LDFM

Application information

DocID023585 Rev 4

11/36

6

Application information

6.1

External capacitors

The LDFM requires external capacitors for regulator stability. These capacitors must be

selected to meet the requirements of minimum capacitance and equivalent series

resistance (see Figure 25: "Stability plane adj (COUT, ESR)" and Figure 26: "Stability plane

3.3 V (COUT, ESR)"). It is advisable to locate the input/output capacitors as close as

possible to the relative pins.

6.1.1

Input capacitor

An input capacitor with a minimum value of 1 µF is required with the LDFM. 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 capacitors can be used for

this capacitor.

6.1.2

Output capacitor

It is possible to use ceramic capacitors but the output capacitor must meet the

requirements for minimum amount of capacitance and E.S.R. (equivalent series resistance)

value.

A minimum capacitance of 2.2 µF is a good choice to guarantee the stability of the

adj (COUT, ESR)" and Figure 26: "Stability plane 3.3 V (COUT, ESR)", showing the allowable

ESR range as a function of the output capacitance.

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

temperature range to assure stability. Also, capacitor tolerance and variation with

temperature must be kept in consideration in order to assure the minimum amount of

capacitance at all times.

6.2

Enable pin operation

The Enable pin can be used to turn OFF the regulator when pulled down, so drastically

reducing the current consumption. When the enable feature is not used, this pin must be

signal source used to drive the Enable pin must be able to swing above and below the

must not be left floating because it is not internally pulled down/up.

6.3

Power Good

The LDFM features an open drain Power Good (PG) pin to sequence external supplies or

high when the output is within the PG tolerance window. Typical values for this resistor

range from 10 kΩ to 100 kΩ.