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DRV10987: Failing at first step of setting up DRV10987 - no buck and 3.3V out!

David M1
Prodigy 110 points
Part Number: DRV10987

Hi,

I am having trouble with the standalone chips. Before integrating into a circuit, I want to check I can communicate with them on the I2C bus/generally make them work from the non-TI controller I am using with the standard I2C libraries.

Unfortunately, I hit a roadblock before that - there is no activity on the SW pin, so no 5V so no 3.3V... There is however 1.8V showing on the 1.8V pin. I am powering the device from a 9V source; i.e. above the threshold voltages, but quite low to avoid damaging anything when I start plugging the motor into it later. I have checked there is actually 9V going into it.

I soldered it myself, and have checked all the pins have continuity and no cross continuity... done two parts, and both show the same behaviour. The switching inductor and capacitor are 47uH and 10uF. All the other 3.3 and 1.8V caps are 100nF, so not quite the values for of 1uF, but I'm not expecting that to be the problem on what I assume is a linear regulator... What am I doing wrong???

I was wondering if I needed to write some registers to start it, but it's not showing up on an I2C bus scanner so I'm kinda stuck!

I have the S (standby) variant, not the D (sleep) variant. Any help appreciated!

  • 0
    TI__Expert 6065 points

    Hey David,

    For the standby device, the 5V linear regulator should always be on. Thus this is abnormal behavior. My suggestions are below.

    1) If you want to evaluate the DRV10987 quickly independently of any other hardware issues, I would recommend using our DRV10987 EVM (www.ti.com/.../DRV10987EVM).

    2) Make sure that the 47uH inductor and 10uF cap aren't damaged. You can do this by looking at their capacitance and inductance values. Also, make sure that they follow the guidelines from table 36 in the datasheet below. The inductor current rating is especially important.

    3) Make sure the DRV10987 device isn't damaged by:

    a. See what the Icc of the device is and if its above max 16mA.

    b. Make sure that the DRV10987 didn’t get damaged when connecting the battery by using an oscilloscope to capture the Vcc rising when battery is connected and make sure the Vcc didn’t go above 28V absolute max

    4) If the above steps dont work, just follow exactly the External Components table 36 in the datasheet. 

    Let me know if this helps.

  • 0 in reply to Sanmesh Udhayakumar
    Prodigy 110 points

    Hi Sanmesh,

    Thanks for the advice. I measured the current and found it was very high, so a bit further investigation and it seems I had some weak contact between the ground pad on the bottom and some of the other pins (actually hadn't realised the breakout overlapped with the ground pad). I resoldered the device with the ground pad insulated and the buck convertor now works, along with the 3.3 and 1.8. Surprised the chip survived frankly...

    I'll try I2C again tomorrow... hopefully that still works as well, but if it doesn't i'll solder up another.

    EVM interesting, but I'm mainly concerned with checking it plays nicely with the other things in the I2C bus, communicates as expected, doesn't fill the board with electrical noise etc... I kinda trust that it can spin the motor I have.

    Thanks again!

    David