VDDH measurement with the ADC (nrf52840 QIAAC0)

[Abderrezak Mekkaoui]

Dear All,

I am measuring VDD and VDDH using the internal SAADC. In normal mode (VDDH not connected to VDD) the reported results are good (3.0V and 1.8V for example). But in high voltage mode (VDDH connected to VDD), the VDD measurement is correct but not that of VDDH (1.9V and 3V) instead of (3V and 3V). Same results with 3 boards from 3 different vendors. Is this behavior normal?

Thanks

[Abderrezak Mekkaoui]

Hi Haakonsh

VDDH not connected to VDD => VDDH is supplied externally. VDD is provided by the nRF chip. Figure 209: Circuit configuration no. 2 schematic

VDDH connected to VDD => VDDH is shorted to VDD and supplied externally. Figure 210: Circuit configuration no. 3 schematic.

In both cases NO DCDC is used. (Both DCDC regulators are disabled: DCDCEN0=0; DCDCEN1=0).

Ref. nRF52840 Product Specification v1.0

Thanks

[haakonsh]

Aah, now I understand. 

Well, that is undefined behavior, as the REG0 is not in use measuring the voltage of its output makes little sense. 

Hope that clarifies it a bit. 

[Abderrezak Mekkaoui]

Thank you. The documentation states that the input to the ADC could be VDD, VDDH/5,AIN0.....Somewhat misleading. Just wanted to make sure the beahavior is expected because in the case VDD=VDDH, measuring VDD is enough.

[haakonsh]

I understand the confusion, my best guess is that the analog reference of VDDH/5 is sampled somewhere in the regulator's internal circuit who's not in its operational state, as opposed to the VDDH input pin.