L4949ED-E, L4949EP-E

Application information

Doc ID 16823 Rev 1

13/19

3.5

Reset circuit

The block circuit diagram of the reset circuit is shown in Figure 7. The reset circuit

supervises the output voltage.

The reset threshold of 4.5 V is defined with the internal reference voltage and standby

output divider.

The reaction time of the reset circuit originates from the discharge time limitation of the reset

capacitor CT and is proportional to the value of CT.

The reaction time of the reset circuit increases the noise immunity. Standby output voltage

drops below the reset threshold only a bit longer than the reaction time results in a shorter

reset delay time.

The nominal reset delay time is generated for standby output voltage drops longer than

approximately 50ms.

The typical reset output waveforms are shown in Figure 8.

3.6

Sense comparator

The sense comparator compares an input signal with an internal voltage reference of typical

1.23V. The use of an external voltage divider makes this comparator very flexible in the

application.

It can be used to supervise the input voltage either before or after the protection diode and

to give additional informations to the microprocessor like low voltage warnings.

Figure 7.

Block circuit of reset circuit

t

RD

C

T

2V

•

2

μA

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=