CAT4008W-T2 Datasheet, PDF (8/14 Pages) ON Semiconductor – 8-Channel Constant Current LED Driver

CAT4008
PIN DESCRIPTION
Name
GND
SIN
CLK
LATCH
LED1-LED8
BLANK
SOUT
RSET
VDD
Function
Ground
Serial data input pin
Serial clock input pin
Latch serial data to output registers
LED channel 1 to 8 cathode terminals
Enable / disable all channels
Serial data output pin.
LED current set pin
Positive supply Voltage
PIN FUNCTION
GND is the ground reference pin for the device. This
pin must be connected to the ground plane on the PCB.
SIN is the serial data input. Data is loaded into the
internal register on each rising edge of CLK.
CLK is the serial clock input. On each rising CLK
edge, data is transferred from SIN to the internal 8-bit
serial shift register.
LATCH is the latch data input. On the rising edge of
LATCH, data is loaded from the 8-bit serial shift
register into the output register latch. On the falling
edge, this data is latched in the output register and
isolated from the state of the serial shift register.
LED1 – LED8 are the LED current sink channels.
These pins are connected to the LED cathodes. The
current sinks drive the LEDs with a current equal to
about 51 times RSET pin current. For the LED sink
to operate correctly, the voltage on the LED pin must
be above 0.4V.
BLANK is the LED channel enable and disable
input pin. When low, LEDs are enabled according to
the output latch register content. When high, all
LEDs are off, while preserving the data in the output
latch register.
SOUT is the serial data output of the 8-bit serial shift
register. This pin is used to cascade several devices
on the serial bus. The SOUT pin is then connected to
the SIN input of the next device on the serial bus to
cascade.
RSET is the LED current setting pin. A resistor is
connected between this pin and ground. Each LED
channel current is set to about 51 times the current
pulled out of the pin. The RSET pin voltage is regulated
to 1.2V.
VDD is the positive supply pin voltage for the entire
device. A small 1µF ceramic is recommended close
to pin.
CURRENT SETTING RESISTOR
Table 1 lists standard resistor values for various LED
current settings.
Table 1. LED Current and RSET resistor values
LED Current [mA]
10
20
30
40
60
80
R_SET [kΩ]
6.19
3.09
2.05
1.54
1.02
0.768
Doc. No. MD-5034 Rev. C
8
© 2009 SCILLC. All rights reserved.
Characteristics subject to change without notice