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DRV8837C: OCP protection for the system

Dylan You
Intellectual 2630 points
Part Number: DRV8837C
Other Parts Discussed in Thread: DRV8212, DRV8837

Dear Teams,

My customer is using DRV8837C for their smart lock end equipment. They have following questions would like to confirm:

The Iocp (min) is 1.2A, and the tDEG is 1us. Following picture is the start-up current. Considering the application scenario like that: Everyday there are maybe 5 times the smart lock will turn on, which further caused the start-up current goes up to around 1.4A with more than 1us deglitch time. Then, DRV8837C will go into OCP status, and the phase current will decrease. Such kind of application scenario will continue maybe 5 years or even longer. Do you think are there any risks for this case? Do you think whether it is reliable if customer used the chipset like that?

Thanks!

Dylan

  • 0
    TI__Intellectual 2630 points

    Dear Teams,

    Another thing I want to confirm with is whether the motor can working properly if the start-up current is too large, maybe 1.5A or even larger?

    Thanks!

    Dylan

  • 0 in reply to Dylan You
    TI__Mastermind 37683 points

    Hi Dylan,

    Dylan You said:
    Do you think are there any risks for this case? Do you think whether it is reliable if customer used the chipset like that?

    If start-up current increases as the age of the motor increases, at some point when the current is above the OCP threshold, it will trigger OCP fault and the motor will not spin. In this case, you'll need to use a driver with higher current ratings. The DRV8212 is a better option for this application. It has same pinout as the DRV8837C with the exception of pin 7 (nSLEEP) which becomes MODE pin in the DRV8212. The MODE pin configures the control interface mode (either PWM or PH/EN). The DRV8212 has peak output current of 4-A and an autosleep feature that places the driver in a low-power sleep mode when both inputs (IN1 and IN2) are low for 2.6ms.

    Dylan You said:
    Another thing I want to confirm with is whether the motor can working properly if the start-up current is too large, maybe 1.5A or even larger?

    As I mentioned above, OCP may trigger. The DRV8212 with a higher current ratings might be a better option. Let me know if you have any questions about this device.

  • 0 in reply to Pablo Armet
    TI__Intellectual 2630 points

    Hi Armet,

    Really appreciated for your support! My customer still have following questions, could you help me answer it?

    1. If the start-up current will not changed, maybe keep at 1.4A that is larger than OCP threshold, whether it will affect the lifetime of the chipset considering the customer user case (Turn on the lock many times everyday)?

    2. f the start-up current will not changed, maybe keep at 1.4A that is larger than OCP threshold, whether it has any risks of damaging the chipset considering the customer user case (Turn on the lock many times everyday)?

    Thanks!

    Dylan

  • 0 in reply to Dylan You
    TI__Mastermind 37683 points

    Hi Dylan,

    Today is a holiday here in the US. I'll provide you with answers to your questions by tomorrow.

  • 0 in reply to Pablo Armet
    TI__Intellectual 2630 points

    Hi Armet,

    Thanks! 

    I’d like to update more information about this case here:

    1. Schematic diagram of DRV8837 and its external circuit showing in attached picture
    2. The input PWM waveform for IN1 and IN2 follows this sequence: 00- 01 – 00. Thus, it should used fast decay mode
    3. At the moment the winding current suddenly drop, the IN1 and IN2 is Low and High status. However, the OCP should be triggered because the winding current is greater than 1.2A. Then, why the absolute OUT1-OUT2 voltage (blue waveform) does not have a decreasing trend that tend to move to 0V? In my opinion, the absolute winding voltage OUT1-OUT2 should decrease because the OCP fault triggered all the FETs turned OFF.

    Thanks!

    Dylan

  • 0 in reply to Dylan You
    TI__Mastermind 37683 points

    Hi Dylan,

    Since we have moved the discussion over to email, I will close this thread for now and post again once we have answered your questions.