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TPS40170: TPS40170 circuit

PAN-M
Mastermind 8375 points
Part Number: TPS40170

Dear all.

The TPS40170 device of our customer broke(1pc) and so I get their circuit.
I have a doubt to this circuit.
1) Gate registance of FET
2) BOOT registance
3) Double inductance
Please teach me the mistake of circuit which breaks a device.

Rtps40170_question.pdf

Regards,
PAN-M

  • 0
    TI__Mastermind 40040 points

    Hi,

    Details of the failure are not provided?  For example are you able to make the device fail every time? Under what condition the device failed?  Start up?  Steady state (Load/Unloaded)? Load step? 

    R58 can cause cross conduction between Q15 and Q16, Please try reducing R58 from 4.7R to 0R and retest?

    I checked the compensation values, it looks like you maybe marginally stable, have you checked transient response to ensure you have enough phase margin?

    PS: it was not clear to me what value you are using for C37?  But I am assuming its very small<100pF.

  • 0 in reply to David Baba
    Mastermind 8375 points

    Details of the failure are not provided?
    -> This schematics is one module, the failures occur at end user.
    For example are you able to make the device fail every time?
    -> Yes, 100PPM/lot
    Under what condition the device failed?  Start up?
    -> Sorry, I don't know the failars situation.
    Steady state (Load/Unloaded)? Load step?
    -> Same as above.
    R58 can cause cross conduction between Q15 and Q16, Please try reducing R58 from 4.7R to 0R and retest?
    -> Sorry, R58 is R68. OK, I will send your comment to our customer.
    I checked the compensation values, it looks like you maybe marginally stable, have you checked transient response to ensure you have enough phase margin?
    -> They have FRA, so I think it's being checked.
    PS: it was not clear to me what value you are using for C37?  But I am assuming its very small<100pF.
    -> C37 is not mount.

    Regards,
    PAn-M

  • 0 in reply to PAN-M
    Mastermind 8375 points

    The phase margin is attached;

    TPS40170_FRA.pdf

  • 0 in reply to PAN-M
    TI__Mastermind 40040 points

    Thanks for the plots.

    I cant read very clearly, but it does appear that you have at least 45 degrees of phase margin?  And the plots look fine, if so?

    Can you varify the corss over frequency please?  Thats where the gain crosses over the zero dB point.

    Thanks.

  • 0 in reply to David Baba
    Mastermind 8375 points

    Can you read cross over frequency?

    TPS40170_FRA_2.pdf

  • 0 in reply to PAN-M
    TI__Guru**** 191445 points

    I do not support TPS40170 directly, but I would like to comment.  Your crossover frequencies are all in the range of 600 to 630 Hz.  The is very low BW.  If you look at the phase, you are above 45 degrees well past 100 kHz.  I think a crossover frequency in the 70 to 80 kHz range would yield better performance.

  • 0 in reply to PAN-M
    TI__Mastermind 40040 points

    Yes, I agree with John,

     

    Your cross over frequency seems extremely low.  Set the  cross over frequency to 1/10 th of your switching frequency.  You can do this by increasing the Resistor that is in series with your capacitor going from Feedback to Comp.  This will set a higher mid band gain and increase your cross over frequency.  The high frequency will give you a better transient response on the output minimizing the perturbations and should avoid OVP conditions.

     

    Hope this helps?