LTC3525D-3.3 400mA Micropower Synchronous Step-Up DC/DC Converter with Pass Through Mode U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®3525D-3.3 is a high efficiency synchronous stepup DC/DC converter that can start up with an input as low as 0.85V. It offers a compact, high efficiency alternative to charge pumps in single cell or dual cell alkaline or Li-ion applications. Only three small external components are required. The LTC3525D features a fixed output voltage of 3.3V. In shutdown, VOUT is connected to VIN through the inductor. VOUT Connected to VIN in Shutdown Up to 95% Efficiency 0.85V Minimum Input Start-Up Voltage Fixed Output Voltage of 3.3V Delivers 60mA at 3.3V from a 1V Input, or 140mA at 3.3V from a 1.8V Input Burst Mode® Operation: IQ = 7µA VIN Range: 0.5V to 4.5V Only Three External Components VIN > VOUT Operation Antiringing Control Short-Circuit and Overtemperature Protection Very Low Profile of 1mm Tiny 6-Pin SC70 Package The device includes a 0.5Ω N-channel MOSFET switch and a 0.8Ω P-channel synchronous rectifier. Peak switch current ranges from 150mA to 400mA, depending on load, providing enhanced efficiency. Quiescent current is an ultralow 7µA, maximizing battery life in portable applications. U APPLICATIO S ■ ■ ■ ■ Other features include anti-ringing control and thermal shutdown. The LTC3525D is available in a tiny 6-pin SC70 package. MP3 Players Portable Instruments Glucose Meters Digital Cameras , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents Pending. U TYPICAL APPLICATIO LTC3525D-3.3 Efficiency and Power Loss vs Load Current L1* 10µH 100 100 90 SW VOUT 3.3V 140mA PASS THROUGH ON SHDN GND VOUT GND 10µF 1µF EFFICIENCY (%) VIN 1.8V to 3.2V EFFICIENCY 70 1 60 POWER LOSS 50 0.1 40 3525 TA01 VIN = 3V VIN = 2.4V VIN = 1.2V 30 20 0.01 *MURATA LQH32CN100K53 POWER LOSS (mW) VIN 10 80 LTC3525D-3.3 0.1 1 10 LOAD (mA) 100 0.01 1000 LT3525 • TA02 3525d33f 1 LTC3525D-3.3 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN, VOUT Voltage ........................................ –0.3V to 6V SW Voltage ................................................. –0.3V to 6V SW Voltage < 100ns ................................... –0.3V to 7V ⎯S⎯H⎯D⎯N Voltage ............................................. –0.3V to 6V Operating Temperature Range (Notes 2, 5).......................................... –40°C to 85°C Storage Temperature Range................... –65°C to 125°C Lead Temperature (Soldering, 10 sec) .................. 300°C TOP VIEW SHDN 1 6 SW GND 2 5 GND VIN 3 4 VOUT SC6 PACKAGE 6-LEAD PLASTIC SC70 TJMAX = 125°C θJA = 256°C/W IN FREE AIR, θJA = 150°C/W ON BOARD OVER GROUND PLANE ORDER PART NUMBER SC6 PART MARKING LTC3525DESC6-3.3 LCQZ Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, V⎯S⎯H⎯D⎯N = 1.2V, VOUT = 3.3V unless otherwise noted. PARAMETER CONDITIONS MIN Input Start-Up Voltage ● 3.20 TYP MAX 0.85 1 UNITS V 3.30 3.40 V 15 µA Output Voltage (Note 6) Quiescent Current, VOUT ⎯S⎯H⎯D⎯N = VIN (Note 4) 7 Quiescent Current, VIN ⎯S⎯H⎯D⎯N = VIN (Note 4) 0.5 3 µA Quiescent Current, VIN - Shutdown ⎯S⎯H⎯D⎯N = 0V, VOUT = VIN = 3.3V Including Switch Leakage 3 10 µA NMOS Switch On Resistance (Note 3) 0.5 Ω PMOS Switch On Resistance (Note 3) 0.8 Ω A Peak Current Limit 0.4 0.45 ⎯S⎯H⎯D⎯N Threshold 0.4 0.6 1 V 0.01 1 µA ⎯S⎯H⎯D⎯N Input Current V⎯S⎯H⎯D⎯N = VIN or VOUT 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 LTC3525DE is 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 controls. Note 3: Specification is guaranteed by design and not 100% tested in production. Note 4: Current Measurements are performed when the LTC3525D 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 impair device reliability. Note 6: Consult LTC Marketing for other output voltage options. 