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LP8869-Q1: Calculation tool consultation

Alan Xia
Genius 9670 points
Part Number: LP8869-Q1

Tool/software:

Hi team，

I have two inquiries about the calculation tool parameters of LP8869. Please help me look at the following questions, thank you!
1. The switching frequency calculated by the tool based on 8867-9 (c) is different from the result calculated based on the datasheet. Why is this?

2. The VBG in the manual is 1.2v, why is the value defined in the tool 1.21v? Is this a typo or is there some other consideration?

3.The calculated initial voltage value does not match the measured value

  • 0
    TI__Expert 3611 points

    Hi Alan,

    For 1&2, please refer to the datasheet.

    For 3, as LP8869-Q1 is a switching device, it could have a overshoot at the output voltage. If there's no PWM input, the output voltage will be finally regulated to v_init. At the beginning, the output is in no-load condition, so, the discharging process of the output capacitor will be slow, resulting a long settling time.

    Best regards,

    Suchen

  • 0 in reply to Suchen Dong
    TI__Genius 9670 points

    Hi Suchen，

    Thank you for your answer. Please also help confirm the following information:

    1. What do the data dynamic and constant in the calculation tool mean? Switching loss and conduction loss?

    2. For thermal data measured directly on the IC surface using thermocouple wires, the thermal resistance coefficient of 0.9 in the table below should be used to calculate Tj, right?

  • 0 in reply to Alan Xia
    TI__Expert 3611 points

    Hi Alan,

    Alan Xia said:
    1. What do the data dynamic and constant in the calculation tool mean? Switching loss and conduction loss?

    I think so, but I need to check for an accuracy answer. Please notice that the result is just a reference.

    Alan Xia said:
    2. For thermal data measured directly on the IC surface using thermocouple wires, the thermal resistance coefficient of 0.9 in the table below should be used to calculate Tj, right?

    You are right. Please use Tj = Tc + (ψJT × Power) to calculate the Tj.

    Best regards,

    Suchen