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Final Electrical Specifications
LTC1517-3.3 Micropower, Regulated 3.3V Charge Pump in a 5-Pin SOT-23 Package
June 1998
FEATURES
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DESCRIPTION
The LTC(R)1517-3.3 is a micropower charge pump DC/DC converter that produces a regulated 3.3V output. The input voltage range is 2V to 4.4V. Extremely low operating current (typically 6A with no load) and low external parts count (one 0.1F flying capacitor and two small bypass capacitors at VIN and VOUT) make the part ideally suited for small, light load battery-powered applications. The total printed circuit board area of the application circuit shown below is only 0.045in2. The part operates as a Burst ModeTM switched-capacitor voltage doubler to produce a regulated output. The part has thermal shutdown capability and can survive a continuous short circuit from VOUT to GND. The device is available in a 5-pin SOT-23 package.
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Ultralow Power: ICC = 6A Typ Short-Circuit/Thermal Protected 3.3V 4% Regulated Output VIN Range: 2V to 4.4V Output Current: 8mA (VIN 2V) 15mA (VIN 2.5V) No Inductors Ultrasmall Application Circuit (0.045in2) 800kHz Switching Frequency Available in 5-Pin SOT-23
APPLICATIONS
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Cellular Telephones Battery-Operated Equipment Local Power Supplies Handheld Instruments PCMCIA Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
Efficiency vs Output Current
100 TA = 25C C1 = 0.1F COUT = 6.8F
0.1F
80
EFFICIENCY (%)
5 C1 - LTC1517-3.3 VIN VIN 2V TO 4.4V 3.3F 1 GND 2
4 C1 +
60
VOUT 3 6.8F VOUT = 3.3V 4% IOUT = 8mA (VIN 2V) IOUT = 15mA (VIN 2.5V)
1517-3.3 TA01
40
20
0 0.001
0.01 1 10 0.1 OUTPUT CURRENT (mA)
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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VIN = 2V VIN = 2.5V
100
1517 TA02
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LTC1517-3.3
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW VIN GND VOUT 1 2 3 4 C1 + 5 C1 -
VIN to GND ...................................................- 0.3V to 6V VOUT to GND ................................................- 0.3V to 6V VOUT Short-Circuit Duration ............................. Indefinite Operating Temperature Range: Commercial (Note 2) .............................. 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1517CS5-3.3
S5 PACKAGE 5-LEAD PLASTIC SOT-23
S5 PART MARKING LTEF
TJMAX = 125C, JA = 256C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 2V to 4.4V, C1 = 0.1F, CIN = 3.3F, COUT = 6.8F, TMIN to TMAX, unless otherwise noted.
SYMBOL VIN VOUT ICC fOSC tON PARAMETER Operating Input Voltage Output Voltage Input Supply Current VOUT Ripple Oscillator Frequency VOUT Turn-On Time VIN = 2.5V 2V VIN 4.4V, IOUT 8mA 2.5V VIN 4.4V, IOUT 15mA 2V VIN 4.4V, IOUT = 0 VIN = 2.5V, IOUT = 15mA, COUT = 6.8F CONDITIONS
q q q q
MIN 2.0 3.17 3.17
TYP 3.3 3.3 6 50 800 1
MAX 4.4 3.43 3.43 15
UNITS V V V A mVP-P kHz ms
The q denotes specifications that apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired.
Note 2: Commercial grade parts are designed to operate over the temperature range of - 40C to 85C but are neither tested nor guaranteed beyond 0C to 70C.
PIN FUNCTIONS
VIN (Pin 1): Charge Pump Input Voltage. May be between 2V and 4.4V. VIN should be bypassed with a 3.3F low ESR capacitor as close as possible to the pin for best performance. GND (Pin 2): Ground. Should be tied to a ground plane for best performance. VOUT (Pin 3): Regulated Output Voltage. VOUT should be bypassed with a 3.3F low ESR capacitor as close as possible to the pin for best performance. C1 + (Pin 4): Charge Pump Flying Capacitor Positive Terminal. C1 - (Pin 5): Charge Pump Flying Capacitor Negative Terminal.
