CAT37 datasheet(6/13 Pages) TI

6 / 13 page

CAT37

Doc. No. MD-5005 Rev. T

Characteristics subject to change without notice

OPERATION

The CAT37 device is a high efficiency, constant fre-

quency, 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 95mV and

the current through the external resistor will set the

regulated current in the LEDs at:

095

ILED

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

Figure 2. CAT37 Block Diagram

Current

Sense

Amp

CAT37

PWM

& Logic

1.2MHz

Oscillator

GND

Over Voltage

Protection

(22V)

VIN

ILED

SHDN

VIN

Error

Amp

0.095V

REF

90kΩ

6kΩ

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