• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 168 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS65218D0: Switching Frequency Accuracy

Kuramochi Tadahiko
Guru 28715 points
Part Number: TPS65218D0

Hi,

Is switching frequency accuracy applied below spec?

Best Regards,

Kuramochi

  • 0
    TI__Intellectual 950 points
    Hi TQ,

    I believe so, but to make sure I have forwarded to your question to responsible apps engineer. Thanks

    Tuomo
  • 0
    TI__Mastermind 30280 points

    TQ,

    Yes, as I mentioned in this other thread (e2e.ti.com/.../2924355) the switching frequency, fSW, for the DC-DC converters DCDC1-3 in PWM operation will be the same as fOSC.

  • 0 in reply to Brian Berner
    Guru 28715 points

    Hi Brian-san,

    Switching frequency varies over ±12% depending on output current/voltage as attached.

    PWM周期 (002).xls

    Is this spec out sample ?

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Mastermind 30280 points

    Kuramochi-san,

    In my previous response, I was incorrect. I apologize for the confusion, but after I examine the datasheet closely and  see that fSW=2.4MHz for DCDC4. The fSW for DCDC1-3 is not specified.

    The DC-DC converters are hysteretic in the TPS65218D0, which is why you are measuring the frequency as a function of output current/voltage.

    It is common to use hysteretic converters for non-automotive devices, but it is not always obvious in the datasheet. This is why my initial answer stated that fOSC=fSW, because usually hysteretic converters specify a range of acceptable switching frequencies.

    However, I was able to verify fOSC for DCDC4 when Reg. 0x19, bit 7 = 0b (fPWM for DCDC4) and VIN=5V such that DCDC4 is operating in buck-only mode (see attached scope shot).

    Measuring the switching frequency for DCDC4 when it is operating as a buck-boost is more difficult, which is why VIN >> 3.3V (4V is a safe margin, but I used 5V).