nrf52840 DC/DC convertor enable and J-TAG.

[Namklak]

Hi,

it appears to me that when running code under J-TAG, the DC/DC convertor can not be enabled. (note this is "REG1", DCDECEN0 REG0 is not being used).

I've tried both NRF_POWER->DCDCEN = 1; without the SoftDevice init'ed, and sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE) with SoftDevice init'ed, and DEC4/DEC6 does not change at all.

My group is trying to debug manufacturing fallout of new boards - with code on the board that toggles a GPIO line before and after enabling the DC/DC convertor, the nrf reboots 50uS after enabling the DC/DC convertor.  We also see a ramp down of DEC4 from 1.3VDC to 0.85VDC, which is the where the nrf M4 reboots.

If we run this same board with the same code with JTAG, DEC4 does not change at all where enabling the DC/DC convertor.

On existing boards already shipped, when the DC/DC is enabled, we see small ramps on DEC4 as the DC/DC convertor starts.

Again, the question is, does the 52840 not allow enabling of the DC/DC convertor?

Thanks,

Namklak

[Namklak]

crap.  The question was supposed to be
Does the 52840 not allow the enabling of the DC/DC convertor WHILE UNDER JTAG CONTROL?

[Jared]

Hi there,

The nRF52840 will automatically use LDO mode during debug mode. As far as I know, there isn't any option to force it to DCDC mode in debug mode . The regulator that will be used after leaving debug mode is application dependent. 

regards

Jared 

[Namklak]

This confirmed my suspicion.

Note that while debugging, if code "enables" the DC/DC Convertor, the chip register will claim it is running.  But that is a lie.

[Jared]

Yeah, I think the debug mode will override whatever that is set in the DC/DC register.