CAT37 CATALYST [Catalyst Semiconductor], CAT37 Datasheet - Page 6

• Manufacturer Part Number: CAT37
• Description: CMOS White LED Driver Boost Converter
• Manufacturer: CATALYST [Catalyst Semiconductor]

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
Doc. No. 5005, Rev. R
= 0.095/R1
VIN
Note: SOT23 Pin Numbers
C1
4
Over Voltage
SHDN
5
CAT37
VIN
Protection
(22V)
GND
2
L1
Figure 2. CAT37 Block Diagram
1
SW
Current
Sense
Amp
+
-
1.2 MHz
6
& Logic
Clock
PWM
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 95mV.
D1
Error
Amp
+
-
0.095V
REF
FB
3
R1
I LED
C2