LT1963 datasheet(9/16 Pages) LINEAR

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LT1963 Series

1963fa

Figure 1. Kelvin Sense Connection

SHDN

1963 F01

OUT

VIN

SENSE

GND

LT1963

LOAD

PI FU CTIO S

OUT: Output. The output supplies power to the load. A

minimum output capacitor of 10

µF 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 LT1963

(LT1963-1.8/LT1963-2.5/LT1963-3.3), 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 resistance (RP)ofPCtraces

between the regulator and the load. These may be elimi-

nated 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 600

µA 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 LT1963, this is the input to

the error amplifier. This pin is internally clamped to

±7V.

It has a bias current of 3

µA 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. The SHDN pin is used to put the LT1963

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 cur-

rent, typically 3

µA. 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 1

µF to 10µF is sufficient. The LT1963 regu-

lators 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.

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