Best way to adjust startup voltage?

[dav01]

Setup: nrf52840 (without internal dc/dc), VDD = 3.3V

Assuming the VDD rail ramps up slowly, the nrf52 will start booting at it's power-on reset threshold of 1.75V (POR).

Question: any tips on smart ways to adjust the startup voltage to say 3.2V (without adding external components)?

i.e. make sure to wait in a low-power state during early boot.

[haakonsh]

You'll want as fast rise time as possible, otherwise, you're going to be spending a lot of time on Power On Reset and that consumes a lot of power. If your rise time is too slow you won't get out of POR at all. 

Question: any tips on smart ways to adjust the startup voltage to say 3.2V (without adding external components)?

 That being said I don't know of any way create a voltage drop without adding any other components.  

 

i.e. make sure to wait in a low-power state during early boot.

 I'm not following, what are you trying to achieve?

[dav01]

Hi Haakonsh,

The system is designed to run at 3.3V, but the VDD rail has a slow rise-time (5-10mSec), and as soon as the nrf52 sees 1.65V+ it boots which is expected, but I'd like to hold off booting until we are >3.2V for x mSec's.

[haakonsh]

You can't do that without adding external components, you'll need a power supply supervisor circuit. Either discrete or as an IC (if it exist). 

[dav01]

heh, true, thanks!