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DRV2700: Can't get the IC to start switching

Part Number: DRV2700

Hello,

I have soldered a DRV2700 chip into an adapter and added components around it on a breadboard - please refer to the scheme below including the voltages I've measured at the pads. However, I can't observe any switching or inductor current. Based on my measurements I believe

1. The charge pump is working (voltage on the pin is higher than the supply voltage).

2. The voltage on the BST pin is ~ 1 diode drop less than the supply voltage, so I believe that current can go through the inductor and the internal diode.

3. The feedback voltage is right.

4. The enable pin works (EN = 0, Isupply = 0 mA; EN = 1, Isupply = 4 mA)

So the thing that doesn't appear to work is the internal transistor switching on and off. I'm out of ideas and I'd be very grateful if someone could provide any tips on the debugging. 

  • Hey Martin,

    I have checked your schematic, everything seems fine... The only thing that comes to mind right now is: did you do a transition of EN pin from low to high? If not, then try to connect everything and then do this.

    Otherwise I ll need some more time to figure this one out. Let me know how it goes!

    Best regards,
    Marko
  • Hi Marko,
    thanks for the reply. Yes I have tried that - the only effect is that the power consumption goes to 0 and then back to 4 mA. The chip might be damaged, but I did my best when reflow-soldered it etc. I'm wondering if the voltage on REXT should be 1.3V when there is no load, but since I have no information on the internal circuits I can't say.

    Best regards,
    Martin
  • Hey Martin,

    Yes, it should be 1.3V when there is no load.

    What does look weird, your Cpump voltage is quite low, what I have normally seen is above 5V. Could you check the cap value you put there? That could be the reason why the transistor does not want to switch.

    Please check that and let me know!

    Best regards,
    Marko
  • Hi Marko,

    I apologise for my late reply. I desoldered Cpump cap and replaced it with a new one (checked it to be 100n with a multimeter). The behaviour is still the same. However, on increasing the supply to +5V I get 6.05V on Vcap, so it seems to be supply dependent and can be above 5V. Also, I got the current consumption wrong (apologies) - it's 13 mA at Vdd=3.6 and 20 mA at Vdd=5V (0 mA when EN=0).

    Best regards,

    Martin

  • Hey Martin,

    Two things: could you send me the inductor part you are using? Sometimes there can be a problem between an inductor type and REXT you are using. Also, please send me a scope screenshot of SW pin.

    Then we can take a look and maybe find an answer.

    Thank you,
    Marko
  • Hi Marko,

    Thanks for the reply. Please find an oscilloscope shot of the BST pin attached - there is nothing interesting in there, just a static voltage of Vdd-Vdiode so 4.4V (Vdd = 5V). Exactly the same thing is also on the SW pin, only the voltage goes up to the supply.The screenshot shows the turn-on ramp and it's clear that DRV2700 doesn't perform a single switching cycle.

    The inductor is radial 10uH / 0.3A. I know it's slightly underrated (was lying around on my bench), but I think it should be enough to see at least something. My REXT is consistent with the schematic above, 15 kOhm.

    It sounds like buying a new chip and resoldering everything.

    Best regards,

    Martin

  • Martin,

    Can you purchase and use the DRV2700EVM? I also suggest using a different inductor with the correct rated current. It should at least switch a few times or try to swtich..