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DRV135: Gain problem

Francis295
Prodigy 60 points
Part Number: DRV135


I am currently using DRV135UA from TI in my design. I am using it as single ended to differential conversion circuit. Power supply for the IC is +15V,-15V with 1uF capacitor on both rails. VO+ is connected to -SENSE via 10uF cap and VO- to -SENSE via 10uF cap. My input voltage range w.r.t GND is -5V to 5V. So as per datasheet i should get 10V for 5V input and -10V for -5V input, across VO+ and VO-. But my observed readings are given below.
Input Output
5 23.050
-5 -23.040
then i shorted the both 10uF caps with 0 ohms resistors. then i am getting this
Input Output
5 10.850
-5 -10.830
then i tried putting a load of 1.105K ohms resistor between VO+ and VO-, voltage reduced to
Input Output
5 10.340
-5 -10.320
Again i increased load to 660 Ohms then voltage reading again reduced to
Input Output
5 10.060
-5 -10.040
So in order to get a gain of exact 6dB what should i do?? as per datasheet there is no minimum load requirement to get the specified gain
  • 0
    TI__Genius 14390 points
    Hi Francis,

    I see the same behavior in the TINA model for the DRV135. With the DC blocking capacitors in the sense lines, I get a DC gain of ~13.3dB (23V out with 5V in). With no DC blocking capacitors, this drops to ~6.73dB (10.85V out at 5V in).

    Since the datasheet specification of 6dB gain is a typical specification into a 600 ohm load, it may move somewhat due to lot-to-lot variation and load impedance.

    If your application requires a precise 6dB/2x gain at DC, you may see better DC performance by building a single-ended to differential converter using two precision op amps - one as a buffer, the other as an inverter.
  • 0 in reply to Alex Davis
    Prodigy 60 points
    So without putting a load is there a way to get the gain of 6dB??
  • 0 in reply to Francis295
    TI__Genius 14390 points
    Francis,
    Using the DRV135, you could put an attenuator on your input signal to bring the overall gain down to 6dB. Another option, as I mentioned in my previous post would be to build a single-ended to differential converter from a dual op amp, which would give you much more flexibility in configuring your gain.