60 –60 –40 –20 0 TEMPERATURE (˚C) 80 0.70 –50 100 –30 –10 10 30 –50 TEMPERATURE (°C) 70 90 Fixed Frequency Switching Waveform and VOUT Ripple 2.5 3.0 3.5 VOUT (V) 4.0 SW PIN 2V/DIV 5.0 VOUT and IIN During Soft-Start VOUT 1V/DIV SW PIN 2V/DIV INPUT CURRENT 0.2A/DIV SHDN PIN 1V/DIV VOUT 50mV/DIV AC COUPLED 35262b2f 4.5 35262b2f Burst Mode Waveforms VOUT 10mV/DIV AC COUPLED 2.0 35262b2f G14 35262b2f 200ns/DIV VIN = 1.2V VOUT = 3.3V AT 50mA COUT = 4.7μF 7.0 1.5 35262b2 20μs/DIV VIN = 1.2V VOUT = 3.3V AT 5mA COUT = 10μF Load Step Response (from Burst Mode Operation) VOUT 100mV/DIV AC COUPLED VOUT = 3.3V COUT = 10μF 200μs/DIV 35262b2f 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 35262b2f 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) Load Step Response (from Burst Mode Operation) 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 35262b2f 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 nect 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: 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 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. FB (Pin 5): Feedback Input to the gm Error Amplifier. Con- 35262b2fa 6 LTC3526-2/LTC3526B-2 BLOCK DIAGRAM L1 2.2μH CIN 2.2μF 3 1 SW VIN VOUT VSEL VBEST WELL SWITCH VB VOUT ANTI-RING 4 SHDN SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION – + 4M Σ VREF IPK COMP 1.195V IPK UVLO COUT 4.7μF 5 R1 + – MODE CONTROL CLK IZERO COMP ERROR AMP SLEEP COMP START-UP LOGIC FB SLOPE COMP IZERO 2MHz OSC VOUT 1.6V TO 5.25V 6 R2 + – VIN 0.85V TO 5V VREF CLAMP THERMAL SHUTDOWN TSD WAKE CSS EXPOSED PAD GND 7 2 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. 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. 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. 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. 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 Oscillator An internal oscillator sets the switching frequency to 2MHz. Shutdown 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. 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 700mA, independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. 35262b2fa 8 LTC3526-2/LTC3526B-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 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. 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. 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 COMPONENT SELECTION 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). 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: SCHOTTKY DIODE L> 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. ( VIN(MIN) • VOUT(MAX) VIN(MIN) where: ) 2 • RIPPLE • VOUT(MAX) Ripple = Allowable inductor current ripple (amps peakpeak) VIN(MIN) = Minimum input voltage PCB LAYOUT GUIDELINES VOUT(MAX) = Maximum output voltage 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. 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 GND 2 + VIN 3 6 VOUT 5 FB MINIMIZE TRACE ON FB AND SW 4 SHDN VIN 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 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 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 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 35262b2fa 11 LTC3526-2/LTC3526B-2 TYPICAL APPLICATIONS 1-Cell to 1.8V Converter with <1mm Maximum Height for Low-Noise Applications 100 90 2.2μH* VOUT = 1.8V 80 SW 1μF VOUT 1.8V 150mA VOUT VIN LTC3526B-2 SHDN OFF ON EFFICIENCY (%) VIN 1V TO 1.6V 511k 4.7μF** FB GND 70 60 50 40 30 1M 20 35262b2fA02a VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *FDK MIPF2520D2R2 **MURATA GRM219R60J475KE19D 0 0.1 1 10 100 LOAD CURRENT (mA) 1000 35262b2f TA02b 1-Cell to 3.3V 100 90 2.7μH* VOUT = 3.3V SW VIN 1V TO 1.6V VOUT VIN 1μF OFF ON LTC3526-2 SHDN 1.78M 10μF FB GND 22pF VOUT 3.3V 75mA EFFICIENCY (%) 80 70 60 50 40 30 1M 35262b2fA04a 20 VIN = 1.5V VIN = 1.2V VIN = 0.9V 10 *TAIYO-YUDEN NP03SB2R7M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 35262b2f TA04b 35262b2fa 12 LTC3526-2/LTC3526B-2 TYPICAL APPLICATIONS 2-Cell to 3.3V 100 90 2.7μH* VOUT = 3.3V 80 SW 1μF OFF ON VOUT 3.3V 200mA VOUT VIN LTC3526-2 SHDN EFFICIENCY (%) VIN 2V TO 3.2V 1.78M 4.7μF FB GND 70 60 50 40 30 1M 20 35262b2fA05a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 *TAIYO-YUDEN NP03SB2R7M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 35262b2f TA05b 3.3V Converter with Output OR’d with 5V USB Input MBR120ESFT 5V USB 2.2μH VOUT 3.3V/5V