CAT32 Datasheet, PDF (6/14 Pages) Catalyst Semiconductor – CMOS White LED Driver

CAT32
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
L1
D1
Vin
C1
1
C2
SW
Over Voltage
Protection
(22V)
1.2 MHz
Oscillator
CAT32
6 VIN
5 SHDN
GND
2
PWM
& Logic
Current
Sense
Amp
100mV
Current
Control
IS
RSET
4
RSET
LED
3
ILED
225x
ILED = 225 x IS
SOT23 Pin Numbers
Figure 2. CAT32 Block Diagram
Doc. No. 5001, Rev. AC
6