3525d33f 2 LTC3525D-3.3 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted. Maximum Output Current vs VIN (for VOUT to Drop 2.5%) Maximum Startup Load vs VIN (Resistive Load) 300 No-Load Input Current vs VIN 50 250 45 250 40 200 35 150 IIN (µA) 150 LOAD (mA) IOUT (mA) 200 100 100 30 25 20 15 10 50 50 5 0 0.5 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 4.5 0.5 1.0 1.5 2.0 VIN (V) 3.0 2.5 3525 G01 100 2.5 90 50 0.1 40 30 0.1 1 10 LOAD (mA) 4.0 1.0 0.5 COUT = 22µF 0 COUT = 10µF –0.5 –1.0 1.0 0.5 –0.5 –1.5 –2.0 –2.0 100 –2.5 3525 G04 10 20 30 40 50 LOAD (mA) 60 70 80 COUT = 10µF –1.0 –1.5 0 COUT = 22µF 0 VIN = 3V VIN = 2.4V VIN = 1.2V 0.01 1000 –2.5 0 20 40 60 80 100 120 140 160 180 LOAD (mA) 3525 G06 35 0.3 30 0.2 25 20 COUT = 10µF 15 Start-Up Delay Coming Out of Shutdown 120 100 SWITCHING DELAY (µs) 0.4 CHANGE IN VOUT (%) BURST FREQUENCY (kHz) 40 0.1 0 –0.1 –0.2 10 COUT = 22µF 0.1 1 LOAD (mA) 10 3525 G12 80 60 40 20 –0.3 5 0 3525 G07 VOUT Variation vs Temperature (Normalized to 25°C) Light Load Burst Frequency vs Load 4.5 1.5 CHANGE IN VOUT (%) POWER LOSS CHANGE IN VOUT (%) EFFICIENCY (%) 1 60 POWER LOSS (mW) 70 3.5 VIN = 2.4V 2.0 1.5 10 EFFICIENCY 2.5 3.0 VIN (V) Load Regulation 2.5 VIN = 1.2V 2.0 80 2.0 3525 G03 Load Regulation 100 1.5 3525 G02 Efficiency and Power Loss vs Load 20 0.01 0 1.0 0 –0.4 –40–30–20–10 0 10 20 30 40 50 60 70 80 TEMPERATURE (°C) 3525 G13 0 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 4.5 3525 G14 3525d33f 3 LTC3525D-3.3 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted. Output Voltage Ripple Output Voltage Ripple IOUT = 5mA IOUT = 5mA IOUT = 40mA IOUT = 40mA 50mV/DIV IOUT = 80mA 50mV/DIV IOUT = 80mA VIN = 1.2V COUT = 10µF 50µs/DIV 3525 G16 VIN = 1.2V COUT = 22µF 50µs/DIV 3525 G17 50mA Load Step Response Output Voltage Ripple IOUT = 5mA IOUT = 100mA OUTPUT RIPPLE 50mV/DIV 50mV/DIV LOAD CURRENT 20mA/DIV IOUT = 190mA VIN = 2.4V COUT = 22µF 50µs/DIV 3525 G18 VIN = 1.2V COUT = 22µF 500µs/DIV 3525 G21 100mA Load Step Response OUTPUT RIPPLE 50mV/DIV LOAD CURRENT 50mA/DIV VIN = 2.4V COUT = 22µF 500µs/DIV 3525 G22 3525d33f 4 LTC3525D-3.3 U U U PI FU CTIO S ⎯S⎯H⎯D⎯N (Pin 1): Logic Controlled Shutdown Input. Connect to a voltage >1V to enable the LTC3525D. Connect to a voltage <0.4V to disable the LTC3525D and connect VIN to VOUT through the inductor. VOUT (Pin 4): Output Voltage Sense and the Output of the Synchronous Rectifier. Connect the output filter capacitor from VOUT to GND, close to the IC. A minimum value of 10µF ceramic is recommended. Use 22µF for reduced output ripple. The pass-through mode feature connects VOUT to VIN through the inductor when ⎯S⎯H⎯D⎯N is <0.4V. GND (Pins 2, 5): Ground. VIN (Pin 3): Input Voltage. The LTC3525D is powered from VIN until VOUT exceeds VIN. Once VOUT is greater than (VIN + 0.2V typical), it is powered from VOUT. Place a ceramic bypass capacitor from VIN to GND. A minimum value of 1µF is recommended. SW (Pin 6): Switch Pin. Connect an inductor from this pin to VIN. An internal antiringing resistor is connected across SW and VIN after the inductor current has dropped to zero to minimize EMI. W BLOCK DIAGRA SW VIN 6 3 VOUT VSEL VBEST WELL SWITCH VB 4 VOUT SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION + – OFFSET VREF UVLO ADJUST VREF IPK UVLO – + + IPK COMPARATOR STARTUP – ADJUST LOGIC IVAL + SHUTDOWN IVALLEY COMPARATOR TSD – WAKE + THERMAL SHUTDOWN OFFSET – SHDN 1 INTEGRATOR FB VREF SLEEP COMPARATOR ADJUST 5 2 GND GND 3525 BD 3525d33f 5 LTC3525D-3.3 U OPERATIO The LTC3525D is a high performance Burst Mode operation only, synchronous