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  1. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    LTC's DC674B Eval Board uses PFET FDC658AP and NFET Si3434DV and has max output of 2A and 10-cell battery.

    My goal was 5A charging so I can achieve that now, but only with active cooling. I still...
  2. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    Update - I've gone back to my previous board design with D-PAK (TO-252) FETs and have installed STD52P3LLH6 and STD65N3LLH5

    P-FET:
    Qg= 33nC @ 4.5V
    Rds-on = 17mR max

    N-FET:
    Qg = 3.6nC @...
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    Closed: Re: Synchronous Buck Converter FET selection

    Thanks treez, I wanted to keep the gate traces as short and away from other components as possible so adding 0-ohm resistors and pulldowns/pullups makes layout harder. I really like the idea of...
  4. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    EP,
    That is a good point. I just checked the 5V sq wave at the same horizontal resolution and I get 400ns+ fall times so I am probably reaching the limitations of this scope.

    I guess it would be...
  5. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    Just replaced with a new IC, same behavior.

    I just tried turning on the circuit while cool and touching the choke and FETs. The FETs are getting hot first, the choke stays cool until the FETs...
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    Closed: Re: Synchronous Buck Converter FET selection

    I have ordered a few different FETs with more similar characteristics to the demo board (capable of 2A)

    I have these installed right now:
    P-CH: DMP3056LSS-13
    "30V, 7.1A"
    65mOhms @ Vgs = 4.5V...
  7. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    Thanks, it is all making much more sense now, the power dissipation in the MOSFETs needs to be a trade-off between rds-on losses and switching losses. This converter is higher frequency than my...
  8. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    Thanks EP
    I think primarily it is only the P-FET getting too hot (hard to tell, but the P-FET gets hot first) so I ordered some different P-FETs to try with lower Qg.
    SI7143DP-T1-GE3
    30V, 35A...
  9. Replies
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    Closed: Re: Synchronous Buck Converter FET selection

    Thanks for the responses, all.

    Unfortunately there is no LTC4011 model for LTspice or demo sim.

    I've tried to make a few oscilloscope measurements but the circuit can only be powered for 10-15...
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    Closed: Re: Synchronous Buck Converter FET selection

    I added 22R gate resistors to the first version with FDD6637 and SUD50N04-8M8P-4GE3 FETs and the P-FET immediately smoked out and blew a pin off. I decided not to add pads for them because the...
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    Closed: Re: Synchronous Buck Converter FET selection

    Is there a good equation or application note for calculating switching losses you could recommend? The LTC4011 datasheet only gives an equation for the power dissipated by the LTC4011 from driving...
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    Closed: Synchronous Buck Converter FET selection

    I've built an LTC4011 circuit, schematic here:

    154046

    Everything works but the FETs get scorching hot in seconds.



    I had previously built another with FDD6637 and SUD50N04-8M8P-4GE3 FETs...
  13. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    When Switch B turns on and SW1 node (ch2) goes low, it seems Switch C also turns on and SW2 node (ch1) goes low, pulling down both sides of the choke at the same time, this is normal?
    At the same...
  14. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    The new P-FETs are operating correctly now. Both my lost shipment and replacement shipment showed up today so I tried replacing just the P-FET and nothing else and this fixed the overheating issue...
  15. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    Okay that is what I thought. Sometimes the float voltage is 31.9 (expected), mostly on initial power up, then after battery is connected and disconnected, float voltage will be 29.05V sometimes, or...
  16. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    The battery voltage is higher than the instant-on threshold so it's either operating incorrectly or something else is the problem.
    (oops my picture did not attach properly in my last post, here it...
  17. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    I looked back in the datasheet and there is a brief mention in pin description of BGATE that the pin is internally limited to CSP-BGATE = 9.5V so a P-FET rated for Vgs +/- 20V max should be fine.
    It...
  18. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    Yup, I have replaced the P-FET with one I pulled off my old board. Battery now receives 9.7A (designed at 10A) but still gets very hot.
    The gate is still only being pulled down for a Vgs about...
  19. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    Received replacement chips today and have the board working again.

    I have 1uF on both inductor soft start and battery charge soft start. I've ordered the capacitors required to slow down the...
  20. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    Do you mean the component selected for ITH and Vc pins? I used the same value as the Eval board, however those are different from the values in the typical application so I was not quite sure what...
  21. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    The main component differences between last rev and this rev are more input and output capacitance with higher Irms ratings because capacitors were getting warm at full load. Also the improvement in...
  22. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    EP,
    Could you explain what the point is of having a high and a low sense resistor for the inductor? Most of the examples and similar circuits I've looked at and read about only have a single sense...
  23. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    By doing their job, what do you mean? The FETs associated with D3 are the same in the waveform I attached and the waveform at SW2 matches the waveform of the gate drive.

    I left 0ohm jumpers for...
  24. Closed: Re: Buck/Boost Battery Charger works on dummy load, but does not charge batteries

    I finally have my new design of the battery charger prototyped and it seems to have more switching issues. When allowed to run at full load, it makes hissing/squeeling noises and everything gets hot...
  25. Closed: Altium "Align to Grid" command not moving all components

    In Altium v18.1.9 PCB layout, I frequency drag components around and they end up snapping to some pad or trace and I end up with all my components at oddball coordinates like X: 900.537mil / Y:...
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