VDD power sources

The main supply voltage (VDD) is sourced from the 5 V domain, external power supply, and coin cell battery.

For the 5 V domain, there is one fixed 3 V buck regulator and one voltage follower regulator that follows the VDD_nRF voltage. The coin cell battery and external power supply are not regulated.

5 V domain:
- Fixed 3 V buck regulator
- VDD_nRF voltage follower
External power supply
Coin cell battery

The power sources are routed through a set of load switches which are controlled by logic to prioritize the power sources in the correct manner.

If the high voltage regulator of the nRF52840 is used, the Development Kit (DK) is supplied from the VDD_nRF voltage follower regardless of the state of the other power sources.

Figure 1. Power supply circuitry

The internal transistor body diode powers the VSUPPLY net, which is used to supply the gates that control the enable signal for the power switches. If 5 V is present, the switches for external supply and battery are disabled. If external supply is present, the switch for the battery is disabled.

The power switches can be bypassed by shorting one or more solder bridges.

Table 1. Power switch bypass solder bridges
Power source	Power switch bypass	Voltage level
Regulator	SB34	3.0 V
External supply	SB36	1.7 V to 3.6 V

Figure 2. Power switch bypass solder bridges

Power switch bypass solder bridges on nRF52840 DK

Note: Connect only one power source at a time. Shorting the solder bridges removes the reverse voltage protection.

For more information on power sources, see nRF52840 power source.