LTC3539/LTC3539-2 2A, 1MHz/2MHz Synchronous Step-Up DC/DC Converters FEATURES DESCRIPTION n The LTC®3539/LTC3539-2 are synchronous, 2A step-up DC/DC converters with output disconnect. Synchronous rectification enables high efficiency in the low profile 2mm × 3mm DFN package. Battery life is extended with a 700mV start-up voltage and operation down to 500mV once started. n n n n n n n n n n n n Delivers 3.3V at 900mA From 2 Alkaline/NiMH Cells Delivers 5V at 900mA From a Lithium-Polymer Battery VIN Start-Up Voltage: 700mV 1.5V to 5.25V VOUT Range Up to 94% Efficiency VIN > VOUT Operation 1MHz (LTC3539) or 2MHz (LTC3539-2) Fixed Frequency Operation Output Disconnect Selectable Burst Mode® or PWM Operation 10μA Quiescent Current Logic Controlled Shutdown: <1μA Requires Only 6 External Components Low Profile (2mm × 3mm × 0.75mm) DFN Package APPLICATIONS n n n n n A switching frequency of 1MHz (LTC3539) or 2MHz (LTC3539-2) 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 LTC3539/LTC3539-2 feature a pin-enabled automatic Burst Mode operation at light load conditions. Anti-ring circuitry reduces EMI by damping the inductor in discontinuous mode. Additional features include a low shutdown current of under 1μA and thermal overload protection. The LTC3539/LTC3539-2 are offered in a 2mm × 3mm × 0.75mm DFN package. Medical Instruments Portable Bar Code Scanners Noise Canceling Headphones Portable GPS Navigation Handheld PCs L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Wide VIN, High Power 3.3V Regulator Efficiency and Power Loss vs Load Current 4.7μH 100 2.2μF VOUT 1M OFF ON SHDN GND 22pF FB PGND VOUT 3.3V 600mA 22μF 100 70 60 V = 2.4V 50 VIN = 3.3V OUT 40 10 POWER LOSS 30 562k POWER LOSS (mW) LTC3539 MODE EFFICIENCY 80 SW VIN PWM BURST 1000 90 EFFICIENCY (%) VIN 1.8V TO 3.6V 1 20 3539 TA01a FREQUENCY = 1MHz FREQUENCY = 2MHz 10 0 0.1 1 10 100 ILOAD AVERAGE (mA) 0.1 1000 3539 TA01b 3539f 1 LTC3539/LTC3539-2 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, MODE Voltage ............................ –0.3V to 6V VOUT ............................................................. –0.3V to 6V Operating Temperature (Notes 2, 5) ......... –40°C to 85°C Storage Temperature Range................... –65°C to 125°C TOP VIEW 8 VOUT SW 1 PGND 2 7 MODE 9 6 FB GND 3 5 SHDN VIN 4 DCB PACKAGE 8-LEAD (2mm s 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 60°C/W TO 85°C/W (NOTE 6) EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3539EDCB#PBF LTC3539EDCB#TRPBF LDCS 8-Lead (2mm × 3mm) Plastic DFN –40°C to 85°C LTC3539EDCB-2#PBF LTC3539EDCB-2#TRPBF LDPH 8-Lead (2mm × 3mm) 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 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 MIN Input Voltage Range After Start-Up 0.5 Minimum Start-Up Voltage ILOAD = 1mA, VOUT = 0V Output Voltage Adjust Range TYP 0.7 l 1.5 l 1.170 MAX UNITS 5 V 0.88 V 5.25 V 1.200 1.230 V 1 50 nA VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V 0.01 1 μA Quiescent Current - Active Measured on VOUT, Non-Switching 300 500 μA Quiescent Current - Burst Measured on VOUT, FB >1.230V 10 18 μA Feedback Voltage Feedback Input Current VFB = 1.2V Quiescent Current - Shutdown N-Channel MOSFET Switch Leakage Current VSW = 5V 0.1 10 μA P-Channel MOSFET Switch Leakage Current VSW = 5V, VOUT = 0V 0.1 20 μA N-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.09 Ω P-Channel MOSFET Switch On Resistance VOUT = 3.3V 0.125 Ω 2.6 A N-Channel MOSFET Current Limit l 2 3539f 2 LTC3539/LTC3539-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified 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 Maximum Duty Cycle VFB = 1.15V l Minimum Duty Cycle VFB = 1.3V l Switching Frequency LTC3539 LTC3539-2 l l MODE Input High Voltage MIN TYP 87 90 0.7 1.8 1 2 SHDN Input High Voltage 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 LTC3539E/LTC3539E-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. MHz MHz 0.3 0.3 V 1 μA 0.88 VSHDN = 1.2V VSHDN = 3.3V % V V SHDN Input Low Voltage SHDN Input Current 1.3 2.4 0.88 VMODE = 1.2V UNITS % 0 MODE Input Low Voltage MODE Input Current MAX 0.3 1 0.3 V 1 2 μA μA 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. 