boost converter requiring only three small external components. Its simplicity and small size make it a high efficiency alternative to charge pump designs. It is designed to start-up from a single alkaline or nickel cell, with input voltages as low as 0.85V, or from two or three cells (or a Li-ion battery), with voltages as high as 4.5V. Once started, VIN can be as low as 0.5V (depending on load current) and maintain regulation. The output voltage is preset internally to 3.3V. Peak switch current is 400mA minimum, providing regulation with load currents up to 150mA, depending on input voltage. After the ⎯S⎯H⎯D⎯N pin rises, there is a short delay before switching starts. The delay is 20µs to 120µs, depending on input voltage (see Typical Performance Characteristics curve). Synchronous rectification provides high efficiency operation while eliminating the need for an external Schottky diode. A start-up oscillator allows the LTC3525D to start with input voltages as low as 1V. It remains in start-up mode until two conditions are met. VOUT must exceed VIN by at least 0.2V typical and either VIN or VOUT must be greater than 1.8V typical. The LTC3525D can maintain regulation with an input voltage equal to or greater than VOUT. Note, however, that the synchronous rectifier is not enabled in this mode, resulting in lower efficiency and reduced output current capability. The operating quiescent current is only 7µA typical, allowing the converter to maintain high efficiency at extremely light loads. Shutdown The LTC3525D is shut down by pulling ⎯S⎯H⎯D⎯N below 0.4V, and made active by raising it above 1V. Note that ⎯S⎯H⎯D⎯N can be driven as high as 6V, however, if it is more than 0.9V above the higher of VIN or VOUT, the ⎯S⎯H⎯D⎯N input current will increase from zero to 1.5µA. Pass-Through Mode When the LTC3525D is in shutdown, the internal P channel MOSFET switch is turned on. This allows VIN to be connected to VOUT through the inductor in shutdown, creating a pass-through mode. Start-up During startup, the synchronous rectifier is not enabled, and the internal P-channel synchronous rectifier acts as a follower, causing the peak voltage on SW to reach (VIN + 1V) typical. This limits inrush current by maintaining control of the inductor current when VOUT is less than VIN. To reduce power dissipation in the P-channel synchronous rectifier when the output is shorted, a foldback feature is incorporated that reduces the peak inductor current when VIN is more than 1.7V greater than VOUT. 3525d33f 6 LTC3525D-3.3 U OPERATIO INDUCTOR CURRENT 100mA/DIV LOAD CURRENT 50mA/DIV 10µs/DIV 3525 F01 Figure 1. Inductor Current Changing as a Function of Load Normal Operation Power Adjust Feature Once VOUT has increased more than 0.2V typical above VIN, and either voltage is above 1.8V, normal operation begins, with synchronous rectification enabled. In this mode, the internal N-channel MOSFET connected between SW and GND stays on until the inductor current reaches a maximum peak value, after which it is turned off and the P-channel synchronous rectifier is turned on. It stays on, delivering current to the output, until the inductor current has dropped below a minimum value at which point it turns off and the cycle repeats. When the output voltage reaches its regulated value both switches are turned off and the LTC3525D goes to sleep, during which time the output capacitor supplies current to the load. Once the output voltage drops approximately 9mV below the regulation value the IC leaves sleep mode and switching is resumed. The LTC3525D incorporates a feature that maximizes efficiency at light load while providing increased power capability