tps43061 calculations

(11)
Dmax = (Vout - Vinmin)/Vout = (24.55-10)/24.55 = 14.55/24.55 = 0.593
Dmin = (Vout - Vinmax)/Vout = (24.55 - 14.4)/24.55 = 10.15/24.55 = 0.413

(12)
Fswontime = Dmin/Tonmin = 0.413/100ns = 4.13MHz

(13)
Fswofftime = (1-Dmax)/Toffmin = 0.407/250ns = 1.63Mhz

Select Fsw = 750KhZ = 0.75MHz


(15)
Iin = Iout/(1-Dmax) = 8A/0.407 = 19.66A

(16)
L(uH) >= Vout/(In*Kind*4*Fsw) = 24.55V/(19.66A*0.4*4*0.75MHz) = 1.04uH

Select 1uH (SRP1265A 2.3mOhm 30A)

(18)
ILrms = SQRT((Iout/(1-Dmax))^2 + ((Vinmin*Dmax)/(SQRT(12)*L*Fsw))^2) = SQRT(386.36+5.21) = 19.8A

(19)
ILpeak = Iout/(1-Dmax) + (Vinmin*Dmax)/(2*L*Fsw) = 19.66 + (10*0.593)/(2*1uH*0.75MHz) = 21.64A

(21)
Rcs = Vcsmaxtyp/(1.2*ILpeak) = 68mV/(1.2*21.64) = 2.62mOhm
Select Rcs = 5mOhm/1W parallel to 5mOhm/1W = 2.5mOhm/2W

(22)
PRcs = (68mV*68mV)/2.5mOhm = 1.85W

(24)
Cout > (Dmax*Iout)/(Fsw*Voutripple) = (0.593*8A)/(0.75MHz*0.25V) = 25uF
Select 27.6uF (10u + 4*(2*2*2u) on module, note: the 4 outputs on module have also 100uF electrolytic)

(25)
Igd = (Qghs+Qgls)*Fsw = (6.8nC+6.8nC)*0.75MHz = 0.0102A = 10.2mA

The target efficiency of the design dictates the acceptable power loss in the MOSFETs. The two largest
components of power loss in the low-side FET are switching and conduction losses. Both losses are highest at
the minimum input voltage when low-side FET current is maximum.

For our purpose:
NOTE: Therefore when Vbat < 10V we should not allow motor drive but only battery charging until Vbat > 12V again.
Normally we keep charging the battery but if motors are used intensely the Vbat may become too low.

(26)
Pcondls = Dmax*ILrms^2*Rdsonls = 0.593*19.8^2*0.0077 = 1.79W

(27)
Psw = (Fsw/2)*(Coss*Vout^2 + ((Vout*Iout)/(1-Dmax))*((Qgd*Rg)/(VCC-Vgs))) = (0.375Mhz)*(440p*24.55^2 + ((24.55*8A)/(1-0.593))*(3.6n*1.5)/(5.5-1.8))
= (0.375MHz)*(0.265u + 482.56*1.46n) = 0.375MHz*0.97u = 0.36W

(28)
Pcondhs = (1-Dmax)*ILrms^2*Rdsonhs = 0.407*19.8^2*0.0077 = 1.23W

(29)
Pdt = Vsd*ILrms*(Tnonoverlap1 + Tnonoverlap2)*Fsw = 0.7*19.8A*(65ns+65ns)*0.75MHz = 1.35W


Voltage divider: Rhs=10k, Rls=0.523k

(43)
Rcomp = (40/3)*(2*3.14*Cout*Rsense*Vout*Fco*(Rsh+Rsl))/(Rsl*Vinmin*Gea) =
= (40/3)*(2*3.14*27.6u*2.5mOhm*24.55V*Fco*(10k+0.523k)/(0.523k*10V*1100) = 10000 (we selected Rcomp=10k)
Fco = 10000/259.44 = 38.5kHz

(44)
Ccomp = 1/(2*3.14*(Fco/10)*Rcomp) = 1/(2*3.14*3.85k*10k) = 4.1nF
We selected 100nF

(46)
Chf = 1/(20*3.14*Fco*Rcomp) = 1/(20*3.14*38.5k*10k) = 41.3pF
Select 100pF