3539f 3 LTC3539/LTC3539-2 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current and VIN, VOUT = 1.8V Efficiency vs Load Current and VIN, VOUT = 3.3V 100 1000 100 90 1000 90 100 50 POWER LOSS 1 40 30 20 VIN = 1V VIN = 1.2V VIN = 1.5V 10 0 0.1 1 EFFICIENCY 60 10 50 40 POWER LOSS 30 0.1 1 20 VIN = 1.2V VIN = 1.8V VIN = 3V 10 0.01 1000 10 100 LOAD CURRENT (mA) 100 70 0 0.1 1 10 100 LOAD CURRENT (mA) 3539 G01 Efficiency vs Load Current and VIN, VOUT = 5V 90 90 80 80 40 POWER LOSS 30 VIN = 2.4V VIN = 3.6V VIN = 4.2V 10 0 0.1 1 10 100 LOAD CURRENT (mA) 60 1200 50 20 400 10 200 0 0.5 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VIN (V) 3539 G04 3539 G05 OUTPUT CURRENT (mA) LOAD RESISTANCE (Ω) 40 30 20 VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V VOUT = 5V 10 0 0.75 0.85 0.95 VIN (V) 1.05 1.15 3539 G06 Normalized Current Limit vs VOUT 1.10 60 50 0.1 0.65 VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V VOUT = 5V 4.5 4.0 Burst Mode Threshold Current vs VIN and VOUT VOUT = 3.3V 10 800 600 Minimum Load Resistance During Start-Up vs VIN 100 1000 30 0.1 1000 1000 1600 1400 3539 G03 10000 1800 70 40 1 20 VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V VOUT = 5V IOUT (mA) 10 50 Maximum Output Current vs VIN 2000 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 3539 G11 NORMALIZED CURRENT LIMIT (A) 60 IIN (μA) 100 EFFICIENCY 70 POWER LOSS (mW) EFFICIENCY (%) 100 1000 0.1 1000 3539 G02 No Load Input Current vs VIN 100 POWER LOSS (mW) 10 60 80 POWER LOSS (mW) EFFICIENCY 70 EFFICIENCY (%) 80 EFFICIENCY (%) (TA = 25°C unless otherwise noted) 1.05 1.00 0.95 0.90 0.85 0.80 1.0 1.5 2.0 2.5 3.0 3.5 VOUT (V) 4.0 4.5 5.0 3539 G16 3539f 4 LTC3539/LTC3539-2 TYPICAL PERFORMANCE CHARACTERISTICS RDS(ON) vs VOUT VFB vs Temperature 0.25 1.2 0.25 PMOS 0.15 0.10 NMOS 0.05 CHANGE IN VFB (%) 0.50 NORMALIZED RDS(ON) (Ω) 1.3 0.20 RDS(ON) (Ω) RDS(ON) Change vs Temperature 0.30 1.1 1.0 0.9 0.8 0 1.5 2.0 2.5 3.0 3.5 4.0 VOUT (V) 4.5 5.0 –0.25 –0.50 –0.75 0.7 –50 5.5 0 –30 –10 10 30 50 TEMPERATURE (°C) 70 90 3539 G07 –1.00 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 3539 G08 Start-Up Voltage vs Temperature 80 100 3539 G09 Burst Mode SW and IL(AC) Fixed Frequency SW and IL(AC) 0.80 0.75 1mA LOAD VIN (V) 0.70 0.65 NO LOAD SW PIN 2V/DIV SW PIN 5V/DIV VOUT 20mV/DIV AC-COUPLED VOUT 20mV/DIV AC-COUPLED INDUCTOR CURRENT 500mA/DIV INDUCTOR CURRENT 200mA/DIV 0.60 0.55 0.50 –50 –25 0 25 50 TEMPERATURE (°C) 75 500ns/DIV VIN = 2.4V VOUT = 3.3V AT 400mA COUT = 22μF 3539 G12 5μs/DIV 3539 G13 VIN = 3.3V VOUT = 5V COUT = 22μF 100 3539 G10 Load Step, Fixed Frequency Load Step, Burst Mode Operation VOUT 50mV/DIV AC-COUPLED VOUT 50mV/DIV AC-COUPLED LOAD CURRENT 200mA/DIV LOAD CURRENT 200mA/DIV 500μs/DIV VIN = 2.4V VOUT = 3.3V COUT = 22μF ILOAD = 100mA TO 250mA STEP 3539 G14 500μs/DIV VIN = 2.4V VOUT = 3.3V COUT = 22μF ILOAD = 20mA TO 170mA 3539 G15 3539f 5 LTC3539/LTC3539-2 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-ring resistor is connected from SW to VIN to minimize EMI. FB (Pin 6): Feedback Input to the gm Error Amplifier. Connect resistor divider tap to this pin. The output voltage can be adjusted from 1.5V to 5.25V by: VOUT = 1.20V • [1 + (R2/R1)] MODE (Pin 7): Burst Mode Pin. A logic controlled input to select either automatic Burst Mode operation or forced fixed frequency operation. PGND (Pin 2), GND (Pin 3): Signal and Power Ground. Provide a short direct PCB path between PGND, GND and the (–) side of the input and output capacitors. MODE = High: Burst Mode operation at light loads VIN (Pin 4): Battery Input Voltage. Connect a minimum of 2.2μF ceramic decoupling capacitor from this pin to ground. MODE = Low: Fixed frequency PWM Mode VOUT (Pin 8): Output Voltage Sense and Drain of the Internal Synchronous Rectifier. PCB trace length from VOUT to the output filter capacitor should be as short and wide as possible. SHDN (Pin 5): Logic Controlled Shutdown