LTC3528/LTC3528B 1A, 1MHz Synchronous Step-Up DC/DC Converters in 3mm × 2mm DFN FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Delivers 3.3V at 200mA from a Single Alkaline/ NiMH Cell or 3.3V at 400mA from Two Cells VIN Start-Up Voltage: 700mV 1.6V 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 12μA Quiescent Current (LTC3528) Low Noise PWM Operation (LTC3528B) Internal Synchronous Rectifier Logic Controlled Shutdown: <1μA Anti-Ringing Control Low Profile (3mm × 2mm × 0.75mm) DFN Package ■ ■ ■ ■ A switching frequency of 1MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The current mode PWM is internally compensated, simplifying the design process. The LTC3528 enters Burst Mode operation at light loads, while the LTC3528B features continuous switching at light loads. Anti-ringing circuitry reduces EMI by damping the inductor in discontinuous mode. Additional features include a low shutdown current, open-drain power good output, shortcircuit protection and thermal overload protection. The LTC3528/LTC3528B are offered in an 8-lead 3mm × 2mm × 0.75mm DFN package. APPLICATIONS ■ The LTC®3528/LTC3528B are synchronous, fixed frequency step-up DC/DC converters with output disconnect. High efficiency synchronous rectification, in addition to a 700mV start-up voltage and operation down to 500mV once started, provides longer run-time for single or multiple cell battery-powered products. , LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Medical Instruments Flash-Based MP3 Players Noise Canceling Headphones Wireless Mice Bluetooth Headsets TYPICAL APPLICATION Efficiency and Power Loss 100 4.7μH 90 1000 VOUT = 3.3V VIN = 2.4V 100 VIN 4.7μF VOUT PGOOD OFF ON 499k LTC3528 SHDN GND 33pF VOUT 3.3V 400mA 10μF FB EFFICIENCY (%) VIN 1.8V TO 3.2V 80 EFFICIENCY 10 70 60 1 POWER LOSS 50 287k POWER LOSS (mW) SW 0.1 3528 TA01a 40 30 0.01 0.1 1 10 100 0.01 1000 LOAD CURRENT (mA) 3528 TA01b 3528fa 1 LTC3528/LTC3528B 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 PGOOD......................................................... –0.3V to 6V Operating Temperature Range (Notes 2, 5) .............................................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C TOP VIEW SHDN 1 FB 2 PGOOD 3 8 VIN 9 VOUT 4 7 SGND 6 PGND 5 SW DDB PACKAGE 8-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 76°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 LTC3528EDDB#PBF LTC3528BEDDB#PBF LTC3528EDDB#TRPBF LTC3528BEDDB#TRPBF LCYD LDDG 8-Lead (3mm × 2mm) Plastic DFN 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C –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 ● 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 Minimum Start-Up Voltage CONDITIONS ILOAD = 1mA Output Voltage Adjust Range MIN ● 0.70 ● 1.7 1.6 ● 1.170 TA = 0°C to 85°C TYP MAX UNITS 0.88 V 5.25 5.25 V V 1.200 1.230 V 1 50 nA Feedback Voltage (Note 7) Feedback Input Current VFB = 1.3V Quiescent Current—Shutdown VSHDN = 0V, Not Including Switch Leakage, VOUT = 0V 0.01 1 μA Quiescent Current—Active Measured on VOUT, Nonswitching (Note 4) 300 500 μA Quiescent Current—Burst Measured on VOUT, FB > 1.230V N-Channel MOSFET Switch Leakage Current VSW = 5V P-Channel MOSFET Switch Leakage Current VSW = 5V, VOUT = 0V 12 20 μA 0.1 10 μA 0.1 10 μA N-Channel MOSFET Switch On Resistance 0.175 Ω P-Channel MOSFET Switch On Resistance 0.250 Ω ● N-Channel MOSFET Current Limit Current Limit Delay Time to Output (Note 3) Maximum Duty Cycle VFB = 1.15V ● Minimum Duty Cycle VFB = 1.3V ● Frequency ● 1.0 88 1.5 A 60 ns 93 % 