MC33063A, MC34063A Calculation for Vin=3v-6.4v
Vout=9V 500mAh
Conditions for requirement
Vout=9V
Iout=500mA
Fmin=24 KHz
Vin=3V
Vripple (p-p)=100mV-Don’t mind the voltage ripple as the solenoid and Hbridge can work at high voltage
Vsat=0.45V- VF=900mV-
Calculation to work out the correct passive components
1.
Determine the ratio of switch conduction ton versus diode conduction toff time.
ton / toff =( Vout + VF - Vin ) / (Vin - Vsat)
=(9 + 0.9 –3) / (3 - 0.45)
ton / toff = 6.9/2.55=2.7
2.
The cycle time of the LC network is equal to ton+ toff.
ton+ toff. = 1 / Fmin
= 1 / (24 * 103)
= 41.6 µS
3. Calculate ton and toff from the ratio of ton/toff in #1 and the sum of ton + toff in
#2.
toff = (41.6 * 10-6) / (2.7+1)
=11.24µS
ton = 41.6µS – 11.24µS
=30.36µS
4. The maximum on−time, ton (max), is set by selecting a value for CT.
CT= 4 * 10-5 ton
-5
-6
= 4 * 10 * (37.7 * 10 )
CT =1508pF=1.508nf
5. The peak switch current is:
Ipk(switch) = 2 * Iout((ton / toff)+1)
=2(0.5) * (2.7+1)
=3.7A
6. A minimum value of inductance can be calculated since the maximum on−time and
peak switch current are known.
Lmin= ( (Vin-Vsat)/ Ipk(switch) ) * ton
Lmin= ((3-0.45) / 3.7) * (30.42*10-6)
Lmin=20.93µ H
7. Value for the current limit resistor, Rsc, can now be determined by using the
current level of Ipk(switch) when Vin = 6.4 V(battery full charged).
Should Vin be the minimum possible or Max?
Lipk(switch)=((Vin-Vsat)/Lmin)*ton(max)
= ((3V – 0.45) /(20.93*10-6))*30.36 * 10-6
=3.7A
Rsc = 0.33/3.7
=0.0890Ω
8. An approximate value for an ideal output filter capacitor is:
CO= (Iout / Vripple(p-p))* ton
=(0.50/0.1)* (30.36 * 10-6)
=153UFDoes it seems correct?
9. The nominal output voltage is programmed by the R1, R2 divider.
Vout=1.25(1+(R2/R1))
R1=2.2k
9V=1.25(1+(R2/2.2))
6.2= (R2/2.2)
R2=13.64K