LTC3523/LTC3523-2 Synchronous 600mA Step-Up and 400mA Step-Down DC/DC Converters FEATURES DESCRIPTION n The LTC®3523/LTC3523-2 combine a 600mA step-up DC/DC converter with a 400mA synchronous step-down DC/DC converter in a tiny 3mm × 3mm package. The 1.2MHz/2.4MHz switching frequencies minimize the solution footprint while maintaining high efficiency. Both converters feature soft-start and internal compensation, simplifying the design. n n n n n n n n n n Dual High Efficiency DC/DC Converters: Step-Up (VOUT = 1.8V to 5.25V, ISW = 600mA) Step-Down (VOUT = 0.615V to 5.5V, IOUT = 400mA) 1.8V to 5.5V Input Voltage Range Up to 94% Efficiency Pin Selectable Burst Mode® Operation 45μA Quiescent Current in Burst Mode Operation 1.2MHz (LTC3523) or 2.4MHz (LTC3523-2) Switching Frequency Independent Power Good Indicator Outputs Integrated Soft-Start Thermal and Overcurrent Protection <3μA Quiescent Current in Shutdown Small 16-Lead 3mm × 3mm × 0.75mm QFN Package Both the step-up and step-down converters are current mode controlled and utilize an internal synchronous rectifier for high efficiency. The step-up supports 0% duty cycle operation and the step-down converter supports 100% duty cycle operation to extend battery run time. If the MODE pin is held high, both converters automatically transition between Burst Mode operation and PWM operation improving light load efficiency. Fixed, low noise 1.2MHz/2.4MHz PWM operation is selected when MODE is grounded. APPLICATIONS n n n n Digital Cameras Medical Instruments Industrial Handhelds GPS Navigators The LTC3523/LTC3523-2 provide a sub-3μA shutdown mode, overtemperature shutdown and current limit protection on both converters. The LTC3523/LTC3523-2 are housed in a 16-lead 3mm × 3mm × 0.75mm QFN package. 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 LTC3523 Efficiency and Power Loss vs Load Current 2-CELL ALKALINE 100 + 47μF 4.7μH VIN1 VIN2 SW1 VBAT 4.7μH SW2 10pF VOUT 10μF 634k FB1 PGOOD1 365k SHDN1 LTC3523 511k FB2 MODE VIN 511k PGOOD2 VOUT2 STEP-DOWN OUTPUT 10μF 1.2V 200mA 80 60 P0WER LOSS 50 40 20 OFF ON 3523 TA01a 0 0.1 1 STEP-UP STEP-DOWN 10 OFF ON 10 VIN = 2.4V VOUT1 = 3.3V VOUT2 = 1.2V fOSC = 1.2MHz 30 SHDN2 GND1 GND2 GND3 100 EFFICIENCY 70 POWER LOSS (mW) VOUT1 STEP-UP OUTPUT 3.3V 200mA 1000 90 EFFICIENCY (%) VIN 1.8V TO 3.2V 1 10 100 LOAD CURRENT (mA) 0.1 1000 3523 TA01b 3523fb 1 LTC3523/LTC3523-2 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN1, VIN2, VBAT, VOUT Voltages .................... –0.3V to 6V SHDN1, PGOOD1, PGOOD2, FB1 Voltages .. –0.3V to 6V SHDN2, FB2, MODE Voltages ...... –0.3V to (VIN2 + 0.3V) SW1 Voltage DC.............................................................. 0.3V to 6V Pulse < 100ns .......................................... –0.3V to 7V SW2 Voltage Pulse < 100ns ......... –0.3V to (VIN2 + 0.3V) Operating Temperature Range (Notes 2, 3) .............................................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C SHDN2 GND3 VBAT SHDN1 TOP VIEW 16 15 14 13 FB1 1 12 FB2 VIN1 2 11 PGOOD2 17 PG00D1 3 10 MODE VOUT 4 6 7 8 SW1 GND1 GND2 SW2 9 5 VIN2 UD PACKAGE 16-LEAD (3mm s 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3523EUD#PBF LTC3523EUD-2#PBF LTC3523EUD#TRPBF LTC3523EUD-2#TRPBF LCYC LDDR 16-Lead (3mm × 3mm) Plastic DFN 16-Lead (3mm × 3mm) 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 l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN1 = VIN2 = VBAT = 2.4V, VOUT = 3.3V, unless otherwise specified. PARAMETER CONDITIONS l