SN74AVC1T45: A output abnormal when there is a cap on B input

Hollis Liu

Part Number: SN74AVC1T45
Other Parts Discussed in Thread: SN74AXC1T45

Hi team,

My customer is using our SN74AVC1T45DRLR as a logic Level Translator. The direction is from B to A. And the issue is the A output is abnormal when there is a cap(C157) on B input. When they remove the C157, the A output is normal 1.8V. Do you have any comments here? It seems the C157 has bad effect here. But i don't konw why.

The abnormal output is as below.

The normal output is as below,

over 6 years ago

0 ShreyasRao over 6 years ago

TI__Guru 62440 points

Hi Hollis,

The 1nF cap is causing slow rising edge inputs and hence the outputs will have oscillations due to it.
Please refer to the white paper on this which talks about this effect along with scopeshots:
www.ti.com/.../slla364a.pdf

The transition rate in the ROC is violated (5ns/V). I would recommend to not have slow rising inputs ( remove the cap).
I would also recommend using the SN74AXC1T45 which we released about a year back which also have 10ns/V input transition rate and eliminates many signal integrity issues.
www.ti.com/.../scea058a.pdf

0 ShreyasRao over 6 years ago in reply to ShreyasRao

TI__Guru 62440 points

Also, where is the TX line going? Do you have another translator for it?

You could consider using the 2 SN74AXC1T45 like the configuration shown in the app note page 5 below:
www.ti.com/.../scea065.pdf

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SN74AVC1T45: A output abnormal when there is a cap on B input