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DRV2700: Input voltage has an obvious drop when start up

qieshiniao shi
Prodigy 30 points
Part Number: DRV2700

When we test for DRV2700EVM, we use the configuration: GAIN0 -> high, GAIN1->high, output is the highest +/- 105V, we find that the input voltage VDRV has an obvious drop when DRV2700EVM starts up:

Can anyone help for this? Thanks a lot!

  • 0
    TI__Expert 8691 points
    Hello,

    Is this causing an issue with the operation of the EVM? I do not understand your question.
  • 0 in reply to Kelly Griffin
    Prodigy 30 points

    Hi Kelly, 

        Thanks for your reply! This input voltage drop will affect the power supply for other parts. We designed a circuit referred to DRV2700EVM, and find it is the same as the DRV2700EVM that the input voltage has an obvious drop. Since the input voltage also supply for the MCU system and other parts, and the MCU system will reset directly due to the input voltage drop. 

  • 0 in reply to qieshiniao shi
    TI__Expert 8691 points
    The EVM is pulling power directly from the USB or the external power supply. There is no external circuitry supplying power to our device. I believe the voltage is dropping here because the USB power rail cannot supply enough instantaneous current to charge the boost converter of the DRV2700. What are you using as your power source? You may need some external circuitry to manage the power being consumed by different parts of your system.
  • 0 in reply to Kelly Griffin
    Prodigy 30 points

    Hi Kelly,

        We tried for three different power sources: battery power, USB charger, and DC power supply, and find they all have the drop with different levels. We also find that the DRV2700 circuit will have big ripple wave on the power rail. So, for the DRV2700 part, do we have any other solution to reduce the influence for the power rail?  

    Using the external circuitry to manage the power of different parts is another solution. We also need to supply power for MCU system and analog sensor circuit. could you recommending any power supply topology to avoid the influence for the DRV2700? We need to use battery power for the system. Below is the diagram:

    Thanks for your support!

    Best Regards

    Qieshiniao

  • 0 in reply to qieshiniao shi
    TI__Expert 3515 points

    Do you have the voltage drop data for different power supply? That would be helpful for us to review. Thanks.

  • 0 in reply to LLouis
    Prodigy 30 points

    Our power topology is as follows:

    Our system will reset with USB power supply and will not reset with battery power supply(280mAh, and smaller battery will reset).

    We tested the voltage drop for VCC_DRV, VCC, VBAT and VBUS signals.

    The following graphs are the testing result. The green signal in the graph is DRV2700 EN signal as the trigger signal.

    1. MCU resets with USB power supply,  VCC_DRV drops about 1.26V:

    2. MCU doesn't reset with battery power supply， VCC_DRV drops about 690mV:

    3. MCU resets with USB power supply, VCC drops about 1V:

    4. MCU doesn't reset with battery power supply, VCC drops about 550mV:

    5. MCU doesn't reset with battery power supply , VBAT drops about 450mV:

    6. MCU resets with USB power supply, VBUS drops about 580mV:

  • 0 in reply to user5607594
    TI__Expert 8691 points
    Hello,

    It looks like the issue is the power limit on your supply voltage. With the proper battery, you are able to solve the problem. One thing you could try is limiting the boost current limit using the R_ext resistor on the REXT pin. Figure 20 in the datasheet lists the relationship between peak current and REXT.
  • 0 in reply to user5607594
    TI__Expert 3515 points

    Besides Griffin suggestion, you can try add more coupling capacitor,(> 22uF) in the power path, to provide more capacity for inrush ramping current. Thanks.

  • 0 in reply to Kelly Griffin
    Prodigy 10 points

    Hello Kelly,

    Thanks for your great support. We have set Rext 6.05K from the beginning,which meets the max boost current limit.

    We also tried to add 22uF、100uF couple capacitors to the input voltage，but not available. 

    There is the same voltage-drop issue accured in the DRV2700EVM on our hands.

    Would you please help double check if there is the same voltage-drop situation in the DRV2700EVM ?

    And we do not find the discription about the transient current when EN is enable in the DRV2700 datasheet.(No load)

    Would you please help check that?

    Thanks!

    Julian

  • 0 in reply to user5135231
    TI__Expert 8691 points
    Can you try increasing R_EXT to 15kOhm or 20kOhm? This will limit the current and should also limit the inrush current when the device is turned enabled.
    We can check the voltage drop on the EVM.
    I do not think this is a specification that we normally put in the datasheet.
  • 0 in reply to Kelly Griffin
    Prodigy 30 points

    Hi Kelly, LLouis,

        Thanks for your support! We increase R_EXT to 20kOhm, and the voltage drop decreases. For the USB power supply, MCU currently doesn't reset. The output driving waveform will have an about 6ms rising edge, and we will evaluate the influence for our load.  And there is Also obvious ripples on power rail, do you have any suggestions to reduce the ripple wave? Thanks a lot!

       The following is the testing results after changing R_EXT to 20kOhm, The green signal in the graph is DRV2700 EN signal as the trigger signal. 

    Voltage Drop:

        1. With battery supply, VCC_DRV drops about 188mV:

    2. With USB power supply, VCC_DRV drops about 236mV:

    3. With battery power supply, VCC drops about 176mV:

    4. With USB power supply, VCC drops about 188mV:

    5.  With battery power supply, VBAT drops about 148mV:

    6. With USB power supply, VBUS drops about 236mV:

    Output driving waveform has an about 6ms rising edge:

    Ripple wave on the power rail:

    1. With battery power supply, with the load, the ripple wave on the VCC_DRV has two parts as 178mV and 140mV:

    2. With USB power supply, with the load, the ripple wave on the VCC_DRV has two parts as 204mV and 190mV:

    3. With battery power supply, with the load, the ripple wave on VCC has two parts as 132mV and 110mV:

    4. With USB power supply, with the load, the ripple wave on VCC has two parts as 178mV and 145mV:

  • 0 in reply to user5607594
    TI__Expert 8691 points
    It will be difficult to reduce the ripple because the DRV2700 will be pulling high peak currents from the supply rail. My suggestion is to add more bypass capacitance near the DRV2700 supply pin.
  • 0 in reply to Kelly Griffin
    Prodigy 30 points

    Hi Kelly,

        OK, we will try for it. Thanks for your kindly support!

    Best Regards

    Allen