Minimum Start-Up Voltage Frequency MIN LTC3523 LTC3523-2 l l 0.9 1.8 TYP MAX UNITS 1.6 1.8 V 1.2 2.4 1.5 2.65 MHz MHz 3 Quiescent Current–Shutdown VSHDN1 = VSHDN2 = 0V, VOUT = 0V, VIN1 = VIN2 = VBAT 0.5 Quiescent Current –Sleep Measured from VSUPPLY, VIN1 = VIN2 = VBAT = 2.4V 45 μA Quiescent Current VOUT – Sleep Measured from VOUT = 3.3V (Note 4) 15 μA SHDN1, SHDN2 Input High 1 V SHDN1, SHDN2 Input Low SHDN1, SHDN2 Input Current VSHDN = 5.5V PGOOD1, PGOOD2 Threshold Referenced to the Feedback Voltage PGOOD1, PGOOD2 Low Voltage IPGOOD = 1mA PGOOD1, PGOOD2 Leakage VPGOOD = 5.25V MODE Input High MODE Input Low –6 μA 0.35 V 1.4 2 μA –9 –14 % 0.35 0.01 V 1 1.0 μA V 0.35 V 3523fb 2 LTC3523/LTC3523-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN1 = VIN2 = VBAT = 2.4V, VOUT = 3.3V, unless otherwise specified. PARAMETER CONDITIONS MODE Leakage Current VMODE = 5.5V MIN Soft-Start Time TYP MAX 0.01 1 500 UNITS μA μs Step-Up Converter Input Voltage Range Output Voltage Adjust Range (Note 6) l 1.8 5.25 V l 1.8 5.25 V l 1.16 1.20 1.23 V Feedback Input Current FB1 VFB1 = 1.25V 0 50 nA N-Channel Switch Leakage VSW = 5.5V 0.20 2 μA P-Channel Switch Leakage VSW = 5.5V, VOUT = 0V 0.20 2 μA N-Channel Switch On Resistance VOUT = 3.3V VOUT = 5V 0.36 0.22 Ω Ω P-Channel Switch On Resistance VOUT = 3.3V, ISW = 100mA VOUT = 5V, ISW = 100mA 0.33 0.31 Ω Ω 1000 mA 40 ns Feedback Voltage FB1 l Peak Inductor Current (Note 7) Current Limit Delay to Output (Note 6) Maximum Duty Cycle VFB = 1V l Minimum Duty Cycle VFB = 1.5V l 600 80 87 % 0 % Step-Down Converter Input Voltage Range Output Voltage Range (Note 6) Feedback Voltage FB2 l 1.8 5.5 V l 0.615 5.5 V l 585 600 615 mV 0 50 Feedback Input Current FB2 VFB2 = 0.625V Reference Voltage Line Regulation IOUT = 100mA (Notes 5, 6) 0.04 %/V Output Voltage Line Regulation IOUT = 100mA, 1.6V < VIN < 5.5V (Note 6) 0.04 %/V Output Voltage Load Regulation IOUT = 0mA to 600mA (Note 6) 1.0 % 100 % Maximum Duty Cycle l Peak Inductor Current (Note 7) 650 mA N-Channel Switch On Resistance VIN2 = 2.4V 0.33 Ω P-Channel Switch On Resistance VIN2 = 2.4V 0.58 Ω SW Leakage VSHDN2 = 0V, VSW2 = 0V or 5V, VIN2 = 5.5V 0.20 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 LTC3523/LTC3523-2 are guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process control. Note 3: The LTC3523/LTC3523-2 include an overtemperature shutdown that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when the overtemperature shutdown is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 400 nA 2 μA Note 4: Current is measured into the VOUT pin since the supply is bootstrapped to the output for the step-up. The current will reflect to the input supply by: (VOUT/VIN) • Efficiency. The outputs are not switching in sleep. Note 5: The LTC3523/LTC3523-2 are tested in a propriety test mode that connects FB2 to the output of the error amplifier. Note 6: Specification is guaranteed by design and not 100% tested in production. Note 7: Current measurements are performed when the LTC3523/ LTC3523-2 are not switching. The current limit values in operation will be somewhat higher due to the propagation delay of the comparator. 