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Original question:

CCS/SM72295: DC-DC the boost configuration does not work

CCS/SM72295: full bridge driver

TA1S
Prodigy 60 points
Part Number: SM72295
Other Parts Discussed in Thread: TIDA-00120, CSD19535

Tool/software: Code Composer Studio

Hi 

I hawe problem with sm72295 buck converter  actually i use Typical Application Circuit

and also try wiht tida0120 PMP7605 

it is working most of the time normally  but time totime converter dors not start up

 also try wiht tida0120 PMP7605 and tida120 software  i have same result 

additional info if converter  not start up i see input side signal with osciloscope 

and Hsa and Hsb volate is missing 

and after severel  restart it will be start up suddenly 

can you advice 

Best Regards

A. Cem Cezali 

  • 0
    Prodigy 60 points

    and Hsa and Hsb volate is missing 

    it will be "HSA and HSB voltage is missing "

    sorry for mistake

  • 0
    TI__Genius 12990 points

    Hi A. Cem Cezali,

    thanks for reaching out about SM72295 and welcome to e2e!

    have you changed any component on your schematic or is the circuit taken exactly from TIDA-00120 () 

    When you refer to HSA and HSB are you referring to the pin of SM72295? or the switch node of legA or legB? are both legs of the full bridge acting the same?

    if both HSA and HSB are not there then there may be an issue with the high-side supply preventing the high-side FET from turning on the bus voltage to the switch node (HS). are you seeing LOA and LOB output signals from SM72295? the low-side needs to turn on to replenish the bootstrap every switching cycle.

    what is your switching frequency and VCC voltage?

    what is your VCC capacitor value? what is your HB-HS bootstrap capacitor value?

    what FET are you using and do you know if they are damaged? are all the FETs in the full bridge the same? A significantly larger FET than that used in the TIDA can lead to the bootstrap cap not replenishing itself fully and eventually lead to UVLO in which the driver shuts off the output.

    can you show me your schematic if anything has changed? Also during start up or working operation can I see a cycle or two of LOA,HOA, HSA and HBA (with respect to GND) waveforms for legA?

    thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 60 points

    Hi Jeff

     Thank you for your answer

    I had few  protype with sm72295

    also i have copy of TIDA-00120 even pcb  

    let talk about tida-00120

    VCC is 10V frequency ~ 200Khz

    capcitor value 0.47uf

    all fets is ok because its working most of the time 

    All components exactly same except  mosfets i used csd19532 instead  of csd18532 

    gate charge  csd19532 is 48nc  csd18532 is 44nc its not big difference

    only one thig  tida-0120 working more stable working  than my prototypes 
    my prototype is using csd19535 TO3 case HB HS capcitor value 0.68uf its

    blue HOA orange LOA

    blue HOB orange LOB

    at working condition

    i will send not working condition soon

    Best Regards 

    Cem

  • 0 in reply to TA1S
    Prodigy 60 points

    Hi Jeff

    i could not send  cycle  when is not working condition  

    i trying to measure last SM72295 burnd out  i have to order and its took 3 week  

      sorry for this 

    Regards

    Cem 

  • 0 in reply to TA1S
    TI__Genius 12990 points

    Hi Cem,

    thanks for the update, take your time getting the board up again.

    from the waveform you sent the signal at first appears to look ok (with some dead-time). However when I see the reference of the waveforms I can see that they go negative and almost as much as it goes positive. Your Oscope might be in AC mode? or if not, this tells me there is either something wrong with sm72295 PGND connection on the PCB or with your test measurement setup. Did you change the PGND on your prototype setup? can you tell me exactly where you are probing the reference of LOA/HOA (it should be pin 23 of SM72295 or something connected close)? are you connecting AGND (for the 5V VCC) and PGND at one point near the device?

    thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 60 points

    Hi Jeff

    Yes my scope is ac mode 

    my reference conected to exatly Pgnd just few cm distance from SM72295 pin 23

    Mean Time when i use csd19535 kcs 0.68uf is enough or more higher capacitor is necessery for bootstrap 

    and i will try external bootstrap supply for startup .just for testing ?

    Thank you

     CEM

  • 0 in reply to TA1S
    Prodigy 60 points

    Hi Again

    cancel this question  " Mean Time when i use csd19535 kcs 0.68uf is enough or more higher capacitor is necessery for bootstrap"

    its close to enough i read other  questions answers and you detrmine 10 times higher cap is enough 

    Thank you

    Cem

     

  • 0 in reply to TA1S
    TI__Genius 12990 points

    Hi Cem,

    thanks for the update,

    let me know if you have any more questions and feel free to post your update test results.

    thanks,