0 0.7 1.0 1.3 % MHz 3528fa 2 LTC3528/LTC3528B ELECTRICAL CHARACTERISTICS The ● 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 MIN SHDN Input High Voltage TYP MAX 0.88 UNITS V SHDN Input Low Voltage 0.25 V 0.3 1 μA –10 –13 % SHDN Input Current VSHDN = 1.2V PGOOD Threshold Percentage Referenced to Feedback Voltage Falling PGOOD Low Voltage IPGOOD = 1mA VOUT = 1.6V, IPGOOD = 1mA 0.05 0.05 0.1 0.2 V V PGOOD Leakage Current VPGOOD = 5.5V 0.01 1 μA 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 LTC3528E 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. –7 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 76°C/W. Note 7: The IC is tested in a feedback loop to make the measurement. TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current and VIN for VOUT = 1.8V (LTC3528) 90 80 100 60 10 POWER LOSS 50 40 1 30 20 VIN = 1V VIN = 1.2V VIN = 1.5V 10 0 0.01 0.1 10 100 1 LOAD CURRENT (mA) 0.1 0.01 1000 3528 G01 1000 EFFICIENCY 80 100 70 60 10 POWER LOSS 50 40 1 30 20 VIN = 1V VIN = 1.5V VIN = 2.4V 10 0 0.01 0.1 10 100 1 LOAD CURRENT (mA) POWER LOSS (mW) 70 POWER LOSS (mW) EFFICIENCY (%) 100 EFFICIENCY EFFICIENCY (%) 90 Efficiency vs Load Current and VIN for VOUT = 3V (LTC3528) 1000 100 (TA = 25°C unless otherwise noted) 0.1 0.01 1000 3528 G26 3528fa 3 LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current and VIN for VOUT = 3.3V (LTC3528) 100 (TA = 25°C unless otherwise noted) Efficiency vs Load Current and VIN for VOUT = 5V (LTC3528) 1000 1000 100 EFFICIENCY 130 EFFICIENCY 90 110 100 POWER LOSS 60 1 50 VIN = 1.2V VIN = 1.8V VIN = 2.4V VIN = 3V 40 30 0.01 0.1 1 10 70 10 POWER LOSS 60 50 VIN = 1.2V VIN = 2.4V VIN = 3.6V VIN = 4.2V 0.1 40 0.01 1000 100 EFFICIENCY (%) 70 80 30 0.01 0.1 1 10 POWER LOSS (mW) 10 POWER LOSS (mW) 80 100 90 IIN (μA) 90 EFFICIENCY (%) No-Load Input Current vs VIN (LTC3528) 1 30 10 1 3 VIN (V) 4 5 3528 G03 3528 G02 3528 G04 Minimum Load Resistance During Start-Up vs VIN Maximum Output Current vs VIN 800 Start-Up Delay Time vs VIN 130 10000 120 700 110 600 500 DELAY (μs) 1000 RLOAD (Ω) IOUT (mA) 2 LOAD CURRENT (mA) LOAD CURRENT (mA) 400 300 100 100 90 80 70 200 VOUT = 1.8V VOUT = 3.3V VOUT = 5V 100 0 1 1.5 2 3 2.5 VIN (V) 3.5 4 60 50 10 4.5 0.7 0.8 0.9 1.5 2 50 VOUT = 1.8V 4 60 VOUT = 3V VOUT = 3.3V RISING RISING RISING 40 30 IOUT (mA) IOUT (mA) 4.5 Burst Mode Threshold Current vs VIN 40 30 FALLING 3.5 3528 G07 Burst Mode Threshold Current vs VIN 20 3 2.5 VIN (V) 3528 G06 Burst Mode Threshold Current vs VIN 40 1 1 VIN (V) 3528 G05 IOUT (mA) VOUT = 1.8V VOUT = 3V VOUT = 3.3V VOUT = 5V 50 0.1 1000 100 70 FALLING 20 FALLING 20 10 10 0 1 1.1 1.3 1.2 VIN (V) 1.4 1.5 0 1 2 1.5 2.5 VIN (V) 3528 G08 3528 G09 0 1 1.5 2 VIN (V) 2.5 3 3528 G10 3528fa 4 LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted) Oscillator Frequency Change vs VOUT Burst Mode Threshold Current vs VIN RDS(ON) vs VOUT 450 0.50 60 VOUT = 5V NORMALIZED TO VOUT = 3V 0.25 400 40 IOUT (mA) RISING FALLING 20 –0.25 350 –0.50 RDS(ON) (mΩ) FREQUENCY CHANGE (%) 0 –0.75 –1.00 –1.25 300 PMOS 250 200 –1.50 NMOS –1.75 150 –2.00 1 2 1.5 4 3 2.5 2 VIN (V) 3.5 3 VOUT (V) 4 4.5 Oscillator Frequency Change vs Temperature 2 2.5 3.5 3 VOUT (V) 4 NORMALIZED TO 25°C 5 VFB vs Temperature 1.200 20 3 4.5 3528 G13 RDS(ON) Change vs Temperature 30 1.195 2 1 0 –1 10 VFB (V) CHANGE (%) FREQUENCY CHANGE (%) 4 5 3528 G12 3528 G11 5 100 1.5 –2.25 0 1.190 0 –2 1.185 –10 –3 –4 –5 –50 –30 30 –10 10 50 TEMPERATURE (°C) 70 –20 –50 90 30 –10 10 50 TEMPERATURE (°C) –30 70 90 1.180 –50 –30 50 –10 10 30 TEMPERATURE (°C) Burst Mode Quiescent Current vs VOUT (LTC3528) Start-Up Voltage vs Temperature 850 90 3528 G16 3528 G15 3528 G14 70 Fixed Frequency VOUT Ripple and Inductor Current Waveforms 13.5 VOUT 20mV/DIV 800 CURRENT (μA) START-UP VOLTAGE (mV) VIN = 1.2V 750 700 12.5 IL 200mA/DIV VIN = 1.2V VOUT = 3.3V COUT = 22μF CFF = 33pF IOUT = 100mA 11.5 650 600 –50 –30 30 –10 10 50 TEMPERATURE (°C) 70 90 3528 G17 2μs/DIV 3528 G19 10.5 1 2 3 VOUT (V) 4 5 3528 G18 3528fa 5 LTC3528/LTC3528B TYPICAL PERFORMANCE CHARACTERISTICS Burst Mode Waveforms (TA = 25°C unless otherwise noted) Load Step Response (Fixed Frequency, 3.6V to 5V) VOUT and IIN During Soft-Start VOUT 1V/DIV VOUT 20mV/DIV VOUT 100mV/DIV IIN 200mA/DIV SHDN PIN INDUCTOR CURRENT 100mA/DIV VIN = 3.6V VOUT = 5V COUT = 22μF CFF = 33pF ILOAD = 30mA 5μs/DIV VIN = 1.2V VOUT = 3.3V COUT = 10μF L = 4.7μH 3528 G20 LOAD CURRENT 200mA/DIV VIN = 3.6V VOUT = 5V COUT = 10μF L = 4.7μH 50μs/DIV 3528 G23 200μs/DIV 3528 G21 VIN = 3.6V VOUT = 5V COUT = 10μF L = 4.7μH VOUT 100mV/DIV VOUT 100mV/DIV LOAD CURRENT 100mA/DIV LOAD CURRENT 100mA/DIV VIN = 1.2V VOUT = 3.3V COUT = 10μF L = 4.7μH 50μs/DIV 20μs/DIV 3528 G22 Load Step Response (Burst Mode Operation, 1.2V to 3.3V, LTC3528) Load Step Response (Fixed Frequency, 1.2V to 3.3V) Load Step Response (Burst Mode Operation, 3.6V to 5V, LTC3528) VOUT 100mV/DIV LOAD CURRENT 200mA/DIV 3528 G24 VIN = 1.2V VOUT = 3.3V COUT = 10μF L = 4.7μH 50μs/DIV 3528 G25 PIN FUNCTIONS SHDN (Pin 1): Logic Controlled Shutdown Input. There is an internal 4MΩ pull-down resistor on this pin. • SHDN = High: Normal operation • SHDN = Low: Shutdown, quiescent current < 1μA FB (Pin 2): Feedback Input. Connect resistor divider tap to this pin. The output voltage can be adjusted from 1.6V to 5.25V by: R2 VOUT = 1.20V • 1+ R1 PGOOD (Pin 3): Power Good Comparator Output. This open-drain output is low when VFB < 10% from its regulation voltage. VOUT (Pin 4): Output Voltage Sense and Drain Connection of the Internal Synchronous Rectifier. PCB trace length from VOUT to the output filter capacitor (4.7μF minimum) should be as short and wide as possible. SW (Pin 5): 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. PGND (Pin 6): Power Ground. Provide a short direct PCB path between PGND and the (–) side of the input and output capacitors. SGND (Pin 7): Signal Ground. Provide a short direct PCB path between SGND and the (–) side of the input and output capacitors. 3528fa 6 LTC3528/LTC3528B PIN FUNCTIONS VIN (Pin 8): Battery Input Voltage. Connect a minimum of 1μF ceramic decoupling capacitor from this pin to ground. 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. BLOCK DIAGRAM L1 4.7μH CIN 4.7μF 8 5 SW VIN ANTI-RING VOUT VSEL VBEST 1 SHDN SHUTDOWN SHUTDOWN WELL SWITCH VB VOUT GATE DRIVERS AND ANTI-CROSS CONDUCTION 4M Σ VREF PK COMP VREF PK UVLO UVLO FB IZERO COMP 3 BURST PGOOD + – + – MODE CONTROL (LTC3528) CLK R1 ERROR AMP SLEEP COMP START-UP LOGIC COUT 10μF 2 SLOPE COMP IZERO 1MHz OSC VOUT 1.6V TO 5.25V 4 R2 – + + – VIN 0.7V TO 5V VREF FB CLAMP VREF – 10% FB THERMAL SHUTDOWN SOFT-START TSD WAKE PGND SGND EXPOSED PAD 6 7 9 3528 BD 3528fa 7 LTC3528/LTC3528B OPERATION (Refer to Block Diagram) The LTC3528/LTC3528B are 1MHz synchronous boost converters housed in an 8-lead 3mm × 2mm DFN package. With the ability to start-up and operate from inputs less than 0.88V, the 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 and requires minimal output filtering. Internal soft-start and internal loop compensation simplifies the design process while