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LTC3525D-3.3 400mA Micropower Synchronous Step-Up DC/DC Converter with Pass Through Mode FEATURES

DESCRIPTIO

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(R) Operation: IQ = 7A 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 LTC(R)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. The device includes a 0.5 N-channel MOSFET switch and a 0.8 P-channel synchronous rectifier. Peak switch current ranges from 150mA to 400mA, depending on load, providing enhanced efficiency. Quiescent current is an ultralow 7A, maximizing battery life in portable applications. Other features include anti-ringing control and thermal shutdown. The LTC3525D is available in a tiny 6-pin SC70 package.
, 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.
APPLICATIO S

MP3 Players Portable Instruments Glucose Meters Digital Cameras
TYPICAL APPLICATIO
LTC3525D-3.3 Efficiency and Power Loss vs Load Current
L1* 10H
100 90
LTC3525D-3.3 VIN 1.8V to 3.2V PASS THROUGH ON SHDN GND 1F VOUT GND 10F VIN SW VOUT 3.3V 140mA
80 EFFICIENCY (%) EFFICIENCY 70 60 POWER LOSS 50 40
3525 TA01
30 20 0.01 0.1 1 10 LOAD (mA)
*MURATA LQH32CN100K53
U
100 10 POWER LOSS (mW) 1 0.1 VIN = 3V VIN = 2.4V VIN = 1.2V 100 0.01 1000
LT3525 * TA02
U
U
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LTC3525D-3.3 ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW SHDN 1 GND 2 VIN 3 6 SW 5 GND 4 VOUT
VIN, VOUT Voltage ........................................ -0.3V to 6V SW Voltage ................................................. -0.3V to 6V SW Voltage < 100ns ................................... -0.3V to 7V SHDN Voltage ............................................. -0.3V to 6V Operating Temperature Range (Notes 2, 5).......................................... -40C to 85C Storage Temperature Range................... -65C to 125C Lead Temperature (Soldering, 10 sec) .................. 300C
SC6 PACKAGE 6-LEAD PLASTIC SC70 TJMAX = 125C JA = 256C/W IN FREE AIR, JA = 150C/W ON BOARD OVER GROUND PLANE
ORDER PART NUMBER LTC3525DESC6-3.3
SC6 PART MARKING 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 = 25C. VIN = 1.2V, VSHDN = 1.2V, VOUT = 3.3V unless otherwise noted.
PARAMETER Input Start-Up Voltage Output Voltage Quiescent Current, VOUT Quiescent Current, VIN Quiescent Current, VIN - Shutdown NMOS Switch On Resistance PMOS Switch On Resistance Peak Current Limit SHDN Threshold SHDN Input Current VSHDN = VIN or VOUT (Note 6) SHDN = VIN (Note 4) SHDN = VIN (Note 4) SHDN = 0V, VOUT = VIN = 3.3V Including Switch Leakage (Note 3) (Note 3) 0.4 0.4
CONDITIONS
MIN 3.20
TYP 0.85 3.30 7 0.5 3 0.5 0.8 0.45 0.6 0.01
MAX 1 3.40 15 3 10
UNITS V V A A A A
1 1
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 0C to 85C. Specifications over the -40C to 85C 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 125C 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.
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V A
W
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WW
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LTC3525D-3.3 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted.
Maximum Output Current vs VIN (for VOUT to Drop 2.5%)
300 250 200 LOAD (mA) IOUT (mA) IIN (A) 150 150 100 50 0 0.5 50 250
1.0
1.5
2.0
2.5 3.0 VIN (V)
3.5
Efficiency and Power Loss vs Load
100 90 80 EFFICIENCY (%) EFFICIENCY 70 60 POWER LOSS 50 40 30 20 0.01 0.1 1 10 LOAD (mA) VIN = 3V VIN = 2.4V VIN = 1.2V 100 0.1 1 10 POWER LOSS (mW) 100
CHANGE IN VOUT (%)
1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 0 10 20 30 40 50 LOAD (mA) 60 70 80 COUT = 10F COUT = 22F
CHANGE IN VOUT (%)
Light Load Burst Frequency vs Load
40 35 BURST FREQUENCY (kHz) CHANGE IN VOUT (%) 30 25 20 COUT = 10F 15 10 COUT = 22F 5 0 0.1 1 LOAD (mA) 10
3525 G12
SWITCHING DELAY (s)
UW
4.0
3525 G01
3525 G04
Maximum Startup Load vs VIN (Resistive Load)
50 45 200 40 35 30 25 20 15 10 5 0 4.5 0.5 1.0 1.5 2.0 VIN (V) 2.5 3.0
3525 G02
No-Load Input Current vs VIN
100
0 1.0
1.5
2.0
2.5 3.0 VIN (V)
3.5
4.0
4.5
3525 G03
Load Regulation
2.5 2.0 1.5 VIN = 1.2V 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5
Load Regulation
VIN = 2.4V
COUT = 22F
COUT = 10F
0.01 1000
0
20
40
60
80 100 120 140 160 180 LOAD (mA)
3525 G07
3525 G06
VOUT Variation vs Temperature (Normalized to 25C)
0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -40-30-20-10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
3525 G13
Start-Up Delay Coming Out of Shutdown
120 100 80 60 40 20 0 1.0 1.5 2.0 2.5 3.0 VIN (V) 3.5 4.0 4.5
3525 G14
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LTC3525D-3.3 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25C unless otherwise noted.
