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BQ24703EVM: BQ24703EVM Volt outut spike

Niv Calif
Prodigy 60 points

Part Number: BQ24703EVM

In my board we use BQ24703 (charger) and TPS54339 (DC2DC, Vout=5v, Vin = 12-19.5v).

Vac_adapter = 19.5v

Vbat = 12-16.8v

Vcharge = 16.8v

 

 

In the steady state we see clean 5v from TPS54339 Vout, but when we plug in Vac_adapter (to charge the battery) we find a huge spike (>5.5v) in TPS54339 Vout.

We measure also with TI EVM boards (BQ24703, TPS54339), measure scope images attached (5v spike, Vin vs 5v).

Just to be clear, we use short wired for measure the 5V vout. 

Maybe you have any suggestion to clean TPS54339 Vout?

  • 0
    TI__Guru 56650 points
    When you plug in Vac_adapter (to charge the battery), the Vsys voltage jumps from Vbat to near Vac_adapter voltage. This is a normal direct power path charger normal behave. According to your post, the question is about the TPS54339 Vout spike. So, I think the Vsys transient causes the TPS54339 Vout spike. Three options:

    1. Make Vsys not jumps up. So, TPS54339 doesn't have input transient and Vout spike. For example: put TPS54339 on Vbat. But, the drawback it: the TPS54339 cannot operate if Vbat is too low or the battery is absent.
    2. Change the charger part from direct power path part to a NVDC part. The NVDC part put Vsys on Vbat (similar as item 1). But, it can provide minimum Vsys to keepTPS54339 operating even if Vbat is too low or the battery is absent.
    3. You may modify the post title and put TPS54339 in your title and re-post it to non-isolate DC DC forum ("BSR_MCP") and ask the TPS54339 input transient response.
  • 0 in reply to Wang5577
    Prodigy 60 points
    I will order NVDC TI EVM (BQ24773EVM-540) to ensure this topology can solve my problem.
    thank you very much!
  • 0 in reply to Wang5577
    Prodigy 60 points

    Hey again,

    Actually i don't think NVDC topology will solve my problem.  

    In our Vac_adapter connector the Vcc connected before ground and so see 600mv spike in DC2DC 5v regulator (TPS54339)

    But, when we use with another connector plug (ground first and Vcc second) we see smaller spike (200mv Max).

    Do you think we can find another solution to solve this problem? 

    Thanks,

    Niv.

  • 0 in reply to Niv Calif
    TI__Guru 56650 points

    "In our Vac_adapter connector the Vcc connected before ground and so see 600mv spike in DC2DC 5v regulator (TPS54339)"

    Do you mean you see 600mV TPS54339 output spike when you add input source to bq24773 input or bq24703 input? What is the bq24773 or bq24703 output voltage change, when you add input source?

    "when we use with another connector plug (ground first and Vcc second) we see smaller spike (200mv Max)."

    What is the bq24773 or bq24703 output voltage change, when you add input source?

    Do you take any waveform to show your test result?

  • 0 in reply to Wang5577
    Prodigy 60 points

    "Do you mean you see 600mV TPS54339 output spike when you add input source to bq24773 input or bq24703 input? What is the bq24773 or bq24703output voltage change, when you add input source?"

    Yes, we see 600mV output spike when add input source to bq24703(19.5v). the output voltage change to 19.5v, from battery voltage to 19.5v, battery voltage change between 12v (empty) 16.8v (full charge).

    "What is the bq24773 or bq24703 output voltage change, when you add input source?"

    bq24703 output voltage change to 19.5v (voltage input source).

    "Do you take any waveform to show your test result?"

    Sure, you can see here 3 pictures,  TPS54339 voltage output (blue) Vs bq24703 output (yellow).