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DRV134: Line drivers 6db gain is decreasing when two devices outputs are shorted

Part Number: DRV134
Other Parts Discussed in Thread: INA217, TINA-TI


I am using DRV134 device as line driver in my audio bus application. The bus consists of two DRV134 devices with the outputs shorted together i.e +V0 of one device is shorted with +V0 of other device and like wise -V0. This shorting is by using a 200meters cable. Inputs of the DRV134 devices will be different i.e from different mics(INA217 is ther between mic and line driver input). My problem is the 6db gain mentioned in the datasheet for DRV134 is dropping down to 3 to 4db when the two line drivers outputs are shorted. Should I not short the outputs of the line drivers? If I shouldn't short the line drivers outputs how can form the audio bus?

  • Hi Venkat,

    the DRV134 is not intended to form an audio bus by connecting the outputs of several DRV134 together. This can result in huge load currents. And you will have the more damping the more DRV134 are connected together.

  • Hai,

    Thanks for the reply.

    Please suggest me a line driver device which can be used in my apllication.

    My application is a full duplex communication system. It is a very urgent requirement
  • Hi Venkat,

    As mentioned in your other post, directly shorting two DRV134s together probably won't work well. The reduction in gain you're seeing is due to the loading effect of the first DRV on the second.

    Adding some additional resistance (say 50 ohms) to the outputs of the DRV134s after the DRV134's sense connection as shown below should help with this application. You'll still see some attenuation of the signal present on the bus - the test circuit below showed around 6dB of attenuation - but the added resistance should help isolate the two DRVs from each other. You'd essentially be turning the bus into a summing circuit, which you could then buffer at each end to drive your speaker or headphone output. If a gain of 6dB overall is required, your line receiver or op amp could be configured for additional gain to compensate for the loss. 

    Another option, if half-duplex operation would work, would be to use an analog switch (A CD4066, for instance) to connect the DRV134 to the bus only when transmission is required.

    For reference, I'm including the TINA-TI SPICE file here if you would like to try this circuit out in simulation.

  • Venkat

    We haven't heard back from you so we assume this resolved your issue. If not post a reply below, or create a new thread if this one has timed-out.