Output Voltage Ripple
IOUT = 5mA IOUT = 40mA IOUT = 80mA 50s/DIV
3525 G16
VIN = 1.2V COUT = 10F
Output Voltage Ripple
IOUT = 5mA IOUT = 100mA IOUT = 190mA 50mV/DIV
VIN = 2.4V COUT = 22F
50s/DIV
4
UW
Output Voltage Ripple
IOUT = 5mA 50mV/DIV IOUT = 40mA IOUT = 80mA 50s/DIV
3525 G17
50mV/DIV
VIN = 1.2V COUT = 22F
50mA Load Step Response
OUTPUT RIPPLE 50mV/DIV LOAD CURRENT 20mA/DIV
3525 G18
VIN = 1.2V COUT = 22F
500s/DIV
3525 G21
100mA Load Step Response
OUTPUT RIPPLE 50mV/DIV LOAD CURRENT 50mA/DIV 500s/DIV
3525 G22
VIN = 2.4V COUT = 22F
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LTC3525D-3.3 PI FU CTIO S
SHDN (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. 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 1F is recommended. 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 10F ceramic is recommended. Use 22F for reduced output ripple. The pass-through mode feature connects VOUT to VIN through the inductor when SHDN is <0.4V. 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.
BLOCK DIAGRA
VOUT VSEL VBEST VB 4 VOUT SHUTDOWN SHUTDOWN GATE DRIVERS AND ANTI-CROSS CONDUCTION OFFSET VREF UVLO VREF UVLO - IPK WELL SWITCH
SHDN 1
IPK COMPARATOR STARTUP LOGIC - IVAL SHUTDOWN TSD WAKE +
INTEGRATOR ADJUST 5 GND 2 GND
SLEEP COMPARATOR
+
THERMAL SHUTDOWN
-
+
W
U
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SW 6
VIN 3
+ -
ADJUST
+
OFFSET
-
ADJUST
IVALLEY COMPARATOR
FB VREF
3525 BD
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LTC3525D-3.3 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. Synchronous rectification provides high efficiency operation while eliminating the need for an external Schottky diode. 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 7A typical, allowing the converter to maintain high efficiency at extremely light loads. Shutdown The LTC3525D is shut down by pulling SHDN below 0.4V, and made active by raising it above 1V. Note that SHDN can be driven as high as 6V, however, if it is more than 0.9V above the higher of VIN or VOUT, the SHDN input current will increase from zero to 1.5A.
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After the SHDN pin rises, there is a short delay before switching starts. The delay is 20s to 120s, depending on input voltage (see Typical Performance Characteristics curve). 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 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. 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.
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LTC3525D-3.3 OPERATIO U
INDUCTOR CURRENT 100mA/DIV LOAD CURRENT 50mA/DIV 10s/DIV
3525 F01
Figure 1. Inductor Current Changing as a Function of Load
Normal Operation 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 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 10F output capacitor. An anti-ring circuit damps any oscillation at the switch node when the inductor current falls to zero.
Power Adjust Feature 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 47F will result in higher peak currents than necessary at light load. This will lower the light load efficiency. 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.
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LTC3525D-3.3 OPERATIO
The maximum average load current that can be supported is given by: IO(MAX) = 0.3 * VIN * Amps VO
Where 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 4.7H and 15H are recommended. In most applications 10H 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.
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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 1F is recommended. If the battery is more than a few inches away, a bulk tantalum decoupling cap of at least 10F is recommended on VIN. The output capacitor should also be a ceramic, located close to the VOUT and GND pins. A minimum value of 10F is recommended. Increasing the value of the output capacitor to 22F 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.
