Datasheet

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LTC1503-1.8/LTC1503-2

High Efficiency Inductorless

Step-Down DC/DC Converters

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Input Voltage Range: 2.4V to 6V

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Fixed Output Voltages: 1.8V ±4%, 2V ±4%

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Output Current: Up to 100mA

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No Inductors

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Typical Efficiency 25% Higher than LDOs

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Low Operating Current: 25

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Low Shutdown Current: 5

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600kHz Switching Frequency

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Shutdown Disconnects Load from V

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Soft-Start Limits Inrush Current at Turn-On

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Short-Circuit and Overtemperature Protected

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Available in 8-Pin MSOP and SO Packages

The LTC

1503-1.8/LTC1503-2 are switched capacitor

step-down DC/DC converters that produce a regulated

output from a 2.4V to 6V input. The parts use switched

capacitor fractional conversion to achieve high efficiency

over the entire input range. No inductors are required.

Internal circuitry controls the step-down conversion ratio

to optimize efficiency as the input voltage and load condi-

tions vary. Typical efficiency is 25% higher than that of a

low dropout (LDO) linear regulator.

Regulation is achieved by sensing the output voltage and

enabling the internal switching network as needed to

maintain a fixed output voltage. This method of regulation

enables the parts to achieve high efficiency at extremely

light loads. Low operating current (25µA with no load, 5µA

in shutdown) and low external parts count (two 1µF flying

capacitors and two 10µF bypass capacitors) make the

LTC1503-1.8/LTC1503-2

ideally suited for space con-

strained battery-powered applications. The parts are fully

short-circuit and overtemperature protected.

The

LTC1503-1.8/

LTC1503-2 are available in 8-pin MSOP

and SO packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

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Cellular Phones

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Handheld Computers

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Smart Card Readers

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Low Power DSP Supplies

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Portable Electronic Equipment

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Handheld Medical Instruments

Efficiency vs Input Voltage

Single Li-Ion to 2V DC/DC Converter

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

–

SHDN/SS

OUT

–

GND

LTC1503-2

1µF

1503-1.8/2 TA01

1µF

10µF

1-CELL Li-Ion OR

3-CELL NiMH

10µF

OUT

= 2V

OUT

= 100mA

INPUT VOLTAGE (V)

EFFICIENCY (%)

1503-1.8/2 TA02

100

LTC1503-2

OUT

= 2V

OUT

= 100mA

OUT

= 1mA

“IDEAL” LDO

Summary of content (12 pages)

