LT1963A Series
U
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PI FU CTIO S
OUT: Output. The output supplies power to the load. A
minimum output capacitor of 10mF 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.
output will 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 several microamperes, and the
SHDN pin current, typically 3mA. If unused, the SHDN pin
must be connected to VIN. 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 critical
applications, small voltage drops are caused by the resis-
tance(RP)ofPCtracesbetweentheregulatorandtheload.
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 exter-
nal PC traces will add to the dropout voltage of the regu-
lator. The SENSE pin bias current is 600mA 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.
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 1mF to 10mF 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.
ADJ: Adjust. For the adjustable LT1963A, this is the input
totheerroramplifier.Thispinisinternallyclampedto±7V.
It has a bias current of 3mA 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
GND
LOAD
V
IN
R
P
1963 F01
SHDN: Shutdown. The SHDN pin is used to put the
LT1963A regulators into a low power shutdown state. The
Figure 1. Kelvin Sense Connection
1963af
10
Linear [ Linear ]
