CAT32 datasheet(6/14 Pages) CATALYST

6 / 14 page

CAT32

Doc. No. MD-5001 Rev. AD

Characteristics subject to change without notice

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

Current

Sense

Amp

CAT32

ILED = 225 x IS

ILED

PWM

& Logic

Current

Control

1.2MHz

Oscillator

100mV

RSET

GND

RSET

LED

Over Voltage

Protection

(22V)

225x

VIN

SHDN

VIN

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