3523fb 3 LTC3523/LTC3523-2 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted) Normalized FBx Reference vs Temperature Normalized Oscillator Frequency vs Temperature 1.00125 NORMALIZED FBx VOLTAGE (V) NORMALIZED FREQUENCY (Hz) 1.05 1.00000 0.99875 0.99750 0.99625 0.99500 –45 –25 15 35 55 –5 TEMPERATURE (°C) 75 VOUT_BST 2V/DIV IL_BST 200mA/DIV SHDN1 2V/DIV 1.00 VOUT = 3.3V VIN = 2.4V COUT = 10μF L1 = 4.7μH 0.95 –45 15 35 55 –5 TEMPERATURE (°C) –25 Inrush Current Control for the Step-Down Converter OUTPUT RIPPLE 20mV/DIV SHDN2 2V/DIV VOUT = 1.2V VIN = 2.4V COUT = 10μF L1 = 4.7μH 200μs/DIV 3523 G04 LOAD CURRENT 20mA/DIV 3523 G05 VOUT = 3.3V 500μs/DIV VIN = 2.4V COUT = 10μF L1 = 4.7μH 20mA TO 70mA STEP 1.2 RDS(ON) vs Output Voltage for the Step-Up Converter 0.50 0.80 BOOST CURRENT LIMIT 1.0 0.45 0.70 0.40 0.60 BUCK CURRENT LIMIT 0.6 0.4 0.50 0.40 0.30 NMOS 55 35 –5 15 TEMPERATURE (°C) 75 3523 G07 0 NMOS 0.25 0.20 0.10 0.10 –25 0.30 0.15 0.20 0.2 PMOS 0.35 PMOS RDS(0N) (Ω) RDS(ON) (Ω) 0.8 3523 G06 VOUT = 1.2V 500μs/DIV VIN = 2.4V COUT = 47μF L1 = 4.7μH CF = 68pF 10mA TO 30mA STEP RDS(ON) vs Input Voltage for the Step-Down Converter Current Limit vs Temperature 0 –45 Load Transient Response Step-Down OUTPUT RIPPLE 20mV/DIV LOAD CURRENT 20mA/DIV IL_BCK 200mA/DIV 3523 G03 75 Load Transient Response Step-Up VOUT_BCK 1V/DIV 200μs/DIV 3523 G02 3523 G01 CURRENT LIMIT (A) Inrush Current Control for the Step-Up Converter 0.05 1 1.5 2 2.5 3 3.5 4 INPUT VOLTAGE (V) 4.5 5 3523 G08 0 1 1.5 2 2.5 3 3.5 4 OUTPUT VOLTAGE (V) 4.5 5 3532 G09 3523fb 4 LTC3523/LTC3523-2 TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted) Step-Up No-Load Input Current vs VIN 1.3 500 1.2 450 1.0 PMOS 0.9 NMOS 0.8 0.7 Mode Transition Response VOUT_BST 50mV/DIV 400 1.1 INPUT CURRENT (μA) NORMALIZED RDS(ON) (Ω) Normalized RDS(ON) vs Temperature VOUT = 5V 350 VOUT_BCK 20mV/DIV 300 MODE 2V/DIV 250 200 VOUT = 3.3V 150 VOUT1 = 3.3V 200μs/DIV VOUT2 = 1.2V VIN = 2.4V IOUT1 = 20mA IOUT2 = 25mA COUT1 = COUT2 = 10μF L1 = L2 = 4.7μH 100 0.6 0.5 –45 50 –25 55 35 15 TEMPERATURE (°C) –5 VOUT = 2.8V 0 75 1.5 2 3.5 3 2.5 4 INPUT VOLTAGE (V) 3523 G10 3523 G11 Maximum IOUT vs VIN for the Step-Up Converter VOUT = 3.3V Maximum IOUT vs VIN for the Step-Down Converter 450 VOUT = 5V MAXIMUM OUTPUT CURRENT (mA) MAXIMUM OUTPUT CURRENT (mA) 500 450 VOUT = 2.5V 400 350 300 250 200 150 100 50 1 2 3 4 INPUT VOLTAGE (V) 5 3523 G13 VOUT = 1.8V 400 VOUT = 2.5V 350 VOUT = 1.2V 300 250 200 150 100 50 0 0 5 4.5 3523 G12 1 1.5 2 2.5 3 3.5 4 INPUT VOLTAGE (V) 4.5 5 3523 G14 PIN FUNCTIONS FB1 (Pin 1): Step-Up Converter Feedback Input to the Error Amplifier. Connect resistor divider tap to this pin. The output voltage can be adjusted from 1.8V to 5.25V by: ⎛ R1⎞ VOUT(STEP-UP) = 1.2V • ⎜1+ ⎟ ⎝ R2⎠ See Block Diagram. VIN1 (Pin 2): Step-Up Converter Power Voltage Input. This pin can be connected to a different supply than VIN2. This pin must be connected to a valid supply voltage. PGOOD1 (Pin 3): Step-Up Converter Power Good Comparator Output. This open-drain output is pulled low when VFB1 < –9% of its regulation voltage. VOUT (Pin 4): Step-Up Converter Output Voltage Sense Input and Drain of the Internal Synchronous Rectifier MOSFET. Driver bias is derived from VOUT. PCB trace length from VOUT to the output filter capacitor(s) should be as short and wide as possible. 