Datasheet

LT1962 Series
11
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pin FuncTions
OUT (Pin 1): Output. The output supplies power to the
load. A minimum output capacitor of 3.3µF 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 (Pin 2): Sense. For fixed voltage versions of the
LT1962 (LT1962-1.5/LT1962-1.8/LT1962-2.5/LT1962-3/
LT1962-3.3/LT1962-5), 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 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 10µA 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.
BYP
(Pin 3): Bypass. The BYP pin is used to bypass the
reference of the LT1962 to achieve low noise performance
from the regulator. The BYP pin is clamped internally to
±0.6V (one V
BE
). A small capacitor from the output to
this pin will bypass the reference to lower the output volt-
age noise
. A maximum value of 0.01µF can be used for
reducing
output voltage noise to a typical 20µV
RMS
over
a 10Hz to 100kHz bandwidth. If not used, this pin must
be left unconnected.
GND (Pin 4): Ground.
SHDN (Pin 5): Shutdown. The SHDN pin is used to put
the LT1962 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
current, typically 1µA. If unused, the SHDN pin must be
connected to V
IN
. The device will not function if the SHDN
pin is not connected.
NC (Pins 6, 7): No Connect. These pins are not internally
connected. For improved power handling capabilities,
these pins can be connected to the PC board.
IN (Pin 8): 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 LT1962 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.
Figure 1. Kelvin Sense Connection
IN
SHDN
1962 F01
R
P
OUT
V
IN
SENSE
GND
LT1962
R
P
4
2
1
5
8
+
+
LOAD
ADJ (Pin 2): Adjust. For the adjustable LT1962, this is the
input to the error amplifier. This pin is internally clamped
to ±7V. It has a bias current of 30nA which flows into the
pin. The ADJ pin voltage is 1.22V referenced to ground
and the output voltage range is 1.22V to 20V.
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