5

LTC1844 Series

1844ia

IN(Pin 1): Power for LTC1844 and Load. Power is supplied

to the device through the IN pin. The IN pin should be

locally bypassed to ground if the LTC1844 is more than a

few inches away from another source of bulk capacitance.

In general, the output impedance of a battery rises with

frequency, so it is usually adviseable to include an input

bypass capacitor in battery-powered circuits. A capacitor

in the range of 0.1

µF to 1µF is usually sufficient. The

LTC1844 is designed to withstand reverse voltages on the

IN pin with respect to both ground and the output pin. In

the case of a reversed input, which can happen if a battery

is plugged in backwards, the LTC1844 will act as if there

is a large resistor in series with its input with only a small

amount of current flow.

GND (Pin 2): Ground and Heat Sink. Solder to a ground

plane or large pad to maximize heat dissipation.

SHDN (Pin 3, Fixed and SD Devices): Shutdown, Active

Low. This pin is used to put the LTC1844 into shutdown.

The SHDN pin current is typically less than 10nA. The

SHDN pin cannot be left floating and must be tied to the

input pin if not used. If reverse-battery protection is

desired, the SHDN pin must be tied to the input pin through

a large value resistor (10k to 1M).

PI FU CTIO S

ADJ (Pin 4, Adjustable Devices): Output Adjust. For the

adjustable versions of the LTC1844, this is the input to the

error amplifier. It has a typical bias current of 30nA flowing

into the pin. The ADJ pin reference voltage is 1.25V

referenced to ground. The output voltage range is 1.25V to

6V and is typically set by connecting ADJ to a resistor

divider from OUT to GND. See Figure 2.

BYP (Pin 4, Fixed/Pin 3, BYP Devices): Noise Bypass.

The BYP pin is used to augment the internal noise filter to

improve low noise performance. A small low leakage

bypass capacitor from this pin to ground will filter the input

of the error amplifier to lower the output voltage noise.

Any value may be used; larger values will result in lower

output noise, but will increase initial power-up time.

Shutdown exit delay time after a brief shutdown (<10ms)

will not be affected. If not used, this pin must be left

unconnected.

OUT (Pin 5): Voltage Regulated Output. The OUT pin

supplies power to the load. A minimum output capacitor of

1

µFisrequiredtoensurestability.Largeroutputcapacitors

may be required for applications with large transient loads

to limit peak voltage transients. See the Applications

Information section for more information on output

capacitance.