CAT37 Datasheet, PDF (6/11 Pages) Catalyst Semiconductor – CMOS White LED Driver Boost Converter

CAT37
Operation
The CAT37 device is a high efficiency, constant
frequency, 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 95 mV and the current
through the external resistor will set the regulated current in
the LEDs at:
I_LED
+
0.095
R1
Block Diagram
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 95 mV.
L1
D1
VIN
5
1
C1
C2
VIN
SW
4
SHDN
Over Voltage
Protection
(22 V)
CAT37
GND
2
1.2 MHz
Oscillator
90 kW
PWM
& Logic
+
−
Current
Sense
Amp
−
Error ⁺
Amp
6 kW _FB
3
0.095 V
REF
I_LED
R1
Figure 13. CAT37 Block Diagram
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