nRF5340-DK operating voltage at 1.8V?

[SteveG128]

Hi,

I'm trying to get my firmware running on a nRF5340-DK before I have my real hardware. I've connected a MAX86171 via I2C to the DK, the MAX86171 has a nominal operating voltage of 1.8V. I've configured the DK to operate off the external supply connector and connected a 1.8V supply to the DK.

The problem is the I2C signals (SDA, SCL, P1.02 and P1.03) don't move at 1.8V. If I remove the MAX86171 and increase the external supply to 3.0V, the I2C signals appear signal properly.

My questions:

1. Can I run the nRF5340-DK at 1.8V and expect the I2C and another GPIO acting as an interrupt input to be fully functional?

2. Should I expect a uBlox NORA-B1 series BLE module to operate properly at 1.8V? The data sheet states an operating voltage of 1.7V to 3.6V

Regards

Steve

[Jared]

Hi,

Yes, you should expect both the nRF5340 and a module based on it to be fully functional at 1V8. What power supply source are you using and have you set a current limit on it?

Is MAX86171 supplied directly from your external supply?

regards

Jared 

[SteveG128]

Jared,

I'm using a bench supply and the current limit is well above any expected current requirements of the DK.

I'm using connector P1 pin 1 of the DK for the MAX86171 1.8V

More importantly, if I remove the MAX86171 and simply watch SCL and SDA with the scope, there is no activity on the signals until I supply 3V (it may be a lower voltage, I just tested 1.8V and 3V). My shield board pulls up both signals with 4K7 resistors to the DK's Vdd.

Steve 

[Jared]

Hi Steve,

Which version of NCS are you using?

SteveG128 said:

More importantly, if I remove the MAX86171 and simply watch SCL and SDA with the scope, there is no activity on the signals until I supply 3V (it may be a lower voltage, I just tested 1.8V and 3V)

Could you share a minimal sample that would reproduce this, so I could recreate this on my DK?

regards
Jared 

[SteveG128]

Hi Jared,

I'm using Version 2.1.0.

I can duplicate the issue using the sample ncs\v2.1.0\zephyr\samples\drivers\i2c_fujitsu_fram

It doesn't matter if there is a I2C device, just the pull-ups on SCL and SDA are required.

Steve

[Jared]

Steve,

I tried to reproduce this with the i2c_fujitsu_fram sample but wasn't able to. I connected a power supply to the P21 external supply connector and saw that there indeed was activity on both SCL and SDA when I lowered the voltage. At 1V8 I would see several resets which I think is brown-out resets but it became stable when I increased it to about 1V9. I did not use external pull ups, instead I modified the dts to activate the internal pullups with pin ctrl like this: