NCP1546

http://onsemi.com

3

PACKAGE PIN DESCRIPTION

PIN NO.

PIN SYMBOL

FUNCTION

1

BOOST

The BOOST pin provides additional drive voltage to the on−chip NPN power transistor. The

resulting decrease in switch on voltage increases efficiency.

2

This pin is the main power input to the IC.

3

This is the connection to the emitter of the on−chip NPN power transistor and serves as the

switch output to the inductor. This pin may be subjected to negative voltages during switch off−

time. A catch diode is required to clamp the pin voltage in normal operation. This node can

stand −1.0 V for less than 50 ns during switch node flyback.

4

SHDNB

The shutdown pin is active low and TTL compatible. The IC goes into sleep mode, drawing less

than 1.0

mA when the pin voltage is pulled below 1.0 V.

This pin should be left floating in normal position.

5

SYNC

This pin provides the synchronization input.

6

GND

Power return connection for the IC.

7

the oscillator frequency is divided by four, and current limit folds back to about 1 ampere. These

features protect the IC under severe overcurrent or short circuit conditions.

8

comparator. Driving of this pin should be avoided because on−chip test circuitry becomes active

whenever current exceeding 0.5 mA is forced into the IC.

9, 11, 12, 14, 15, 18

NC

No Connection

PIN CONNECTIONS

1

2

3

4

5

6

7

8

9

18

17

16

15

14

13

12

11

10

BOOST

Vsw

SHDNB

NC

NC

NC

NC

GND

NC

NC

SYNC

18−Lead DFN