NCP1546
PACKAGE PIN DESCRIPTION
PIN NO.
1
2
3
PIN SYMBOL
BOOST
V
IN
V
SW
FUNCTION
The BOOST pin provides additional drive voltage to the on−chip NPN power transistor. The
resulting decrease in switch on voltage increases efficiency.
This pin is the main power input to the IC.
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.
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.
This pin provides the synchronization input.
Power return connection for the IC.
The FB pin provides input to the inverting input of the error amplifier. If V
FB
is lower than 0.29 V,
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.
The V
C
pin provides a connection point to the output of the error amplifier and input to the PWM
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.
No Connection
4
SHDNB
5
6
7
SYNC
GND
V
FB
8
V
C
9, 11, 12, 14, 15, 18
NC
PIN CONNECTIONS
BOOST
V
IN
V
IN
V
IN
Vsw
V
SW
V
SW
SHDNB
NC
1
2
3
4
5
6
7
8
9
18
17
16
15
14
13
12
11
10
NC
V
C
V
FB
NC
NC
GND
NC
NC
SYNC
18−Lead DFN
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