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DRV8210: Getting a jittery signal when solenoid is connected

Vivek Bhageria
Intellectual 260 points
Part Number: DRV8210
Other Parts Discussed in Thread: TPS631000

Hi

In the following graph, the blue signal is the IN1 and the yellow signal is OUT1.

When the solenoid is not connected, the signals are smooth and clean. However, when the solenoid is connected, I get such jittery signal.

Following is the board layout of where the IC is on the board.

I am not able to understand the reason for such behavior. Could it be that the switching of the solenoid is causing interference in the 3V3 signal? Is it also possible for this to cause changes in the input signal?

  • 0
    TI__Guru 53145 points

    Hello,

    Today is a US holiday.  Team will respond tomorrow.

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    TI__Mastermind 37403 points

    Hello Vivek,

    Can you share the driver stage schematic?

    Are there bulk capacitors on the VM power supply? I would start by increasing the VM capacitance.

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 260 points

    Hello Pablo

    Following is the schematic:

    There are two 22uF capacitors in the VM supply.

  • 0 in reply to Vivek Bhageria
    TI__Mastermind 37403 points

    Hello Vivek,

    The schematic looks okay to me. Nothing obvious that would point to the root cause. 

    Vivek Bhageria said:
    Could it be that the switching of the solenoid is causing interference in the 3V3 signal? Is it also possible for this to cause changes in the input signal?

    This could be plausible. TO figure out, use an external power supply for the 3v3 rail instead of and LDO or converter in your board. Another alternative solution is to add some capacitance on the 3V3 rail to damp the low frequency ripples. 

    Let me know if the above suggestion works.

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 260 points

    Hello Pablo

    I tried your suggestions and here are my findings:

    Using an external power supply - works fine conditionally

    Using a battery - works fine conditionally

    Let me explain the conditional scenario:

    I am using TPS631000 buck-boost converter and the input is from AA cells. What I found is that if the input to the Buck Boost converter is 3.2+ volts, everything works fine. If the input voltage drops below 3.2v (battery supply or external supply), the buck boost converter gives me those ripples whenever I try to switch the solenoid.

    This seems weird because the current drawn by the solenoid is about 150 mA at 3v input. According to the datasheet of TPS631000, it should not have any problem handling this load.

    The following image is with 2.9v input. It has those jitters

    The following image is with 3.3v input. No jitters

  • 0 in reply to Vivek Bhageria
    TI__Mastermind 37403 points

    Hello Vivek,

    Vivek Bhageria said:
    This seems weird because the current drawn by the solenoid is about 150 mA at 3v input. According to the datasheet of TPS631000, it should not have any problem handling this load.

    I browsed through the TPS631000 datasheet. The graph below shows the efficiency for various input voltages. Below 2.8V, the efficiency drops drastically. 

    I believe the solenoid switching is somehow affecting the operation of the buck-boost converter. If you try driving a purely resistive load, do the ripples appear when VIN < 3.2V? Or it only occurs when driving a solenoid?

    I think we should involve the power management team for help with the TPS631000 issue. Can you ask a new related question with the TPS device as the product so it gets routed to the power management team forum. I will continue to support this thread.

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 260 points

    Hello Pablo

    I raised a question for the power management team. I also connected a resistive load, about 14.5 ohms, 227 mA current.

    Here the signal remains ok till 2.7V input.

    Decreasing the input voltage further starts showing those fluctuations. Following capture is at 2.45v input

  • +1 in reply to Vivek Bhageria
    TI__Mastermind 37403 points

    Vivek,

    Thank you for doing the suggested tests. It looks like it is not solely the solenoid causing the issue. The converter input threshold when the spikes appear may be different between the solenoid and resistor but it is not just caused by the solenoid. 

    My theory is that the current flowing through the outputs of the DRV is causing misbehavior in the buck-boost converter. Hopefully the power management team can shine some light on this.

    What I'm curious about is how this interaction between the DRV output and the converter occurs. Is the VM supply of the DRV also going to the input of the buck-boost? If so, then a plausible explanation is that the load switching is causing VM to become unstable to the point that triggers the spikes on the converter. Sometime, when the DRV is switching between driving and coast decay, the excess current flowing back to the supply can cause "VM pumping". To avoid VM pumping, it is recommended to switch between driving and slow decay (also referred to as braking). During slow decay, current recirculates between the two LS FETs and the load so no current flows back to the VM supply.

    How are you switching the output? Do you switch to slow or coast decay mode or you driving it continuously (DC)

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 260 points

    Hello Pablo

    Thank you so much for such detailed explanations.

    Regarding the VM supply:

    The battery voltage supplies the buck-boost converter. The buck-boost converter is configured for fixed 3.3v output. The DRV is supplied by the output of the buck-boost converter.

    A block diagram of the system looks like this:

    The solenoid has two positions - open and close.

    To Open the solenoid, we supply a pulse of 50 ms on IN1. To close the solenoid, we supply a pulse of 50 ms on IN2. A signal graph of the two signals look like this:

    Currently, to open the solenoid, we switch IN1-IN2 as 10->00

    If I understand correctly what you are saying, for the signals IN1 and IN2, I should go from 10 -> 11 -> 00 to avoid the spike?

  • 0 in reply to Vivek Bhageria
    TI__Mastermind 37403 points

    Hello Vivek,

    Thank you for the detailed information. 

    to answer your question, yes you should switch from driving phase to braking (10 >> 11). Try this and observe of the issue goes away. 

    regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Intellectual 260 points

    Hi Pablo

    Your suggestions have resolved th spike issue. Thank you so much. I will mark this thread as resolved.