TCA9535: ticf & tocf timing

Yang Wu

Expert 3370 points

Part Number: TCA9535

Tool/software:

Hi Team,

The datasheet requires ticf & tocf as below. based on VCC = 3.3V, the min ticf and tocf is ~12ns.

While the real test in my customer board is 3ns. is there any risk? if yes, how to remove this risk?

thanks a lot.

Best regards,

Yang

4 months ago

0 Clemens Ladisch 4 months ago

Guru 318050 points

These values are copied from the I²C specification.

I²C devices themselves actually have no lower limit on the rise/fall time, but when the edges are too short, this might induce ringing in long traces, and generate wrong clock pulses.

To slow down falling edges, configure the pin with a lower drive strength (I²C does not require more than 3 mA), or add a small series resistor.

0 Tyler Townsend 4 months ago

TI__Guru 50688 points

Hi Yang,

I agree with Clemens here.

Regards,

Tyler

0 Yang Wu 4 months ago in reply to Clemens Ladisch

TI__Expert 3370 points

Hi Clemens,

Thanks a lot for your reply. do you have some recommendation about the resistor value? I understand it's good to keep the current less than 3mA, right?

Best regards,

Yang

0 Clemens Ladisch 4 months ago in reply to Yang Wu

Guru 318050 points

The pull-up resistors must be sized so that the total current does not exceed 3 mA.

The series resistors should not affect the voltage (much), so they must be smaller. Try something like 22 Ω or 33 Ω.

0 Tyler Townsend 4 months ago in reply to Clemens Ladisch

TI__Guru 50688 points

Hi Yang,

There is a good application note to refer to when choosing the right pull-up resistor value:

https://www.ti.com/lit/an/slva689/slva689.pdf?ts=1720204726016&ref_url=https%253A%252F%252Fwww.google.com%252F

As Clemens already mentioned, the series resistors should not affect the voltage that much. They will have some voltage drop across it, but it should be little to not affect the VOL to much.

Regards,

Tyler

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TCA9535: ticf & tocf timing