CAT32 CATALYST [Catalyst Semiconductor], CAT32 Datasheet - Page 6

• Manufacturer Part Number: CAT32
• Description: CMOS White LED Driver
• Manufacturer: CATALYST [Catalyst Semiconductor]

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