nRF52840 Preview DK v0.9.x

VDD power sources

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

For the 5 V domain, there are two regulators, 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.

For more information about power sources, see section nRF52840 power source.

The power sources are routed through a set of load switches, which is controlled by logic to give the correct priority of the power sources.

This means that if the high voltage regulator of the nRF52840 is used, the board will be supplied from the VDD_nRF voltage follower regardless of the state of the other power sources.

Figure 1. Power supply circuitry

The power switches work in the way that the body diode of the internal transistor powers the VSUPPLY net, which supplies the gates controlling the enable signal of the 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
Coin cell battery SB35 Battery
External supply SB36 1.7 V– 3.6 V
Figure 2. Power switch bypass solder bridges

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

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