EM78P809N
8-Bit Microcontroller
current leakage from the /RESET pin is about ±5µA, it is recommended that R should
not be greater than 40K. 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.
Vdd
R
/RESET
D
EM78P809N
Rin
C
Fig. 35. External Power-Up Reset Circuit
4.18.2 Residue-Voltage Protection
When battery is replaced, device power (VDD) is taken off but residue-voltage remains.
The residue-voltage may trip below VDD minimum, but not to zero. This condition may
cause a poor power-on reset. Fig.35 and Fig.36 show how to build the residue-voltage
protection circuit.
Vdd
Vdd
33K
EM78P809N
Q1
10K
/RESET
40K
1N4684
Fig. 36. Residue Voltage Protection Circuit 1
60 •
Product Specification (V1.0) 07.26.2005
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
