LT1963A Series
pin FuncTions
OUT: Output. The output supplies power to the load.
A minimum output capacitor of 10µF is required to
prevent oscillations. Larger output capacitors will be
required for applications with large transient loads to limit
peak voltage transients. See the Applications Information
section for more information on output capacitance and
reverse output characteristics.
be off when the SHDN pin is pulled low. The SHDN pin can
be driven either by 5V logic or open-collector logic with a
pull-up resistor. The pull-up resistor is required to supply
the pull-up current of the open-collector gate, normally
severalmicroamperes,andtheSHDNpincurrent,typically
3µA. If unused, the SHDN pin must be connected to V .
IN
The device will be in the low power shutdown state if the
SHDN pin is not connected.
SENSE: Sense. For fixed voltage versions of the LT1963A
(LT1963A-1.5/LT1963A-1.8/LT1963A-2.5/LT1963A-3.3),
the SENSE pin is the input to the error amplifier. Optimum
regulation will be obtained at the point where the SENSE
pin is connected to the OUT pin of the regulator. In criti-
cal applications, small voltage drops are caused by the
IN: Input. Power is supplied to the device through the IN
pin. A bypass capacitor is required on this pin if the device
is more than six inches away from the main input filter
capacitor. In general, the output impedance of a battery
rises with frequency, so it is advisable to include a bypass
capacitor in battery-powered circuits. A bypass capacitor
in the range of 1µF to 10µF is sufficient. The LT1963A
regulators are designed to withstand reverse voltages
on the IN pin with respect to ground and the OUT pin. In
the case of a reverse input, which can happen if a battery
is plugged in backwards, the device will act as if there is
a diode in series with its input. There will be no reverse
current flow into the regulator and no reverse voltage
will appear at the load. The device will protect both itself
and the load.
resistance (R ) of PC traces between the regulator and the
P
load. These may be eliminated by connecting the SENSE
pin to the output at the load as shown in Figure 1 (Kelvin
Sense Connection). Note that the voltage drop across
the external PC traces will add to the dropout voltage of
the regulator. The SENSE pin bias current is 600µA at
the nominal rated output voltage. The SENSE pin can be
pulled below ground (as in a dual supply system where
the regulator load is returned to a negative supply) and
still allow the device to start and operate.
ADJ: Adjust. For the adjustable LT1963A, this is the input
to the error amplifier. This pin is internally clamped to ±±V.
It has a bias current of 3µA which flows into the pin. The
ADJ pin voltage is 1.21V referenced to ground and the
output voltage range is 1.21V to 20V.
IN
OUT
LT1963A
R
P
+
+
SHDN SENSE
LOAD
V
IN
GND
R
P
1963A F01
SHDN:Shutdown.TheSHDNpinisusedtoputtheLT1963A
regulatorsintoalowpowershutdownstate.Theoutputwill
Figure 1. Kelvin Sense Connection
1963aff
13
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