1

LTC3803

3803i

Constant Frequency

Current Mode Flyback

DC/DC Controller in ThinSOT

August 2003

FEATURES

APPLICATIO S

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 represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

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Adjustable Slope Compensation

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Internal Soft-Start

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Constant Frequency 200kHz Operation

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±1.5% Reference Accuracy

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Current Mode Operation for Excellent Line and Load

Transient Response

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No Minimum Load Requirement

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Low Quiescent Current: 240

µA

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Low Profile (1mm) SOT-23 Package

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Telecom Power Supplies

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42V and 12V Automotive Power Supplies

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Auxiliary/Housekeeping Power Supplies

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Power Over Ethernet

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

Final Electrical Specifications

ThinSOT is a trademark of Linear Technology Corporation.

5V Output Nonisolated Telecom Housekeeping Power Supply

TYPICAL APPLICATIO

The LTC

flyback controller optimized for driving 6V-rated N-channel

MOSFETs in high input voltage applications. Constant

frequency operation is maintained down to very light

loads, resulting in less low frequency noise generation

over a wide range of load currents. Slope compensation

can be programmed with an external resistor.

The LTC3803 provides

±1.5% output voltage accuracy

and consumes only 240

µA of quiescent current. Ground-

referenced current sensing allows LTC3803-based con-

verters to accept input supplies beyond the LTC3803’s

feature allows efficient operation at high input voltages.

For simplicity, the LTC3803 can also be powered from a

regulator. An internal undervoltage lockout shuts down

the LTC3803 when the input voltage falls below 4.6V,

guaranteeing at least 4.6V of gate drive to the external

MOSFET.

The LTC3803 is available in a low profile (1mm) 6-lead

SOT-23 (ThinSOT

LTC3803

GND

NGATE

SENSE

UPS840

300

µF*

6.3V

X5R

4.7

µF

100V

X5R

10

µF

10V

X5R

5V

2A MAX

3803 TA01

68m

Ω

20k

10k

56k

0.0022

µF

105k

FDC2512

T1: COOPER CTX02-15242

*THREE 100

µF UNITS IN PARALLEL

T1

•

•

36V TO 72V

Efficiency vs Load Current

0.1

50

60

70

10

3803 TA02

40

30

0

1

20

10

90

80