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TPS62816-Q1: PWM duty cycle unstable

Meng Liu
Intellectual 1765 points
Part Number: TPS62816-Q1

Hi Expert

my customer application scenario as below:

Input voltage: 5V output voltage: 0.85V  Iout max: 3.5A   f=1.8M   RF=100K 

L=220nH  input cap: 30uF+100nF  output cap:4*22uF  mode pin tie to Vin(FPWM mode)  Css=47nF

Power up when full load, the SW will unstable as below: Vin=4V Iout=3.5A

increase input voltage: Vin= 5.5V Iout=3.5A

I guess it relate to comp, so I change the 100K to 10K and then doesn't have above issue but Comp 1 doesn't suitable for customer because Comp 1‘s output dynamic not good enough. so customer need choose Comp 2.

My question is:

1. why have above issue?

2. How to let device work on Comp 2 and doesn't have above issue?

  • 0
    TI__Intellectual 1420 points

    Hi Meng,

    I will have a look at the waveforms and BOM and provide you my feedback by beginning of next week.

    Regards
    Nelson

  • 0 in reply to Nelson
    TI__Intellectual 1420 points

    Hi Meng,

    Thanks a lot for your patience. I tried to reproduce your issue using our EVM and the BOM values you mentioned.

    Cout= 4x GCM31CR71A226KE02.

    However, I'm not able to see the duty cycle variations that you show in your pictures. It can be that the effective capacitance is below 84.7uF (72uF/Vout).


    Would you mind sharing more details about your setup?

    1. Part numbers for inductor and capacitors
    2. PCB Layout images or files
    3. Which kind of load are you using? A pure resistor?

    Vin=5V Vout=0.85V Rcf=100kΩ Iout=3.5A

    Vin=5V Vout=0.85V Rcf=100kΩ Iout=0A

    Best regards
    Nelson