3523fb 5 LTC3523/LTC3523-2 PIN FUNCTIONS SW1 (Pin 5): Step-Up Converter Switch Pin. Connect the inductor between SW1 and VIN1. Keep these PCB trace lengths as short and wide as possible to reduce EMI and voltage overshoot. If the inductor current falls to zero or SHDN1 is low, an internal 150Ω anti-ringing resistor is connected from SW1 to VIN1 to minimize EMI. GND1 (Pin 6): Step-Up Converter Power Ground. Connect this pin to the ground plane. GND2 (Pin 7): Step-Down Converter Power Ground. Connect this pin to the ground plane. SW2 (Pin 8): Step-Down Converter Switch Pin. Connect one end of the inductor to SW2. Keep these PCB trace lengths as short and wide as possible to reduce EMI and voltage overshoot. If large feedback resistors, above 500k are used, then it will be necessary to use a lead capacitor connected to the output voltage and FB2. SHDN2 (Pin 13): Step-Down Converter Logic Controlled Shutdown Input. Do not leave this pin floating. • SHDN2 = High: Normal free-running operation, 1.2MHz/2.4MHz typical operating frequency. • SHDN2 = Low: Shutdown, quiescent current < 1μA. This pin cannot exceed the voltage on VIN2. GND3 (Pin 14): Analog Ground. The feedback voltage dividers for each converter must be returned to GND3 for best performance. VIN2 (Pin 9): Step-Down Converter Power Voltage Input. This pin can be connected to a different supply than VIN1. This pin must be connected to a valid supply voltage. Note: When laying out your PCB provide a short direct path between GND1 and the (–) side of the step-up output capacitor(s) and GND2 and the step-down output capacitor.These pins are not connected together internally. MODE (Pin 10): Step-Up and Step-Down Converter Mode Selection Pin. Do not leave this pin floating. VBAT (Pin 15): Analog Voltage Input. Connect this pin to the higher of VIN1 or VIN2. • MODE = Low: PWM mode SHDN1 (Pin 16): Step-Up Converter Logic Controlled Shutdown Input. • MODE = High: Automatic Burst Mode operation PGOOD2 (Pin 11): Step-Down Converter Power Good Comparator Output. This open-drain output is pulled low when VFB2 < –9% of its regulation voltage. FB2 (Pin 12): Step-Down Converter Feedback Input to the Error amplifier. Connect resistor divider tap to this pin. The output voltage can be adjusted from 0.6V to 5.5V by: ⎛ R3⎞ VOUT(STEP-DOWN) = 0.6 V • ⎜1+ ⎟ ⎝ R4⎠ • SHDN1 = High: Normal free-running operation, 1.2MHz/2.4MHz typical operating frequency. • SHDN1 = Low: Shutdown, quiescent current < 1μA. This pin cannot exceed the voltage on VIN1. Exposed Pad (Pin 17): Die attach pad must be soldered to PCB ground for electrical contact and optimum thermal performance. See Block Diagram. 3523fb 6 LTC3523/LTC3523-2 BLOCK DIAGRAM L1 4.7μH + 16 CIN 47μF 2 SHUTDOWN AND VBIAS 5 VIN1 SHDN1 SW1 BULK CONTROL SIGNALS VOUT ANTI-RING SHDN OSC + – CURRENT SENSE PWM/ILIM COMP MODE + ILIM REF CC1 + CC2 RZ FB1 R1 FB1 + – COUT 10μF 1 R2 1.2V SLP 1.2V –9% STEP-UP OSC OSCILLATOR 15 MODE START-UP SOFT-START AND THERM REG PGOOD1 – + IZERO COMP gm ERROR AMPLIFIER SLOPE COMPENSATION 3 VOUT STEP-UP 1.8V TO 5.25V 4 PWM LOGIC AND DRIVERS MODE –+– VBAT 0.6V 1.2V 1V REFERENCE SLP MODE 10 THERMAL SHDN SHARED 9 STEP-DOWN VIN2 + SLOPE COMPENSATION + ZERO CURRENT COMP SLP PWM/ILIM COMP ILIM REF 11 13 + – – PGOOD2 – + SHDN2 SHUTDOWN AND VBIAS + – 0A PWM LOGIC AND DRIVERS MODE OSC SW2 L2 4.7μH 8 VOUT STEP-DOWN 0.615V TO 5.5V FB2 VOUT LIMIT COMP 0.6V –9% MODE SHDN RZ 0.66V MODE gm ERROR AMPLIFIER CC1 GND2 + – VIN 1.8V TO 5.5V – + R3 FB2 COUT 10μF 12 R4 0.6V START-UP SOFT-START AND THERM REG GND1 GND2 GND3 6 7 14 3523 BD 3523fb 7 LTC3523/LTC3523-2 OPERATION The LTC3523 and LTC3523-2 are synchronous step-up and step-down converters housed in a 16-pin QFN package. Operating from inputs down to 1.8V, the devices feature fixed frequency, current mode PWM control for exceptional line and load regulation and transient response. With low RDS(ON) and internal MOSFET switches, the devices maintain high efficiency over a wide range of load current. Operation can be