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VEFT1-SMT Dual Output Series Dc-Dc Converter
Rev. 11-2005
- Miniꢀuꢀ loading
Application Notes:
The converter needs a ꢀiniꢀuꢀ of 10% loading to
ꢀaintain output regulation. Operation under no-load
conditions will not cause iꢀꢀediate daꢀages but
ꢀay reduce reliability, and cause perforꢀance not to
ꢀeet specifications.
- Input filtering
To reduce the reflected ripple current and ꢀiniꢀize
EMI, especially when the converter input is ꢀore
than 2” away froꢀ the DC source, it is recoꢀꢀended
to connect a low ESR electrolytic capacitor between
Vin and Gnd. The values suggested are as shown in
Table 1. If additional filtering is required, the
capacitance ꢀay be increased, or expanded to an LC
network as shown in Figure 1.
- Regulation
With a seꢀi-regulated design, the converter’s output
voltage varies with load current and will change
proportionally to the input voltage. If regulated
output is needed, an external regulator can be used
as shown in Figure 2.
Table 1
Input Voltage
5 V
External Input Capacitance
- Protection
The converter has ꢀiniꢀal protection against input
over-voltage or output over-load, and ꢀay be
perꢀanently daꢀaged if exposed to these conditions.
mn input claꢀping device can be used for input
voltage liꢀiting. mn input fuse or an output fuse
can also be used to protect against over-loading.
4.7 µF
2.2 µF
2.2 µF
1.0 µF
12 V
15 V
24 V
- Output filtering
- Dual outputs used as a single output
mn output capacitor is needed to ꢀeet output ripple
requireꢀents as shown in Table 2.
The +Vout and -Vout can be used to obtain a single
output that is the suꢀ of the two outputs. In this
case, the COM pin shouldn’t be used.
Output capacitance ꢀay be increased for additional
filtering, but should not exeed 10µF or expanded to
an LC network as in Figure 1.
- External Regulator
mn external 3-terꢀinal regulator can be connected
to the output of the converter to achieve full
regulation. Make sure the converter’s output voltage
provides sufficient head rooꢀ for the regulator. mn
additional benefit is that the built-in protection
features in the regulator, such as OCP, OTP, etc, will
protect the converter also. In a coꢀpliꢀentory
supply, a negative output regulator ꢀust be used to
achieve the negative regulated output.
Table 2
External Ouput Capacitance
Vout
5 V
10 µF
4.7 µF
2.2 µF
9 V
12 V
15 V
24 V
1 µF
0.47 µF
+Vout
REG
REG
+Vin
COM
DD
C
C
DDCC
-Vin
-Vout
L
L
+Vout
+Vin
C
REG
REG
+Vout
COM
-Vout
COM
+Vin
-Vin
C
DC DC
C
L
-Vin
DD
C
C
DDCC
-Vout
REG
REG
<Figure 1>
V-Infinity, LLC, 20050 SW 112th Ave., Tualatin, OR 97062
www.v-infinity.com
1-866-372-1258
CUI [ CUI INC ]
