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Low power 20 mA switched current loop driver

alwin van tol
Prodigy 110 points
Other Parts Discussed in Thread: DRV201

For a sensor I need a 20mA current loop driver that does not produce heat.

Example if the loop voltage is 20V and the loop resistor is 100 Ohm then a linear Current loop driver dissipates 20V * 20mA - ( 20mA * 20mA * 100 Ohm) = 360 mW

I'm allowed to dissipate max 40mW. The only way to achieve this is to use a switched voltage regulator, measure the current  and regulate the voltage (using a loop back)

Another solotion is to use a switched 20mA LED driver. Does sombody have experience with this, because I think a led driver is not very accurate ?

Some H-Bridges for stepper motors have a current sense but I don't think this wil work.

The best option would be if there is a standard IC (for instance a switched current regulator) available on the market that does the job . Does sombody know if there is a standard 'switched current loop driver' or a 'programmable switched current regulator' available on the market, with high efficiency and high accuracy < 0.05% and low rimple (< 0.05% F.S an f > 500kHz ) on the output?

 

Thanks Alwin van Tol.

 

  • 0
    TI__Guru 63905 points

    Hello Alwin,

    This is a very interesting design problem you're trying to solve, may I ask what the final application is and where the max 40mW dissipation spec comes from?

    None of the dedicated current loop transmitters currently offered have the capability you're looking for.  There are some DRVXXX parts that offer PWM outputs for motor and solenoid driving, but most that I found with a quick search are designed for much higher currents at low accuracy.  The DRV201 is an interesting part that has an output current range that seems appropriate with 10bits from 0-100mA resulting in 0.1mA step sizes.  However the relative accuracy is +/-10bits resulting in a +/-1mA output relative accuracy. 

    Besides one of the DRV parts with some intelligent feedback, I'm coming up at a loss for other op-amp/linear product solutions to this design.  Ideas are welcome from the community!!

    I've worked briefly with TI's LED driver products, but I am not sure about the absolute accuracy of their output currents.  May I suggest you post your question in the power group's forum as well to see if they have a product that you might be able to configure for your application.

    LED Driver Forum:
    http://e2e.ti.com/support/power_management/led_driverslcd_bias/default.aspx

    Non-Isolated DC-DC Forum:
    http://e2e.ti.com/support/power_management/non-isolated_dcdc/default.aspx

    I will ask a few colleagues if they have any suggestions for your design and will reply with their suggestions if any.

    Regards,
    Collin Wells
    Precision Analog 

  • 0 in reply to Collin Wells
    Guru 21975 points

    Alwin,

    Most 4-20mA sensors operate in two-wire mode. That is where the sensor electronics are powered from a distance. The sensor electronics is modulating the current it draws from the loop, powered from the far end. Is this the type of sensor you are designing? Or do you have a local power source at your end of the loop and you are sourcing current?

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 110 points

    Hello Bruce

    Thank you for your response

    We (want to) use the 20mA Current loopt in pyranometers, see www.kippzonen.com > products > pryranometers

    In stead of a 2 wire current loop we use a three wire current loop (power 12 - 24V, ground, output-signal)

    A pyranometer measures the amount of solar enegery by means of a themopile. If the electronics produces to much heat then the temperature of the cold plate of the themopile is increased by the heat. This have an impact on the output signal of the thermopile (and the amount of solar energy measured by the instrument). Therefore all electronics inside the instrument must be very low power, the lower the better.

    Regards,

    Alwin van Tol

  • 0 in reply to Collin Wells
    Prodigy 110 points

    Hello Collin

    Thank you for your response

    We (want to) use the 20mA Current loopt in pyranometers, see www.kippzonen.com > products > pryranometers