TXB0108 Interface to Xilinx Not Working

Ron Mancuso

Other Parts Discussed in Thread: TXB0108

Hello,

I have used three TXB0108 in my design as shown below. This is to interface a Spartan 6 @ 2.5V to another Spartan 6 @ 3.3V. The results have been unexpected to say the least.There are no pullups or pulldowns. This is just straight logic as shown in the datasheet and application note. The only functional bit appears to be the clock, but even that looks ugly. The chip select, for example, will dip from 3.3V to 0 for a second (on the B side) and then float up to ~1.2V. Don't understand.

Any help would be appreciated.

Thanks,

Ron

over 9 years ago

0 Nirav Patel over 9 years ago

TI__Expert 6335 points

Ron,

I don't have an immediate explaination for you. A few ideas and questions:

1. The TXB family of translators only supports push-pull interfaces. Please confirm that the Spartan-6 interface is *not* open-drain.
2. The Spartan-6 interface must be able source and sink +/- 2 mA for the TXB to recognize a Logic Low and Logic High.
3. Do you have any oscilloscope waveform captures that you can share?
4. What interface (or I/O standard) are you trying to pass through the translator?

Best Regards,
Nirav

0 Ron Mancuso over 9 years ago in reply to Nirav Patel

Prodigy 30 points

Hello Nirav,

I was despairing anyone would answer - so thanks for the response.

1. Yes.

2. Default is +/- 12 mA. I've set to +/- 24 mA. No effect.

3. Yes.

Simple 5 MHz clock. 2.5V to 3.3V. If you see, the VCCB waveform does go to 3.3V, but never reaches 0.

Before trigger on a chip select. Looks right. Input is steady at 2.5V. Output is 3.3V

But when active, looks like this.

4. Simple LVCMOS 2.5 to LVCMOS 3.3. Very vanilla.

I'm kicking myself for not doing what I always did and put 200 ohm resistors in. This is frustrating.

Any ideas?

Thanks,

Ron

Logic

Logic forum

TXB0108 Interface to Xilinx Not Working