at heavy load by adjusting the peak and valley of the inductor current as a function of load. Lowering the peak inductor current to 150mA at light load optimizes efficiency by reducing conduction losses in the internal MOSFET switches. As the load increases, the peak inductor current is automatically increased to a maximum of 400mA. At intermediate loads, the peak inductor current may vary from 150mA to 400mA. Figure 1 shows an example of how the inductor current changes as the load increases. Please note that output capacitor values greater than 47µF will result in higher peak currents than necessary at light load. This will lower the light load efficiency. The LTC3525D has been designed for low output voltage ripple. The output voltage ripple is typically only 20mV peak-to-peak at light load and 60mV peak-to-peak at full load using the minimum recommended 10µF output capacitor. An anti-ring circuit damps any oscillation at the switch node when the inductor current falls to zero. The valley of the inductor current is automatically adjusted as well, to maintain a relatively constant inductor ripple current. This keeps the switching frequency relatively constant. 3525d33f 7 LTC3525D-3.3 U OPERATIO The maximum average load current that can be supported is given by: IO(MAX) = 0.3 • VIN • η Amps VO Where η is the efficiency (see Typical Performance Characteristics). The “burst” frequency (how often the LTC3525D delivers a burst of current pulses to the load) is determined by the internal hysteresis (output voltage ripple), the load current and the amount of output capacitance. All Burst Mode operation or hysteretic converters will enter the audible frequency range when the load is light enough. However, due to the low peak inductor current at light load, circuits using the LTC3525D do not typically generate any audible noise. Component Selection Inductor values between 4.7µH and 15µH are recommended. In most applications 10µH will yield the best compromise between size and efficiency. The inductor should be a low-loss ferrite design and must be rated for peak currents of at least 400mA without saturating. Inductors with lower DC resistance will improve efficiency. Note that the inductor value does not have a significant effect on ripple current, so while lower values will increase the operating frequency, they do not reduce output voltage ripple. Some recommended inductor examples are Murata LQH32C, Coilcraft LPO4812, LPO3310, DO3314, DS1608 and MSS4020, Sumida CDRH2D14 and Taiyo Yuden NR3015T. A ceramic input bypass capacitor should be located as close as possible to the VIN and GND pins of the IC. A minimum value of 1µF is recommended. If the battery is more than a few inches away, a bulk tantalum decoupling cap of at least 10µF is recommended on VIN. The output capacitor should also be a ceramic, located close to the VOUT and GND pins. A minimum value of 10µF is recommended. Increasing the value of the output capacitor to 22µF will result in lower output ripple. Higher capacitor values will only offer a small reduction in output ripple, while reducing light load efficiency by causing the peak inductor current to increase above its minimum value of 150mA. The input and output capacitors should be X5R or X7R types, not Y5V. 3525d33f 8 LTC3525D-3.3 U OPERATIO Table 1. Inductor Vendor Information SUPPLIER PHONE FAX WEBSITE Murata USA: (814) 237-1431 USA: (814) 238-0490 www.murata.com Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com Sumida USA: (847) 956-0666 USA: (847) 956-0702 www.sumida.