iru3065 International Rectifier Corp., iru3065 Datasheet - Page 13

• Manufacturer Part Number: iru3065
• Description: Positive To Negative Dc To Dc Controller
• Manufacturer: International Rectifier Corp.

When I
age V
The above equation is used to select the current sens-
ing resistor R
Substitution of equation (16) into equation (13) results
in the relationship between frequency and output cur-
rent, that is
The above equation indicates that the switching fre-
quency decreases when output current increases dur-
ing power limit mode.
When I
maximum. Substitution of V
(6) into equation (13) results in the maximum switching
frequency:
Therefore, the inductance can be selected according
to the maximum desired frequency as shown in the fol-
lowing:
Fig. 24 and Fig.25 shows the theorectical predication
and calculation results for the output voltage and fre-
quency versus output current.
I
f
f
f
L
OCP
S
S(MAX)
S(MAX)
OUT
=
OUT
OUT
=
L I
=V
=I
=
=I
=
1
2
V
OUT(NOM)
OCP
IN
PEAK
OCP
S
V
.
V
, the output voltage equals nominal volt-
VI
OUT(NOM)
, the switching frequency reaches its
IN
V
R
V
V
IN
SEN
VI
S
IN
. From equation (15),we have
OUT(NOM)
(
(V
SEN
V
(V
(V
1 -
(V
D
OUT(NOM)
(V
) f
V
IN
D
- V
IN
IN
2 I
D
- V
+ V
(V
I
) L I
- V
+ V
S(MAX)
PEAK
- V
OUT(NOM)
IN
OUT
OUT(NOM)
V
OUT
D
) L
OUT(NOM)
OUT
+ V
D
IN
-
=V
)
-
+V
D
--(18)
PEAK
OUT(NOM)
) R
I
PEAK
-
)
D
)
S
and equation
---(17)
---(19)
---(20)
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Figure 24- The comparison between predicted and
Figure 25 - The comparison between predicted
measured output voltage versus output current
and measured switching frequency versus
6
5
4
3
2
1
0
1200
1000
Predicted fs(KHz)
800
600
400
200
0
Switching frequency versus output current
0
0
Predicted (-Vout)
Vout versus output current
0.2
output current
0.2
Output current (amp)
Output current (A)
IRU3065(PbF)
0.4
0.4
Experiment fs (kHz)
Measured -Vout
0.6
0.6
13
0.8
0.8