DC-DC Converter Control Circuits
MC34063A/B
Design Formula Table
Calculation
ton/toff
(ton/toff)max
CT
IPK(SWITCH)
RSC
L(MIN)
CO
Step-UP
VOUT + VF − VIN(MIN)
VIN(MIN) − VSAT
1
f MIN
4.0 ×10−5 ton
I2 OUT(MAX)
( t off
t on
+ 1)
0.3 / IPK(SWITCH)
(
VIN(MIN) − VSAT
IPK(SWITCH)
)
×
t on(max)
9 IOUT t on
VRIPPLE(PP)
Step-Down
VOUT + VF
VIN(MIN) − VSAT
1
f MIN
4.0 ×10−5 ton
I2 OUT(MAX)
0.3 / IPK(SWITCH)
(
VIN(MIN) − VSAT −
I PK(SWITCH)
VOUT
)
×
t on(max)
I (t PK(SWITCH) on + t off )
8VRIPPLE(PP)
Voltage Inverting
VOUT + VF
VIN − VSAT
1
f MIN
4.0 ×10−5 ton
I2 OUT(MAX)
( t off
t on
+ 1)
0.3 / IPK(SWITCH)
(
VIN(MIN) − VSAT
I PK(SWITCH)
)
×
t
on(max)
9 IOUT t on
VRIPPLE(PP)
TERMS AND DEFINITIONS
VSAT - Saturation voltage of the output switch.
VF - Forward voltage drop of the output rectifier.
The following power supply characteristics must be chosen:
VIN - Nominal input voltage.
VOUT - Desired output voltage.
IOUT - Desired output current.
fMIN- Minimum desired output switching frequency at the selected values of VIN and IO.
VRIPPLE(p-p) – Desired peak-to-peak output ripple voltage. In practice the calculated capacitor value will need to be
increased due to its equivalent series resistance and board layout. The ripple voltage should be kept
to a low value since it will directly affect the line and load regulation.
Jan. 2011 - Rev. 1.0
- 12 -
HTC