minimizing the number of external components. slowly ramps the peak inductor current from zero to its peak value of 1.5A (typical), allowing start-up into heavy loads. The soft-start time is approximately 0.5ms. The soft-start circuitry is reset in the event of a commanded shutdown 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 LTC3528 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 12μA. Operation can be best understood by referring to the Block Diagram. Shutdown LOW VOLTAGE START-UP The LTC3528/LTC3528B includes an independent start-up oscillator designed to operate at an input voltage of 0.70V (typical). Soft-start and inrush current limiting are provided during start-up, as well as normal operating mode. When either VIN or VOUT exceeds 1.6V 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 availability of the power source to supply sufficient power to the output at the low voltages, and the maximum duty cycle, which is clamped at 93% 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 LTC3528/LTC3528B contains internal circuitry to provide soft-start operation. The internal soft-start circuitry Oscillator An internal oscillator sets the frequency of operation to 1MHz. The converter is shut down by pulling the SHDN pin below 0.25V, and activated by pulling SHDN 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 noninverting input is internally connected to the 1.20V 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 1.6V to 5.25V. R2 VOUT = 1.20V • 1+ 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. The current limit comparator delay to output is typically 60ns. Peak switch current is limited to approximately 1.5A, independent of input or output voltage, unless VOUT falls below 0.7V, in which case the current limit is cut in half. 3528fa 8 LTC3528/LTC3528B 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 20mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. The LTC3528 will automatically 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 vs VIN. The load 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. 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 LTC3528/LTC3528B is 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 enables inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, a Schottky diode cannot be connected between SW and VOUT. The output disconnect feature also allows VOUT to be forced above the programmed regulation voltage, without any reverse current into a battery on VIN. Thermal Shutdown If the die temperature exceeds 160°C, the LTC3528/ LTC3528B will enter thermal shutdown. All switches will be turned off and the soft-start capacitor will be discharged. The device will be enabled again when the die temperature drops by approximately 15°C. In Burst Mode operation, the LTC3528 continues switching at a fixed frequency of 1MHz, using the same error amplifier and loop compensation for peak current mode control. This control method minimizes output transients when switching between modes. In Burst Mode operation, energy is delivered to the output until it reaches the nominal regulated value, then the LTC3528 transitions to sleep mode where the outputs are off and the LTC3528 consumes only 12μA of quiescent current from VOUT. Once the output voltage has drooped slightly, switching resumes again. This maximizes efficiency at very light loads by minimizing switching and quiescent current losses. Burst Mode output ripple, which is typically 1% peak-to-peak, can be reduced by using more output capacitance (10μF or