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DRV595: Differential Input

Sukwon Yoo
Prodigy 70 points
Part Number: DRV595

Hello-

I am using DRV595 to drive TEC. In the datasheet, it says "To use the DRV595 with a single-ended source, use a voltage divider to bias IN- to 3.0V, and apply the single-ended signal to IN+." Is there a reason why it needs to be specifically biased at 3V? Will it be okay to bias IN- to 1.25V and apply the single-ended signal to IN+?

Thanks,

  • 0
    TI__Mastermind 24835 points
    Hi Sukwon,
    Yes, the IN- needs to be biased at 3V in the application. The internal bias voltage on the input pins are 3V, so it's actually something like a reference volage. If you try to connect the INN and INP to GND through 1uF capacitors, you could find that the DC voltage on INN and INP pins is around 3V. So please follow the datasheet description.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 20 points
    Hi Shawn, thanks for the response (I'm working with Sukwon). I'm still puzzled, though, as the data sheet says the common mode input range is from 0.5 to 4.5V, and there are several plots showing behavior over that range and more. I understand that the amplifier inputs may be biased at 3V, so if we're at nominally 1.25V then we'd have an input bias current of 30uA to deal with (60kOhms at our gain of 20dB), but we're OK with that. Is there some reason the '595 can not be operated with a wider common mode input? Thanks.
  • 0 in reply to Fred Huettig
    TI__Mastermind 24835 points
    Hi Fred,
    Thanks for your explanation. I agree with you that there is a bias current on the input if 1.25V bias current is used, and this current(uA level) won't damage the device. But you need to know that the input amplitude range is maximized when 3V bias voltage is used. So when 1.25V bias voltage is used, the input amplitude is also limited. And most of our validation data is actually based on 3V DC bias, becasue this is the typical application case.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 20 points

    Hi Shawn, excellent point about the reduced input range when biasing away from mid-scale, thank you.  In our case even with the lowest gain (10x) we should have plenty of margin as we only need +/-4V output, so with IN- at 1.25V then IN+ only needs to swing between 0.85 and 1.65.  Based on your update I think we're OK.  It wouldn't be terrible to add some offset & gain to work with a 3V midpoint, but this circuit is replicated 4 times per board so if there's no need for extra parts we'd rather not add them.  Thanks again.  -Fred

  • 0 in reply to Fred Huettig
    TI__Mastermind 24835 points
    Hi Fred,
    Thanks for the explanation that helps me understand the application better. Looks like the input range is not an issue for this application. As 1.25V bias is not a typical case, we actually don't have much data for this configuration. So in theory there is no obvious issue in it, but we are not sure about the reliability/stability for it.
    Best regards,
    Shawn Zheng