Application notes

LD2980ABxx - LD2980Cxx

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7

Application notes

7.1

External capacitors

Like any low-dropout regulator, the LD2980 requires external capacitors for regulator

stability. This capacitor must be selected to meet the requirements of minimum capacitance

and equivalent series resistance. We suggest to solder input and output capacitors as close

as possible to the relative pins.

7.2

Input capacitor

An input capacitor whose value is 1 µF is required with the LD2980 (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.

7.3

Output capacitor

The LD2980 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 ESR (equivalent series resistance) value. The Figure 4 and Figure 5

show the allowable ESR range as a function of the output capacitance. These curves

gain, the stability improves for higher output versions and so the suggested minimum output

capacitor value, if low ESR ceramic type is used, is 1 µF for output voltages equal or major

than 3.8 V, 2.2 µF for output voltages from 2.85 to 3.3 V, and 3.3 µF for the other versions.

However, if an output capacitor lower than the suggested one is used, it’s possible to make

stable the regulator adding a resistor in series to the capacitor (see Figure 1 and Figure 2 to

choose the right value according to the used version and keeping in account that the ESR of

ceramic capacitors has been measured @ 100 kHz).

7.4

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.

7.5

Inhibit input operation

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

reducing the current consumption down to less than 1 µA. When the inhibit feature is not

proper operation, the signal source used to drive the inhibit pin must be able to swing above