CAT4109V-GT2 Datasheet, PDF (7/11 Pages) ON Semiconductor – 3-Channel Constant-Current RGB LED Driver with Individual PWM Dimming

BLOCK DIAGRAM
VDD
1.2V Ref
LED1 LED2 LED3
RSET3
Current Setting
RSET2
RSET1
Current Setting
Current Setting
CURRENT
SINKS
OE
PWM1
PWM2
PWM3
PGND
GND
CAT4109
Tight current regulation for all channels is possible
over a wide range of input and LED voltages due to
independent current sensing circuitry on each
channel. The LED channels have a low dropout of
0.4V or less for all current ranges and supply
voltages. This helps improve heat dissipation and
efficiency.
Upon power-up, an under-voltage lockout circuit sets
all outputs to off. Once the VDD supply voltage is
greater than the under-voltage lockout threshold, the
device channel can be turned on. The on/off state of
each channel LED1, LED2 and LED3 is
independently controlled repectivelly by PWM1,
PWM2, PWM3. When a PWMx is high, the
associated LEDx channel is turned on.
Figure 2. CAT4109 Functional Block Diagram
BASIC OPERATION
The CAT4109 uses 3 independent current sinks to
accurately regulate the current in each LED channel
to 400 times the current sink from the corresponding
RSET pin. Each of the resistors tied to the RSET1,
RSET2, RSET3 pins set the current respectively in
the LED1, LED2, and LED3 channels. Table 1 shows
standard resistor values for RSET and the
corresponding LED current.
Table 1. RSET Resistor Settings
LED Current [mA]
20
60
100
175
RSET[kΩ]
24.9
8.45
5.23
3.01
© 2009 SCILLC. All rights reserved.
7
Characteristics subject to change without notice
Doc. No. MD-5042, Rev. A