9160 IO default statue

[lemon]

Hi，

Our customer is using nrf9160.There is a problem about powem_on circuit .

Attach is the schematic diagram:

Here VBAT is 4V,PW_ON is connecting to the nrf9160 p0.27 pin.

As the bleeder circuit shows,when SW2 push ,PW_ON voltage should be 4*100/139 ≈ 2.8V，this will enable the power_ic to output 3.3V voltage 

to make the system power on .

However when PW_ON connecte to P0.27，the PW_ON voltage come to 1V which couldn't enable the power_ic.

I think this is probably because the resistance in parallel is causing the voltage divider to work abnormally,so I connect a 100K resistance between PW_ON 

and P0.27 pin , and it works fine.

I want to know which status the nrf9160 gpio in before system power on ? In this case ,should we only to change the bleeder circuit resistance value ?

Brs,

Lemon

[Håkon Alseth]

Hi,

 

Have you measured R32 and R33 in case they're not the value as stated in the schematic, or if they have switched place?

 

Kind regards,

Håkon

[lemon]

Hi，

I have measured R32 and R33 and they are the values as the the schematic shows.

When I cut PW_ON line,It works fine.

Brs,

Lemon

[Håkon Alseth]

Hi,

 

How is the GPIO configured on the nRF side?

If you check the NRF_P0->PIN_CNF[27] register, it should indicate if the pin is configured with input or output, with any corresponding pull-resistor.

 

39k parallel with a pull-down of approx. 13k gives around 1 V at the PW_ON signal.

 

It could also be the board setting:

P0.27, if using the nrf9160dk_nrf9160 board, is default set to the UARTE0 RTS pin. Be sure to change this in case HWFC is enabled.

 

Kind regards,

Håkon

[lemon]

Hi,

The firmware is the factory code,and haven't been reprogram.

If I connected the P0.27 to PW_ON,nRF91 couldn't power on, as the VDD3.3_EN cann't enable 

the power IC to power the system on.

I guess there is about 13K resistance at P0.27 so that can be 1V .

Brs,

Lemon

[Håkon Alseth]

Hi,

 

lemon said:

The firmware is the factory code,and haven't been reprogram.

If I connected the P0.27 to PW_ON,nRF91 couldn't power on, as the VDD3.3_EN cann't enable 

the power IC to power the system on.

I guess there is about 13K resistance at P0.27 so that can be 1V .

The nRF is unpowered at this point in time? If so, this is a flaw in your schematic.

By applying voltage directly to a GPIO when the nRF is unpowered, you are powering it through the ESD protection inside the nRF.

By connecting a 100k series resistor, you are restriction the current flow through the unpowered GPIO, and the circuit runs as initially intended.

 

Kind regards,

Håkon

[lemon]

Hi，

Thanks for your reply.

It's very useful.

Brs,

Lemon