46.5 External Reset Circuit

The external Reset circuit is connected to the RESET pin when the external Reset function is used. The circuit is not necessary when the RESET pin is not driven low externally by the application circuitry.

The reset switch can also be removed, if a manual reset is not desired. The RESET pin itself has an internal pull-up resistor, therefore it is optional to add any external pull-up resistor.

A pull-up resistor makes sure that the reset does not go low and unintentionally causing a device reset. An additional resistor has been added in series with the switch to safely discharge the filtering capacitor, that is preventing a current surge when shorting the filtering capacitor which again can cause a noise spike that can have a negative effect on the system.

Figure 46-5.  External Reset Circuit Schematic (General Purpose)(2)

The following reset circuit is intended to improve EFT immunity but does not filter low frequency glitches which makes it unsuitable as an example for applications requiring debouncing on a reset button.

Figure 46-6. External Reset Circuit Schematic (EFT Immunity Enhancement) (2)
Note:
  1. The device features an internal pull-up resistor on the RESET pin; therefore, an external pull-up is optional.
  2. These values are only given as a typical example. Refer to the Power Supply Electrical Characteristics to determine values given in system parameters to meet reset timing requirements (TRST).
Note: Reset circuit recommendations to improve EFT/ESD/EMI immunity can be found in the “Basic 32-Bit MCU Design and Troubleshooting Checklist” guide on the Microchip web site, www.microchip.com.