USB SW VBATT 1.8V TO 3.2V VOUT VIN 1μF OFF ON LTC3526-2 SHDN GND LDO 1.78M DC/DC 4.7μF FB 1M 35262b2fA07a 35262b2fa 13 LTC3526-2/LTC3526B-2 TYPICAL APPLICATIONS 2-Cell to 5V 100 VOUT = 5V 90 3.3μH* SW VIN 2V TO 3.2V VOUT VIN 1μF LTC3526-2 SHDN OFF ON VOUT 5V 150mA 3.24M 22pF 10μF FB GND EFFICIENCY (%) 80 70 60 50 40 30 1.02M 20 35262b2fA06a VIN = 3.0V VIN = 2.4V VIN = 1.8V 10 *TAIYO-YUDEN NP03SB3R3M 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 35262b2f TA06b Li-Ion to 5V 100 3.3μH* 90 VOUT = 5V VIN 2.7V TO 4.3V VOUT VIN 1μF OFF ON LTC3526-2 SHDN 3.24M 10μF FB GND 22pF VOUT 5V 200mA 70 60 50 40 30 1.02M 35262b2fA08a *TAIYO-YUDEN NP03SB3R3M EFFICIENCY (%) 80 SW 20 VIN = 4.2V VIN = 3.6V VIN = 3.0V 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 35262b2f TA08b 35262b2fa 14 LTC3526-2/LTC3526B-2 PACKAGE DESCRIPTION DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 0.61 ±0.05 (2 SIDES) PIN 1 BAR PACKAGE TOP MARK OUTLINE (SEE NOTE 6) 0.38 ± 0.05 4 2.00 ±0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 ± 0.05 0.50 BSC 1.42 ±0.05 (2 SIDES) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 6 1 (DC6) DFN 1103 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 1.37 ±0.05 (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 35262b2fa 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 LTC3526-2/LTC3526B-2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1613 800mA ISW, 1.4MHz, Step-Up DC/DC Converter VIN: 1.1V to 10V, VOUT(MAX) = 34V, IQ = 3mA, ISD < 1μA, 5-Lead SOT-23 Package LT1615 350mA ISW, Micropower, Step-Up DC/DC Converter VIN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20μA, ISD < 1μA, ThinSOTTM Package LT1618 1.5A ISW, 1.4MHz, Constant Current/Constant Voltage Step-Up DC/DC Converter VIN: 1.6V to 18V, VOUT(MAX) = 35V, IQ = 1.8mA, ISD < 1μA, DFN, MSOP Packages LT1930/LT1930A 1A ISW, 1.2MHz/2.2MHz, Step-Up DC/DC Converters VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD < 1μA, ThinSOT Package LTC3400/LTC3400B 600mA ISW, 1.2MHz, Synchronous Step-Up DC/DC Converters 92% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5V, IQ = 19μA/300μA, ISD < 1μA, ThinSOT Package LTC3401 1A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38μA, ISD < 1μA, 10-Lead MS Package LTC3402 2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency VIN: 0.5V to 5V, VOUT(MAX) = 6V, IQ = 38μA, ISD < 1μA, 10-Lead MS Package LTC3421 3A ISW, 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12μA, ISD < 1μA, QFN24 Package LTC3422 1.5A ISW, 3MHz Synchronous Step-Up DC/DC Converter with Output Disconnect 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25µA, ISD < 1µA, 3mm × 3mm DFN Package LTC3423/LTC3424 1A/2A ISW, 3MHz, Synchronous Step-Up DC/DC Converter 95% Efficiency VIN: 0.5V to 5.5V, VOUT(MAX) = 5.5V, IQ = 38μA, ISD < 1μA, 10-Lead MS Package LTC3426 2A ISW, 1.2MHz, Step-Up DC/DC Converter 92% Efficiency VIN: 1.6V to 4.3V, VOUT(MAX) = 5V, ISD < 1μA, SOT-23 Package LTC3427 500mA ISW, 1.25MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, IQ = 350μA, ISD < 1μA, 2mm × 2mm DFN Package LTC3428 500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up DC/DC Converters with Output Disconnect 92% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, ISD < 1µA, 2mm × 2mm DFN Package LTC3429 600mA ISW, 500kHz, Synchronous Step-Up DC/DC Converter with Output Disconnect and Soft-Start 96% Efficiency VIN: 0.5V to 4.4V, VOUT(MAX) = 5V, IQ = 20μA/300μA, ISD < 1μA, ThinSOT Package LTC3458 1.4A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter/Output Disconnect/Burst Mode Operation 93% Efficiency VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, IQ = 15μA, ISD < 1μA, DFN12 Package LTC3458L 1.7A ISW, 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect, Automatic Burst Mode Operation 94% Efficiency VOUT(MAX) = 6V, IQ = 12μA, DFN12 Package LTC3459 70mA ISW, 10V Micropower Synchronous Boost Converter/Output Disconnect/Burst Mode Operation VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10μA, ISD < 1μA, ThinSOT 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 LTC3526/LTC3526B 500mA ISW, 1MHz, Synchronous Step-Up DC/DC Converter in 2mm × 2mm DFN VIN: 1V to 5V, VOUT(MAX) = 5.25V, IQ = 9µA, ISD < 1μA, 2mm × 2mm DFN Package ® ThinSOT is a trademark of Linear Technology Corporation. 35262b2fa 16 Linear Technology Corporation LT 0807 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006