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P82B96: I2C access to EEPROM

Taku Murayama
Intellectual 1820 points
Part Number: P82B96
Other Parts Discussed in Thread: P82B715, TCA9803, TCA9517

Can P82B96 or P82B715 access EEPROM as I2C? Do you have any other reccomendation?

  • 0
    Guru 307600 points

    Both devices can be used to extend I²C buses. There is nothing special about EEPROMs.

    What is the actual problem you're trying to solve? In many cases, an I²C buffer like the TCA9803 might be more appropriate.

  • 0
    TI__Guru 65990 points

    As Clemen's has pointed out, the P82B96 devices are used to drive high capacitive loads from long cables. It simply mirrors the I2C bus driver, if an EEPROM sends information then it should also pass through the P82B96 or P82B715 if they can drive the bus low enough/strong enough to send the signal back to the opposite side.

    -Bobby

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1820 points

    Dose TCA9803 support 5m harness？

  • 0 in reply to Taku Murayama
    Guru 307600 points

    The I²C specification specifies a limit of 400 pF for the entire bus to ensure that the signals work at all speeds.

    Cables can have capacitances between about 65 pF/m and 115 pF/m. So this might or might not work at full speed, but you can always reduce the speed.

  • 0 in reply to Taku Murayama
    TI__Guru 65990 points

    As Clemen's pointed out, cable cap per length can vary. For CAT5 cables they generally have around 50pF/m, at 5m this gives us roughly 250pF. You also need to be careful about inductive loading from cabling, this can cause undershoots or overshoots which could cause damage to devices connected directly to it. Placing clamping diodes can be one way to help attenuate undershoots, you may also want to consider using series resistors to lower the di/dt when driving low. TCA9803 could potentially work, TCA9517 could be another option. For either one (they are pin to pin) I recommend placing the A side of the devices on the cable end since A side has larger noise margin (30% of VCCA) and it makes it easier to pass a low from A to B side. 

    -Bobby