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LM5164：输出电压VOUT带载时超出范围，VFB电压被抬高

he he
Prodigy 10 points
Part Number: LM5164

Tool/software:

Using TYPE3 power supply, RFB1 and RFB2 are 680K and 62K respectively, the VOUT voltage is 14.96V at no load; when loaded with 0.8A, the VOUT voltage becomes 15.04V, which exceeds the range of VOUT calculated by the resistive-capacitive error, and the VFB voltage is also raised synchronously; I would like to know how to calculate the range of VOUT for this output voltage, and how to calculate the range of VFB voltage that appears in the output voltage. I would like to know how this output voltage VOUT range is calculated, and the reason why the VFB voltage is elevated.

  • +1
    TI__Guru 59241 points

    Hello He

    LM5164 regulates the valley voltage at the FB pin. 

    For example,

    Assuming RFB1=90kOhm, RFB2=10kOhm for 10:1 step down,

    If no voltage ripple at the FB pin, VOUT will be 12V (1.2V internal reference voltage x 10 = 12V) 

    If there is 100mV pk-pk ripple at the FB pin, VOUT will be 12V + (100mV x 10)/2 = 12.5V (average).

    -EL

  • 0 in reply to EricLee
    Prodigy 10 points

    I test the voltage ripple of the FB pin at no load and with load, the ripple voltage value is almost the same, only the frequency is different, is this frequency different affects the voltage of the FB pin?

  • 0 in reply to he he
    TI__Guru 59241 points

    Hello He

    The ripple at 0.8A load is 111mV and no load ripple is 136mV. Please measure the VOUT using oscilloscope and compare them again ? Also, please check your Multimeter measures 'average' voltage or 'RMS' voltage. 

    -EL 

  • 0 in reply to EricLee
    TI__Guru 59241 points

    I will be out of office and I will not be able to reply this E2E post anymore.
    If you are still trying to resolve the issue, please don't reply on this post, but create a NEW post to get a help from other engineers quickly.
    -EL