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TPS53915 VDD Current Draw (switching)

Lance Collins
Intellectual 535 points
Other Parts Discussed in Thread: TPS53915

The spec for the TPS53915 describes I-VDD as 1850uA-max, but with "Power conversion enabled (no switching)". Not sure what this means and I need to know what the maximum VDD current is when there is switching. 1850uA seems too low - I was expecting more to drive the internal top and bottom FET gate capacitance. And it should be frequency dependent as well. My switching frequency is 1MHz.

  • 0
    TI__Guru**** 191445 points

    That is the way these currents are specified.  The Electrical Characteristics table shows the specifications for the TPS53915 IC.  The specifications are tested "open loop" for the standalone IC, so the current is measured in two conditions, with the device disabled, and with the device enabled, but not switching.  In the switching condition, that is closed loop with an inductor, filter capacitor and feedback.  That is an "application specific" parameter, not a characteristic of the IC itself.

    We may possibly have light or no load efficiency data, but I do not have it at hand right now.

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    I was able to locate some data. Vin = 12 V, Vdd = 5 V, Vout = 1.2 V, Iout = 0.188 mA

    500 kHz skip, Idd = 1.279 mA
    300 kHz skip, Idd = 1.292 mA
    300 kHz, FCCM, Idd = 5.429 mA
  • 0 in reply to JohnTucker
    Intellectual 535 points

    Yes, it's application specific, but I still need to know what it is for my application. Since I do not know what the internal gate charge is I can not compute the VDD current. The current depends on the total gate charge and the switching frequency. Total gate charge is also dependent on the input voltage (due to internal FET Gate-Drain charge).

    VDD current = Q-total * F-sw;

    Q-total = Q-GS + Q-GD, where Q-GD = INT(C-GD(V)*dVin) (integrated over voltage because of non-linear C-GD dependence on V).

    Can you give me a ballpark number for one particular application? Such as [V-in=12V, VDD=5V, F-sw=1MHz], or [V-in=5V, VDD=5V, F-sw=500KHz], or even V-in=18V, VDD=18V, F-sw=whatever]

    Any ballpark number will do and I can extrapolate from there to get an approximation.

  • 0 in reply to Lance Collins
    Intellectual 535 points

    Thanks John. I can work with this. I'll close the issue and assign it answered.