Datasheet
NCP3065, NCV3065
http://onsemi.com
9
APPLICATIONS
Figures 16 through 24 show the simplicity and flexibility
of the NCP3065. Two main converter topologies are
demonstrated with actual test data shown below each of the
circuit diagrams.
Figure 16 gives the relevant design equations for the key
parameters. Additionally, a complete application design aid
for the NCP3065 can be found at www.onsemi.com.
(See Notes 8, 9, 10) Step−Down Step−Up
t
on
t
off
V
out
) V
F
V
in
* V
SWCE
* V
out
V
out
) V
F
* V
in
V
in
* V
SWCE
t
on
t
on
t
off
f
ǒ
t
on
t
off
) 1
Ǔ
t
on
t
off
f
ǒ
t
on
t
off
) 1
Ǔ
C
T
C
T
+
381.6 @ 10
*6
f
osc
* 343 @ 10
*12
I
L(avg)
I
out
I
out
ǒ
t
on
t
off
) 1
Ǔ
I
pk
(Switch)
I
L(avg)
)
DI
L
2
I
L(avg)
)
DI
L
2
R
SC
0.20
I
pk (Switch)
0.20
I
pk (Switch)
L
ǒ
V
in
* V
SWCE
* V
out
DI
L
Ǔ
t
on
ǒ
V
in
* V
SWCE
DI
L
Ǔ
t
on
V
ripple(pp)
DI
L
ǒ
1
8 f C
O
Ǔ
2
) (ESR)
2
Ǹ
[
t
on
I
out
C
O
) DI
L
@ ESR
V
out
V
TH
ǒ
R
2
R
1
) 1
Ǔ
V
TH
ǒ
R
2
R
1
) 1
Ǔ
I
out
V
ref
ńR
sense
V
ref
ńR
sense
8. V
SWCE
− Darlington Switch Collector to Emitter Voltage Drop, refer to Figures 7, 8, 9 and 10.
9. V
F
− Output rectifier forward voltage drop. Typical value for 1N5819 Schottky barrier rectifier is 0.4 V.
10.The calculated t
on
/t
off
must not exceed the minimum guaranteed oscillator charge to discharge ratio.
Figure 16. Design Equations
The Following Converter Characteristics Must Be Chosen:
V
in
− Nominal operating input voltage.
V
out
− Desired output voltage.
I
out
− Desired output current.
DI
L
− Desired peak−to−peak inductor ripple current. For maximum output current it is suggested that DI
L
be chosen to be
less than 10% of the average inductor current I
L(avg)
. This will help prevent I
pk
(Switch)
from reaching the current limit threshold
set by R
SC
. If the design goal is to use a minimum inductance value, let DI
L
= 2(I
L(avg)
). This will proportionally reduce
converter output current capability.
f − Maximum output switch frequency.
V
ripple(pp)
− Desired peak−to−peak output ripple voltage. For best performance the ripple voltage should be kept to a low
value since it will directly affect line and load regulation. Capacitor C
O
should be a low equivalent series resistance (ESR)
electrolytic designed for switching regulator applications.