CAT4137

http://onsemi.com

8

Pin Description

VIN is the supply input for the internal logic. The device is

compatible with supply voltages down to 2.2 V and up to

5.5 V. A small bypass ceramic capacitor of 1

mF is

recommended between the VIN and GND pins near the

device. The under−voltage lockout (UVLO) circuitry will

place the device into an idle mode (not switching) whenever

the supply falls below 1.9 V.

SHDN is the shutdown logic input. When the pin voltage is

taken below 0.4 V, the device immediately enters shutdown

mode, drawing nearly zero current. At voltages greater than

1.5 V, the device becomes fully enabled and operational.

GND is the ground reference pin. This pin should be

connected directly to the ground plane on the PCB.

SW pin is the drain terminal of the internal low resistance

power switch. The inductor and the Schottky diode anode

should be connected to the SW pin. Traces going to the SW

pin should be as short as possible with minimum loop area.

This pin contains over-voltage circuitry which becomes

active above 24 V. In the event of an “Open−Led” fault

condition, the device will enter a low power mode and the

SW pin will be clamped to approximately 30 V.

FB feedback pin is regulated at 0.3 V. A resistor connected

between the FB pin and ground sets the LED current

according to the formula:

0.3 V

R1

The lower LED cathode is connected to the FB pin.

Table 4. PIN DESCRIPTIONS

Pin #

Name

Function

1

SW

Switch pin. This is the drain of the internal power switch.

2

GND

Ground pin. Connect the pin to the ground plane.

3

FB

Feedback pin. Connect to the last LED cathode.

4

SHDN

Shutdown pin (Logic Low). Set high to enable the driver.

5

VIN

Power Supply input.