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LP2950: power/temperature related curve

Lillian Liu(SH)
Expert 4620 points
Part Number: LP2950

Tool/software:

Hi team,

LP2950CDT-3.3/NOPB, used for 24V to 3.3v.

When filling out the sizing process for ECSQ, we need to fill out the derating curve, the rated power, the temperature at which the derating starts, and the percentage of the maximum derating (as shown in red in Figure 1 below, the next line is the content of a resistor material, the rated power is 0.063W, the derating starts at 70℃, and it will drop to 0 at 155℃, as shown in Figure 2 below).

In the datasheet, only the curve shown in Figure 3 below is found, and there is no power/temperature related curve. Can you provide the relevant values?

  • 0
    TI__Guru 50025 points

    Hi Lilian,

    The characteristics of LDOs are more complicated than resistors, so I don't think we can give numbers like the temperature at which derating starts because the temperature dependence is not linear and doesn't exactly "derate" anyways. See Figure 5 below.

    The rated power isn't a constant value (or more accurately there isn't a rated power) and depends on the package used and its thermal characteristics and the board layout (heatsinking). The only requirement is that the junction temperature doesn't exceed the maximum rated operating junction temperature of 125C. What we can do is construct a plot using the thermal metrics (in particular RθJA), the operating junction temperature range, and the maximum possible power dissipation given the max input voltage, min output voltage, and max load current. The max power dissipation that this device can achieve within the specified operating region is (30V - 3V) * 100mA = 2.7W, the device can operate between -40C and 125C, and RθJA = 51.3C/W, and with this information the maximum power curve looks like below. The elbow is calculated as 125C - 51.3C/W * 2.7W = -13.5C.

    As for the percentage of maximum derating, I think what you're looking for is the output voltage spec, which is over the load current range, and the line regulation spec, both of which are over the full temperature range. The output voltage spec is 2.4%, and the line reg spec is 0.2%, for a total of 2.6% tolerance. 

    Regards,

    Nick