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LT1963A Series

1963aff

For more information www.linear.com/LT1963A

pin FuncTions

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

severalmicroamperes,andtheSHDNpincurrent,typically

3µA. If unused, the SHDN pin must be connected to VIN.

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 LT1963A

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.

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 LT1963A

(LT1963A-1.5/LT1963A-1.8/LT1963A-2.5/LT1963A-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 criti-

cal applications, small voltage drops are caused by the

resistance (RP) 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 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 LT1963A, 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.TheSHDNpinisusedtoputtheLT1963A

regulatorsintoalowpowershutdownstate.Theoutputwill

Figure 1. Kelvin Sense Connection

SHDN

1963A F01

OUT

VIN

SENSE

GND

LT1963A

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