SN74AXC4T774-Q1: Output distorted while feeding in a 100MHz Signal

Darshan Moodgal

Part Number: SN74AXC4T774-Q1
Other Parts Discussed in Thread: TXV0106-Q1, SN74AVC4T774-Q1

Tool/software:

Though the datasheet claims speed of 310Mbps while converting 1.8V to 3.3 V signal, the measured data comes no where close to this. What could be happening here?

Schematics:

IN:

Out: Measured with an active probe terminated with 50 Ohms

10 months ago

0 Michael Ikwuyum 10 months ago

TI__Guru 50496 points

Hi Darshan,

I suspect the total lumped capacitance is above 15 pF similar to table 6-1 of datasheet.

This can be verified by disconnecting all loads and measuring as close to the device pin as possible with similar probe used for IN, thanks.

Best Regards,

Michael.

0 Darshan Moodgal 10 months ago in reply to Michael Ikwuyum

Prodigy 85 points

Not much improvement:

Modified Schematics:

NEW: Capture at pin 12, active probe capacitance is 0.6pF

0 Darshan Moodgal 10 months ago in reply to Michael Ikwuyum

Prodigy 85 points

Also, the conversion is from 1.8V to 1.1V - not sure if that's contributing to it and all 4 channels are being used.

0 Michael Ikwuyum 10 months ago in reply to Darshan Moodgal

TI__Guru 50496 points

Hi Darshan,

Yes, it is contributing as I see significant improvement i.e. device is translating and high level is reaching 1.1 V as opposed to previous waveform.

Data sheet shows tpd of about 12 ns for 1.8 V to 1.1 V, roughly indicating 83 Mbps as 42 MHz (i.e. 1/tpd). You may confirm by observing waveform for 42 MHz per the 1.1 V and increasing back to 100 MHz for VCCB up to 3.3 V showing the contribution as higher voltages support higher speeds compared to smaller voltages.

You may also see SN74AVC4T774-Q1 tpd indicating a rough estimate for 83 MHz (note that using tpd is a low estimate as reference), or TXV0106-Q1, thanks.

Best Regards,

Michael.

0 Darshan Moodgal 10 months ago in reply to Michael Ikwuyum

Prodigy 85 points

Hi Michael,

Thanks for explanation, appreciate it!

Is there an alternate device(preferably pin compatible) that supports 100Mhz?

Thanks,

Darshan

0 Michael Ikwuyum 10 months ago in reply to Darshan Moodgal

TI__Guru 50496 points

Hi Darshan,

The SN74AVC4T774-Q1 recommendation would be the only exact P2P alternate recommendation.

I would recommend AVC as the best solution for the translation. Please further note that data rates can be characterized by their VOH/VOL levels. Hence, no level shifter concerns if the logic levels are met, thanks.

Best Regards,

Michael.

0 Darshan Moodgal 10 months ago in reply to Michael Ikwuyum

Prodigy 85 points

Thanks Michael for your prompt response, we tested with SN74AVC4T774-Q1 and the results did improve significantly, we shall proceed with it!

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SN74AXC4T774-Q1: Output distorted while feeding in a 100MHz Signal