CAT4237

http://onsemi.com

3

Table 3. DC ELECTRICAL CHARACTERISTICS

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

Operating Current

0.6

0.1

1.5

0.6

mA

Shutdown Current

0.1

1

mA

FB Pin Voltage

285

300

315

mV

FB pin input leakage

1

mA

Programmed LED Current

R1 = 10 W

R1 = 15 W

R1 = 20 W

28.5

19

14.25

30

20

15

31.5

21

15.75

mA

SHDN Logic High

SHDN Logic Low

Enable Threshold Level

Shutdown Threshold Level

0.4

0.8

0.7

1.5

V

Switching Frequency

0.8

1.0

1.3

MHz

Switch Current Limit

350

450

600

mA

Switch “On” Resistance

1.0

2.0

W

Switch Leakage Current

1

5

mA

Thermal Shutdown

150

°C

Thermal Hysteresis

20

°C

Undervoltage Lockout (UVLO) Threshold

1.9

V

Overvoltage Threshold

35

V

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 place 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 35 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

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.