EM78P468LAQ EMC [ELAN Microelectronics Corp], EM78P468LAQ Datasheet - Page 43

• Manufacturer Part Number: EM78P468LAQ
• Description: 8-BIT Microcontroller
• Manufacturer: EMC [ELAN Microelectronics Corp]

Product Specification (V1.0) 03.15.2006
(This specification is subject to change without further notice)
4.7 Power-on Considerations
4.7.1
4.7.2
Any microcontroller (as with this LSI) is not warranted to start operating properly before
the power supply stabilizes in steady state. This LSI is equipped with Power On Reset
(POR) with detection level range of 1.6V to 1.8V. The circuitry eliminates the extra
external reset circuit but will work well only if the VDD rises quickly enough (50 ms or
less). However, under critical applications, extra devices are still required to assist in
solving power-on problems.
This circuit implements an external RC to produce a reset pulse (see Fig.12). The pulse
width (time constant) should be kept long enough to allow VDD to reach minimum
operation voltage. This circuit is used when the power supply rise time is slow. Because
the current leakage from the /RESET pin is about ± 5 µ A, it is recommended that R should
not be great than 40K. In this way, the voltage at Pin /RESET is held below 0.2V. The
diode (D) acts as a short circuit at power-down. The capacitor, C, is discharged rapidly
and fully. Rin, the current-limited resistor, prevents high current discharge or ESD
(electrostatic discharge) from flowing into Pin /RESET.
When battery is replaced, device power (VDD) is disconnected but residue-voltage
remains. The residue-voltage may trips below minimum VDD, but above zero. This
condition may cause poor power on reset. Fig.13 and Fig.14 show how to build a
residue-voltage protection circuit
External Power-on Reset Circuit
Residue-Voltage Protection
Fig. 13 Circuit 1 for the Residue Voltage Protection
Fig. 12 External Power on Reset Circui t
8-BIT Microcontroller
EM78P468L
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