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# TCA9617A: VOL of B

Part Number: TCA9617A

Hi supporter

Datasheet shows VOL B side is 0.5V. Is this value related with external pull up resisters? If not, how could it keep always 0.5V?

Another question is TCA4311 is also bi-directional, why it doesn't need static voltage offset?

Regards

David

• Hi David,

Yes, external pull-up resistance values will have some effect on the VOL voltage of TCA9617A's B side, since lower resistances will require the device to sink higher currents. The relationship between VOL and IOL for the B side is shown in Figure 2 of the datasheet.

For TCA4311, there is some small offset introduced between the input low voltage and the output low voltage. You can read more about it in Section 8.1.4.1 of the datasheet. This way, the device is able to distinguish between when it is driving a low level (in order to propagate the bus state from one side to the other) and when the low level is being driven by another I2C device connected to that pin.

Please note that the TCA4311A is recommended over the TCA4311 for new designs.

Regards,
Max
• In reply to Max Robertson:

Hi Max

Thanks for quick response! Then how to calculate IOL? For example, if pull up resister is 3.3kphm, pull up voltage is 3.3V, then what is value of IOL?

Regards

David

• In reply to David Zhao:

David,

You can calculate IOL by: (Vpullup-VOL)/Rpullup

For your case, it looks like it will be [3.3V-0.53V(typical)]/3.3k = 0.84mA

Thanks,

-Bobby