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Load Independent 5mA constant current source (Load Resistance 650 ohm to 750 ohm).

Rajesh Matere
Prodigy 205 points
Other Parts Discussed in Thread: LM334, ADS1247, REF102, LM4132

Hi, 

We are looking for Load Independent constant current source, current value will be 5mA. Load resistance will vary from 650 Ohm to 850 Ohm. Input power is 5V.

Also, it should have lower temperature coefficient, because this is going to be implemented in Sensor application.

Do we have IC for this application?

Op amp based constant current source may have drift in output with temperature. 

I experimented the same with LM334, but output is varying with change in load.

Thank you,

Regards,

Rajesh Matere.

  • 0
    TI__Guru 71526 points

    Hello Rajesh, 

      There are a few different approaches you can take here. 

    First is a dc REF, as described in this App Note: www.ti.com/.../litabsmultiplefilelist.tsp . 

    Next is a currentDAC, such as: www.ti.com/.../dac8801   .

    And third, since you are employing a sensor, I'm assuming you will also have to measure the sensor output, so here is an ADC with an integrated iDAC specifically for sensor applications: www.ti.com/product/ADS1247  .  

    Please let us know which would be the preferred method, then we can provide more details for that approach. 

    Regards,

    ~Leonard  

  • 0 in reply to LeonardEllis
    Prodigy 205 points

    Hi Leonard,

    Thanks for the input.

    First link showing following error.

    Could you please share it again?

    Visio-Drawing1.pdf

    Thank you,

    Regards,

    Rajesh Matere.

  • 0 in reply to Rajesh Matere
    TI__Guru 71526 points

    Hi Rajesh,

    Not sure what happened with that first link.  Here it is again,  Make A Precision Current Source or Current Sink Analog & Mixed-Signal sbva001 - TI.com 

    plus, the App Note the intro page references: www.ti.com/lit/an/sbva001/sbva001.pdf .

    ~Leonard

  • 0 in reply to LeonardEllis
    Prodigy 205 points

    Hi Leonard,

    Thanks for the updated link.

    Here I have attached my current design and application design overview.

    Yes, we need programmable amplifier with Ratio-metric  or Analog output and 5mA constant current for bridge excitation (resitance may varry from 650R to 85R).

    I think ADS124x has digital output lines and we do not have controller in that design. 

    If you have idea of programmable gain amplifier with Ratio-metric  or Analog output (0-5V), also if it can give me 5mA constant current will work for us.

    Otherwise, option with REF102 looks feasible for us. Please advice me on this.

    Design Overview.pdf

    Thank you,

    Regards,

    Rajesh M

  • 0 in reply to Rajesh Matere
    TI__Guru 64175 points

    Hi Rajesh,

    Take a look at TIPD102 for a configurable current source.  If you're only interested in a current sink you can use the first stage of the design on it's own.

  • 0 in reply to Collin Wells
    Prodigy 205 points

    Hi Collin,

    Thanks for suggestion, it really work and I simulated it on TINA.

    I do have size constraint on board,  so I am looking for less component solution.

    While working on TI website, I found following design.

    Will this work as Load independent ( 650R to 850R) 5mA constant current source?

    Thank you,

    Regards,

    Rajesh Matere.

  • 0 in reply to Rajesh Matere
    TI__Guru 64175 points

    Hi Rajesh,

    I've found most of TI's reference circuits to be very accurate and correct.  Therefore while I'm not an expert in the LM4132 I believe the engineers that put the circuit together were and knew what they were doing.  The load shown in the schematic is 1k so while it may not work with higher impedances due to compliance issues it should work fine with lower (650R - 850R) values.

    If you'd like to double-check I recommend that you start a new thread with the LM4132 as the product number and your thread will get routed to the experts for the LM4132. 

  • 0 in reply to Collin Wells
    Prodigy 205 points

    Hi Collin,

    Okay.

    Thanks for your guidance.

    Regards,

    Rajesh Matere.