Input. There is an internal 4MΩ pull-down on this pin. SHDN = High: Normal operation. Exposed Pad (Pin 9): The exposed pad must be soldered to the PCB ground plane. It serves as another ground connection, and as a means of conducting heat away from the die. SHDN = Low: Shutdown, quiescent current <1μA. BLOCK DIAGRAM VIN 1 VOUT 4 SW VIN VSEL VBEST WELL SWITCH VB VOUT 8 VOUT SHDN – VREF IPK UVLO UVLO 3 SLOPE COMPARATOR + 1MHz/2MHz OSC CLK THERMAL SHUTDOWN TSD BURST 9 VREF FB ERROR AMPLIFIER/SLEEP COMPARATOR LOGIC AND BURST MODE CONTROL 7 MODE R1 IZERO START-UP PWM BURST FB – IPK COMPARATOR VREF 6 IZERO COMPARATOR + SHUTDOWN + SHUTDOWN 5 – OFF ON R2 GATE DRIVERS AND ANTI-CROSS CONDUCTION EXPOSED PAD CLAMP WAKE SOFT-START 2 PGND 3 GND 3539 BD 3539f 6 LTC3539/LTC3539-2 OPERATION DETAILED DESCRIPTION The LTC3539 is a high power synchronous boost converter in an 8-lead 2mm × 3mm DFN package. With the ability to start up and operate from inputs of 700mV, the 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. The switching frequency of the LTC3539 is nominally 1MHz, while the LTC3539-2 switches at 2MHz. Operation of the LTC3539 and LTC3539-2 is identical in all other respects. With its low RDS(ON) and low gate charge internal N-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3539 achieves high efficiency over a wide range of load current. Burst Mode operation maintains high efficiency at very light loads, reducing the quiescent current to just 10μA. Converter operation can be best understood by referring to the Block Diagram. Low Voltage Start-Up The LTC3539 includes an independent start-up oscillator designed to start up at an input voltage of 0.7V (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. Once 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 ability of the power source to supply sufficient energy to the output at the low voltages, and the 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 LTC3539/LTC3539-2 contains internal circuitry to provide soft-start operation. The internal soft-start circuitry ramps the peak inductor current from zero to its peak value of 2.6A (typical) in approximately 0.5ms, allowing start-up into heavy loads. The soft-start circuitry is reset in the event of a thermal shutdown or shutdown command. Oscillator: An internal oscillator sets the switching frequency to 1MHz for the LTC3539, and 2MHz for the LTC3539-2. Shutdown: The part is shutdown by pulling the SHDN pin below 0.3V, and activated by pulling the SHDN pin above 0.88V. Note that SHDN can be driven above VIN or VOUT, as long as it is limited to less than the absolute maximum rating. Error Amplifier: The error amplifier is a transconductance type. The non-inverting input is internally connected to the 1.2V reference and the inverting 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. A voltage divider from VOUT to ground programs the output voltage via FB from 1.5V to 5.25V. VOUT = 1.2V • [1 + (R2/R1)]. Current Sensing: Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage which 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. Peak switch current is limited to approximately 2.6A, independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. 3539f 7 LTC3539/LTC3539-2 OPERATION Zero Current Comparator: The zero current comparator monitors the inductor current to the output and shuts off the synchronous rectifier once this current reduces to approximately 40mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. Synchronous Rectifier: The P-channel MOSFET synchronous rectifier is disabled when VOUT is much less than VIN. This is to control inrush current and to prevent inductor current from running away 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. The ringing of the resonant circuit formed by L and CSW (capacitance on SW pin) is low energy, but can cause EMI radiation. Output Disconnect: The LTC3539 is designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows VOUT to go to zero volts during shutdown, drawing no current from the input source. It also provides 