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BQ24450: Help understand equation to calculate Rp on datasheet pages 13 and 14.

muga metal
Prodigy 20 points
Part Number: BQ24450

Hi,

I am trying to understand the equation to calculate value of Rp in datasheet SLUS929C (BQ24450) pages 13-14.

For the first example using PNP drive transistor, the equation is shown as follows:

The data sheet mentions minimum voltage drop at pin 16-15 is 2.0V (@25mA max).

So shouldn't RP = V15 / IRp

=(Vin - 0.7 - 2.0)/(Imax/hfe)  [Imax = current through  Qext and hfe= Beta of Qext]

=(Vin-2.7)/Imax/hfe

Thanks.