2024-10-07 12:56 AM
Hi,
the maximum I2C input low voltage is stated as 0,35V for the STUSB4761.
Is this a typo?
Because in NXP I2C spec this level is stated as 0,3VDD
We are using a PCA9516 I2C Multiplexer (0,5V Low) and observe massive connection failures with STUSB4761.
Regards
Michael
2024-10-07 05:05 AM
Nothing would indicate it's a typo. 0.35 V is less than 0.3*VDD so is compatible with the NXP I2C spec.
> We are using a PCA9516 I2C Multiplexer (0,5V Low) and observe massive connection failures with STUSB4761.
Likely will need to debug this further. Look at the SDA/SCL signals on the line to see if they are valid or not. Ensure you have appropriate external pullups present.
2024-10-07 07:17 AM
0.35 V is less than 0.3*VDD
That is the problem.
I2C Spec allows up to 1.5V for a valid Low_In (0.3*Vdd @ 5V )
STUSB fails if I2C low level is above 0.4V. (No ACK)
Furthermore it will detect a logical high above 1.2V.
1.2V is less than 1.5V.
Please explain how this could be compatible to NXP I2C spec.
I replaced the PCA9515 against a Nfet Switch / Level Shifter on SDA and the failure is gone.
2024-10-07 07:41 AM
> That is the problem.
You're right, I misread.
To the original question, it's unlikely to be a typo, especially as you've confirmed the issue. It appears this is done to prevent latch-up.
2024-10-15 12:39 AM
>this is done to prevent latch-up.
Where is this explanation from?
Can't find this in NXP I2C Spec
STUSB4761 Datasheet:
2.3.4 I²C interface
An I2C interface can be used for non-volatile-memory customization.
This interface ist not electrical compliant to I2C Spec. and incompatible with common I2C Multiplexer.
A very annoying fact for a I2C component without address pins.
Thank you for comfirmation.