NRF52820-QDAA-R datasheet(54/437 Pages) NORDIC

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Power and clock management

If the power failure warning is enabled, and the supply voltage is below the threshold, the power-fail

comparator will prevent the NVMC from performing write operations to the flash.

The comparator features a hysteresis of VHYST, as illustrated in the following figure.

Supply (VDD or VDDH)

VPOF

VPOF+VHYST

1.7V

BOR

Figure 18: Power-fail comparator (BOR = brownout reset)

To save power, the power-fail comparator is not active in System OFF or System ON when HFCLK is not

running.

5.3.2 USB supply

When using the USB peripheral, a 5 V USB supply needs to be provided to the VBUS pin.

The USB peripheral has a dedicated internal voltage regulator for converting the VBUS supply to 3.3 V used

by the USB signalling interface (D+ and D- lines, and pull-up on D+). The remainder of the USB peripheral

(USBD) is supplied through the main supply like other on-chip features. As a consequence, VBUS and

either VDDH or VDD supplies are required for USB peripheral operation.

When VBUS rises into its valid range, the software is notified through a USBDETECTED event. A

USBREMOVED event is sent when VBUS goes below its valid range. Use these events to implement the

USBD start-up sequence described in the USBD chapter.

When VBUS rises into its valid range while the device is in System OFF, the device resets and transitions to

System ON mode. The RESETREAS register will have the VBUS bit set to indicate the source of the wake-up.

See VBUS detection specifications on page 69 for the levels at which the events are sent (VBUS,DETECT

and VBUS,REMOVE) or at which the system is woken up from System OFF (VBUS,DETECT).

When the USBD peripheral is enabled through the ENABLE register, and VBUS is detected, the regulator

is turned on. A USBPWRRDY event is sent when the regulator's worst case settling time has elapsed,

indicating to the software that it can enable the USB pull-up to signal a USB connection to the host.

The software can read the state of the VBUS detection and regulator output readiness at any time through

the USBREGSTATUS register.

4463_156 v1.0

NRF52820-QDAA-R Datasheet(PDF) 54 Page - Nordic Semiconductor