DocID13496 Rev 4 11/25
L9777 Functional description
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3 Functional description
3.1 Voltage regulator
This device supply an always active 5 V regulated voltage on pin V
CC
with a current
capability up to 200 mA. V
CC
voltage has an accuracy of 2% over a wide supply voltage
(V
I
= 5.6 V to 31 V) and temperature range (T
J
= -40 °C to 150 °C).
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 50 mA. 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).
A minimum filter time of 1 μs (TRR1) is guaranteed if VCC goes down to 2.5 V and
V
S
> 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.
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