em78p134n ELAN Microelectronics Corp, em78p134n Datasheet - Page 50

• Manufacturer Part Number: em78p134n
• Description: 8-bit Microcontroller With Otp Rom
• Manufacturer: ELAN Microelectronics Corp

EM78P134N
8-Bit Microcontroller with OTP ROM
44 •
5.11 Power-on Considerations
Any microcontroller is not warranted to start operating properly before the power supply
has stabilized to a steady state. The EM78P134N has a built-in Power-on Reset (POR)
with reset level range of 1.7V to 1.9V. The circuitry eliminates the extra external reset
circuit. It will work well if Vdd rises quickly enough (50ms or less). However, under
critical applications, extra devices are still required to assist in solving power-on
problems.
5.11.1 External Power-on Reset Circuit
The circuits shown in the
figure implement an
external RC to produce a
reset pulse. The pulse
width (time constant) should
be kept long enough to
allow Vdd to reach the
minimum operating voltage.
This circuit is used when the
power supply has a slow
power rise time. Because
the current leakage from the /RESET pin is ± 5 μA, it is recommended that R should not
be greater than 40K. This way, the voltage at Pin /RESET is held below 0.2V. The
diode (D) functions as a short circuit at power-down. The “C” capacitor is discharged
rapidly and fully. Rin, the current-limited resistor, prevents high current discharge or
ESD (electrostatic discharge) from flowing into Pin /RESET.
(This specification is subject to change without further notice)
Figure 5-20 External Power-on Reset Circuit
/RESET
VDD
Product Specification (V1.6) 06.02.2010
Rin
C
R
D