I2C bus high level threshold voltage

[Oystein]

Hi

I am powering the nRF52840 from a 3.3V DC power supply and connecting it with a IMU thats cannot go higher than 1.9V on the I2C bus

I use 1.8V.

Will the I2C coomuncation work with nRF52840 if powered from a 3,3V DC and the I2C bus lines are externally pulled up to 1.8V DC with 4.7k ohm pull ups?

Øystein

[JONATHAN LL]

Hi,

The nRF52840 has two modes, High voltage mode and normal mode. 

In High voltage mode you can select the output voltage on VDD\GPIO, between 1.8V (default) and 3.6V

In normal mode then the voltage of the GPIO's follow the VDD voltage, so if you supply 3V on VDD then you have 3V on the pins. 

https://infocenter.nordicsemi.com/topic/ps_nrf52840/power.html?cp=5_0_0_4_2_0_1#gpio_levels 

https://infocenter.nordicsemi.com/topic/ps_nrf52840/uicr.html#register.REGOUT0 

Alterative options is to use level shifters. 

Will the I2C coomuncation work with nRF52840 if powered from a 3,3V DC and the I2C bus lines are externally pulled up to 1.8V DC with 4.7k ohm pull ups?

This is not a good idea in normal voltage mode if supply voltage is more then 1.8V. 

Regards,
Jonathan

[Oystein]

HI

I have desinged the powering like NORMALK VOLTAGE MODE, DC/DC REG 1 ENABLED

So both VDD and VDDH pin is connected to my 3.3V power supply.

Two more questions though.

1. If I had connected the powering as HIGH VOLTAGE mode and set VDD output voltage to 1.8V in REG0, will that VDDIO high level be applied for all GPIO pins, or can I set in some other registers that only the I2C bus shall be 1.8V levels, and all the other GPIO pins shall be 3.3V level?

2. It says Output voltage from REG0 regulator stage. The maximum output voltage from this stage is given as VDDH - V_VDDH-VDD. 
I did not understnad what voltage V_VDDH refers to?

3. If I understand it correctly, In NORMAL MODE powered by a 3.3V power supply, I will need a voltage level translator, like https://www.ti.com/lit/ds/symlink/tca9406.pdf?ts=1715424827946&ref_url=https%253A%252F%252Fwww.google.com%252F, if I want to interface it with a 1.8V IMU using the I2C bus. But you ewrite This is not a good idea in normal voltage mode if supply voltage is more then 1.8V. 
Please explain why this is not a good idea?

Kr

Øystein

[JONATHAN LL]

Oystein said:

1. If I had connected the powering as HIGH VOLTAGE mode and set VDD output voltage to 1.8V in REG0, will that VDDIO high level be applied for all GPIO pins, or can I set in some other registers that only the I2C bus shall be 1.8V levels, and all the other GPIO pins shall be 3.3V level?

All GPIO pins will be the same voltage so all would be 1.8V in that case. no way to individually control the voltage on the pins. 

Oystein said:

2. It says Output voltage from REG0 regulator stage. The maximum output voltage from this stage is given as VDDH - V_VDDH-VDD. 
I did not understnad what voltage V_VDDH refers to?

Its VDDH - V_VDDH-VDD, not that readable but its noted in the spec, https://infocenter.nordicsemi.com/topic/ps_nrf52840/power.html?cp=5_0_0_4_2#unique_562478892 , so it refers to the difference that needs to be between VDDH and VDD for it to work as intended.  

Oystein said:

3. If I understand it correctly, In NORMAL MODE powered by a 3.3V power supply, I will need a voltage level translator, like https://www.ti.com/lit/ds/symlink/tca9406.pdf?ts=1715424827946&ref_url=https%253A%252F%252Fwww.google.com%252F, if I want to interface it with a 1.8V IMU using the I2C bus. But you ewrite This is not a good idea in normal voltage mode if supply voltage is more then 1.8V. 
Please explain why this is not a good idea?

With no level shifter it would not be a good Idea if you supply the nRF52840 with more then 1.8V in normal voltage mode was what I meant, since the nRF52840 supports operating voltage down to 1.8V and that would match the I2C bus voltage. So with supplementary circuitry like a level shifter it is ok supply with a higher voltage. Sorry for the ambiguity. 


Regards,
Jonathan