CAT4137

© Catalyst Semiconductor, Inc.

7

Doc. No. MD-5012 Rev. B

Characteristics subject to change without notice

PIN DESCRIPTION

VIN is the supply input for the internal logic. The

device is compatible with supply voltages down to

2.2V and up to 5.5V. A small bypass ceramic

capacitor of 1µF 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 1.9V.

SHDN

¯¯¯¯¯ is the shutdown logic input. When the pin

voltage is taken below 0.4V, the device immediately

enters shutdown mode, drawing nearly zero current.

At voltages greater than 1.5V, 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 24V. 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

30V.

FB feedback pin is regulated at 0.3V. A resistor

connected between the FB pin and ground sets the

LED current according to the formula:

The lower LED cathode is connected to the FB pin.

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.