TCA9509: I have a question about the external pull-up on the A side.

The datasheet says:

For the TCA9509 to function correctly, all devices on the A-side must be able to pull the A-side below the voltage input low contention level (V_ILC). This means that the V_OL of any device on the A-side must be below V_ILC min.

The V_OL can be adjusted by changing the I_OLthrough the device which is set by the pull-up resistance value. The pull-up resistance on the A-side must be carefully selected to ensure that the logic levels will be transferred correctly to the B-side.

So this depends on the drive strength of the other devices on the A side.

Also note that V_CCA must be lower than V_CCB. If you can remove the pull-ups on the B side, the TCA9800 would be a better choice.

Thanks for your response.

The drive strength of the other device on the A side is 4 mA.
please tell me if this has any effect as the operation of the IC.

The TCA9800 will also be considered.

Best regards.

What matters is the V_OL at 4 mA.

Along with what Clemens has said, if you are just looking for a buffer the TCA9517A, or TCA9617B can also be used. These devices, including the TCA980x series have restrictions on what devices can be connected to what side.

Specifically the TCA9517A has a higher output offset voltage so it allows you to use a device with a higher VOL. As long as the VOL of your device is lower than the VILC of the TCA9517A which is 0.45V it should work. Just keep in mind that the maximum voltage offset of this device is 0.6V on the B side of the device. So that means that any device on the B side has to be able to accept a VOL of 0.6V.

The TCA9517A has no restriction on the supply voltages so you can orient this device with either supply being on B or A.

Best,

Chris

Thank you for your response.
This solved my problem, but please tell me one more thing.
My current circuit is VCCA=VCCB(+3.3V). Please let me know how this affects the operation of the IC.

Best regards.

Just a note I had to edit my original reply above to change "As long as the VOL of your device is higher than the VILC " to "As long as the VOL of your device is lower than the VILC ". Now it is correct.

For the TCA9517A there are no restrictions on the supply voltages* so it doesn't matter if VCCA=VCCB. This will not change the functionality of your device.

*The datasheet does recommend that VCCA<=VCCB. However, this device was tested with VCCA>VCCB and it was still functional it just didn't meet the exact propagation delay spec in the datasheet. If you would like to read more you can reference this E2E post.

If any of these responses answered your question please hit the green button under the response. This closes out the thread and shows other users what the right answer to your question was.

Best,

Chris

Hey Chris-san,
Thank you for your response.

If the device is TCA9509 and the power supply is VCCA = VCCB, what is the effect on the device?

Best regards.
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I can't make any guarantees as to how the device would function in this state. Since this is operating outside of the datasheet parameters and it was never tested for this operation.

My guess however is that it would still work but you would see some timing issues due to added prop delays. The device might not be able to operate at the speed you want it to. The safe bet here is to use the TCA9517A which was designed to have both supplies equal each other.

Best,

Chris