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TPS1211-Q1: Bootstrap capacitor EQUATION

ABKD
Intellectual 300 points
Part Number: TPS1211-Q1

Hello,

There is equation 4 in the datasheet for TPS1211-Q1 for CBST (bootstrap cap) as below snap -

Here, the query is: in above equation charge Qg in coulomb is added with capacitor C1 in farad. How is this possible adding two quantities of different unit?

Instead, it should be CBST > (Qg total / Vg) + (10x C1), where Vg = gate voltage.

This will convert all quantities to farad & their addition is possible.

Can anyone comment correction in above equation.

Regards,

Abhishek D.

  • +1
    TI__Guru** 105791 points

    Hi Abhishek,

    You are correct. It should be Qg total / delta (V(BST – SRC)).

    where delta (V(BST – SRC)) = Charge Pump Turn OFF voltage - Charge Pump Turn ON voltage which is close to 1V. That' why it is missing in the equation (4).

    We will clarify and add more explanation in the next data sheet revision.

    you can treat equation (4) as CBST > (Qg total / 1V ) + (10x C1)

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Intellectual 300 points

    Delta V(BST_SRC) will be 0.6V