greater). As the load current increases, the LTC3528 automatically leaves Burst Mode operation. Note that larger output capacitor values may cause this transition to occur at lighter loads. The regulator will also leave Burst Mode operation if a load transient occurs which causes the inductor current to repeatedly reach current limit. Once the LTC3528 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 until soft-start is done and VOUT is at least 0.24V greater than VIN. The LTC3528B features continuous PWM operation at 1MHz. At very light loads, the LTC3528B will exhibit pulse-skip operation. 3528fa 9 LTC3528/LTC3528B APPLICATIONS INFORMATION VIN > VOUT OPERATION properly soldered will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. The LTC3528/LTC3528B 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. COMPONENT SELECTION Inductor Selection The LTC3528/LTC3528B can utilize small surface mount chip inductors due to their fast 1MHz switching frequency. Inductor values between 2.2μH and 4.7μH 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. SHORT-CIRCUIT PROTECTION The LTC3528/LTC3528B output disconnect feature allows an 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 750mA (typical). SCHOTTKY DIODE Although 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. The minimum inductance value is given by: PCB LAYOUT GUIDELINES where: L> ( VIN(MIN) • VOUT(MAX) – VIN(MIN) 1.2 • Ripple • VOUT(MAX) ) µH Ripple = Allowable inductor current ripple (amps peakpeak) The high speed operation of the LTC3528/LTC3528B demands careful attention to board layout. A careless layout will not produce the advertised performance. Figure 1 shows the recommended component placement. A large ground copper area with the package backside metal pad VIN(MIN) = Minimum input voltage VOUT(MAX) = Maximum output voltage + VIN SHDN 1 CIN 8 VIN 7 SGND FB 2 LTC3528 PGOOD 3 VOUT 4 COUT 6 PGND 5 SW 3528 F01 MULTIPLE VIAS TO GROUND PLANE Figure 1. Recommended Component Placement for Single Layer Board 3528fa 10 LTC3528/LTC3528B APPLICATIONS INFORMATION 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 handle the peak inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core area to support the peak inductor currents of 1.5A seen on the LTC3528/LTC3528B. 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 LPO2506, MSS5131 MSS6122, MOS6020 ME3220, DO1608C 1812PS Coiltronics SD14, SD18, SD20 SD25, SD52 Sumida (847) 956-0666 www.sumida.com CD43 CDC5D23B CDRH5D18 CR43 TDK VLP, VLF VLCF, SLF Toko (408) 432-8282 www.tokoam.com D53, D63 D73, D75 Wurth (201) 785-8800 www.we-online.com WE-TPC type M, MH 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 10μF to 22μF output capacitor is sufficient for most applications. Values larger than 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 LTC3528/LTC3528B is designed to be stable with output capacitor values of 10μF or greater. 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 which 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 33pF 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 10μF 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. 