best understood by referring to the Block Diagram. PWM Comparators Soft-Start The current limit comparator shuts off the N-channel switch for the step-up and P-channel switch for the step-down once its current limit threshold is reached. The current limit comparator delay to output is typically 40ns. Peak switch current is limited to approximately 1000mA for the step-up and 650mA for the step-down independent of input or output voltage. Both the step-up and step-down converters on the LTC3523 /LTC3523-2 provide soft-start. The soft-start time is typically 500μs. The soft-start function resets in the event of a commanded shutdown or thermal shutdown. Oscillator The frequency of operation is set by an internal oscillator to a nominal 1.2MHz for the LTC3523 and nominal 2.4MHz for the LTC3523-2. The oscillator is shared by both converters. Shutdown The step-up and the step-down converters have independent shutdown pins. To shut down a converter, pull SHDNx below 0.35V. To enable a converter, pull SHDNx above 1.0V. Error Amplifiers Power converter control loop compensation is provided internally for each converter. The noninverting input is internally connected to the 1.2V reference for the step-up and 0.6V for the step-down. The inverting input is connected to the respective FBx for both converters. Internal clamps limit the minimum and maximum error amp output voltage for improved large signal transient response. A voltage divider from VOUT to ground programs the output voltage via the respective FBx pins from 1.8V to 5.25V for the stepup and 0.615V to 5.5V for the step-down. From the Block Diagram the design equation for programming the output voltages is VOUT = 1.2V • [1 + (R1/R2)] for the step-up and VOUT = 0.6V • [1 + (R3/R4)] for the step-down. The PWM comparators are used to compare the converters external inductor current to the current commanded by the error amplifiers. When the inductor current reaches the current commanded by the error amplifier the inductor charging cycle is terminated and the rectification cycle commences. Current Limit 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 20mA. This prevents the inductor current from reversing in polarity improving efficiency at light loads. Power Good Comparator Both converters have independent open drain power good comparators which monitor the output voltage via their respective FBx pins. The comparator output will allow the PGOODx to be pulled up high when the output voltage (VOUT) has exceeded 91% of it final value. If the output voltage decreases below 91%, the comparator will pull the PGOODx pin to ground. The step-up comparator has 3.3% of hysteresis and the step-down has 6.6% relative to FBx voltage for added noise immunity. Step-Down Overvoltage Comparator The step-down overvoltage comparator guards against transient overshoots greater than 10% of the output voltage by turning the P-channel switch off until the transient has subsided. 3523fb 8 LTC3523/LTC3523-2 OPERATION Step-Up Anti-Ringing Control The anti-ring circuitry connects a resistor across the inductor to prevent high frequency ringing on the SW1 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. Step-Up Output Disconnect The LTC3523/LTC3523-2 step-up is designed to provide 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. Controlling the P-channel MOSFET body diode 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, an external Schottky diode cannot be connected between SW1 and VOUT. Thermal Shutdown If the