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com Table 2. Capacitor Vendor Information SUPPLIER PHONE FAX WEBSITE Murata USA: (814) 237-1431 USA: (814) 238-0490 www.murata.com Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com TDK (847) 803-6100 (847) 803-6296 www.component.tdk.com AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com SHDN SHDN SW LTC3525D-3.3 VIN GND GND VIN VOUT VOUT 3525 F02 Figure 2. Recommended Component Placement 3525d33f 9 LTC3525D-3.3 U TYPICAL APPLICATIO Single Alkaline or NiMH to 3.3V Converter with 1mm Profile 6.8µH* 1V to 1.6V 3 1 PASS THROUGH ON 2 LTC3525D-3.3 6 SW VIN SHDN VOUT GND GND VOUT 3.3V 60mA 4 5 10µF** 6.3V 1µF 3525 TA04 *COILCRAFT LPO3310-682MXD **MURATA GRM219R60J106KE191D 2-Alkaline or NiMH to 3.3V 10µH* 1.8V to 3.2V 3 1 PASS THROUGH ON 2 LTC3525D-3.3 VIN SW SHDN VOUT GND GND 6 VOUT 3.3V 140mA 4 5 1µF 10µF 3525 TA05 *MURATA LQH32CN1002K53 3525d33f 10 LTC3525D-3.3 U PACKAGE DESCRIPTIO SC6 Package 6-Lead Plastic SC70 (Reference LTC DWG # 05-08-1638 Rev B) 0.47 MAX 0.65 REF 1.80 – 2.20 (NOTE 4) 1.00 REF INDEX AREA (NOTE 6) 1.80 – 2.40 1.15 – 1.35 (NOTE 4) 2.8 BSC 1.8 REF PIN 1 RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 – 0.40 0.65 BSC 0.15 – 0.30 6 PLCS (NOTE 3) 0.80 – 1.00 0.00 – 0.10 REF 1.00 MAX GAUGE PLANE 0.15 BSC 0.26 – 0.46 0.10 – 0.18 (NOTE 3) SC6 SC70 1205 REV B NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. DETAILS OF THE PIN 1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE INDEX AREA 7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70 8. JEDEC PACKAGE REFERENCE IS MO-203 VARIATION AB 3525d33f 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 LTC3525D-3.3 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1615/LT1615-1 300mA/80mA (ISW), High Efficiency Step-Up DC/DC Converter VIN: 1V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD <1µA, ThinSOT™ Package LT1930/LTC1930A 1A (ISW), 1.2MHz/2MHz, High Efficiency Step-Up DC/DC Converter High Efficiency, VIN: 2.6V to 16V, VOUT(MAX) = 34V, IQ = 4.2mA/5.5mA, ISD <1µA, ThinSOT Package LTC3400/LTC3400B 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter 92% Efficiency, VIN: 0.5V 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) = 5.5V, IQ = 38µA, ISD <1µA, MS Package LTC3402 2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 97% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5.5V, IQ = 38µA, ISD <1µA, 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, QFN-24 Package LTC3429/LTC3429B 600mA, 500kHz Single/Dual Cell Micropower Synchronous Boost Converter with Output Disconnect 95% Efficiency, VIN: 1V to 4.5V, VOUT(MAX) = 5V, IQ = 20µA, ISD <1µA, SC70 Package LTC3458 1.4A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, ISD <1µA, 3mm × 4mm DFN Package LTC3458L 1.7A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect VIN: 1.5V to 6V, VOUT(MAX) = 6V, ISD <1µA, 3mm × 4mm DFN Package LTC3459 60mA, 10V Micro Power Synchronous Boost Converter 95% Efficiency, VIN: 1.5V to 6V, VOUT(MAX) = 10V, IQ =10µA, ISD <1µA, ThinSOT Package LT3464 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA, ISD <1µA, ThinSOT Package LT3427 500mA (ISW), 1.2MHz, Step-Up DC/DC Converter with Output Disconnect VIN: 1.8V to 5V, VOUT(MAX) = 5V, ISD <1µA, 2mm × 2mm DFN Package ® LTC3525-3/LTC3525-3.3/ 400mA Synchronous Step-Up DC/DC Converter with Output LTC3525-5 Disconnect VIN: 0.5V to 4.5V, VOUT(MAX) = 5V, IQ = 7µA, ISD <1µA, SC70 Package LTC3526/LTC3526B VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 9µA, ISD <1µA, 2mm × 2mm DFN-6 Package 500mA. 1MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect ThinSOT is a trademark of Linear Technology Corporation. 3525d33f 12 Linear Technology Corporation LT/LWI 1006 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006