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DRV134 - question about phase

Not sure if this is the correct group to post this. If anyone can suggest a more appropriate place, please do so.

I've just built a stereo balanced audio line driver using a pair of Texas/Burr-Brown DRV134s. I've successfully built these with AD SSM2142s in the past, but the AD devices are becoming hard to source and the DRV134 is reputed to be better, so I used them this time.

The problem is that the V+ and V- outputs (on pins 1 and 8) are in phase. This doesn't help when you're driving a differential input - the result is silence, of course! I've wired the DRV134s up in accordance with the data sheet, including the 10uF NP caps between signal and sense pins. The only minor difference from typical application is that the power supply is +/-12V rather than +/-15V.

Does anyone know of any condition under which the DRV134 outputs would be in phase? Or have I simply misunderstood what this device is supposed to do?

Reply to
Clive Backham
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If you have wired up the DRV134 as shown in figure 2 of:

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I see no way the two outputs can be in phase. Have you looked at the two outputs on a scope?

Reply to
John Popelish

Thanks for your response.

Yes, I followed the B-B data sheet, and have checked the outputs on a scope. They are definitely in phase. I've checked the PCB layout and am fairly sure it's correct. But of course I could have made an error that I haven't spotted. It's like proof reading your own words - it's easy to miss a mistake.

So I guess what I'm asking is whether there is any way of wiring up the DRV134 that delivers in-phase outputs. If I knew that, I could then revisit the PCB to check whether that has happened.

Reply to
Clive Backham

If the chip is totally unpowered, the input signal leaks to both outputs through the various network resistors. Is it possible there is a short circuit between the two outputs (measure with a meter)?

I can't quite figure out what would happen if you reversed the two sense feedback paths, but I don't think it produces your symptom. This chip is pretty simple. An inverter and two subtractors that take the difference of the input and its inverse, with the subtraction reversed for one of the outputs. I see no obvious way you could reverse the sense of one of the subtractions without altering the other.

Is the common signal on both outputs a good copy of the input, or it a very different magnitude? Is there any load across the two outputs during your testing?

Reply to
John Popelish

John, I've done some more testing and owe you an apology for wasting your time. The signals ARE out of phase, as should be expected. I am using a software 'scope, and was also using the PC as a signal generator. It seems that the 'scope must have been picking up the generated signal instead of the output of the line driver. Once I dragged in a second PC to act as signal generator, I discovered that the output is as it should be. Sorry once again, and thanks for taking the time to try and help.

Reply to
Clive Backham

Glad you solved your riddle.

Reply to
John Popelish

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