RT34063A
Design Formula Table
Calculation
t
on
/t
off
Step-up
Step-down
Voltage-Inverting
V
OUT
+
V
F
−
V
IN (MIN)
V
IN (MIN)
−
V
SAT
V
OUT
+
V
F
V
IN (MIN)
−
V
SAT
−
V
OUT
1
f
t
on
+
t
off
t
on
+
1
t
off
V
OUT
+
V
F
V
IN
−
V
SAT
1
f
t
on
+
t
off
t
on
+
1
t
off
(t
on
+ t
off
)
1
f
t
on
+
t
off
t
on
+
1
t
off
t
off
t
on
C
T
Ipk
(SWITCH)
(
t
on
+
t
off
)
−
t
off
4.0
×
10
−
5
t
on
(
t
on
+
t
off
)
−
t
off
4.0
×
10
−
5
t
on
2 I
OUT (MAX)
(
t
on
+
t
off
)
−
t
off
4.0
×
10
−
5
t
on
⎛
t
on
⎞
2 I
OUT (MAX)
⎜
+
1
⎟
⎝
t
off
⎠
0.3/Ipk
(SWITCH)
⎛
(
V
IN(MIN)
−
V
SAT
)
⎞
⎜
⎟
⎜
Ipk
(SWITCH)
⎟
t
on(MAX )
⎠
⎝
⎛
t
on
⎞
2 I
OUT(MAX)
⎜
+
1
⎟
⎝
t
off
⎠
0.3/Ipk
(SWITCH)
⎛
(
V
IN(MIN)
−
V
SAT
)
⎞
⎜
⎟
⎜
Ipk
(SWITCH )
⎟
t
on(MAX )
⎠
⎝
R
SC
0.3/Ipk
(SWITCH)
⎛
(
V
IN(MIN)
−
V
SAT
)
⎞
⎜
⎟
⎜
Ipk
(SWITCH )
⎟
t
on(MAX )
⎠
⎝
L (min)
C
O
9
I
OUT
ton
Vripple (pp)
I
pk(SWITCH )
( t
on
+
t
off
)
8 V
ripple(pp)
9
I
OUT
ton
Vripple (pp)
V
SAT
V
F
: Saturation voltage of the output switch.
: Forward voltage drop of the output rectifier.
The following power supply characteristics must be chosen:
V
IN
V
OUT
I
OUT
f
V
ripple(pp)
: Nominal input voltage.
: Desired output voltage
V
OUT
= 1.25(1+
: Desired output current.
: Minimum desired output switching frequency at the selected values of Vin and I
O.
: Desired peak-to-peak output ripple voltage. In practice, the calculated capacitor value needs to be increased
due to its equivalent series resistance and board layout. The ripple voltage should be kept to a low value
since it directly affects the line and load regulation.
R
2
R
1
)
www.richtek.com
8
DS34063A-13 March 2007
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