die temperature reaches 160°C, the part will go into 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. APPLICATIONS INFORMATION PCB LAYOUT GUIDELINES COMPONENT SELECTION The high speed operation of the LTC3523/LTC3523-2 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 1 shows the recommended component placement. A large ground pin copper area will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. Inductor Selection The LTC3523/LTC3523-2 can utilize small surface mount and chip inductors due to its fast 1.2MHz switching frequency and for the 2.4MHz version, the values are halved. The Inductor current ripple is typically set for 20% to 40% of the peak inductor current (IP). High Figure 1. Recommended Component Placement for Double Layer Board 3523fb 9 LTC3523/LTC3523-2 APPLICATIONS INFORMATION 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 to support the peak inductor currents of 1000mA seen on the LTC3523/LTC3523-2. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. See Table 1 for suggested inductors and suppliers. Step-Up: For the step-up converter a minimum inductance value of 3.3μH is recommended for 3.6V and lower output voltage applications, and a 4.7μH for output voltages greater than 3.6V. Larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will increase size while providing little improvement in output current capability. Step-Down: For most applications, the value of the inductor will fall in the range of 3.3μH to 10μH, depending upon the amount of current ripple desired. A reasonable point to start is to set the current ripple at 30% of the output current. Note that larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will increase size while providing little improvement in output current capability. A 4.7μH inductor will work well for most Li-Ion or 2-cell alkaline/NiMH cell applications 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. Step-Up: A 2.2μF 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. An additional phase lead capacitor connected between VOUT and FB1 may be required with output capacitors larger than 10μF to maintain acceptable phase margin. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Step-Down: 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. Table 2 shows the range of acceptable capacitors for a given programmed output voltage. Minimum capacitance values in the table Table 1. Recommended Inductors L (μH) MAXIMUM CURRENT (mA) DCR (Ω) DIMENSIONS (mm) (L × W × H) ME3220 4.7 to 15 1200 to 700 0.19 to 0.52 3.2 × 2.5 × 2.0 LPS3010 4.7 to 10 720 to 510 0.3 to 0.54 3.0 × 3.0 × 1.0 DO2010 4.7 to 15 800 to 510 0.8 to 1.84 2.0 × 2.0 × 1.0 SD3112 4.7 to 15 740 to 405 0.25 to 0.65 3.1 × 3.1 × 1.2 Cooper www.cooperet.com MIP3226D 4.7 to 10 600 to 200 0.1 to 0.16 3.2 × 2.6 × 1.0 FDK www.fdk.com LQH32CN 4.7 to 15 650 to 300 0.15 to 0.58 3.2 × 2.5 × 1.5 LQH2MC 4.7 to 15 300 to 200 0.8 to 1.6 2 × 1.6 × 0.9 Murata www.murata.com CDRH3D16 4.7 to 15 900 to 450 0.11 to 0.29 3.8 × 3.8 × 1.8 CDRH2D14 4.7 to 12 680 to 420 0.12 to 0.32 3.2 × 3.2 × 1.5 NR3010 4.7 to 15 750 to 400 0.19 to 0.74 3.0 × 3.0 × 1.0 NR3015 4.7 to 15 1000 to 560 0.12 to 0.36 3.0 × 3.0 × 1.5 PART MANUFACTURER Coil Craft www.coilcraft.com Sumida www.sumida.com Taiyo Yuden www.t-yuden.com 3523fb 10 LTC3523/LTC3523-2 APPLICATIONS INFORMATION will increase loop bandwidth resulting in a faster transient response. Maximum capacitance values will produce lower ripple. Table 3 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their entire selection of ceramic parts. Table 2. Step-Down Output Capacitor Range vs Programmed Output Voltage VOUT MINIMUM CAPACITANCE (μF) MAXIMUM CAPACITANCE (μF) 0.8 8.4 33.6 1.2 5.6 22.4 1.5 4.5 17.9 1.8 3.7 14.9 2.5 2.7 10.7 5 1.3 5.4 Table 3. 