GPIO power of the nRF9160 with the LDO from the nRF52833

[Gerard E]

Hello,

I'm working on a project involving both the nRF9160 and the nRF52833 on a single PCB. Since PCB space is at a premium for this project, I would like to know if it is possible to power the GPIO pins of the nRF9160 LTE-M modem with the internal LDO (REG0) of the nRF52833.

The Project will be powered by a regular USB wall power supply at 5 V.

This means that I will use the nRF52833 in high voltage mode.

My questions are:

- Can I use the internal LDO (REG0) of the nRF52833 to power the GPIO of the nRF9160?

- Should I implement some kind of load switch circuitry to comply with the nRF9160 Datasheet_v2.1 chapter 11.1 VDD_GPIO considerations?

The things that could happen with respect to power:

- The nRF9160 reset pin could be used while both VDD and VDD_GPIO are present.

- The nRF9160 enable pin could be pulled low while both VDD and VDD_GPIO are present.

- The GPIO pins of the nRF9160 could receive some voltage from the nRF52833 while the device is "reset" or "disabled".

--- Edit ---
Added schematic screenshot of power connections (without decoupling capacitors)

[JONATHAN LL]

Hi,

From the schematic you shared there seems to be missing some curtail components. Is this early in the prosess and you have not included the rest of the circuitry?(i see that you mention its without decupling caps)

For the nrf9160 we do have guidelines that i recommend you look in to before finishing the design. 

What do you plan on using nrf9160 GPIO's for?

Regards,
Jonathan

[Gerard E]

Hello, I will use some GPIO pins for a UART connection with the nRF52833.
This UART connection will be used for AT commands.

I know that the nRF9160 is capable of much more than I will use it for, but currently I need an LTE-M internet connection and a UART connection with the nRF52833 for AT commands.

Regarding some missing components,
This time I added a screenshot of the nRF9160 including the circuitry connected to the nRF9160.
(The eSIM chip and LTE-M antenna are not yet added to the schematic.)
(GPS will not be used)

My questions still remain:
Is it possible to power VDD_GPIO from the LDO of the nRF52833?
Should I implement some kind of load switch circuitry between the LDO (REG0) of the VDD_nRF52 and VDD_GPIO of the nRF9160?
Do I need to disconnect the UART communication lines from the nRF52833 when the nRF9160 is powered off, reset, disabled etc.?

Kind regards,
Gerard

[run_ar]

Hi,

First, I am sorry for the late reply on this case. second, notice that we will be a little low on staff during until next year due to holidays, so I am afraid you will have to expect delayed answers.

The nRF52833 GPIO output current is limited depending on mode. See: GPIO Electrical Specification. During reset the GPIO's will in general hold it's previous state until it is reset when it will be put in the the disconnected state. So I do not see any reason why that will be an issue. But I'll assign this back to my colleague so he can take a look once he is back in office.

[JONATHAN LL]

Gerard E said:

s it possible to power VDD_GPIO from the LDO of the nRF52833?

The nRF52833 does not support external circuitry supply, so the official answer is no. When supplying something external the nrf52833 might become unstable and act strange and might no longer perform to spec so it is not recomeded.


The nRF52840 does have support for supplying external circetry, but is limited to 20mA. See https://infocenter.nordicsemi.com/topic/ps_nrf52840/power.html?cp=4_0_0_4_2_0_2#unique_1834109135


Regards,
Jonathan