CAT37TDI-TE7 데이터 시트보기 (PDF) - Catalyst Semiconductor => Onsemi

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CAT37TDI-TE7

CMOS White LED Driver Boost Converter

Catalyst Semiconductor => Onsemi 

CAT37

OPERATION

The CAT37 device is a high efficiency, constant

frequency, current regulating boost driver for white LEDs.

The device includes a switch and an internally

compensated loop for the regulation of the current in the

LEDs.

Operation can be best understood by examining the

block diagram. The FB pin is regulated at 95 mV and the

current through the external resistor will set the regulated

current in the LEDs at:

ILED = 0.095/R1

While maintaining LED current regulation, the CAT37

boost converter automatically adjusts the FB pin voltage

to be as low as possible. A low FB pin voltage ensures

high efficiency.

Current through the internal power switch is continuously

monitored cycle-by-cycle. If the current limit is exceeded,

the switch is immediately turned off, protecting the

device, for the remainder of the cycle.

PWM dimming operation can be achieved by switching

the SHDN pin or by pulling the FB pin higher than 95mV.

BLOCK DIAGRAM

VIN

C1

L1

5

VIN

4 SHDN

Over Voltage

Protection

(22V)

CAT37

GND

2

D1

1

C2

SW

1.2 MHz

Clock

PWM

& Logic

+

-

Current

Sense

Amp

Error

Amp

FB

3

0.095V

REF

ILED

R1

Note: SOT23 Pin Numbers are shown

Figure 2. CAT37 Block Diagram

Doc. No. 5005, Rev. S

6

© 2005 by Catalyst Semiconductor, Inc.

Characteristics subject to change without notice

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