Diodes AZ34063U - Manual (Page 9)

1.5A STEP-DOWN/STEP-UP/INVERTING DC-DC CONVERTER AZ34063U
9
Jan. 2013 Rev. 1. 3 BCD Semiconductor Manufacturing Limited
Data Sheet
Typical Applications
Figure 14. Step-Up Converter (Note 5)
Note 5: This is a typical step-up converter configuration. In the steady state, if the resistor divider voltage at pin
5 is greater than the voltage in the non-inverting input, which is 1.25V determined by the internal reference, the
output of the comparator will go low. At the next swithching period, the output switch will not conduct and the
output voltage will eventually drop below its nominal voltage until the divider voltage at pin 5 is lower than 1.25V.
Then the output of the comparator will go high, the output switch will be allowed to conduct. Since V
PIN5
=V
OUT
*
R2/(R1+R2)=1.25(V), the output voltage can be decided by V
OUT
=1.25 * (R1+R2)/R2 (V).
+
-
Ipk
B
1.25V
Reference
Regulator
A
5
S
R
Q
I
PK
C
T OSC
V
IN
12V
C1
100 μF
R3 180
C
T
470pF
L1 150 μH
D1
1N5819
L2 1.0 μΗ
C3
100 μF
Optional
Filter
V
OUT
+
+
U1 AZ34063U
R1 47k
R2
2.2k
C2
330 μF
28V/175mA
+
Rsc
0.22
6
7
8 1
2
3
4
V
OUT