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 STEP-UP VIN > VOUT OPERATION The LTC3523/LTC3523-2 step-up converters will maintain voltage regulation when the input voltage is above the output voltage. Since this mode will dissipate more power, the maximum output current is limited in order to maintain an acceptable junction temperature and is given by: IOUT(MAX ) = 250 – TA T 136 • ⎡⎣(VIN + 1.5) – VOUT ⎤⎦ where TA = ambient temperature. For example, at VIN = 4.5V, VOUT = 3.3V and TA = 85°C, the maximum output current is limited to 449mA. SHORT-CIRCUIT PROTECTION The LTC3523/LTC3523-2’s step-up output disconnect feature allows output short circuit while maintaining a maximum internally set current limit. However, the LTC3523/LTC3523-2 also incorporate internal features such as current limit foldback and thermal shutdown for protection from an excessive overload or short circuit. During a prolonged short circuit of VOUT less than 950mV, the current limit folds back to 2/3 the normal current limit. This 2/3 current limit remains in effect until VOUT exceeds 1V, at which time the normal internal set current limit is restored. When the LTC3523/LTC3523-2 step-down converters output is shorted to ground, the step-down uses a comparator to limit the current through the synchronous rectifying N-channel switch to 650mA. If this limit is exceeded, the P-channel switch is inhibited from turning on until the current through the synchronous rectifying N-channel switch falls below 650mA. THERMAL CONSIDERATIONS To deliver the LTC3523/LTC3523-2’s full-rated power, it is imperative that a good thermal path be provided to dissipate the heat generated within the package. This can be accomplished by taking advantage of the large thermal pad on the underside of the LTC3523/LTC3523-2. It is recommended that multiple vias in the printed circuit board be used to conduct heat away from the LTC3523/LTC3523-2 and into the copper plane with as much area as possible. In the event that the junction temperature gets too high, the LTC3523/LTC3523-2 will go into thermal shutdown and all switching will cease until the internal temperature drops to a safe level at which point the soft-start cycle will be initiated. 3523fb 11 LTC3523/LTC3523-2 APPLICATIONS INFORMATION DUAL BUCK-BOOST AND STEP-UP CONVERTER OPERATION into the step-down’s SHDN2 pin. Note that the overall 3.3V converter efficiency is the product of the individual efficiencies. The LTC3523/LTC3523-2 can be operated in a cascaded configuration as shown in Figure 2, allowing buck-boost and step-up converter operation. Supply rail sequencing is achieved by feeding the step-up converter PGOOD1 VIN 1.8V TO 5.25V 4.7μF 10μH VIN1 VOUT1 STEP-UP OUTPUT 5V 100mA VBAT VIN2 4.7μH SW1 SW2 VOUT FB2 10pF 10μF 768k LTC3523 FB1 PGOOD1 10μF 182k PGOOD2 SHDN2 SHDN1 243k VIN MODE 825k VOUT2 STEP-DOWN OUTPUT 3.3V 50mA GND1 GND2 GND3 100k VIN 3523 F02a OFF ON 100 5V OUTPUT 90 EFFICIENCY (%) 80 70 3.3V OUTPUT 60 50 40 30 VIN = 2.4V VOUT1 = 5V VOUT2 = 3.3V fOSC = 1.2MHz BURST ENABLED 20 10 0 0.1 10 1 100 OUTPUT CURRENT (mA) 1000 3523 F02b Figure 2. Dual Converter Efficiency (Load Applied to Step-Down Output) 3523fb 12 LTC3523/LTC3523-2 TYPICAL APPLICATIONS Power Sequence Operation VIN 1.8V