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About XTR110 Application

Shin Chan
Prodigy 30 points
Other Parts Discussed in Thread: XTR110, OPA454, OPA445, OPA453, OPA452

Hello to all,

Now I intend to apply XTR110 as voltage-controlled current source to a neuromuscular electrical stimulation (NMES) device. Input signal is pulsed biphasic, frequency: 1~400 Hz, power range: 0~5V or 0~10V; obligatory output current(absolute value): 0~100mA, load impedence( refer to human body) 800 odm roughly.

In your experience, is there application example similar to my idea?

I have read datasheet p.8 200mA current pump as one typical application of XTR100 and to modify for my project, is it possible to add external circuit? Therefore the output power can meet my demand.

My problem is that when current pump's characteristic low voltage (≤40 V) is in use, the output of power too low and constant current range is too small; in the case of large load impedence ( such as 800 ohm),output current diminishes failing to accomplish my set goal.

Sorry, my English is not good, hope you can understand my questions above.

I would appreciate any advise.

xiexie,^_^

Shin Chan

  • 0
    TI__Guru 62935 points

    Hello Shin Chan,

    I personally have no experience with such an application, but it sounds like it could be very dangerous and you should take caution in your testing and design.  The link below shows the effects of current passing through the human body, 100mA is very dangerous. 

    http://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

    The circuit in Figure 8 of the XTR110 datasheet will work to provide a +/-200mA current source.

    Yes, with an 800 Ohm load you will experience issues due to the compliance voltage of the current source.   100mA into an 800Ohm load is +80V, so this solution will not work with the XTR110.  With this type of voltage requirement I would suggest a high-voltage op-amp like the OPA445, OPA452, OPA453, OPA454 and either try to directly drive your load or drive a high-side PMOS device making a current source.  A few examples of current source/sinks can be seen in the image below.  These were configured for low-current, but by adjusting the op-amp, MOSFET, resistor values, and supply range these may be modified to accomodate your needs. 

    Good luck!
    Collin Wells
    Precision Analog

     

  • 0 in reply to Collin Wells
    Prodigy 30 points

    Hi Collin,
    Thanks for fast reply and your kind advise.

    Yes, 100mA current is dangerous for human body. Thanks for your reminding, I will be careful. But 100mA just a maximum value of circuit, how much current output for, doctor must be according to the patient's feeling, increasing the current gradually. You know, someone's feeling is not so sensitive, and then the output current must higher, so I must supply a higher possible output value. By the way, you can find the similar products which can output 100mA or higher on the website.

    My problem :

    Is it possible to add external circuit behind the XTR110 +/-200mA current pump's output, which can increase the output power? and how to do it?

    Forgive my broken English, hope you can understand what I said. Thanks a lot.

    xiexie,^_^

    Shin Chan

  • 0 in reply to Shin Chan
    Expert 1495 points

    Hi Shin Chan,

    Safety should never be compromised with. Your circuit design must be such that the operator even by mistake must never be able to set the current to be greater than safe limits. I would recommend that you get the exact requirement from a medical expert and then design your circuit.

    Before trying out on humans there is a lot of validation and certification required for medical applications. Please check with your local authorities.

    Regards,

    JayantD 

     

  • 0 in reply to Jayant Deshpande
    Prodigy 30 points

    Jayant Deshpande said:

    Hi Shin Chan,

    Safety should never be compromised with. Your circuit design must be such that the operator even by mistake must never be able to set the current to be greater than safe limits. I would recommend that you get the exact requirement from a medical expert and then design your circuit.

    Before trying out on humans there is a lot of validation and certification required for medical applications. Please check with your local authorities.

    Regards,

    JayantD 

     

    Hi JayantD
    Thanks for your advice and suggestion.
    The problems you point out that I have discussed with the professional colleagues. As my device's parameters such as the maximum current,the frequence and the pluse width were designed according to the products which have passed the registration between Europe and China. So it will be sure of the security. Of course,  I must make the modification after I have tested and ensure the unreliable. Very thankfull for your remind and it will be more gratefull that you can give more technical suggestions about precision voltage-to-current converter.

    xiexie,^_^
    Shin Chan

  • 0 in reply to Shin Chan
    Expert 1495 points

    Hi Shin Chan,

    You may implement a Howland current source using the op amps suggested by Collin.

    There's nothing more technical I can add to Collin's reply above...

    Wish you all the best,

    JayantD

     

  • 0 in reply to Jayant Deshpande
    TI__Guru 62935 points

    Hi Shin Chan,

    The XTR110 will not work for this application because the compliance voltage will be too high with a 800Ohm load and a 100mA current source. 

    You will need to implement a current source such as the one I showed in the first post, or use a high-voltage high-power op-amp and make a current source out of it either with a howland current pump or otherwise.

    Best Regards,
    Collin Wells
    Precision Analog