CAT37_08 Datasheet, PDF (6/13 Pages) Texas Instruments – CMOS White LED Driver Boost Converter

CAT37
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:
0.095
I_LED = _R1
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 ¯S¯H¯D¯N¯ pin or by pulling the FB pin
higher than 95mV.
BLOCK DIAGRAM
L1
VIN
5
1
C1
VIN
SW
4 _SHDN
Over Voltage
Protection
(22V)
D1
C2
1.2MHz
Oscillator
90kΩ
PWM
& Logic
Error
Amp
6kΩ _FB
3
0.095V
REF
I_LED
R1
CAT37
GND
2
Current
Sense
Amp
Figure 2. CAT37 Block Diagram
Doc. No. MD-5005 Rev. T
6
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice