TXS0104E: TXS0104E to MAX7317 SPI 25MHz

Anthony Campos

Part Number: TXS0104E
Other Parts Discussed in Thread: TXU0104

Tool/software:

We are currently designing a board that interfaces a TXS0104E to two MAX7317's. The Input to the TXS0104E is SPI lines coming from an I/O connector that's connected through some cabling to the Zedboard PMOD connector (only sclk, cs, and mosi). Signal Integrity of TXS0104E output is not what I expect. I want to confirm if 25MHz is indeed within the bounds of this part. I even reduced it to 20MHz and got similar results. The Zedboard is outputting the SPI lines in push-pull configuration, and IO standard set to LVCMOS33, default slew rate and drive strengths.

This is what the SPI transactions look going into the TXS0104E. Again not the greatest quality, but the output is definitely not the same.

Output of TXS0104E (TXS Input supply sourced from Zedboard PMOD 3.3V)

Output of TXS0104E (TXS Input supply sourced from bench supply 2.8V)

2 months ago

0 Clemens Ladisch 2 months ago

Guru 316440 points

The TXS supports up to 12 MHz under optimal circumstances, and cables are not optimal. Use the TXU0104 instead.

0 Anthony Campos 2 months ago in reply to Clemens Ladisch

Prodigy 20 points

12MHz? In determining supported rates we referred these two tables in the datasheet. In 6.9, for push-pull max is 24Mbps, and pulse duration is 41ns. We are running 20MHz right now, so that meets that requirement. On the input transition rise rate, it says 10ns/V max, which is sort of counter-intuitive but our rise time on the SPI signals is much less.

0 Clemens Ladisch 2 months ago in reply to Anthony Campos

Guru 316440 points

24 Mbps = 12 MHz

(One clock cycle has two pulses, high and low. At 20 MHz, one such pulse has a length of 25 ns.)

0 Anthony Campos 2 months ago in reply to Clemens Ladisch

Prodigy 20 points

Exactly, thanks for clarifying. So we should be able to "safely" run at 10MHz.

+1 Anthony Campos 2 months ago in reply to Clemens Ladisch

Prodigy 20 points

I see that the TXU0104 might actually be better for our requirement. Ultimately in our target hardware we would be shifting from 1.8V to 3.3V. This would give us 50MHz operation, plenty of margin to communicate with the MAX7317.

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TXS0104E: TXS0104E to MAX7317 SPI 25MHz