What should VDD level be on unprogrammed device?

[ScottBBBB]

We are supplying the nRF52840 from 5 V into the VDDH pin.  We are not using the USB interface, so VBUS is grounded.

When we apply power to unprogrammed devices and measure the voltage on VDD, which is the output of internal regulators, we see a variety of values.  I've seen a few at 2.4 V, but also some at 2.1, 2.2 V or 2.3 V.  This doesn't make sense to me -- I would think they should be consistent unit to unit.  I've not used this particular Nordic IC before.  What should we expect to see?

Thanks,

Scott

[Kazi Afroza Sultana]

Hello Scott,

Could you Please send your schematic diagram? It should be like this according to your description. 

You can check with our reference design https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html?cp=4_0_0_6_2  as well.

Thanks.

Best Regards,

Kazi Afroza Sultana

[ScottBBBB]

We appear to have figured out what is going on.  We are using a nRF52840-based module from Fanstel, and I had erroneously assumed that there was sufficient bypass capacitance internal to the module to meet the Nordic spec, but it turns out that we needed to add 4.7 uF onto VDD.  Prior to that, VDD had a ton of ripple on it, but now it's a steady 1.8 V as expected.

Scott

[Kazi Afroza Sultana]

Hi Scott,

Seems like your problem is solved. You can verify your own comment so the case can be closed. 

Thanks.

Best Regards,

Kazi Afroza Sultana