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LTC3525D-3.3 OPERATIO
Table 1. Inductor Vendor Information
SUPPLIER Murata Coilcraft Sumida Taiyo Yuden PHONE USA: (814) 237-1431 (847) 639-6400 USA: (847) 956-0666 (408) 573-4150 FAX USA: (814) 238-0490 (847) 639-1469 USA: (847) 956-0702 (408) 573-4159 WEBSITE www.murata.com www.coilcraft.com www.sumida.com www.t-yuden.com
Table 2. Capacitor Vendor Information
SUPPLIER Murata Taiyo Yuden TDK AVX PHONE USA: (814) 237-1431 (408) 573-4150 (847) 803-6100 (803) 448-9411 FAX USA: (814) 238-0490 (408) 573-4159 (847) 803-6296 (803) 448-1943 WEBSITE www.murata.com www.t-yuden.com www.component.tdk.com www.avxcorp.com
U
SHDN SHDN SW LTC3525D-3.3 GND VIN GND VIN VOUT
3525 F02
VOUT
Figure 2. Recommended Component Placement
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LTC3525D-3.3 TYPICAL APPLICATIO
Single Alkaline or NiMH to 3.3V Converter with 1mm Profile
6.8H*
1V to 1.6V
1.8V to 3.2V
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3 1 PASS THROUGH ON 1F 2 LTC3525D-3.3 VIN SHDN GND SW VOUT GND 6 4 5 VOUT 3.3V 60mA 10F** 6.3V
3525 TA04
*COILCRAFT LPO3310-682MXD **MURATA GRM219R60J106KE191D
2-Alkaline or NiMH to 3.3V
10H*
3 1
LTC3525D-3.3 VIN SHDN GND SW VOUT GND
6 4 5 VOUT 3.3V 140mA 10F
PASS THROUGH ON 1F
2
3525 TA05
*MURATA LQH32CN1002K53
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LTC3525D-3.3 PACKAGE DESCRIPTIO U
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 1.80 - 2.40 1.15 - 1.35 (NOTE 4) INDEX AREA (NOTE 6) PIN 1 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
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
2.8 BSC 1.8 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.10 - 0.40
0.10 - 0.18 (NOTE 3)
SC6 SC70 1205 REV B
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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.
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LTC3525D-3.3 RELATED PARTS
PART NUMBER LT 1615/LT1615-1 LT1930/LTC1930A LTC3400/LTC3400B LTC3401 LTC3402 LTC3421 LTC3429/LTC3429B LTC3458 LTC3458L LTC3459 LT3464 LT3427
(R)
DESCRIPTION 300mA/80mA (ISW), High Efficiency Step-Up DC/DC Converter
COMMENTS VIN: 1V to 15V, VOUT(MAX) = 34V, IQ = 20A, ISD <1A, ThinSOTTM Package
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 <1A, ThinSOT Package 600mA (ISW), 1.2MHz, Synchronous Step-Up DC/DC Converter 1A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 2A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter 3A (ISW), 3MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 600mA, 500kHz Single/Dual Cell Micropower Synchronous Boost Converter with Output Disconnect 1.4A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 1.7A (ISW), 1.5MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect 60mA, 10V Micro Power Synchronous Boost Converter 85mA (ISW), High Efficiency Step-Up DC/DC Converter with Integrated Schottky and PNP Disconnect 500mA (ISW), 1.2MHz, Step-Up DC/DC Converter with Output Disconnect 92% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5V, IQ = 19A/300A, ISD <1A, ThinSOT Package 97% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5.5V, IQ = 38A, ISD <1A, MS Package 97% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5.5V, IQ = 38A, ISD <1A, MS Package 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 12A, ISD <1A, QFN-24 Package 95% Efficiency, VIN: 1V to 4.5V, VOUT(MAX) = 5V, IQ = 20A, ISD <1A, SC70 Package VIN: 1.5V to 6V, VOUT(MAX) = 7.5V, ISD <1A, 3mm x 4mm DFN Package VIN: 1.5V to 6V, VOUT(MAX) = 6V, ISD <1A, 3mm x 4mm DFN Package 95% Efficiency, VIN: 1.5V to 6V, VOUT(MAX) = 10V, IQ =10A, ISD <1A, ThinSOT Package VIN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25A, ISD <1A, ThinSOT Package VIN: 1.8V to 5V, VOUT(MAX) = 5V, ISD <1A, 2mm x 2mm DFN Package VIN: 0.5V to 4.5V, VOUT(MAX) = 5V, IQ = 7A, ISD <1A, SC70 Package VIN: 0.5V to 4.5V, VOUT(MAX) = 5.25V, IQ = 9A, ISD <1A, 2mm x 2mm DFN-6 Package
LTC3525-3/LTC3525-3.3/ 400mA Synchronous Step-Up DC/DC Converter with Output LTC3525-5 Disconnect LTC3526/LTC3526B 500mA. 1MHz, Synchronous Step-Up DC/DC Converter with Output Disconnect
ThinSOT is a trademark of Linear Technology Corporation.
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12 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT/LWI 1006 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2006

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