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TPS40211 Boost converter full loading question

water hsiu
Prodigy 30 points
Other Parts Discussed in Thread: TPS40210

Sorry I find out that I posted the wrong palce so I post again here. = ="

Hello,

I want to use TPS40211 to make three converters from 12V input to 24V output, 120W full loading and operating in 100K, 300K and 600KHz respectively. I use the exsample circuit on page 26 of datasheet. And it turns out that the 600kHz one can load about 96W (6 ohm, if load heavier like 5ohm then the IC won't drive the Gate of transistor anymore with output only 12V), but the other 100k and 600kHz ones only about 30~40W. 

The followings list what I have checked :

1. DIS/EN pin : didn't go over 1.2V (max. about 700mV).

2. Overcurrent sense pin : about 1.1V. But it always about the same value from no load to the limit.

So I have a few questions :

1. I think it's the compensation problem happened on the 600kHz one, but I'm just unable to tune the right result.

2. Is TPS40211 can also work in 100k and 300kHz? or if I misunderstand its spec? 

3. I'm not really sure the Fig 2. of the datasheet (page5) meaning exactly. I guess it means,for example, when operating in 600kHz, wit can be during 0.2~0.9 duty cycle, is that correct?

4. Is there other factor that would cause the IC shoutdown I didn't notice?

Please help and thank you.

Regards, shiu

  • 0
    TI__Mastermind 35165 points

    Hi hsiu,

    I have a couple questions to make sure I'm understanding your setup completely.

    1. In your set up, there are 3 separate supplies with different switching frequency, each boosting a 12V input to 24V output at 5A load. Correct?
    2. Can you post a schematic of each design? Please include part numbers for your FET and inductor used.
    3. Can you show some screenshots of the output voltage, soft start pin and switching node when the supplies are not working?

    To answer your questions:

    2. Yes it can work with 100kHz and 300kHz fsw. With 12V to 24V output the duty cycle is approximately 50% which allows all switching frequencies according to Figure 2.
    3. This is correct.
    4. I will need to see some more specifics of your design to get a better idea of why it may be shutting down.

    Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 30 points

    Hi Anthony,

    Thank you so much for replying and so soon!

    About your questions :

    1. Yes, the 3 circuits are seperated exist,all 12 to 24 V at 5A.

    2&3. I have put the schematics and the pictures of waveform in the attatched file.1754.tps40211_120W_100_300_600kHz.rar

    Thanks again.

    Regards,

    Shiu

  • 0 in reply to water hsiu
    TI__Mastermind 35165 points

    Hi Shiu,

    You may be having stability issues for all three designs. It appears so for the 600kHz circuit because there is a lot of jitter in the switching waveform (VDS). How were your compensation components selected and do you have any method of measuring the loop response?

    I believe you can use the TPS40210 models for your compensation in switcherpro or TINA. Use your value of R7 and adjust R5 accordingly for the different reference voltage of the TPS40210.

    Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 30 points
    Hi Anthony,
    About compensation : At the first I followed the steps in the datasheet, but it didn't work, so I adjusted the capacitor and resister value by trial and error in 100k & 300k's case. the 600k is just the same as the example 1 of datasheet. This is the result.
    About loop response : No, all I have is an oscilloscope. Could you give some suggested instruments? maybe I can borrow one.
    I will try switcherpro or TINA ! 
    Thank you.
    Regards,

    Shiu