TO 3.2V 2-CELL ALKALINE + 4.7μF 4.7μH VIN1 VOUT1 STEP-UP OUTPUT 3.3V 200mA VIN2 VBAT 4.7μH SW1 SW2 VOUT FB2 10pF 4.7μF 634k FB1 PGOOD1 365k LTC3523 MODE 511k 10μF VOUT2 STEP-DOWN OUTPUT 1.2V 200mA 511k PGOOD2 SHDN1 SHDN2 GND1 GND2 GND3 100k VIN OFF ON 3523 TA02a VOUT1 2V/DIV PGOOD2 VOUT2 1V/DIV SHDN2 500μs/DIV 3523 TA02b 3523fb 13 LTC3523/LTC3523-2 TYPICAL APPLICATIONS Li-Ion to 5V/150mA, 2.5V/200mA VIN 2.5V TO 4.2V Li-Ion + 4.7μF 10μH VIN1 VOUT1 STEP-UP OUTPUT 5V 150mA VIN2 VBAT 4.7μH SW1 SW2 VOUT FB2 10pF 10μF FB1 768k PGOOD1 SHDN1 243k LTC3523 MODE VIN 768k 10μF VOUT2 STEP-DOWN OUTPUT 2.5V 200mA 243k PGOOD2 SHDN2 GND1 GND2 GND3 OFF ON OFF ON 3523 TA03 Efficiency and Power Loss vs Load Current 1000 100 EFFICIENCY 90 100 70 60 P0WER LOSS 50 40 10 VIN = 3.6V VOUT1 = 5V VOUT2 = 2.5V fOSC = 1.2MHz 30 20 POWER LOSS (mW) EFFICIENCY (%) 80 1 STEP-UP STEP-DOWN 10 0 0 10 1 100 LOAD CURRENT (mA) 0 1000 3523 TA03b 3523fb 14 LTC3523/LTC3523-2 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 p0.05 3.50 p 0.05 1.45 p 0.05 2.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 s 45o CHAMFER R = 0.115 TYP 0.75 p 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 p 0.10 1 1.45 p 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-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 0.25 p 0.05 0.50 BSC 3523fb 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 LTC3523/LTC3523-2 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, ThinSOTTM Package LTC3401 1A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.5V, IQ = 38μA, ISD < 1μA, 10-Pin MS Package LTC3402 2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.5V, IQ = 38μA, ISD < 1μA, 10-Pin MS Package LTC3421 3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect Converter 94% Efficiency, VIN: 0.85V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12μA, ISD < 1μA, 24-Pin (4mm × 4mm) QFN Package LTC3422 1.5A (ISW), 3MHz, Synchronous Step-Up DC/DC with Output Disconnect Converter 94% Efficiency, VIN: 0.85V to 4.5V, VOUT(MAX) = 5.25V, IQ = 25μA, ISD < 1μA, 10-Pin (3mm × 3mm) DFN Package LTC3426 2A (ISW), 1.5MHz, Step-Up DC/DC Converter 92% Efficiency, VIN: 1.6V to 5.5V, VOUT(MAX) = 5V, IQ = 600μA, ISD < 1μA, ThinSOT Package LTC3427 500mA (ISW), 1.25MHz, Synchronous Step-Up DC/DC with Output Disconnect Converter 94% Efficiency, VIN: 1.8V to 5V, VOUT(MAX) = 5.25V, IQ = 350μA, ISD < 1μA, 6-Pin (2mm × 2mm) DFN Package LTC3429/LTC3429B 600mA (ISW), 550kHz, Synchronous Step-Up DC/DC Converters Soft-Start/Output Disconnect 96% Efficiency, VIN: 0.85V to 4.3V, VOUT(MAX) = 5V, IQ = 20μA, ISD < 1μA, ThinSOT Package LTC3459 80mA (ISW), Synchronous Step-Up DC/DC Converter 92% Efficiency, VIN: 1.5V to 5.5V, VOUT(MAX) = 10V, IQ = 10μA, ISD < 1μA, ThinSOT Package LTC3525-3 LTC3525-3.3 LTC3525-5 400mA (ISW), Synchronous Step-Up DC/DC Converters with Output 94% Efficiency, VIN: 0.85V to 4V, VOUT(MAX) = 5V, Disconnect IQ = 7μA, ISD < 1μA, SC-70 Package LTC3526/LTC3526L LTC3526B 500mA (ISW), 1MHz Synchronous Step-Up DC/DC Converters with Output Disconnect 94% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 9μA, ISD < 1μA, 6-Pin (2mm × 2mm) DFN Package LTC3528/LTC3528B 1A (ISW), 1MHz Synchronous Step-Up DC/DC Converters with Output Disconnect 94% Efficiency, VIN: 0.85V to 5V, VOUT(MAX) = 5.25V, IQ = 10μA, ISD < 1μA, 8-Pin (2mm × 3mm) DFN Package ThinSOT is a trademark of Linear Technology Corporation. 3523fb 16 Linear Technology Corporation LT 1108 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008