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LMG1210: Bootstrap capacitor dimensioning

Ricard Picas
Prodigy 170 points
Part Number: LMG1210

Hello, I'm designing a 150V half-bridge inverter with LMG1210 and EPC2034C transistors.

I have doubts about the bootstrap capacitor calculation. The datasheet proposes the use of the following formula:

(0.5 nC + Qrr + QgH + IHB × ton)/ΔV = CBST,min, 

where IHB is the quiescent current of the high-side driver when the transistor is ON (multiplied by Ton). However, on the datasheet only the quiescent current when the high-side is off (HI=0V) is provided (IHB max 850µA, section 6.5 of datasheet).

- Is the quiescent current the same when the high-side is on ? (total current = quiescent (same as when off) + current related to Qrr and QgH).

- Or do we have to consider the gate to source forward leakage of the transistors (Igss)?

Thank you for your help!

  • 0
    TI__Genius 12990 points

    Hi Ricard,

    Thanks for reaching out about lmg1210.

    The HB operating quiescent current, is the quiescent current when the high-side is on and can be found in the datasheet as IHBSO, which is 1nA typical.

    The Igss for the EPC2034 is 9mA max from the datasheet, which is a large amount of leakage compared to the typical value and in this case should be considered in for the bootstrap minimum cap equation.

    Let me know if you have any other questions.

    Thanks,