• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 744 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

SM72295: MOSFET Not Driven

SM72295: MOSFET Not Driven

wang peng1
Prodigy 90 points
Part Number: SM72295


In the process of using 72295, I have encountered a situation in which one of the driver outputs is abnormal. It is usually HOB (PIN_19). It is normal at the beginning, and this happens during the running debugging. Do not know what is the reasons of that.

  • 0
    TI__Genius 12990 points

    Hi Wang, 

    Thanks for asking about sm72295. Im an apps engineer with this part and hope to help.

    Can you take a scopeshot of the issue? Including HOB, HSB, HIB wrt PGND? 

    Can you also share the schematic with 72295?

    Can you confirm PGOOD, VDD, VCC pin voltages have clean signal within spec?

    Thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 90 points

    Hi Jeffrey, Many thanks for your reply. My circuit is as follows.

    The power of 72295 is +5V and +12V. LIA is tied to HIB, HIA is tied to LIB. The input signal is as follow:

    When the supply of the bridge is below 5V (VCC in the above circuit), the output signal is right. The waveforms of HOA and HOB are as follows (references to the GND, I don't have differential probes).

    When VCC is larger than 5V. The waveform of  HOB is abnormal. The current waveform of R3 is something wrong. When VCC = 6V, The waveforms of HOA and HOB are as follows (references to the GND).

    When VCC = 10V, The waveforms of HOA and HOB are as follows (references to the GND). Q2 can't be opened.

    I don't know why. Maybe something is wrong? Can you help me?

    thank,

    peng

  • 0 in reply to wang peng1
    TI__Genius 12990 points
    Hi Peng,

    sorry for the late reply!
    I understand that when VCC(or the H-bridge bus voltage) is more than 5V and is switched via HOA the HO voltage looks abnormal however the HOB voltage does successfully get pulled to GND. when you say VCC you mean VBUS not 75592 +12V?
    Can you confirm the fets and SM72995 are not damaged and can switch properly with no load? what fets are you using?
    For example, Id like to see what all the outputs look like at the same time. Can you show me another scope shot of waveforms at the pin of the issue including a few switching cycles of LOA,LOB,HOA,HOB wrt GND?
    is there current flowing in R3 when HOA is first switched?
    what application is this for?

    thanks,
    Jeff
  • 0 in reply to Jeffrey Mueller
    Prodigy 90 points

    Hi, Jeff,

    Many thanks to your reply.

    The VCC in the circuit is the H-bridge bus voltage. The fets are ok because each time when the VCC is below about 5V, the current flowing in R3 is right.

    Maybe my usage of the 72292 is wrong. During the test, I only use the single shot mode, namely only one switching cycle.

    The bootstrap capacitor maybe hasn't been charged when the low side fets are open for a long time?

    I'll try.

    thanks,

    Peng

  • 0 in reply to wang peng1
    TI__Genius 12990 points

    Hi Peng,

    I see thanks for letting me know!

    the bootstrap takes a few cycles to fully charge however it charges pretty fast once it reaches this point since its only 10xCgate, if you test at lower voltages and current limits you can get use 1khz or something small just to see the highside can switch properly.

    thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 90 points
    Hi, Jeff,
    Many thanks for your reply.
    During my test, I have opened the low side fets for several uS before the normal operation of the bredge.
    Now it is ok.
    thanks,
    peng