EM78P468NBQSSLASHNBQJ datasheet(39/82 Pages) EMC

39 / 82 page

EM78P468N/L

8-Bit Microcontroller

Product Specification (V1.6) 12.31.2007

• 33

(This specification is subject to change without further notice)

6.7.1 External Power-on Reset Circuit

This circuit implements an external RC to produce a reset pulse (see Fig. 6-10). The

pulse width (time constant) should be kept long enough to allow VDD to reach minimum

operation voltage. This circuit is used when the power supply rise time is slow.

Because the current leakage from the /RESET pin is

±5μA, it is recommended that R

should not be greater than 40K. In this way, the voltage at Pin /RESET is held below

0.2V. The diode (D) acts as a short circuit at power-down. The capacitor, C, is

discharged rapidly and fully. Rin, the current-limited resistor, prevents high current

discharge or ESD (electrostatic discharge) from flowing into Pin /RESET.

Fig. 6-10 External Power-on Reset Circuit

6.7.2 Residue-Voltage Protection

When battery is replaced, device power (VDD) is disconnected but residue-voltage

remains. The residue-voltage may trips below minimum VDD, but above zero. This

condition may cause poor power on reset. Fig. 6-11 and Fig. 6-12 show how to build a

residue-voltage protection circuit

Fig. 6-11 Residue Voltage Protection Circuit 1

Fig. 6-12 Residue Voltage Protection Circuit 2

EM78P468NBQS/NBQJ Scheda tecnica(PDF) 39 Page - ELAN Microelectronics Corp