CAT32_14 Datasheet, PDF (6/11 Pages) ON 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 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.
Block Diagram
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.
V_IN
L₁
1
C1
SW
Over Voltage
Protection
(22 V)
+
Current
Sense
Amp −
D₁
1.2 MHz
Oscillator
−
PWM
& Logic
+
100 mV
C₂
LED
3
I_LED
6 ^VIN
5 SHDN
CAT32
GND
2
Current
Control
I_S
4
RSET
R_SET
225x
I_LED = 225 x I_S
Figure 14. CAT32 Block Diagram
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