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 on VIN. Thermal Shutdown: If the die temperature exceeds 160°C, the device will go into thermal shutdown. All switches will be turned off and the internal soft-start capacitor will be discharged. The device will be enabled again when the die temperature drops by about 15°C. Burst Mode Operation When Burst Mode operation is enabled by bringing the MODE pin above 0.88V, the LTC3539 will automatically enter Burst Mode operation at light load current, then return to fixed frequency PWM mode when the load increases. Refer to the typical performance characteristics to see the output load Burst Mode threshold 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 LTC3539 still switches at a fixed frequency, 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 LTC3539 transitions to Sleep mode where the outputs are off and the LTC3539 consumes only 10μA 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 current losses. Burst Mode output voltage ripple, which is typically 1% peak to peak, can be reduced by using more output capacitance (47μF or greater). As the load increases, the LTC3539 will automatically leave Burst Mode operation. Once the LTC3539 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 until soft-start is complete and VOUT is at least 0.24V greater than VIN. When the MODE pin is below 0.3V, the LTC3539 features continuous PWM operation. In this mode, at very light loads, the LTC3539 will exhibit pulse-skip operation. If the MODE pin voltage exceeds the greater of VIN or VOUT by 0.5V, the MODE pin will sink additional current. 3539f 8 LTC3539/LTC3539-2 APPLICATIONS INFORMATION VIN > VOUT Operation COMPONENT SELECTION The LTC3539 will maintain output voltage regulation even when the input voltage is above the desired output. Note that the efficiency and the maximum output current capability are reduced. Refer to Typical Performance Characteristics. Inductor Selection Short-Circuit Protection The LTC3539 output disconnect feature allows an output short circuit while maintaining a maximum internally set current limit. To reduce power dissipation under shortcircuit conditions, the peak switch current limit is reduced to 1.4A (typical). The LTC3539 can utilize small surface mount and chip inductors due to the high switching frequency. Inductor values between 3.3μH and 4.7μH for the LTC3539 and between 1.5μH and 2.5μH for the LTC3539-2 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. However, 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 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, VIN > VOUT operation and short circuit protection features. PCB LAYOUT GUIDELINES The high speed operation of the LTC3539 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. LTC3539 SW 1 PGND 2 GND 3 + VIN 4 8 VOUT 7 MODE 6 FB MINIMIZE TRACE ON FB AND SW 5 SHDN L> VIN(MIN) • ( VOUT(MAX ) − VIN(MIN) ) Ripple • VOUT(MAX ) • f Where: f = 1 for the LTC3539 or 2.2 for the LTC3539-2 Ripple = allowable inductor current ripple (Amps peak-to-peak) VIN(MIN) = minimum input voltage VOUT(MAX) = maximum output voltage The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. High frequency ferrite core inductor materials improve efficiency by reducing frequency dependent power losses compared to cheaper powdered iron types. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must accomodate 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 2.6A seen on the LTC3539. