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TPS65150: TPS65150

Part Number: TPS65150

HI,sir:

A 7-inch display panel(1280rgb * 800, single gate) uses tps65150. When measuring the avdd ripple of black and white images, it is found that the SW signal fluctuates greatly. The measurement positions are as follows: the current of black avdd is 22.78ma, and that of white state is 41.5ma. Please help to answer the following questions

① When SW is high / low, there are fluctuations. How are these fluctuations generated?

② According to the description in 65150 spec, what is the reason for the slight deformation of SW waveform under light load (red circle part below)?

③ Other products use PFM to boost voltage, but the measured avdd ripple is larger than that of PWM. Do ti have the introduction documents of two boost models? I want to know why the PWM boost type ripple is smaller.

  • Hello,

    It appears that some of the pictures in your query did not make them through. Can you please include the relevant pictures that are before question 1 and after questions 1 and 2? Overall, it appears that there is big switching noise coupled onto to AVDD rail. I am not sure what is causing this kind of big switching noise in your system but a very poor grounding scheme could perhaps be one reason. Anyway, please include the missing pictures and I will review again.

    Kind Regards,

    Liaqat

  • HI,sir:

    I have insert picture files.picture1--test location , picture 2--SW and AVDD ripple,picture 3--spec discription of different loading

    See if you can see the picture or download ?

    thanks~

  • Hello,

    ① When SW is high / low, there are fluctuations. How are these fluctuations generated?

    The fluctuations on the AVDD rail seem quite high in your scope plot and we do not see such fluctuations on TI's EVM board. I am not sure what is causing such large fluctuations in the AVDD rail in your applications but one possible cause could be poor grounding scheme.

    ② According to the description in 65150 spec, what is the reason for the slight deformation of SW waveform under light load (red circle part below)?

    I did not see a red circle in the pictures you attached but I believe you are referring to the tapering off of the SW waveform at light load. This slight tapering off effect is caused by the MOSFET Q2 turning on in the block diagram in figure 8 in the datasheet. This MOSFET turns on to keep the boost inductor current in continuous conduction and keep a PWM operation at light load. Shorting external rectifier diode makes SW node voltage effectively same as the slightly lower voltage that is after the rectifier diode, hence causing the slight deformation of SW node waveform during light load operation.

    ③ Other products use PFM to boost voltage, but the measured avdd ripple is larger than that of PWM. Do ti have the introduction documents of two boost models? I want to know why the PWM boost type ripple is smaller.

    PWM boost ripple is smaller compared to PFM ripple because in PWM mode, next switching cycle starts before output voltage has a chance to drop significantly. In PFM mode, a burst of switching pulses is followed by no switching pulses until the output voltage drops to lower threshold level at which point, there is another burst of switching pulses causing the voltage to rise again to higher threshold level. This repeating cycle of pulses followed by no pulses in PFM mode causes a higher voltage ripple because the time between burst of pulses is much longer than the period of continuous pulses in the PWM mode. 

    Kind Regards,

    Liaqat