EM78P447SAP datasheet(28/55 Pages) EMC

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EM78P447S

OTP ROM

4.9 Power On Considerations

Any microcontroller is not guaranteed to start and operate properly before the power supply stays at its steady state.

EM78P447S POR voltage range is 1.2V~1.8V. Under customer application, when power is OFF, Vdd must drop to

below 1.2V and remains OFF for 10us before power can be switched ON again. This way, the EM78P447S will

reset and work normally. The extra external reset circuit will work well if Vdd can rise at very fast speed (50 ms or

less). However, under most cases where critical applications are involved, extra devices are required to assist in

solving the power-up problems.

4.10 External Power On Reset Circuit

The circuit shown in Fig.16 implements an external RC to produce the reset pulse. The pulse width (time constant)

should be kept long enough for Vdd to reached minimum operation voltage. This circuit is used when the power

supply has slow rise time. Because the current leakage from the /RESET pin is about

±5µA, it is recommended that

R should not be greater than 40 K. In this way, the /RESET pin voltage is held below 0.2V. The diode (D) acts as a

short circuit at the moment of power down. The capacitor C will discharge rapidly and fully. Rin, the current-limited

resistor, will prevent high current or ESD (electrostatic discharge) from flowing to pin /RESET.

EM78P447N

/RESET

Vdd

Rin

Fig. 13 External Power-Up Reset Circuit

This specification is subject to change without prior notice.

06.25.2003 (V1.1)

EM78P447SAP 数据表(PDF) 28 Page - ELAN Microelectronics Corp