LD1985

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R102-021.H

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APPLICATION INFORMATION

EXTERNAL CAPACITORS

Like any low-dropout regulator, the UTC LD1985 requires external capacitors for regulator stability. This

capacitor must be selected to meet the requirements of minimum capacitance and equivalent series resistance. We

suggest soldering input and outputting capacitors as close as possible to the relative pins.

INPUT CAPACITOR

An input capacitor whose value is 1μF is required with the UTC LD1985 (amount of capacitance can be

increased without limit). This capacitor must be located a distance of not more than 0.5" from the input pin of the

device and returned to a clean analog ground. Any good quality ceramic, tantalum or film capacitors can be used for

this capacitor.

OUTPUT CAPACITOR

The UTC LD1985 is designed specifically to work with ceramic output capacitors. It may also be possible to use

Tantalum capacitors, but these are not as attractive for reasons of size and cost. By the way, the output capacitor

must meet both the requirement for minimum amount of capacitance and E.S.R. (equivalent series resistance) value.

Due to the different loop gain, the stability improves for higher output versions and so the suggested minimum output

capacitor value, if low E.S.R. ceramic type is used, is 1μF for output voltages equal or major than 3.8V, 2.2μF for

suggested one is used, it's possible to make stable the regulator adding a resistor in series to the capacitor.

IMPORTANT:

The output capacitor must maintain its ESR in the stable region over the full operating temperature to assure

stability. Also, capacitor tolerance and variation with temperature must be considered to assure the minimum amount

of capacitance is provided at all times. This capacitor should be located not more than 0.5" from the output pin of the

device and returned to a clean analog ground.

INHIBIT INPUT OPERATION

The inhibit pin can be used to turn OFF the regulator when pulled low, so drastically reducing the current

regulator output ON at all times. To assure proper operation, the signal source used to drive the inhibit pin must be

Any slew rate can be used to drive the inhibit.

REVERSE CURRENT

The power transistor used in the UTC LD1985 has not an inherent diode connected between the regulator input

and output. If the output is forced above the input, no current will flow from the output to the input across the series

across the two feedback resistors. This current typical value is 160μA. R1 and R2 resistors are implanted type;

typical values are, respectively, 42.6 KΩ and 51.150 KΩ.