The following figure shows two options to connect to the nRF9151 nRESET pin: temporary connected and always connected. For most applications, use the temporary connected option. The always connected option might apply in cases such as serial modem applications. In this case, an external microcontroller or processor interacts with nRF9151, for example through UART, and needs a permanent connection to the nRF9151 nRESET pin.
Use the temporary connected option when the nRESET pin is connected only temporarily, such as during firmware programming in the end-application production phase with an Serial Wire Debug (SWD) programming tool. The nRF9151 resets when the RESET_TEMPORARILY_CONNECTED net is driven low.
Leakage current can flow into or out of the nRESET pin. This depends on the voltage level in the SWD programming tool due to the nRF9151 internal voltage level of 2.2 V. Add a resistor between the SWD tool nRESET pin and nRF9151 nRESET pin to limit this current. This limits the amount of leakage current especially if the SWD tool nRESET pin voltage level is much higher than 2.2 V. The reason for this is the ESD protection diode inside the nRF9151 nRESET pin which starts to conduct when the voltage level at nRF9151 nRESET pin exceeds about 2.8 V. To reduce end product costs, the series resistor does not have to be on the end product PCB design. It can be placed on an external production test board or similar.
Use the always connected option when the end product requires control of the nRESET pin during normal operation. The nRESET circuit example prevents leakage current due to different voltage levels between the RESET_ALWAYS_CONNECTED net and the nRF9151 nRESET pin. However, the control logic is inverted. The nRF9151 resets when the RESET_ALWAYS_CONNECTED net goes high.