CAT37 데이터 시트보기 (PDF) - ON Semiconductor

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CAT37

CMOS White LED Driver Boost Converter

ON Semiconductor 

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

Block Diagram

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 95 mV.

L1

D1

VIN

5

1

C1

C2

VIN

SW

4

SHDN

Over Voltage

Protection

(22 V)

CAT37

GND

2

1.2 MHz

Oscillator

90 kW

PWM

& Logic

+

−

Current

Sense

Amp

−

Error +

Amp

6 kW FB

3

0.095 V

REF

ILED

R1

Figure 13. CAT37 Block Diagram

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