LT1764-1.5 Linear Technology, LT1764-1.5 Datasheet - Page 9

• Manufacturer Part Number: LT1764-1.5
• Description: 3A/ Fast Transient Response/ Low Noise/LDO Regulators
• Manufacturer: Linear Technology

PI FU CTIO S
SHDN (Pin 1): Shutdown. The SHDN pin is used to put the
LT1764 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 7 A. If unused, the SHDN pin
must be connected to V
power shutdown state if the SHDN pin is not connected.
IN (Pin 2): 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 1 F to 10 F is sufficient. The
LT1764 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.
GND (Pin 3): Ground.
U
U
U
IN
. The device will be in the low
V
IN
+
Figure 1. Kelvin Sense Connection
2
1
IN
SHDN
LT1764
GND
3
SENSE
OUT
OUT (Pin 4): Output. The output supplies power to the
load. A minimum output capacitor of 10 F 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 5): Sense. For fixed voltage versions of the
LT1764 (LT1764-1.8/LT1764-2.5/LT1764-3.3), 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 (R
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
regulator. The SENSE pin bias current is 600 A 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 (Pin 5): Adjust. For the adjustable LT1764, this is the
input to the error amplifier. This pin is internally clamped
to 7V. It has a bias current of 3 A 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.
4
5
R
R
P
P
P
) of PC traces between the regulator and the load.
+
1764 F01
LOAD
LT1764 Series
1764fa
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