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TPS54540B: TPS54540B abnormal waveform

Rock Shao
Expert 2850 points
Part Number: TPS54540B

Hi,

The customer used TPS54540B in 24VDC input, output 5V/5A, the waveform was normal at 5V/3A, but when the load increases to 4A-5A, the frequency will rise and the waveform will become abnormal.

Could you please help and confirm if there is any problem with the schematic and layout? And did this IC has design excel? thanks.

Output 4-5A, abnormal SW pin waveform

  • 0
    TI__Mastermind 28640 points

    Hello Rock,

    I have assigned your thread to the appropriate person to address your concerns, they will respond in 24 hours.  Thanks.

    David.

  • 0
    TI__Guru 50120 points

    Hello,

    There is no design calculator tool. 

    For a RT resistance of 825kOhm, using Equation 8, the calculated switching frequency is 119kHz.

    Attached is the exported WEBENCH designer simulation for 24Vin_5Vout_5A_120kHz (https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=C71FCD182FA5A717).

    If the waveforms at 5V/3A are fine but 5V/4-5A are showing issues, then I suspect it is a compensation issue at higher load current.

    Can you try to change the Type 2 compensation network (R_comp/C_comp and Chf) to the WEBENCH values and recheck regulation at full load 5A? 

    Also for the bulk output capacitator C100, what is the ESR value? For Type 2 compensation it usually is expected to use low ESR capacitors.

    Regards,

    Jimmy