CAT4109 Datasheet, PDF (8/12 Pages) ON Semiconductor – 3-Channel Constant-Current RGB LED Driver with Individual PWM Dimming

VDD
RSET3
RSET2
RSET1
OE
CAT4109
BLOCK Diagram
1.2 V Ref
Current Setting
Current Setting
Current Setting
LED1 LED2 LED3
CURRENT
SINKS
PWM1
PWM2
PWM3
PGND
GND
Figure 14. 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 6 shows standard resistor values for RSET
and the corresponding LED current.
Table 6. RSET RESISTOR SETTINGS
LED Current [mA]
RSET [kW]
20
24.9
60
8.45
100
5.23
175
3.01
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 0.4 V 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 respectively by
PWM1, PWM2, PWM3. When a PWMx is high, the
associated LEDx channel is turned on.
http://onsemi.com
8