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TPSM82823A: Would like to estimate the switching frequency

Part Number: TPSM82823A
Other Parts Discussed in Thread: TPS62130,

Tool/software:

Hi team,

Could you please kindly let me know the equation to derive the switching frequency from t_on value? My customer would like to estimate the switching frequency variation based on the input voltage. 

If possible, could you please also let me know the part to part variation of switching frequency?

Best regards,

Shunsuke Yamamoto

  • Hi Shunsuke Yamamoto,

    Thank you for using E2E,

    TPSM82823A operates using DCS control topology and in DCS control topology the switching frequency varies with many factors such as, VIN, VOUT, IOUT & propagation delay.

    You can find more info here - Understanding frequency variation in the DCS-Control(TM) topology

    Thank you & regards,

    Moheddin.

  • Hi Moheddin,

    Thank you for sending the helpful material! I understand why the frequency variation occurs in DCS control, and this is totally expected!

    In this material, the minimum off time of TPS62130 is approximately 120ns is stated. How about the minimum off time of TPSM82823A?

    Best regards,

    Shunsuke Yamamoto

  • Hi Moheddin,

    My customer would also like to know the exact minimum on time of TPSM82823A. Without this information, it is difficult to estimate the frequency variation.

    Best regards,

    Shunsuke Yamamoto

  • Hi Shunsuke Yamamoto,

    My customer would also like to know the exact minimum on time of TPSM82823A. Without this information, it is difficult to estimate the frequency variation.

    The On time is not fixed it varies with respect to the operating conditions, with given VIN, VOUT & switching frequency(4MHz), the TON can be calculated, as per the below formulae. 

    TPSM82823A operates using DCS control topology and in DCS control topology the switching frequency varies with many factors such as, VIN, VOUT, IOUT & propagation delay.

    For example, you can observe the variation of switching frequency in TPSM82823A,  at VIN = 2.4V to 5.5V, Vout = 1.8V, Iout = 100uA to 3A, Temp = 25C.

    Thank you & regards,

    Moheddin.

  • Hi Moheddin,

    Thank you for the reply. I understand that on time is not fixed. But how about the minimum off time? The minimum off time of TPS62130 is approximately 120ns which is stated in the application note you sent me. My customer assumes TPSM82823A also has minimum off time like TPS62130.

    Best regards,

    Shunsuke Yamamoto

  • Hi Shunsuke Yamamoto,

    But how about the minimum off time? The minimum off time of TPS62130 is approximately 120ns which is stated in the application note you sent me.

    This is the value that is coming from the measurements with specific operating conditions. This values varies with respect to load current & output voltage. Here the minimum off time is considered as the off time of HS-FET, just before the converter enters 100% duty cycle mode. You can observe figure 2c & 3c in the application note where the minimum off time is different with respect to output voltage.

    You can easily measure using the EVM with desired output current and VOUT thus reducing the input voltage until the point just before the converter reaches 100% duty cycle mode.

    Thank you & regards,

    Moheddin.

  • Hi Modeddin,

    Thank you for the reply. My customer has evaluated TPSM82823A by TPSM82823AEVM-127 with the parameters below. You can see the switching frequency drops from 2.66MHz to 1.47MHz. Field team and my customer assume this switching frequency drop is caused by the limitation of minimum off time. Thus we would like to know the minimum off time, typical minimum off time is okay.  If you have any causes that you come up with, please kindly let me know?

    Vin(V)

    Vout(V)

    Iout(A)

    Fsw(MHz)

    3.3

    1.5

    0.15

    3.68

    3.3

    2.5

    0.85

    2.66

    3.0

    2.5

    0.85

    1.47

    Best regards,

    Shunsuke Yamamoto

  • Hi  Shunsuke Yamamoto

    Field team and my customer assume this switching frequency drop is caused by the limitation of minimum off time.

    Yes, your understanding is correct, at higher duty cycles, due to the minimum off time, the switching frequency will be reduced.

    In my bench measurements trying with different output voltages, I see a minimum off time of approximately 100ns.

    Regards,

    Moheddin.