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LTC1517-3.3
SI PLIFIED BLOCK DIAGRA
VIN CIN
800kHz OSC
LTC1517-3.3
1517-3.3 BD
APPLICATIONS INFORMATION
Operation The LTC1517-3.3 uses a switched-capacitor charge pump to boost VIN to a 3.3V 4% regulated output. The part achieves regulation by sensing the output voltage through an internal resistor divider and enabling the charge pump when the divided output droops below the comparator's lower trip point (set by VREF). When the charge pump is enabled, a 2-phase nonoverlapping clock controls the internal charge pump switches. Flying capacitor C1 is charged to VIN on phase one of the clock. On phase two of the clock, C1 is stacked in series with VIN and connected to VOUT through an internal switch. This sequence of charging and discharging the flying capacitor occurs at a free running frequency of 800kHz (typ) and continues until the divided output voltage reaches the upper trip point of the comparator. Once the output is back in regulation, the charge pump is disabled. This method of bursting the charge pump on and off enables the LTC1517-3.3 to achieve high efficiency at extremely low output loads. Capacitor Selection For best performance, it is recommended that low ESR capacitors be used for both CIN and COUT to reduce noise and ripple. The CIN and COUT capacitors should be either ceramic or tantalum and should be 3.3F or greater. Ceramic capacitors will provide the smallest size for a given capacitance. If the input source impedance is very low (< 0.5), CIN may not be needed. Ceramic capacitors are recommended for the flying capacitor C1 with values of 0.1F or 0.22F. Smaller value flying capacitors may be used in low IOUT applications. Output Ripple Normal LTC1517-3.3 operation produces voltage ripple on the VOUT pin. Output voltage ripple is required for the parts to regulate. Low frequency ripple exists due to the hysteresis in the sense comparator and propagation delays in the charge pump enable/disable circuits. High frequency ripple is also present mainly from the ESR (equivalent series resistance) in the output capacitor. Typical output ripple with VIN = 2.5V under maximum load is 75mV peak-to-peak with a low ESR 3.3F output capacitor (minimum recommended COUT). For applications requiring VIN to exceed 3.3V or for applications requiring less than 75mV of peak-to-peak ripple, a 6.8F to 10F COUT capacitor is recommended. Slight further decreases in output ripple can be achieved by using COUT capacitors larger than 10F.
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C1 0.1F C1 - C1 + VOUT 2.05M COUT CHARGE PUMP
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+ -
THERMAL SHDN 1.25V REF 1.25M
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LTC1517-3.3
APPLICATIONS INFORMATION
Short-Circuit/Thermal Protection During short-circuit conditions, the LTC1517-3.3 will draw between 40mA and 150mA from VIN, causing a rise in junction temperature. On-chip thermal shutdown circuitry disables the charge pump once the junction temperature exceeds approximately 160C. The charge pump is reenabled once the junction temperature drops to approximately 145C. The LTC1517-3.3 will cycle in and out of thermal shutdown indefinitely without latchup or damage until the VOUT short is removed.
TYPICAL APPLICATION
Low Power Battery Backup Supply with Autoswitchover and No Reverse Current
VOUT = 3.3V, IOUT = 300mA (IOUT = 8mA IN BACKUP MODE)
MAIN SUPPLY 5V
1F BAT54
75k
TRICKLE CHARGE AND LTC1517-3.3 IDD 1 2-CELL NiCd 3.3F
1.1M + 3.9VTRIP 470k 3 4 5 6
LTC1540
RELATED PARTS
PART NUMBER LTC1514-X LTC1515 LTC1516 LTC1517-5 LTC1522 DESCRIPTION Step-Up/Step-Down Switched-Capacitor DC/DC Converter with Low Battery Comparator Step-Up/Step-Down Switched-Capacitor DC/DC Converter with POR Micropower Regulated 5V Charge Pump DC/DC Converter Micropower Regulated 5V Charge Pump in a 5-Pin SOT-23 Package Micropower Regulated 5V Charge Pump DC/DC Converter COMMENTS 3.3V or 5V Output up to 50mA Fixed or Adjustable Output up to 50mA 20mA for VIN 2V, 50mA for VIN 3V IOUT up to 20mA Same as LTC1517-5 with Shutdown
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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LT1521-3.3 2
1 1.5F
0.1F
5
4 3 3.3F
SILICONIX Si2301DS
LTC1517-3.3 2
7 8 LOGIC LOW = BACKUP MODE
1517-3.3 TA03
2
1
15173i LT/TP 0698 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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