LT1963 Series
PI FU CTIO S
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.
SENSE:
Sense. For fixed voltage versions of the LT1963
(LT1963-1.8/LT1963-2.5/LT1963-3.3), 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 resistance (R
P
) of PC traces
between the regulator and the load. These may be elimi-
nated 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 LT1963, this is the input to
the error amplifier. This pin is internally clamped to
±7V.
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.
SHDN:
Shutdown. The SHDN pin is used to put the LT1963
regulators into a low power shutdown state. The 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 cur-
rent, 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.
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 LT1963 regu-
lators 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.
IN
LT1963
OUT
R
P
U
U
U
+
V
IN
SHDN
SENSE
GND
R
P
+
LOAD
1963 F01
Figure 1. Kelvin Sense Connection
1963fa
9
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
