ADS4226 interface with SN74CB3T16210

Prasanthi Busineni

Other Parts Discussed in Thread: ADS4226, SN74CB3T16210, SN74AVC16T245, SN74AVC20T245, ADS4229

Hi,

I want to use ADS4226 as ADC to interface with 2.5V FPGA IO's. I am using ADS4226 as CMOS or Parallel. since ADS4226 gives 1.8V digital IO's i put SN74CB3T16210 between ADS4226 and FPGA 2.5V IO's.

I did SI analysis between ADS4226 and SN74CB3T16210 with and with out 22 ohms termination and I do not see a square wave but a sawtooth wave. but ADS4226 LVDS shows a square wave with termination. but i want to use it as CMOS or Parallel only. please suggest how i can make my SI result better.

thanks

over 11 years ago

0 KW Nam over 11 years ago

TI__Expert 8895 points

Hi,

SN74CB3T16210 is a passive switch which degrades slew rate of signal. This is why you got sawtooth wave.

The better approach is to use SN74AVC16T245 which is active data-bus transceiver. With this, you'll have a good waveform.

Thanks,

0 Prasanthi Busineni over 11 years ago in reply to KW Nam

Prodigy 180 points

Hi KW,

Thanks for the response. We see the same sawtooth wave if we connect to SN74AVC20T245. Also we see the same sawtooth wave if i connect ADS4226 to FPGA input directly.

we are using IBIS model taken from TI site.

thanks

0 Prasanthi Busineni over 11 years ago in reply to Prasanthi Busineni

Prodigy 180 points

Hi KW,

We see a better waveform(slightly square wave) if we simulate it at 40MHz, So we used ADS4229(250MBPS) model instead of ADS4226(160MBPS). but the problem is not solved.

thanks

0 KW Nam over 11 years ago in reply to Prasanthi Busineni

TI__Expert 8895 points

Hi,

Would you send us captured screen of waveform along with setup conditions such as sampling frequency and input frequency? Have you got a chance to measure the slew rate of data lines?

Thanks,

0 Prasanthi Busineni over 11 years ago in reply to KW Nam

Prodigy 180 points

Hi KW,

Attached is the file with different data the I/P frequency to ADS4226 is 80MHz. Please check the document.

thanks

6470.ADS4226 INTERFACE to SN74CB3T16210 Interface.docx

0 KW Nam over 11 years ago in reply to Prasanthi Busineni

TI__Expert 8895 points

Hi,

5-inch of trace length would give you a strong uncertainty of waveform. Would you try to shorten the trace to SN74AVC16T245 as much as you can?

Thanks,

0 Prasanthi Busineni over 11 years ago in reply to KW Nam

Prodigy 180 points

Hi KW,

If you see the last two pages of the document we removed the 5 inches trace and we simulated as what is there on the board. I will try to make the traces as short as possible.

Alternately i got an answer as below

"The signal is usually not square wave after traveling through long paths due to parasitics or unmatched impedance. Usually there is a decision circuit to transform these corrupted "square" wave back into square wave at the receiver end (FPGA in this case). The decision circuit might be just a simple inverter or as complicate as a PLL. By looking at the waveforms, probably a simple inverter will be good enough to tell "0" or "1"."

Any comments?

0 KW Nam over 11 years ago in reply to Prasanthi Busineni

TI__Expert 8895 points

Hi,

I am not very familiar with "decision circuit". If this refers to digital conversion, you may have to consider the feasibility of FPGA interface with this. We can release the related EVM schematics to you if needed.

Thanks,

0 Prasanthi Busineni over 11 years ago in reply to KW Nam

Prodigy 180 points

Hi,

Thanks for answering. please share the schematics that will be useful.

thanks

0 KW Nam over 11 years ago in reply to Prasanthi Busineni

TI__Expert 8895 points

7268.ADS42XX_58C28EVM-SCH_C.pdf

Hi,

Please find attached EVM schematic which is for ADS42xx.

Thanks,

0 Prasanthi Busineni over 11 years ago in reply to KW Nam

Prodigy 180 points

Hi KW,

Thank you for your reply

The SPI for ADS4226 is working now. I could write and read that data into the ADS4226.

Problem being the drive strength to to SEN seems to be not enough.

thanks

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ADS4226 interface with SN74CB3T16210