CAT32

6

Doc. No. 5001, Rev. AC

OPERATION

The CAT32 device is a high efficiency, constant

frequency, current regulating boost converter.

The device includes a switch and an internally

compensated loop for the regulation of the LED current.

Operation can be best understood by examining the

block diagram. The RSET pin is regulated at 100mV and

the current through the external resistor will set the

regulated current in the LEDs (from 5mA to 40mA) with

a multiplication factor of 225.

While maintaining LED current regulation, the CAT32

automatically adjusts the LED pin voltage to be as low as

possible. A low LED 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 RSET pin higher than

0.1V.

BLOCK DIAGRAM

Figure 2. CAT32 Block Diagram

SOT23 Pin Numbers

Vin

1.2 MHz

Oscillator

D1

L1

C1

4

2

RSET

LED

Current

Sense

Amp

SW

1

CAT32

3

ILED

C2

GND

ILED = 225 x IS

Current

Control

PWM

& Logic

IS

100mV

RSET

SHDN

6

5

VIN

Over Voltage

Protection

(22V)

225x