P82B96: Datasheet questions

Hello Itoh-san,

I'd love to help out.

Kazuki Itoh said:

1.When Low is input to Txy/Rxy, the output low voltage should be 0.88V, which is higher than Txy buffer high threshould 0.7V. But this is ok because Txy buffer is open-collector output, right?

I believe you are understanding correctly. When this device receives a low signal on Rxy(/Txy), it pulls Sxy to a buffered low. This buffered low is deliberately higher-voltage than what would be required to cause the device to pull low on Txy. If this did not exist, the device would not be able to tell when it should be releasing the bus since it would always see its own low signal, causing it to "latch" improperly in a feedback loop.

I2C lines are driven by open-collector only. This prevents the possibility of contention on the bus. You can think of it this way: a device is either pulling down or not pulling down...it can't "transmit a logic high." This is why it is perfectly acceptable to have Txy connected to Rxy, even when Txy is not pulling low.

Kazuki Itoh said:

2. How can I calculate the Txy buffer low output?

The Txy output drives an I2C low on the bus, so the minimum output low can be treated as GND. Section 9.3.2 of the datasheet indicates that this device has large pull-down capability compared to standard I2C devices.

Kazuki Itoh said:

3. Does TI have any infromation for VOL when current is other than 0.2mA or 3mA? How can I calculate it for 10mA or 15mA?

Do we have formula to calculate that out?

Note that the maximum recommended operating condition for the Sxy output is 3 mA max. The performance of this device over 3 mA is not guaranteed.

You should consider increasing the size of your main enclosure pull-up resistors if you are expecting current sinking at levels such as 10 mA and 15 mA.

I hope this helps!

Best,

Danny