L9777

Functional description

Doc ID 13496 Rev 2

11/25

3

Functional description

3.1

Voltage regulator

A short circuit protection to GND is provided (see Figure 6).

By means of tracking regulator, it is available a second output regulated voltage on pin VDD

with a current capability up to 50mA. This regulated output is switchable on/off by external

pin VDD_EN.

Figure 6.

VCC versus output current IVCC

3.2

Reset

The reset circuit monitors the output voltage VCC. In case of internal reset threshold, if the

output voltage stays lower than VCCUN for a filter time TRR, then NMI goes low.

This filter time depends on the distance between the VCC output and the under voltage

reset threshold (VCCUN): this solution increases the noise immunity of the voltage regulator

be-cause the filter time between the reset event and the falling of NMI output changes

according to the depth of spike on output voltage (see following picture).

5.6 V.

Figure 7.

Filter time between VCC and NMI

Otherwise, in case of external reset threshold fixed by means of external resistor divider on

pin RADJ, there is only a constant filter time (TRRADJ) of 1 µs min value.

VCC

VCCREF

IVCC

ISHORT

ILIM

VCC

NMI

TRR1

VCC

NMI

V1

TRR2

VCCUN

2.5V