nRF9151 Hardware Enable/Disable by another MCU with least consumption

[Abomin3v3l]

Hello.

****************************** 1 ******************************

In the picture above, it's the original circuit for 9151 in our schematic, for this block of pins of the 9151. The ENABLE pin is constantly tied to level 1 by connecting ENABLE to VDD through a 10K resistor.

In this case, in the idea of this project of the picture above, the 9151 was the head/master of the PCB, so no any issues with this picture above. This was the previous board.

****************************** 2 ******************************

Then here begins the idea of our new and current schematic that I'm working on. It will be added to the board a module based in a 54L15. The nRF54L15 will be the head/master and the 9151 will be just a slave of the 54L15, and they would communicate via TX/RX UART, burning on the 9151 a firmware compatible with the Mosh serial terminal of Nordic. As the product is a 3.6V battery-powered, the idea is that the 54L15 stays most of time in sleep mode and be waked-up by a RTC chip at programmed horaries, and that while the 54L15 is in sleep the 9151 be disabled in hardware holding ENABLE pin of 9151 to 0 during this period. But then as we can see in this second picture, there would be a considerable consumption via resistor R13 if Q1 keeps conducting to ground.

****************************** 3 ******************************

My idea was to do as in this third picture, where the ENABLE of 9151 is directly controlled by an output of 54L15, with a pull-down. Do you see any problem with this?

****************************** 4 ******************************

There is the nRESET signal of the programming interface, pin 9 of 9151, but as far as I know there is an internal pull-up on this pin, so anyway, if we hold nRESET in 0, there would be some consumption also.

****************************** 5 ******************************

Also, I would like to ask what is the typical current consumption (in uA) of 9151 when its ENABLE pin is keept tied to ground, recognizing level 0.

Regards,

Jeferson Pehls.

[Simonr]

Hi Jeferson

Having a pulldown as in alternative 3 here, will likely draw some current, though not a lot. I think it should be fine to connect it to the nRF54L15 without pulldown since the nRF9151 ENABLE pin is a high impedance pin. You can leave the footprint for the pulldown just in case though.

Regarding the current consumption, the System Disabled mode the entire device can be powered down by presenting the appropriate voltage to the ENABLE pin. See page 51 of nRF9151 product specification: https://docs.nordicsemi.com/bundle/ps_nrf9151/page/nRF9151_html5_keyfeatures.html If the system disabled mode is used, there shouldn't be any excess current AFAIK.

Best regards,

Simon

[Abomin3v3l]

Hi Simon.

We did like this in the PCB, starting with the jumper assembled and the pull-down assembled, and with the pull-up not assembled.

There will be 4 connections among the 54L15 and the 9151: TX, RX, RTS, CTS.


So that we have 2 options:

(1) Implement this what is shown below, disassembling the jumper and the pull-down and assembling a 10K for R1, so the consmption can go down to 2uA according to the document.

Ultra low power PPP connection using nRF9151.pdf

(2) Or keep the circuit as the first picture, so that maybe we can go even lower than 2uA, because when ENABLE = 0 then supposedly almost all internal hardware of 9151 is disabled. The most of time ENABLE would be kept in 0, so no consumption via the pull-down most of time also. The pull-down is just to guarantee level 0 when the board is just powered-up, while the 54L15 is not forcing yet a specific logic level at the ENABLE pin.