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can DRV135 and INA134 be used in a multi drop configuration?

Pawandeep Singh
Prodigy 105 points
Other Parts Discussed in Thread: INA134, DRV135

Hi,

I have an audio system where we are using a DRV135 and upto thirteen INA134 receivers over a twisted pair unshielded cable. the bus length is about 400meters with a receiver placed every 30 odd meters.  Is this a suitable topology for DRV135 to driver?

My logic is the input impedance of INA device is 50k-ohm while the DRV can swing upto 85ma into a line impedance down to 600ohm. So effectively there is sufficient head room.

We are having  a bit of problem, with amplification level falling through out the bus in field. the problem was never faced in lab.

Any one with working knowledge of these devices who can help?

  • 0
    TI__Guru* 95145 points
    Hi Pawandeep,

    Is there any important differences between the field setup and the lab setup? You were testing the 400m bus and multiple receivers at the lab?
    Is the signal attenuating closer to the end of the bus?

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0
    Prodigy 105 points

    The signal is attenuating through out the line. As if the drv is saturated. I request a validation that is the multidrop architecture ok?

  • 0 in reply to Ivan Salazar
    Prodigy 105 points

    Hi Ivan,

    Thanks for responding. We are using the following configuration in field.

    The line has several joints and couplers. Every 25 meters,

    the line is put through a coupler with a 2 meter length, ending in a terminal board. From terminal board two cables leave- one for the bus down the line and one to the local amplifier unit.

    Two DRVs are placed at either end, with a DPDT relay. One of the sources having the DRV takes a role as master and connects to the line, the other end's DRV is disconnected using that sides relay through an interlock. So there is never a chance that both DRVs shall be simultaneously on the line (will this matter, if they do?).

    The shields continuity is maintained through out the 400 meter bus. and connected to source grounds through a 50V Ceramic capacitor at each end. Similarly the shield is connected to each amplifier's GND also using a 50 V capacitor. We are using isolated SMPS at both ends and there is a separate wire that runs to connect the two grounds, to safeguard against any GPD between the two ends. We are not earthing the shield as significant potenital difference can exist between the two end's Metal casing, which is earthed. (in way a REFERENCE EARTH POTENTIAL DIFFERENCE exists.) 

    Of course, the test set up in lab does not have as many joints or a GPD between the two ends, but would that matter. 

  • 0 in reply to Pawandeep Singh
    Genius 3295 points
    Hi Pawandeep,

    Would you mind posting a schematic?

    Is it possible for the inputs to be reversed?

    Mike T.