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DRV2700: Current Control

Tugba YILMAZ
Prodigy 20 points
Part Number: DRV2700
Other Parts Discussed in Thread: LM321LV, TLV9002

Hi,

I want to design a current control circuit with MOSFET and op-amp in a feedback loop. My main goal is to be able to trigger the gate of the MOSFET with an MCU and supply 12V to the output. If possible, I want to receive feedback from the negative connection of the circuit. The feedback loop will be for safety purposes and will be connected to the MCU. Additionally, the current drawn should vary with the change in resistance due to temperature, using a thermistor connected to the circuit, and this information should be relayed to the MCU. Through the feedback circuit, the system should not be allowed to exceed the specified current limit. This control circuit is going to connect to a heater coil. Maybe this information help you to understand what I try to explain.

I find this DRV2700 op-amp but Im not sure if this is suitable for this application. When I search for current feedback opamps, it leads me to high-speed opamps. I am really really new with this topic and I'm not sure what should I use. Your help means a lot to me.

Best regards.

  • 0
    TI__Expert 7620 points

    Hello,

    Thanks for reaching out. DRV2700 is a differential piezo driver, I don't think this is what you are looking for. I have moved this ticket to our general purpose amps team, which I think will have something more suitable for your application. For them to have more information, can you provide some of the op amp specs you are looking for?

    Regards,
    Sydney Northcutt 

  • 0 in reply to Sydney Northcutt
    TI__Guru*** 145736 points

    Hello Tugba,

    Minus the thermistor section. Can it be like this?

    Switched heater fixed to high side. Monitor current and software decides if heater is on or off.

    How much current does the heater draw? 

    If the circuit must take action for over current, would the result be heater off or limit current to some value?

  • 0 in reply to Ron Michallick
    Prodigy 20 points

    Yes, this is what is in my mind. heater will draw 4Amps. If there is any kind of a problem that causes heater to draw more than 4amps, heater must turn off, but also ntc value should determinate the current up to 4amp.

    Can you suggest me an opamp for that matter?

  • 0 in reply to Tugba YILMAZ
    TI__Guru*** 145736 points

    Tugba,

    I'm starting to understand better.  

    To get a low resistance NMOS switch at 4A, It is best to use 12V as a gate voltage. You have the option to pulse width modulate the gate signal control the average current of the heater. 

    The op amp current measurement can either measure average current as shown. Or it could be changed to measure live current for each pulse , that would require a faster amplifier, more ADC reads or a comparator circuit that detects a current fault.   

    This simple NTC circuit is not linear Vadc vs Temp, MCU math could approximate temperature based on ADC voltage. 

    What is the MCU voltage?

    I expect that just about any 5V op amp should be acceptable for block diagram circuit shown.

  • 0 in reply to Ron Michallick
    Prodigy 20 points

    MCU voltage is 3.3V. I'm pretty sure you are right. But since I dont have enough knowledge on this topic, I have to ask, does LM321LV acceptable?

  • 0 in reply to Tugba YILMAZ
    TI__Guru*** 145736 points

    LM321LV can be used for the middle op amp.

    or you could use TLV9002 for middle and bottom amplifiers