CAT4139

http://onsemi.com

7

Pin Description

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

compatible with supply voltages down to 2.8 V and up to

5.5 V. It is recommended that a small bypass ceramic

capacitor (4.7

mF) be placed between the VIN and GND pins

near the device. If the supply voltage drops below 1.9 V, the

device stops switching.

SHDN is the shutdown logic input. When the pin is tied to

a voltage lower than 0.4 V, the device is in shutdown mode,

drawing nearly zero current. When the pin is connected to a

voltage higher than 1.5 V, the device is enabled.

GND is the ground reference pin. This pin should be

connected directly to the ground plane on the PCB.

SW pin is connected to the drain of the internal CMOS

power switch of the boost converter. 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. An over−voltage detection circuit

is connected to the SW pin. When the voltage reaches 24 V,

the device enters a low power operating mode preventing the

SW voltage from exceeding the maximum rating.

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.

Figure 17. Simplified Block Diagram

VOUT

Current

Sense

Ref

300 mV

C1

Thermal

Shutdown

& UVLO

1 MHz

Oscillator

Over Voltage

Protection

PWM

&

Logic

Driver

C2

GND

SW

FB

+

–

+

–

SHDN