Application information

LD39020

12/30

DocID025316 Rev 3

6

Application information

6.1

Soft start function

The LD39020 has an internal soft start circuit. By increasing the startup time up to 100µs,

without the need of any external soft start capacitor, this feature is able to keep the

regulator inrush current at startup under control.

6.2

Output discharge function

The LD39020 integrates a MOSFET connected between Vout and GND. This transistor is

activated when the EN pin goes to low logic level and has the function to quickly discharge

the output capacitor when the device is disabled by the user.

The device is available with or without auto-discharge feature.

See Table 10: "DFN1x1-4L order codes" for more details.

6.3

Input and output capacitors

The LD39020 requires external capacitors to assure the regulator control loop stability.

Any good quality ceramic capacitor can be used but, the X5R and the X7R are suggested

since they guarantee a very stable combination of capacitance and ESR overtemperature.

Locating the input/output capacitors as closer as possible to the relative pins is

recommended.

The LD39020 requires an input capacitor with a minimum value of 1 μF.

This capacitor must be located as closer as possible to the input pin of the device and

returned to a clean analog ground.

The control loop of the LD39020 is designed to work with an output ceramic capacitor.

This capacitor must meet the requirements of minimum capacitance and equivalent series

resistance (ESR), as shown in Fig17. To assure stability, the output capacitor must

maintain its ESR and capacitance in the stable region, over the full operating temperature

range.

The LD39020 shows stability with a minimum effective output capacitance of 220 nF.

However, to keep stability in all operating conditions (temperature, input voltage and load

variations), a minimum output capacitor of 0.47 µF is recommended.

The suggested combination of 1 μF input and output capacitors offers a good compromise

among the stability of the regulator, optimum transient response and total PCB area

occupation.