Datasheet

LT1762 Series
11
Rev B
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PIN FUNCTIONS
OUT (Pin 1): Output. The output supplies power to the
load. A minimum output capacitor of 2.2µF 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): Output Sense. For fixed voltage ver-
sions of the LT1762 (LT1762-2.5/LT1762-3/LT1762-
3.3/LT1762-5), 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 sup-
ply system where the regulator load is returned to a nega-
tive supply) and still allow the device to start and operate.
ADJ (Pin 2): Adjust. For the adjustable LT1762, 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 (see curve of ADJ Pin Bias Current vs Temperature
in the Typical Performance Characteristics). The ADJ pin
voltage is 1.22V referenced to ground and the output volt-
age range is 1.22V to 20V.
BYP (Pin 3): Bypass. The BYP pin is used to bypass the
reference of the LT1762 regulators 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 voltage 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 LT1762 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 resis-
tor 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 be in low
power shutdown state if the SHDN pin is not connected.
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 LT1762 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
1762 F01
R
P
OUT
V
IN
SENSE
GND
LT1762
R
P
4
2
1
5
8
+
+
LOAD
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