MC34063A
DC/DC CONVERTER CONTROL CIRCUIT
SPEC NO: DS34063A-P2
V
SAT
V
F
= Saturation voltage of the output switch.
= Forward voltage drop of the ringback rectifier
F
MIN
-
Minimum desired output switching frequency
at the selected values for V
IN
and I
OUT
.
The following power supply characteristics must be
chosen:
V
IN
V
OUT
-
Nominal input voltage.
-
Desired output voltage,
V
OUT
=1.25 (1 + RB/RA)
V
RIPPLE (P-P)
-
Desired peak-to-peak output ripple voltage.
In practice, the calculated value will need to
be increased due to the capacitor equivalent
series resistance and board layout. The
ripple voltage should be kept to a low value
since it will directly effect the line and load
regulation.
I
OUT
-
Desired output current.
!
APPLICATION EXAMPLES
200µH
L
+
8
RS
0.25
V
IN
7
6
+
100µF
MC34063A
5
DRI
IPK
VCC
FB
CS 1
SE
TC
4
GND
470pF
CT
RA
1.2K
RB
3.6K
2
3
D1
1N5821
C
O
470µF
V
OUT
5V/500mA
C1
Line Regulation
Load Regulation
Short Circuit Current
V
IN
= 10V ~20V @ I
O
=500mA
V
IN
= 15V, @ I
O
=10mA ~ 500mA
V
IN
=15V, @ R
L
= 0.1Ω
Fig. 1 Step-Down Converter
40mV
5mV
1.3A
R1
8 DRI
RS
V
IN
+
C1
7
6
5
IPK
VCC
FB
CS 1
SE
TC
GND
2
3
4
CT
D1
L
Co
+
V
OUT
R2
Q1
MC34063A
RS
RB
Fig. 2 Step-Down Converter with External PNP Saturation Switch
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: (8863)577-2500 FAX:(8863)577-2510
6
AIC [ ANALOG INTERGRATIONS CORPORATION ]