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested suppliers and representative components. *Single cell applications (VIN < 1.6V) should use a 2.2μH inductor for the LTC3539 VIN MULTIPLE VIAS TO GROUND PLANE 3539 F01 Figure 1. Recommended Component Placement for Single Layer Board 3539f 9 LTC3539/LTC3539-2 APPLICATIONS INFORMATION An output capacitor of up to 100μF is required at lower output voltages. Even with VOUT greater than 3V, larger values up to 100μF 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. Table 1. Representative Inductors VENDOR PART/STYLE Coilcraft (847) 639-6400 www.coilcraft.com MSS5131 LPS4018-222 MSS6132 MOS6020 Murata www.murata.com LQH55D LQH66S Sumida (847) 956-0666 www.sumida.com CDRH4D22 CDRH4D28C CDRH5D28 CDR6D23 TDK (847) 803-6100 www.component.tdk.com VLF5014ST Toko (408) 432-8282 www.tokoam.com D53LC D63LCB Wurth (201) 785-8800 www.we-online.com WE-TPC Type LH, X WE-PD Type XS A small ceramic capacitor in parallel with a larger tantalum capacitor may be used in demanding applications which have large load transients. A feedforward capacitor across the top resistor of the feedback divider (from VOUT to FB) is usually required to improve transient response. 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. 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 parts. Output and Input Capacitor Selection The internal loop compensation of the LTC3539 is designed to be stable with output capacitor values of 10μF or greater. Although ceramic capacitors are recommended, low ESR (equivalent series resistance) tantalum capacitors may be used as well. Table 2. Capacitor Vendor Information Low ESR 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 22μF to 47μF output capacitor is sufficient for output voltages of 3V or greater. 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 TYPICAL APPLICATIONS 1 Cell to 1.8V 1 Cell to 3.3V 2.2μH VIN 1V TO 1.6V 2.2μH VIN 0.9V TO 1.6V 2.2μF VIN VIN MODE VOUT SHDN *AT HIGH LOAD CURRENTS, A TANTALUM CAPACITOR WILL IMPROVE PERFORMANCE. 22pF FB GND PGND 2.2μF SW VIN LTC3539 1M OFF ON 2.2μH VIN 3V TO 4.5V 2.2μF SW LTC3539 PWM BURST Li-Ion Cell to 5V VOUT 1.8V 500mA 22μF* x5 1.91M 3539 TA02 PWM BURST MODE VOUT 1M OFF ON SHDN 22pF FB GND PGND SW LTC3539-2 VOUT 3.3V 350mA 22μF x2 562k 3539 TA03 PWM BURST MODE VOUT 1M OFF ON SHDN 22pF FB GND PGND VOUT 5V 750mA 22μF 309k 3539 TA04 3539f 10 LTC3539/LTC3539-2 PACKAGE DESCRIPTION DCB Package 8-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1718 Rev A) 0.70 ±0.05 1.35 ±0.05 3.50 ±0.05 1.65 ± 0.05 2.10 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 1.35 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.115 TYP R = 0.05 5 TYP 2.00 ±0.10 (2 SIDES) 0.40 ± 0.10 8 1.35 ±0.10 1.65 ± 0.10 3.00 ±0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER PIN 1 BAR TOP MARK (SEE NOTE 6) (DCB8) DFN 0106 REV A 4 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 1.35 REF BOTTOM VIEW—EXPOSED PAD 0.00 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 3539f 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. 11 LTC3539/LTC3539-2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS 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 95% Efficiency VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12μA, ISD <1μA, with Output Disconnect 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 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, 3mm × 3mm 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, 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 LTC3525L-3 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect 95% Efficiency VIN: 0.88V to 4.5V, VOUT(MAX) = 3V, IQ = 7μA, ISD <1μA, SC-70 Package LTC3526/ LTC3526B 500mA, 1MHz Synchronous Step-Up DC/DC Converter 94% Efficiency VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA, ISD <1μA, 2mm × 2mm DFN-6 Package with Output Disconnect LTC3526L 550mA, 1MHz Synchronous Step-Up DC/DC Converter 94% Efficiency VIN: 0.68V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA, ISD <1μA, with Output Disconnect 2mm × 2mm DFN-6 Package LTC3527/ LTC3527-1 Dual 800mA/400mA, 1.2MHz/2.2MHz Synchronous Step-Up DC/DC Converter with Output Disconnect LTC3528/ LTC3528B 1A, 1MHz Synchronous Step-Up DC/DC Converter with 94% Efficiency VIN: 0.68V to 5V, VOUT(MAX) = 5.25V, IQ = 12μA, ISD <1μA, 2mm × 3mm DFN-8 Package Output Disconnect 94% Efficiency VIN: 0.68V to 5V, VOUT(MAX) = 5.25V, IQ = 12μA, ISD <1μA, 3mm × 3mm QFN-16 Package ThinSOT is a trademark of Linear Technology Corporation. 3539f 12 Linear Technology Corporation LT 0408 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008