19
Its pin functions are as shown below:
Pin
Name
Description
1
VIN
This is the positive input supply for the IC switching regulator. A suitable
input by pass capacitor must be present at this pin to minimize voltage
transients and to supply the switching currents needed by the
regulator.
2
GND
Circuit ground
3
OUTPUT
Internal switch. The voltage at this pin switches between (+V IN − V
SAT) and approximately −0.5V, with a duty cycle of approximately V
OUT /V IN. To minimize coupling to sensitive circuitry, the PC board
copper area connected to this pin should be kept to a minimum
4
Feedback Senses the regulated output voltage to complete the feedback loop
5
ON/OFF
Allows the switching regulator circuit to be shut down using logic level
signals thus dropping the total input supply current to approximately
80 µA. Pulling this pin below a threshold voltage of approximately 1.3V
turns the regulator on, and pulling this pin above 1.3V (up to a
maximum of 25V) shuts the regulator down. If this shutdown feature is
not needed, the ON /OFF pin can be wired to the ground pin or it can
be left open; in either case the regulator will be in the ON condition
Switch Module
The switch module is used to turn on/off the power. A self-locking switch is used. It is a single-
pole double-throw switch. When the button is not pressed, pin 1 and 3 are connected, and
pin 4 and 6 are connected, as shown in figure (a). When the button is pressed, pin 2 and 3
are connected, and pin 4 and 5 are connected, as shown in figure (b).
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