CAT4008 Datasheet, PDF (8/13 Pages) Catalyst Semiconductor – 8-Channel Constant Current LED Driver

CAT4008
Table 5. PIN DESCRIPTION
Name
GND
Ground
SIN
Serial data input pin
CLK
Serial clock input pin
LATCH
Latch serial data to output registers
LED1−LED8
LED channel 1 to 8 cathode terminals
BLANK
Enable / disable all channels
SOUT
Serial data output pin.
RSET
LED current set pin
VDD
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 0.4 V.
Function
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 1.2 V.
VDD is the positive supply pin voltage for the entire device.
A small 1 mF ceramic is recommended close to pin.
Current Setting Resistor
Table 6 lists standard resistor values for various LED
current settings.
Table 6. LED CURRENT
AND RSET RESISTOR VALUES
LED Current [mA]
10
R_SET [kW]
6.19
20
3.09
30
2.05
40
1.54
60
1.02
80
0.768
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