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DRV8839: OUTs VOLTAGE TOO LOW

Fernando Luis
Prodigy 30 points
Part Number: DRV8839

Hi all,

We are using a DRV8839 to drive 2 micro solenoids of 3.3V in a custom board. We have tested the 6 boards (prototypes) and we see the same problem: the thing is that when we set the INx and ENx pins to '1' (3.3V) the corresponding OUTx pin just have ~1.3V, even with no load connected. The power pins are routed with thick cooper traces and footprint is designed as suggested by Texas.

Before designing our custom PCBs, we tested the same condiguration in the DRV8839EVM development board. This is our schematic:

As we are working with 3.3V we connect together VM and VCC -like is said in the datasheet-. Another thing is that we connect together the INx and the ENx pins. We did the same in the DRV8839EVM and works.

The solenoid we use just consumes a few tenths of mA.

Also I have made these tests with no results:

  • Changed the VM bulk capacitor.
  • Removed the VM part capacitors.

Our board has enough power to power ther driver and the solenoids. Also the GPIO pins that are connected to the INx pins are ok. I tested both things by soldering wires from our custom board to the DRV8839EVM, bypassing the on-board DRV8839.

I would appreciate any help about what can be making the OUT pins to output just 1.3V. Can be related to a poor ground pad soldering?.

Thank you very much. Best regards,

Fernando

  • 0
    TI__Guru** 114905 points
    Hi Fernando,

    The schematic appears to be good. Have you checked the layout?

    How are you measuring the 1.3V on the output pins? Are you using a meter or a scope? If a scope, is the output pulsing on and off?

    How much current is consumed when the device is powered, nSLEEP is high, and the inputs are low?
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Hi Rick,

    Thank you for your fast response.

    Yes, I checked the layout and the footprint of the component. In the picture you can see the a capture of the driver section:


    All the space you can see without 'red' is actually the ground plane. I just shelved it for better visualization of the connections.

    About the 1.2V, I mesure it with a meter. Sometimes the output fluctuates from the 1.2V to undetermined very low voltage like if the OUT was in High Z.

    Current of our board is about 35mA.


    Thank you very much. Regards,

    Fernando

  • 0 in reply to Fernando Luis
    TI__Guru** 114905 points
    Hi Fernando,

    The layout also appears to be good. Please look at the outputs, VCC, and VM with a scope. This usually provides more information.

    From your description, there could be a problem that the outputs are switching on and off. This could be caused by undervoltage, overcurrent, or thermal issues. If it is undervoltage this will also appear at the VM and VCC pins.
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Hi Rick,

    We found the problem. It was at the pin nSLEEP. The assembler put the resistor in the place of the capacitor, and the capacitor in the place of the resistor.

    Thank you very much. Best regards,

    F.