EM78P5840/5841/5842
8-bit Micro-controller
POR reset voltage is influenced in process or temperature. For some application, a constant reset voltage is
important. Next circuit will support a adjust reset voltage. By adjusting R41 and R46, POR reset voltage will be a
constant (Vpor) and the potential on /RESET pin will drop to 0 when VDD drop to below Vpor. Next plot show
the relative between VDD and Vpor. When R41 = 3.9M ohm and R46 = 910K ohm, /RESET will keep to 0 if
VDD is below 2.24V and will active after VDD upper to 2.1V.
VDD
R41
3M9
R42
2M2
R43
330K
RESET
R44
Q2
22M
C31
104
Q3
C1815
S10
R46
910K
C1815
RESET
Fig 16: External power on reset circuit 2
VDD
2.24V
2.1V
VDD
/RESET
T
Fig 17: The relative between VDD and Vpor
__________________________________________________________________________________________________________________________________________________________________
* This specification is subject to change without notice.
37
2004/11/10 V2.6
ELAN [ ELAN MICROELECTRONICS CORP ]
