L4937N datasheet(6/9 Pages) STMICROELECTRONICS

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Figure 1 : Output Voltage vs. Input Voltage.

Figure 2 : Quiescent Current vs. Supply Voltage.

RESET CIRCUIT

The block circuit diagram of the reset circuit is shown

in fig. 3. The reset circuit supervises the standby out-

put voltage. The reset threshold of 4.7V is defined

by the internal reference voltage and the standby

output divider.

The reset pulse delay time tRD, is defined by the

charge time of an external capacitor CT :

CT x 2V

tRD =

µA

The reaction time of the reset circuit depends on 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. In fact, if the standby output voltage

drops below the reset threshold for a time shorter

than the reaction time tRR, no reset output variation

occurs. The nominal reset delay is generated for

standby output voltage drops longer than the time

necessary for the complete discharging of the ca-

pacitor CT. This time is typically equal to 50

µs if CT

= 100nF. The typical reset output waveforms are

shown in fig.

400

200

L4937N

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L4937N Datasheet(PDF) 6 Page - STMicroelectronics