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TPS40170 DCM mode

ilan mazuz
Intellectual 295 points
Other Parts Discussed in Thread: TPS40170, LM5117

i try and i find that to change resistors it is not easy ,i am runing simulation in orcad it take about 25 minutes i can live with that.

i have another question about DCM mode in TPS40170.is there any problem to work with tps40170 in DCM mode?how the voltage output is stable?

  • 0
    TI__Mastermind 41310 points

    Ilan,

    I have split the thread and moved it to the product line. Your question about DCM mode should be best answered here.

  • 0
    TI__Mastermind 40040 points

    if you need a controller with a Diode emulation mode, suggest looking at the LM5117.  The TPS40170 runs in CCM only.

  • 0 in reply to David Baba
    Intellectual 295 points

    Hi,

    I design buck with tps40170 ic as follow:

    1.vin 36v-52v

    2.vout 7.4v

    3.iout pulse high current about 20A or 10A during 1msec .

    PLS check the ELEC SCH bellow:

    1_601-31-00121-00.pdf

  • 0 in reply to ilan mazuz
    TI__Expert 4365 points

    Hello Ilan;

    Thank you for including the schematic. It's always a great help. As David Baba mentions, this device only runs in CCM mode so there isn't a DCM mode issue. The downside of CMM-only is that efficiency is lower at light load. This may only be an issue if the input power is from a battery or if there is restricted ability to get rid of heat.

    Other general comments:

    You have a 1210 size filter bead in series with the supply input. Make sure it is actually rated for suppression ability at maximum input current. Sometimes these beads have a thermal current rating that misleads you into thinking they still function properly at that current, but ferrites saturate quite easily. So read the data sheet closely to see if it is the correct choice.

    The input capacitors on the input rail are probably okay so far as ripple current rating for the design. Since there appears to be cabling in the input leads you may end up needing some bulk input capacitance in addition to the 2.2uF ceramics shown. Maybe 100uF or  220uF at least. Looking at your step load requirement, it may need even more as a local reservoir, depending on the inductance and resistance of the interconnect from the source supply.

  • 0 in reply to Alan Martin
    Intellectual 295 points
    thank you.
    in my input i have battery and i want that the tps40170 will be fast response load for 20A and the ripple of the voltage should be smaller about 100mv vpp ,i made simulation and i find the cout=700uf and L=1uH how i make the loop control stable with the excel file?