cat4109 ON Semiconductor, cat4109 Datasheet - Page 7

• Manufacturer Part Number: cat4109
• Description: 3-channel Constant-current Rgb Led Driver With Individual Pwm Dimming
• Manufacturer: ON Semiconductor

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
corresponding LED current.
Table 1. RSET Resistor Settings
© 2009 SCILLC. All rights reserved.
Characteristics subject to change without notice
RSET3
RSET2
RSET1
PWM1
PWM2
PWM3
VDD
Figure 2. CAT4109 Functional Block Diagram
OE
LED Current [mA]
resistor
Current Setting
Current Setting
Current Setting
100
175
20
60
1.2V Ref
values
LED1 LED2
for
RSET[kΩ]
RSET
PGND
LED3
24.9
8.45
5.23
3.01
CURRENT
SINKS
and
GND
the
7
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
independently controlled repectivelly by PWM1,
PWM2, PWM3. When a PWMx is high, the
associated LEDx channel is turned on.
channel
LED1,
LED2
and
Doc. No. MD-5042, Rev. A
CAT4109
LED3
is