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DRV8876: Current regulation

na na78
Guru 16770 points
Part Number: DRV8876

Hi

DRV8876 offers current regulation feature set by IMODE.
Current chopping threshold (Itrip) is set through Vref and RIPROPI and the current would be regulated with Itrip.

However, the current regulation feature is one of protection feature.  

So I think we should design the circuit to avoid the situation of current regulation as soon as possible if it is detected.

Is my understanding correct?

BestRegards

  • 0
    TI__Guru** 114905 points

    Hi na na78,

    Current regulation is not a protection feature.

    Current regulation is adjustable and can be used in several ways.

    1) Current regulation can limit the startup and stall current. This can reduce the load on the capacitors and save system cost.
    2) Current regulation can be used to determine if the motor load has exceeded a limit. An example is shown in http://www.ti.com/lit/an/slva858/slva858.pdf . Figure 4 demonstrates how to configure the circuitry to detect current regulation.
    3) Current regulation can be used for overcurrent, but only with external circuitry to assist. The system would have to monitor for current regulation and disable the outputs when current regulation is detected.

     Overcurrent is a protection feature. The overcurrent limit is not adjustable.

  • 0 in reply to Rick Duncan
    Guru 16770 points

    HI Rick

    Thank you for your reply.

    If the Itrip is set as 0.5A, the output current will be regulated to 0.5A.


    It assumed that motor stall current (maximum current) would be 2A.

    In this Itrip settings, output current would be regulated to 0.5A even if the motor is stalling.

    Would never keeping this condition lead to some damage or something harmful effect to the device and motor?

    BestRegards

  • 0 in reply to na na78
    TI__Guru** 114905 points

    Hi na na78,

    If the Itrip is set as 0.5A, the output current will be regulated to 0.5A.


    The DRV8876 will attempt to regulate the current to 0.5A +/- 5%. In most cases, this will occur. but we have seen some cases, such as high VM voltage, where the Tblank time injects more current into the motor than the Toff time removes.


    It assumed that motor stall current (maximum current) would be 2A.

    In this Itrip settings, output current would be regulated to 0.5A even if the motor is stalling.


    Correct, the device will attempt to regulate the current at 0.5A even when the motor is stalling.

    Would never keeping this condition lead to some damage or something harmful effect to the device and motor?


    Assuming by "never keeping this condition" you mean disabling the internal current regulation, the answer is no. The device and motor should operate properly. Please note section 7.3.3.2 of the datasheet which allows disabling the internal current regulation.

     

  • 0 in reply to Rick Duncan
    Guru 16770 points

    Hi Rick

    Sorry my question was unclear.

    I quote you answer.

    >1) Current regulation can limit the startup and stall current. This can reduce the load on the capacitors and save system cost.

    Current regulation can limit stall current.
    So, is there no problem if the motor keeps stall for a long time?

    BestRegards

  • 0 in reply to na na78
    TI__Guru** 114905 points

    Hi na na78,

    Current regulation can limit stall current.
    So, is there no problem if the motor keeps stall for a long time?

    There can be a problem if the motor keeps stall for a long time.

    Stall current builds up heat in the motor which can damage the winding insulation.

    The motor manufacturers should be asked about the operating specifications of the motor.

  • 0 in reply to Rick Duncan
    Guru 16770 points

    Hi Rick

    Thank you for your reply.

    I understand it is not recommended that the motor keeps stall condition for a long time
    even though the motor current is regulated as DRV8876.


    I will ask motor manufactures about detailed motor operation.

    BestRegards