SN74AHC1G32: SN74AHC1G32

Hale Tan

Part Number: SN74AHC1G32

Hi Team!

My customer wonder why the results of their test result of voltage is not stable, whether this will affect normal operation. And can we share the results of our tests result？

Of course, many factors can influence the voltage, I will ask their test condition and circuit design information. Can we provide answers mainly to the last two questions？

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 265620 points

An overshoot of 0.5 V is not yet dangerous.

AHC has weak output drivers that usually do not generate overshoots. TI's measurement is shown in figure 5 of the datasheet; it was done with proper decoupling capacitors and probably with a ground spring on the oscilloscope probe.

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 2970 points

Hi, Clemens!

The below is customer testing NC7ST32P5X result. Its output is stable and at the same condition, SN74AHC1G32 output is unstable.

This makes me wonder if the two systems formed by the external circuit are either over-damped or under-damped, respectively. Did you have some advice or comments to solve the problem?

0 Hale Tan over 1 year ago in reply to Hale Tan

TI__Intellectual 2970 points

This is the schematic they provided.

0 Clemens Ladisch over 1 year ago in reply to Hale Tan

Guru 265620 points

The MC74VHC1G32 and SN74AHC1G32 have the same drive strength. The NC7ST32 is a different device (that is guaranteed to work only with a 5 V supply) and has a much lower drive strength.

The schematic does not show what is connected to the TX_DIS signal line.

It might be possible that the unterminated trace is underdamped. But the AHC output impedance at 3.3 V is about 55 Ω, which is near the typcial trace impedance. You can try adding a small series resistor. But I suspect that the ringing might be a measurement artifact from the loop formed by the oscilloscope's ground clip; a ground spring would reduce that.

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 2970 points

ok. I will ask customer to test with ground spring on the oscilloscope probe. And how much ohm should be a small series resistor?

0 Clemens Ladisch over 1 year ago in reply to Hale Tan

Guru 265620 points

The total impedance (output impedance plus source termination resistance) should be equal to the characteristic impedance of the trace.

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 2970 points

Hi Clemens!

Thanks for your support. I will talk with customer about how to improve test results.

And I think that using an oscilloscope to measure actual test results will be more convincing. So can we provide actual test results by using an oscilloscope?

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 2970 points

Hi Clemens!

Please keep me informed if there is any progress

0 Clemens Ladisch over 1 year ago in reply to Hale Tan

Guru 265620 points

I am not a TI employee.

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Intellectual 2970 points

I'm so sorry!!!

But thank you for your answers!!!

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SN74AHC1G32: SN74AHC1G32