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 3528fa 11 LTC3528/LTC3528B TYPICAL APPLICATIONS 1 Cell to 1.8V Efficiency 100 4.7μH 90 SW VIN 4.7μF VOUT PGOOD OFF ON 33pF 499k LTC3528 80 VOUT 1.8V 250mA EFFICIENCY (%) VIN 0.88V TO 1.6V 10μF FB SHDN 60 50 1M GND 70 VIN = 0.9V VIN = 1.2V VIN = 1.5V 40 3528 TA02a 30 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 3528 TA02b Dual 1 Cell to 1.8V, 3V Sequenced Supply 4.7μH SW VIN 0.88V TO 1.6V VIN 4.7μF 475k VOUT 33pF SHDN VOUT2 1M GND VOUT1 VIN PGOOD1 0.5V/DIV 4.7μH SW VIN 4.7μF Output Voltage Sequencing 10μF FB PGOOD OFF ON 499k LTC3528 VOUT1 1.8V 250mA VOUT 499k LTC3528 PGOOD SHDN GND 33pF VOUT2 3V 200mA 200μs/DIV 3528 TA03b 10μF FB 324k 3528 TA03a 3528fa 12 LTC3528/LTC3528B TYPICAL APPLICATIONS 1 Cell to 3.3V Efficiency 100 4.7μH 90 VIN 4.7μF VOUT 33pF 10μF FB PGOOD OFF ON 499k LTC3528 SHDN VOUT 3.3V 200mA 80 EFFICIENCY (%) SW VIN 0.88V TO 1.6V 287k GND 70 60 50 VIN = 0.9V VIN = 1.2V VIN = 1.5V 40 3528 TA04a 30 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 3528 TA04b 2 Cell to 3.3V Efficiency 100 4.7μH 90 VIN 1.8V TO 3.2V VIN 4.7μF VOUT PGOOD OFF ON 499k LTC3528 SHDN GND 33pF VOUT 3.3V 400mA 10μF FB 287k 80 EFFICIENCY (%) SW 70 60 50 3528 TA05a VIN = 1.8V VIN = 2.4V VIN = 3V 40 30 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 3528 TA05b 3528fa 13 LTC3528/LTC3528B TYPICAL APPLICATIONS 2 Cell to 5V Efficiency 100 4.7μH 90 VIN 4.7μF LTC3528 1M 22μF FB PGOOD OFF ON VOUT 5V 300mA VOUT SHDN 80 EFFICIENCY (%) SW VIN 1.8V TO 3.2V 60 50 316k GND 70 VIN = 1.8V VIN = 2.4V VIN = 3V 40 3528 TA06a 30 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 3528 TA06b Li-Ion to 5V Efficiency 100 4.7μH 90 VIN 4.7μF LTC3528 PGOOD OFF ON VOUT 5V 400mA VOUT SHDN GND 1M 22μF FB 80 EFFICIENCY (%) SW VIN 2.7V TO 4.2V 70 60 50 316k 3528 TA07a VIN = 2.8V VIN = 3.6V VIN = 4.2V 40 30 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) 3528 TA07b 3528fa 14 LTC3528/LTC3528B PACKAGE DESCRIPTION DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702 Rev B) 0.61 ±0.05 (2 SIDES) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.20 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (2 SIDES) R = 0.115 TYP 5 R = 0.05 TYP 0.40 ± 0.10 8 2.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.56 ± 0.05 (2 SIDES) 0.200 REF 0.75 ±0.05 0 – 0.05 4 0.25 ± 0.05 1 PIN 1 R = 0.20 OR 0.25 × 45° CHAMFER (DDB8) DFN 0905 REV B 0.50 BSC 2.15 ±0.05 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 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 3528fa 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 LTC3528/LTC3528B 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, ThinSOTTM 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 LTC3428 500mA ISW, 1.25MHz/2.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 92% Efficiency VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, ISD < 1µA, 2mm × 2mm DFN Package LTC3429 600mA ISW, 500kHz/2.5MHz, 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 with Output Disconnect and 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 and Automatic Burst Mode Operation 94% Efficiency VOUT(MAX) = 6V, IQ = 12μA, DFN Package LTC3459 70mA ISW, 10V Micropower Synchronous Boost Converter with Output Disconnect and 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) = 3V, 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: 0.7V to 5V, VOUT(MAX) = 3V, 3.3V or 5V, IQ = 7μA, ISD < 1μA, SC-70 Package LTC3526/LTC3526B LTC3526-2/LTC3526-2B 500mA, 1MHz/2MHz Synchronous Boost Converters 94% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA/ 250μA, ISD < 1μA, 2mm × 2mm DFN Package LTC3526L 550mA, 1MHz Synchronous Boost Converter 95% Efficiency, VIN: 0.7V to 5.5V, VOUT(MAX) = 5.25V, IQ = 9μA, ISD < 1μA, 2mm × 2mm DFN Package ThinSOT is a trademark of Linear Technology Corporation. 3528fa 16 Linear Technology Corporation LT 1007 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 2007