PAGE 1
LTC1503-1.8/LTC1503-2 High Efficiency Inductorless Step-Down DC/DC Converters U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®1503-1.8/LTC1503-2 are switched capacitor step-down DC/DC converters that produce a regulated output from a 2.4V to 6V input. The parts use switched capacitor fractional conversion to achieve high efficiency over the entire input range. No inductors are required.
PAGE 2
LTC1503-1.8/LTC1503-2 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN, C1+, C1–, C2 +, C2 – to GND ............... – 0.3V to 6.5V SHDN/SS to GND ......................... – 0.3V to (VIN + 0.3V) VOUT Short-Circuit Duration ............................. Indefinite Commercial Temperature Range ............ – 40°C to 85°C Industrial Temperature Range ............... – 40°C to 85°C Specified Temperature Range (Note 2) ... – 40°C to 85°C Storage Temperature Range ................
PAGE 3
LTC1503-1.8/LTC1503-2 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC1503-X Input Operating Current vs Input Voltage LTC1503-X Input Shutdown Current vs Input Voltage 50 1.90 10 VOUT = 0V VSHDN/SS = 0V 40 TA = –40°C 30 TA = 85°C TA = 25°C 20 2 4 3 5 7.5 TA = –40°C 5 TA = 25°C TA = 85°C 2.5 0 6 IOUT = 50mA 1.85 TA = –40°C 1.80 TA = 25°C 4 3 5 6 2 2.10 100 80 1.95 EFFICIENCY (%) TA = 85°C TA = 25°C TA = 25°C IOUT = 100mA 80 EFFICIENCY (%) 2.05 LTC1503-1.
PAGE 4
LTC1503-1.8/LTC1503-2 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC1503-X Output Short-Circuit Current vs Input Voltage 100 VOUT SHORTED TO GND 30 START-UP TIME (ms) OUTPUT CURRENT (mA) 40 LTC1503-X Start-Up Time vs Soft-Start Capacitor TA = –40°C 20 TA = 25°C TA = 85°C 10 0 VIN = 3.6V 10 TA = –40°C 1 TA = 25°C TA = 85°C 0.1 2 3 4 5 0.01 0.01 6 INPUT VOLTAGE (V) 1 10 0.1 SOFT-START CAPACITOR (nF) 1503-1.8/2 G10 Output Load Transient Response (LTC1503-1.
PAGE 5
LTC1503-1.8/LTC1503-2 U U U PI FU CTIO S turn-on (see Applications Information). If neither of the two functions are desired, the pin may be floated or tied to VIN. GND (Pin 7): Ground. Connect to a ground plane for best performance. C2 – (Pin 8): Flying Capacitor Two Negative Terminal. C2 + (Pin 6): Flying Capacitor Two Positive Terminal.
PAGE 6
LTC1503-1.8/LTC1503-2 U W U U APPLICATIO S I FOR ATIO S4 φ2 General Operation The two most common methods for providing regulated step-down DC/DC conversion are linear DC/DC conversion (used by LDOs) and inductor-based DC/DC conversion. Linear regulation provides low cost and low complexity, but the conversion efficiency is poor since all of the load current must come directly from VIN.
PAGE 7
LTC1503-1.8/LTC1503-2 U W U U APPLICATIO S I FOR ATIO S5 φ2 S1 φ1 C1+ VIN VOUT C1 (EXTERNAL) S4 C1– φ2 S2 φ1 S7 φ2 C2 + C2 (EXTERNAL) S6 C2 – φ2 S3 φ1 maintain regulation. This will only occur as VIN/VOUT nears a 3-to-2 or 1-to-1 transition point. For example, under light load conditions, the LTC1503-X can operate in 2-to-1 mode when VIN equals 4.1V with greater than 90% efficiency.
PAGE 8
LTC1503-1.8/LTC1503-2 U W U U APPLICATIO S I FOR ATIO approximately 1.9V. Since the ramp rate on the SHDN/SS pin controls the ramp rate on VOUT, the average inrush current can be controlled through selection of CSS and COUT. For example, a 4.7nF capacitor on SHDN/SS results in a 4ms ramp time from 0.35V to 1.9V on the pin. If COUT is 10µF, the 4ms VREF ramp time results in an average COUT charge current of only 5mA (see Figure 2c). VOUT 1 RLOAD LTC1503-X 5 SHDN/SS 1503-1.
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LTC1503-1.8/LTC1503-2 U W U U APPLICATIO S I FOR ATIO capacitor on VOUT to reduce both the low and high frequency ripple. An RC filter may also be used to reduce high frequency voltage spikes. is disabled once VOUT reaches 0.7V (typ). The part can survive an indefinite short from VOUT to GND. Layout Considerations LTC1503-X VOUT + VOUT 10µF TANTALUM 1µF CERAMIC LTC1503-X 0.5Ω VOUT + 10µF TANTALUM + VOUT 10µF TANTALUM 1503-1.
PAGE 10
LTC1503-1.8/LTC1503-2 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0.118 ± 0.004** (3.00 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) 1 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 2 3 4 0.034 ± 0.004 (0.86 ± 0.102) 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.006 ± 0.004 (0.15 ± 0.
PAGE 11
LTC1503-1.8/LTC1503-2 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH.
PAGE 12
LTC1503-1.8/LTC1503-2 U TYPICAL APPLICATIO DC/DC Converter with Shutdown and Soft-Start LTC1503-1.8 4 1-CELL Li-Ion OR 3-CELL NiMH ON OFF 10µF 1µF 2N7002 2 VIN VOUT C1– C2– 3 1 8 6 C1+ C2+ 5 7 SHDN/SS GND 10µF VOUT = 1.8V IOUT = 100mA 1µF 10nF 1503-1.8/2 TA03 RELATED PARTS PART NUMBER LTC1474/LTC1475 LTC1502-3.3 LTC1514/LTC1515 LTC1555/LTC1556 LTC1627 LTC1754-3.3 LTC1754-5 12 DESCRIPTION Low Quiescent Current Step-Down DC/DC Converter Single Cell to 3.