cat37tdi-t3 Catalyst Semiconductor, cat37tdi-t3 Datasheet - Page 6

• Manufacturer Part Number: cat37tdi-t3
• Description: Cmos White Led Driver Boost Converter
• Manufacturer: Catalyst Semiconductor

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:
BLOCK DIAGRAM
Doc. No. MD-5005 Rev. T
VIN
C1
I
4
LED
CAT37
VIN
SHDN
=
Over Voltage
. 0
Protection
5
R
095
1
(22V)
L1
Figure 2. CAT37 Block Diagram
2
GND
1
SW
Current
Sense
Amp
6
Oscillator
1.2MHz
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
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
higher than 95mV.
& Logic
PWM
D1
through
Error
Amp
90kΩ
¯¯¯¯¯
the
pin or by pulling the FB pin
0.095V
REF
internal
6kΩ
Characteristics subject to change without notice
FB
3
©
power
Catalyst Semiconductor, Inc.
R1
switch
I
LED
C2
is