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Original question:

DRV8305: Charge Pump Supply Debugging

DRV8305: DRV 8305NEPHPRQ1

Mohammad Atif Umar
Prodigy 115 points
Part Number: DRV8305

Hi Garrett,

We are seeing some possible issues with Charge pump circuitry in DRV 8305NEPHPRQ1. We are currently using 1.0uF capacitance of Pin 37 going to BGND, and 2.2uF of Pin 38 going to Vmot.

Are these appropriate values to use? Should the capacitor connections be different for Pin 37, and Pin 38 ?

What should we expect the performance of the Charge pump circuitry be in a typical BLDC 3 phase motor design?

Any thoughts and guidance would be appreciated.

Thanks

Mohammad

  • 0
    TI__Guru 65390 points

    Mohammad,

    Could you show us what issues you are having? Per the datasheet these capacitor values are correct.

    Normal Charge pump operation is specified in the datasheet.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 115 points

    Thanks Adam. How would the circuit function if one of these caps was missing?

    The reason this question is being asked is  because we were seeing VCPH dropping off to Vmot (PVDD) level ≈18.2v.  VCP_LSD was 10v until same voltage of 18.2v then dropped to 0v.  Error for VCPH_UVLO2 was then reported.  So, part would operate error free up to 18.2v.

    Any thoughts as to what might be going?

    Thanks

    Mohammad

  • 0 in reply to Mohammad Atif Umar
    TI__Guru 65390 points

    Mohammad,

    Can you provide a plot showing the sequence mentioned or a simple drawing?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 115 points

    Hi Adam,

    We are wondering what will happen if the VCPH, and VCP_LSD (as shown in the image) are removed /missing. This question is in reference to what was asked earlier with VCPH, and VCP_LSD. Under what conditions (i.e. abnormal conditions) will the charge pump circuit cease to perform  its core function of regulating voltage. From our experience, it seems to be quite susceptible to external conditions (i.e. overtempt conditions, etc) as previous comments show. How can we check that the charge pump is fully functioning or has been damaged? 

    Thanks

    Mohammad

  • 0 in reply to Mohammad Atif Umar
    TI__Guru 65390 points

    Mohammad,

    If either of these two caps is missing then the charge pump voltage will be too low and the device will report a charge pump undervoltage fault. You can read about it here: 

    If those capacitors are installed correctly but the charge pump is damaged, the charge pump will not be able to provide the needed current when the FETs are switching and a CPUV fault will also be triggered.

    Please note that this device conveniently has a two level system for reporting charge pump issues. At ~8V, the charge pump warning will trigger and the gate driver will continue operating. At ~4V the CP fault will trigger and shut down the gate drive output. Please note that this lower fault level is configurable as shown here:

    http://www.ti.com/lit/ds/symlink/drv8305-q1.pdf

    Regards,

    -Adam