RESET CIRCUIT

The blockcircuit diagramof theresetcircuit isshown

in fig.4. The reset circuit supervisesthe standbyout-

put voltage. The reset threshold of 4.7V is defined

by the internal reference voltage and the standby

output divider.

2

µA

The reaction time of the reset circuit dependson the

The reaction time of the reset circuit increases the

noise immunity. In fact,if the standby outputvoltage

drops below the reset threshold for a time shorter

occurs. The nominal reset delay is generated for

standby output voltage drops longer than the time

necessary for the complete discharging of the ca-

µsif

shown in fig. 5.

SENSE COMPARATOR

This circuit comparesan input signal withan internal

voltage reference of typically 1.23V. The use of an

externalvoltage divider makes the comparator very

flexible in the application. This function can be used

to supervisethe input voltage - eitherbefore or after

the protectiondiode - and to give additionalinforma-

tion tothe microprocessorsuch aslow voltagewarn-

ings.

If this feature is not used SI and SO have to con-

nected to GND. In this case the St-by quiescent cur-

rent (14V) increases from 290

µA to 300µA.

Figure 4: Block Diagram of the Reset Circuit.

L4938N - L4938ND - L4938NPD

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