EM78P257
OTP ROM
(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 discharge or ESD (electrostatic discharge) from flowing to pin
/RESET.
V d d
R
EM78P257A/B
D
/RESET
Rin
C
Fig. 22 External Power on Reset Circuit
3. Residue-Voltage Protection
When battery is replaced, device power (Vdd) is taken off but residue-voltage remains. The residue-voltage may
trips below Vdd minimum, but not to zero. This condition may cause a poor power on reset. Fig.23 and Fig.24
show how to build a residue-voltage protection circuit
V d d
Vdd
33K
EM78P257A/B
Q 1
10K
/RESET
1 0 0 K
1 N 4 6 8 4
Fig. 23 Circuit 1 for the residue voltage protection
This specification is subject to change without prior notice.
51
07.27.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
