Other Parts Discussed in Thread: TPS63060, TPS63802, TPS61094
Hello,
While drawing backup power circuit with SLVA676, I found some equations are not fit with their explanation.
1) I_PCH
At part 3.1, equation (1) defines I_PCH as below.
I_PCH = (V_main-V_D1-Vc)/R1,
where I_PCH = pre-charge currnet, V_d1 = voltage drop from diode, Vc = Backup capacitor voltage(normally above 2.2V), R1 = Series resistor.
At part 4, each parameters are assumed as V_main=5, V_D1=1, Vc=2.5, R1=27.
Now I_PCH should be (5-1-2.5)/27=560mA, but the document says I_PCH=150mA.
2) C_min
At part 3.3, equation (6) defines C_min as below.
C_min=2*T*P/(eff*(V_CF^2 - V_CL^2)),
where C_min=Minimum value of backup capacitor, T=backup time, P=backup power.
eff=efficiency and it is about 90%, V_CF and V_CL is 10V and 9.3V respectively.
At part 4, T is assumed as 4ms and P is 5W.
So C_min should be 2*0.004*5/(0.9*(10^2-9.3^2)) = 0.04/13.51 = 0.003, but it was said C_min = 550uF.
Is there any typo or missing parameters at the document?
