TCAL6416R: No ACK signal when VCC is 1.8V and VCCP is 3.3V

Please show an oscilloscope trace of SDA/SCL with the failing I²C transaction.

See below, address 0x20

and focused on start state

The waveforms look OK.

What voltage do you measure at the VCCI pin?

1.75 V.

On the same I2C bus I have a second part at address 0x21. See schematic:

For this part when both power rails are 1.8V it is OK.

Can it be related to the PU resistors value? On my board it is 2.2K.

Adding the VCC (1.8V) and VCCP (3.3V) power up.

The PU is OK. I have no explanation.

Does it start working after you've forced a low pulse on /RESET?

Hi Noam,

To Clemens points, I looked at the previous responses and see no issue with the implementation. The i2c waveforms, schematic, and voltage to VCCI and VCCP looks good.

Noam Weidenfeld said:

1.75 V.

On the same I2C bus I have a second part at address 0x21. See schematic:

Does communicating to the second IO expander with 0x21 work with VCCI = 1.8V and VCCP = 3.3V or are both IO expanders not working? 

Regards,

Tyler

Hi,

Resetting the part didn't help. I also kept the reset signal low during power up and still it didn't solve the problem.

So, I changed VCCP to 1.8V i.e. connected it to VDD_IO, and now I can see the part on address 0x20.

Can it be related to the way VCC and VCCP ramp up? There is nothing about it on the datasheet.

Noam

I think that I switched between VCCI (Should be 23) and VCCP (Should be 21).