P82B96: P82B96D VCC problem

Maurizio Tripodi

Part Number: P82B96

I am wondering if it is possible to use two P82B96D (one Master side and one Slave side) with two different VCC voltages: for example the Master side powered with a 12V VCC to wich the bus pull-up resistor are tied, while the Slave side is powered with a VCC of 5V. On the data sheet I did not find anything preventing or mentioning this specific configuration. Except on a paragraph related to Tx and Ty where it is explicitally stated that voltages on this pins can exceed the VCC voltage because they are not provided with the ESD diodes protection to VCC/GND. If the same happens to Rx and Ry (not mentioned in the data sheet) I believe this configuration could work.

Any feedback?

Reagards.

Maurizio

6 months ago

0 Tyler Townsend 6 months ago

TI__Mastermind 29363 points

Hi Maurizio,

This implementation should work as the recommended operating conditions state that the P82B96 can operate within the voltage range of 2V to 15V for VCC.

Regards,

Tyler

0 Maurizio Tripodi 6 months ago in reply to Tyler Townsend

Prodigy 20 points

Tank you Tyler, I agree with you but, to be sure about that ,someone (from TI or somebody who already tested this configuration) should confirm that no ESD protection diode to the VCC line is provided on both the Rx and Ry input line

Regards.

Maurizio

0 Tyler Townsend 6 months ago in reply to Maurizio Tripodi

TI__Mastermind 29363 points

Hi Maurizio,

What leakage are you concerned with? Do you plan on having the i2c lines a different voltage than VCC, and a different voltage for the transmission side?

Regards,

Tyler

0 Maurizio Tripodi 6 months ago in reply to Tyler Townsend

Prodigy 20 points

Hi Tyler,

my concern is related on the Rx Ry pins when one of the two extender is powered at 5V VCC: on paragraph 9.3.2 it is very clearly written about Tx and Ty: they are not equipped with an ESD protection diode toward VCC so for this pins my configuration will work. But if this diodes are present on the Rx Ry pins they will clamp the bus voltage to the lower VCC (5V) and in this case the configuration won't work.

+1 Clemens Ladisch 6 months ago in reply to Maurizio Tripodi

Guru 273010 points

The absolute maximum ratings allow up to 18 V on the Rx/Ry pins. This implies that there are no diodes.

0 Maurizio Tripodi 6 months ago in reply to Clemens Ladisch

Prodigy 20 points

Clements, thanks for your reply.

So you are suggesting that the absolute maximum ratings at the Rx and Ry pins being an absolute value and not relative to VCC (like VCC+0.7V) as would be if the diodes were present implies the absence of the diodes.

Yes, I reached your same conclusion even if still I do not understand why in the data sheet there is an explicit mention to Tx and Ty while there is not a single word on Rx and Ry (!).

Maurizio

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P82B96: P82B96D VCC problem