LT1764AMPQ Linear Technology, LT1764AMPQ Datasheet - Page 10

• Manufacturer Part Number: LT1764AMPQ
• Description: IC,VOLT REGULATOR,ADJUSTABLE,+1.21 TO +20V,BIPOLAR,SIP,5PIN,PLASTIC
• Manufacturer: Linear Technology

LT1764A Series
PI FU CTIO S
SHDN (Pin 1/1/10): Shutdown. The SHDN pin is used to
put the LT1764A 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 7µA. If unused, the SHDN
pin must be connected to V
the low power shutdown state if the SHDN pin is not
connected.
IN (Pin 2/Pin 2/Pins 12, 13, 14): 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 LT1764A 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.
NC (Pins 2, 11, 15) TSSOP Only: No Connect.
GND (Pin 3/Pin 3/Pins 1, 7, 8, 9, 16, 17): Ground.
OUT (Pin 4/Pin 4/Pins 3, 4, 5): 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
10
U
U
U
DD/TO-220/TSSOP
IN
. The device will be in
Applications Information section for more information on
output capacitance and reverse output characteristics.
SENSE (Pin 5/Pin 5/Pin 6): Sense. For fixed voltage
versions of the LT1764A (LT1764A-1.5/LT1764A-1.8/
LT1764A-2.5/LT1764A-3.3), the SENSE pin is the input
to the error amplifier. Optimum regulation will be ob-
tained 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
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 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 (Pin 5/Pin 5/Pin 6): Adjust. For the adjustable LT1764A,
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.
V
IN
+
Figure 1. Kelvin Sense Connection
2
1
IN
SHDN
LT1764A
GND
3
SENSE
OUT
4
5
R
R
P
P
+
1764 F01
LOAD
P
) of PC
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