CAT4002A, CAT4004A
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6
Table 6. PIN DESCRIPTIONS
Name Function
EN/DIM Device enable (active high) and dimming control
GND Ground reference
LED1 LED1 cathode terminal
LED2 LED2 cathode terminal
LED3 LED3 cathode terminal (CAT4004A only)
LED4 LED4 cathode terminal (CAT4004A only)
RSET Connect external RSET resistor to set the LED current
VIN Device supply input, connect to battery or supply
TAB Connect to GND on the PCB (CAT4004A only)
Pin Function
VIN is the supply pin for the charge pump. A small 1 mF
ceramic bypass capacitor is required between the VIN pin
and ground near the device. The operating input voltage
range is from 2.5 V to 5.5 V. Whenever the input supply falls
below the under−voltage threshold (2.0 V), all the LED
channels are disabled and the device enters shutdown mode.
EN/DIM is the enable and one wire dimming input for all
LED channels. Levels of logic high and logic low are set at
1.3 V and 0.4 V respectively. When EN/DIM is initially
taken high, the CAT400XA becomes enabled and the LED
channel current is set to the full scale according to the
resistor R
SET
. To place the device into “zero current”
shutdown mode, the EN/DIM pin must be held low for 3 ms
typical.
LED1 to LED4 provide the internal regulated current for
each of the LED cathodes. There pins enter a high
impedance zero current state whenver the device is placed
in shutdown mode.
RSET is connected to the resistor (R
SET
) to set the full scale
current for the LEDs. The voltage at this pin is regulated to
0.6 V. The ground side of the external resistor should be star
connected back to the GND of the PCB. In shutdown mode,
the RSET input becomes high impedance.
GND is the ground reference for the device. The pin must be
connected to the ground plane on the PCB.
TAB (CAT4004A only) is the exposed pad underneath the
package. For best thermal performance, the tab should be
soldered to the PCB and connected to the ground plane.
Block Diagram
4 Current Sink
Regulators
Current
Setting DAC
Undervoltage
Lockout
Register
Serial
Interface
RSET
100 kW
EN/DIM
GND
VIN
LED1
LED2
LED3
LED4
Reference
Voltage
Figure 15. CAT4004A Functional Block Diagram
V
IN
