Pin Functions

Output (Pin 5): Reference Output.

Input (Pin 4):Positive Supply.

Ground (Pin 2):Negative Supply or Ground Connection.

Application Hints

The standard application circuit for the LM4125 is shown in

Figure 1. It is designed to be stable with ceramic output

capacitors in the range of 0.022µF to 0.1µF. Note that

0.022µF is the minimum required output capacitor. These

capacitors typically have an ESR of about 0.1 to 0.5

Ω.

Smaller ESR can be tolerated, however larger ESR can not.

The output capacitor can be increased to improve load tran-

sient response, up to about 1µF. However, values above

0.047µF must be tantalum. With tantalum capacitors, in the

1µF range, a small capacitor between the output and the

reference pin is required. This capacitor will typically be in

the 50pF range. Care must be taken when using output

capacitors of 1µF or larger. These application must be thor-

oughly tested over temperature, line and load.

An input capacitor is typically not required. However, a 0.1µF

ceramic can be used to help prevent line transients from

entering the LM4125. Larger input capacitors should be

tantalum or aluminium.

The typical thermal hysteresis specification is defined as the

change in +25˚C voltage measured after thermal cycling.

The device is thermal cycled to temperature -40˚C and then

measured at 25˚C. Next the device is thermal cycled to

temperature +125˚C and again measured at 25˚C. The re-

sulting V

thermal hysteresis. Thermal hysteresis is common in preci-

sion references and is induced by thermal-mechanical pack-

age stress. Changes in environmental storage temperature,

operating temperature and board mounting temperature are

all factors that can contribute to thermal hysteresis.

INPUT CAPACITOR

Noise on the power-supply input can effect the output noise,

but can be reduced by using an optional bypass capacitor

between the input pin and the ground.

PRINTED CIRCUIT BOARD LAYOUT CONSIDERATION

The mechanical stress due to PC board mounting can cause

the output voltage to shift from its initial value. References in

SOT packages are generally less prone to assembly stress

than devices in Small Outline (SOIC) package.

To reduce the stress-related output voltage shifts, mount the

reference on the low flex areas of the PC board such as near

to the edge or the corner of the PC board.

20069832

FIGURE 1.

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