TXS0102: TXS0102, TXB0102 Vil, Vol exactly value

Tim Chu

Part Number: TXS0102
Other Parts Discussed in Thread: TXB0102, SN74AVC2T245, SN74AXC2T245, SN74AXC2T45, SN74AXC4T245, 2N7001T, SN74AXC1T45

Hi there,

After reading the comments and specs of TXS0102, sitll have something need to be clarified.

First is about the relationship between Vol & Vil. As I know from the spec, the Vol equals to Vil + Vdrop of pass-gate transistor, and with the following figure in document "Factors Affecting VOL for TXS and LSF Auto-bidirectional Translation Devices".

In the figure, is the current the one crossing the pass-gate transistor? how can I estimate the possible current value might be in my design? Is the figure the same if it comes to TXS0102?

Can you also indicate what is typical value of this current value? (in normal case)

Also want to check about TXB0102, in the datasheet it only mention Vil value and partial Vol value as below, most of Vol information is missing. Can you help provide the value?

Furthermore, at here the test condition is at IOL = 20uA case, can we take it as a normal condition, for both TXS & TXB series? Again, how's it be considered and calcuated?

I'm asking this because now we encounter an part selecting issue with following design flow:

We're evaluating the potential risks if we use TXS0102 or TXB0102 in the design.

Thanks a lot in advance!

Tim

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 298860 points

The current through the pass transistor is determined by any pull-up resistors. The TXS's internal pull-up resistors are 10 kΩ.

The TXS and TXB have entirely different architectures. See the application notes A Guide to Voltage Translation With TXB-Type Translators, A Guide to Voltage Translation With TXS-Type Translators, Biasing Requirements for TXS, TXB, and LSF Auto-Bidirectional Translators, and Factors Affecting VOL for TXS and LSF Auto-bidirectional Translation Devices.

For an UART, you do not need an auto-bidirectional level shifter. The optimal level shifter for your application is the SN74AXC2T245 or SN74AVC2T245.

0 Tim Chu over 4 years ago

Prodigy 40 points

Hi Climens,

Thanks for reply.

Since based on current design we have already use TXS in layout, current we want to keep it if possible. that's why we're still considering TXS & TXB.

Could you provide more information about calculating the current, I only know it's related to pull-up, but don't know the actual formula for this.

Thanks for the help.

Tim

0 Clemens Ladisch over 4 years ago in reply to Tim Chu

Guru 298860 points

3.3 V / 10 kΩ = 0.33 mA

0 Tim Chu over 4 years ago in reply to Clemens Ladisch

Prodigy 40 points

Hi Clemens,

Back to SN74AXC2T245, I looked into the spec for this product and found it seems to have only one package?

Is the SN74AXC2T45 the same thing? Since I didn't found too much differences between these two, can you help confirm that?

Thank you,

Tim

0 Clemens Ladisch over 4 years ago in reply to Tim Chu

Guru 298860 points

The 2T45 has two channels in the same direction. But for the UART TX/RX signals, you need two separate direction signals, i.e., the 2T245.

0 Tim Chu over 4 years ago

Prodigy 40 points

I see, thanks for pointing this out.

But according to SN74AXC2T245's datasheet, it only shows it has UQFN package, which is quite unconfortable for debugging because these pins are under IC.

Can you help confirm that it still only has one package? Since the last update of the datasheet is at May, 2020.

If so, is there any other alternatives that have package like DCT / DCU?

Thanks.

0 Clemens Ladisch over 4 years ago in reply to Tim Chu

Guru 298860 points

The four-channel SN74AXC4T245 would be available in the TSSOP package. Alternatively, use two 2N7001T (SC70) or SN74AXC1T45 (SOT-23/SC70/SOT-5X3).

0 Tim Chu over 4 years ago

Prodigy 40 points

One more question about using TXB, what's the disadvantages of using TXB on UART application?

So far I know it might have lower driving strength, how can I evaluate the driving strength in my design?

0 Clemens Ladisch over 4 years ago in reply to Tim Chu

Guru 298860 points

The TXB drive strength of 20 µA makes it suitable only for short traces on a single board, without any pull-up/-down resistors. If that is the case, then it will work.

(For high-impedance CMOS inputs, looking at V_IL/V_IH/V_OL/V_OH values does not make sense.)

0 Tim Chu over 4 years ago

Prodigy 40 points

Hi,

Currently I'm looking 2nd source for SN74AXC4T245, SN74AXC1T45, I found you have another "AVC" family that looks similar, the pin is compatible, just wanna know if it is replaceable for AXC family, on UART use case?

Thanks,

Tim

0 Dylan Hubbard over 4 years ago in reply to Tim Chu

TI__Mastermind 45145 points

Hey Tim,

Yes, the AVC family is a good second source alternative for the AXC family. They are pin compatible and share similar channel count options.

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TXS0102: TXS0102, TXB0102 Vil, Vol exactly value