CAT32

http://onsemi.com

6

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 100 mV and the

current through the external resistor will set the regulated

current in the LEDs (from 5 mA to 40 mA) 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 0.1 V.

Block Diagram

Figure 14. CAT32 Block Diagram

Current

Sense

Amp

CAT32

PWM

& Logic

Current

Control

1.2 MHz

Oscillator

100 mV

GND

RSET

SW

LED

Over Voltage

Protection

(22 V)

225x

C1

6

3

4

2

1

5

SHDN

+

−

+

−