em78f644nso28s ELAN Microelectronics Corp, em78f644nso28s Datasheet - Page 164

• Manufacturer Part Number: em78f644nso28s
• Description: Flash Series 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

EM78F648/644/642/641/548/544/542/541N
8-Bit Microcontroller
154 •
6.16 Power-On Considerations
Any microcontroller is not guaranteed to start operating properly before the power
supply reaches its steady state. EM78F64x/54xN is equipped with aPower-On
Voltage Detector (POVD) with a detecting level of 2.0V. Power will work normally if
the Vdd rises fast enough (50ms or less). However, in critical applications, extra
devices are still required to assist in solving power-up problems.
6.17 External Power-On Reset Circuit
The circuit diagram shown below implements an external RC to generate the reset
pulse. The pulse width (time constant) should be kept long enough for Vdd to reached
minimum operational voltage. Apply this circuit when the power supply has a slow rise
time. Since the current leakage from the /RESET pin is about ±5μA, it is recom-
mended that R should not be greater than 40KΩ in order for the /RESET pin voltage is
remain at 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 into /RESET pin.
Internal RC
F641/541N Internal RC Drift Rate (Ta=25 ° C, VDD=5 V± 5%, VSS=0V):
F648/548N Internal RC Drift Rate (Ta=25°C , VDD=5 V± 5%, VSS=0V):
16 MHz
Internal RC
Frequency
4 MHz
8 MHz
455kHz
16MHz
4MHz
8MHz
Temperature
(-40°C~85°C)
± 3%
± 3%
± 3%
Temperature
(-40°C+85°C)
/RESET
Figure 6-29 External Power-Up Reset Circuit
Vdd
±5%
±5%
±5%
±5%
(2.4V~5.5V)
(This specification is subject to change without further notice)
Voltage
± 5%
± 5%
± 5%
(2.2V~5.5V)
Rin
Voltage
±5%
±5%
±5%
±5%
Drift Rate
Drift Rate
Product Specification (V1.0) 05.05.2010
R
C
Process
± 2.5%
± 2.5%
± 2.5%
Process
±4%
±4%
±4%
±4%
D
± 10.5%
± 10.5%
± 10.5%
Total
±14%
±14%
±14%
±14%
Total