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Signaling Line Circuit

suryakanta mohanty
Intellectual 270 points
Other Parts Discussed in Thread: THVD8000

Dear Sir,

Is there any transreceiver or Analog Front End (AFE) device  for designing  Signaling line control circuit for digital fire/smoke sensors? 

The requirement is to design a two wire Loop card which uses different voltage ranges called voltage pulse code modulation (PCM) to send 1 and 0 to sensors connected on the loop line. Devices/fire sensor  consume current responding with 1 and 0. The Loop card also provides power to devices on two wire bus and need to drive either 250 or 500 such sensors.

Pls. suggest.

  • 0
    TI__Mastermind 25705 points

    Hi,

    What's the data rate and distance of the application? You may want to check out a pre-released device THVD8000 for power line communication. This device can transmit both power and data on two wires and support up to around 256 nodes.

    Regards,

    Hao

  • 0 in reply to Hao L
    Intellectual 270 points

    Dear Hao,

    I am not talking about power line communication.

    We are interested in designing a Fire Panel Loop card  circuit for connecting smoke sensors on the line.

    The fire loop protocol is a master-slave, half-duplex and bit oriented protocol. Panel loop card is master and devices act as slaves. Loop card uses different voltage ranges called voltage pulse code modulation (PCM) to send 1 and 0. Devices consume current responding with 1 and 0. Loop card also provides power to devices on two wire bus. Devices have charging capacitor that charges during idle time or startup time. Based on charging, startup time is typically delayed to run loop bus.

    Possibly the circuit can be designed using encoders/decoders etc. 

    Attached is a short document describing the requirements.

    Pls. suggest suitable devices for the application.

    Best Regards

    SuryaControl Loop _AFE.pptx

  • 0 in reply to suryakanta mohanty
    TI__Mastermind 25705 points

    Surya,

    Thanks for your information. I will loop in other experts in TI to take a look.

    Regards,

    Hao

  • 0 in reply to Hao L
    Intellectual 270 points

    Hi Hao,

    I think the part is not suitable. I am looking for modulator which can take two voltage inputs and modulalate it .Pls. find the below the figure for the requirement. Instead of implementing the modulator using discretes, is there a modulator IC available?

    Pls. suggest.

    BR,

    Surya

      te it to gener is  is not for generate pulse code modulation signal. Pls. refer to the attached document.

    Regards

    Surya

  • 0 in reply to suryakanta mohanty
    TI__Prodigy 600 points

    Hi Surya,

    While we do not currently offer a dedicated AFE solution to this function.  We do have a few options to explore.  I'll start with a couple more common approaches and we can drill down from there if needed.

    This idea makes use of the independent half bridges in the DRVxxxx devices to drive the load of the bus lines while the load switches are used to modulate the bus voltage as well as provide the current limit.  The part numbers shown above should be viewed as a starting point.  We can provide alternate part recommendations if anything does not meet your specific specifications.

    A second idea we are exploring would be to make use of TI's Class D audio amplifiers to drive the lines in single ended mode.  The current limit would be a separate device, but you would only need a single supply and the output level can be controlled from the DAC output of an MCU or by using a PWM from the MCU to generate an analog control input to the amplifier.

    Please let us know if either of these solutions are attractive or if you would like to see something else.

    Best Regards,

    David

  • 0 in reply to David Stout
    TI__Prodigy 600 points

    Apologies,  it looks like my image was not correctly attached.

    Please see the attachment for the block diagram to go with the first solution in my previous reply.

    Regards,

    David

  • 0 in reply to David Stout
    Intellectual 270 points

    Dear David,

    Thanks for your response. I agree, we can select the devices after few more rounds of discussion.

    Meanwhile, can you pls. share the other approach.

    Basically , the circuit should be able drive 511 smoke detectors upto 4 km of loop length and should have protection for earth fault, line-line short and line-VCC short.

    Best Regards

    Suryakanta 

  • 0 in reply to suryakanta mohanty
    TI__Prodigy 600 points

    Suryakanta,

    The alternative solution to the first two would involve using one of our half bridge gate driver parts to drive two discrete FET's which then drive one of the + lines to modulate the voltage.  Basically this solution works for modulating between two levels; the higher voltage level would be Vcc of the gate driver and the lower voltage level would be Vee of the gate driver (along with the low side rail of the discrete FET half bridge).  Because the gate driver IC is ground shifted, you would also need level shifters on signals from the MCU to the control pins of the gate driver IC.

    For all three of these solutions, the load of the smoke detectors and line length would have to be considered in the different drivers specs in order to meet the required timing of the protocol you are using.

    Regards,

    David