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DRV595 application circuit

Bob McKnight
Prodigy 20 points
Other Parts Discussed in Thread: DRV595

I would like to see an application circuit for the DRV595 TEC driver IC.

After reading the datasheet, I don't understand how it is used. The datasheet states states "The typical circuit used for this application is to have two feedback loops  one for constant current, and the second to monitor the temperature, and provide adjustments to keep a constant temperature on the laser diode. An error amplifier is used to combine the two feedback loops, along with a control signal from the system. The output of the error amplifier is then fed into the DRV595.

Fundamental question: How do you sense the current for input to the constant current loop?

-Bob McKnight

  • 0
    TI__Guru**** 189399 points

    Hi, Bob,

    There is a circuit published in one of our op amp data sheets that shows the control loop for driving a TEC element, but unfortunately, I can't find it at the moment.

    You basically need a current sensing resistor and something like an INA to feed that back to your control loop.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 40 points
    Hello Don
    On which pins of the chip there a current sensing resistor should be put in to measure current throught the bridge? Are the pin number 28 and 22 good enough for that?
    Best regards
    Simon Mali
  • 0 in reply to Simon Mali
    TI__Expert 6985 points
    Hello Simon! I have looped in Shawn on your question for a reply. Thanks, Jeff
  • 0 in reply to Simon Mali
    TI__Mastermind 24835 points
    Hi Simon,
    Current resistor is used to snese the temperature on the module, and the onstant current source is used for reference. An error amplifier is used to combine, and the output of the error amplifier is then fed into the DRV595. You don't need to know the current through the bridge, because it's used to control the temperature on the module. Please refer to this document about how DRV device works. www.ti.com/.../sloa092.pdf www.ti.com/.../spra873.pdf
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 40 points

    Hello Shawn

    Thank you information regarding this aplication note which provide deeper insight how the filter should be calculated. But I disagree with your opinion that information about current through the load is not needed. Maybe this is the case in ideal world but in real world when employees are connecting various loads on this device current limitation is urgently needed. I mean here current limitation in sense of constant current source not switching the bridge completely off what the case in DRV595 is. Our experience during more than 3 years of use in the field shows that components degrade, concepts in devices changes and we don't wan't to have this situation in the field anymore where the DRV595 is inoperational because of current limitation of whatsoever reason. 

    Now my question is where to put sense resistor (on which pins of DRV595) to measure the current through the bridge and in the next step to lower input voltage if this is possible at all? Or to get this information about current in some other way? If this is not possible we will have to remove this chip out of our design. In this case can you recommend some other ic with similar functionality?

    Best regards

    Simon Mali

  • 0 in reply to Simon Mali
    TI__Mastermind 24835 points
    Hi Simon,
    Thank you for the explanation, I think I understand it. DRV595 has over-current detection internally, but it just shut down the output when output current exceeds the THR. Now you wan to monitor the output current and adapt the input amplitude accordingly.
    I think this is feasible, you could insert a current sense resistor in series with the thermal module load(after the LC filter), and use an op amplifier to measure the voltage drop on the resistor. TI also has the solution for this application, please refer to www.ti.com/.../sboa170a.pdf.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    TI__Expert 6985 points
    Hi Simon! Did this work for you and if so can we close this message thread? Thanks, Jeff
  • 0 in reply to Jeff Kohnle
    Prodigy 40 points

    Hello Jeff

    The proposed solution is not really useful for me. As we know in a Peltier element current can flow in both ways, cooling and heating. And here I have a solution to measure current in only one way.

  • 0 in reply to Simon Mali
    TI__Mastermind 24835 points

    Hi Simon,

    I can't understand why you the current is only one way in this solution. The current can go from OUTP to OUTN or from OUTN to OUTP on DRV595. In this way, it can cool or heat the module. Please let me know if this is not clear.

    Best regards,

    Shawn Zheng 

  • 0 in reply to Shawn Zheng
    TI__Expert 6985 points
    Hello Simon! Did this answer your question? Thanks, Jeff
  • 0 in reply to Jeff Kohnle
    Prodigy 40 points

    Hello Jeff

    Yes this answer my question but I am not satisfied with the answer. I have expected to measure current throught the bridge without complications. This was not the case and instead I get a proposal how to measure current through the load. Beside that the proposed chip is only measuring current in one direction and I need information about current in both directions (peltier is the load). Not to mention the additional signal conditiong which will provide the proper voltages to control current of this ic in closed loop.

    Best regards

    Simon

  • 0 in reply to Simon Mali
    TI__Mastermind 24835 points
    Hi Simon,
    I'm sorry that you are not satisfied with the answer. DRV595 only has rough over-current protection internally, and it doesn't support current sensing. So if you want to achieve the real-time accurate output current value, I'm afraid that a current sensing device/circuit has be to used here.
    Many TI current sense amplifiers support measuring current in Bi-Direction, please find TI solution in this document www.ti.com/.../slyb194c.pdf. I beleve you could find the appropriate solution in it. I'm not an expert in current sense amplifier devices, you could close this thread and post a new thead with 'current sense amplifier' in title if you want more details on this. The TI experts on these devices will give you the most professional suggestion.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    TI__Mastermind 24835 points
    Hi Simon,
    Is there anything we can help on this please? Please let us know if there is anything unclear.
    Best regards,
    Shawn Zheng