TXS0108E: IO level compatibility

Vidhya J

Intellectual 345 points

Part Number: TXS0108E
Other Parts Discussed in Thread: LSF0102, SN74LVC244A

Tool/software:

Hi Team,

There is GPIO, SPI and UART Interface between IC1 and CPU.

Following are the IC1 IO Levels (Type I and II).

VOHmin=3V, VOHmax=3.3V

VOL max=0.4V

VIHmin=3V , VIHmax=3.3V

VIL max=0.6V

It is interfaced to CPU with IO levels as follows.

VOHmin= 2.64V, VOHmax=3.3V

VOL max=0.66V

VIHmin=2.31V, VIHmax=3.3V

VIL max=0.99V

CPU to IC1 interface:

VOH>VIH is not met

VOL<VIL is not met

IC1 to CPU Interface:

VOH>VIH is met

VOL<VIL is met

Both devices operate at 3.3V supply.

TXS0108EPWR level translator if used between both devices, still specs fail.

VOHmin= 2.211V

VIHmin=2.9V

VILmax=0.15V

VOLmax=0.55V

what about LSF0102?

Kindly suggest.

Thanks,

Vidhya

2 months ago

0 Clemens Ladisch 2 months ago

Guru 283290 points

The TXS is a passive switch, not a buffer, so it cannot improve signal levels. (And it does not really have thresholds; see [FAQ] Why are the TXS01xx VIH/VIL specifications so stringent?)

If you do not need level shifting, you can use any buffer, e.g., SN74LVC244A.

But note that all VOx values are specified for a certain test current; with smaller currents, the VOx values are higher. (See [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?) It is likely that you do not need any buffer and can connect IC1 and the CPU directly.

0 Jack Guan 2 months ago

TI__Mastermind 27101 points

Hi Vidhya,

I agree with Clemens' comments here. To add, the LSF0102 will also not spec logic thresholds due to the device being switch-based solution. Please let us know if you have any further questions.

Voltage Translation Application Quick Reference

Regards,

Jack

0 Vidhya J 2 months ago in reply to Clemens Ladisch

Intellectual 345 points

Hi Clemens,

Even if the suggested buffer is used, there will still be violation to meet VOH>VIH and VOL<VIL condition.

Do you still suggest to directly connect IC1 to CPU?

Kindly suggest.

Thanks,

Vidhya

0 Vidhya J 2 months ago in reply to Jack Guan

Intellectual 345 points

Hello Jack,

Do you also suggest to directly connect IC1 and CPU?

Kindly suggest.

Thanks,

Vidhya

0 Clemens Ladisch 2 months ago in reply to Vidhya J

Guru 283290 points

No; it is likely that there is no violation becise the VOx values are specified for current that is much higher than the actual current.

To compute the actual voltages, you need to know the load current (i.e., the input leakage current of the other devices, and any pull-up/-down resistors) and read the FAQ I've linked to above.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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TXS0108E: IO level compatibility