Datasheet
DESIGN EXAMPLE 1 STEP-BY-STEP DESIGN PROCEDURE
( )
OUT1 FD
MAX1
FD
IN min
V V
5.0 0.4
D » 0.540
V V 9.6 0.4
+
+
= =
+ +
(21)
( )
OUT2 FD
MAX2
FD
IN min
V V
3.3 0.4
D » 0.370
V V 9.6 0.4
+
+
= =
+ +
(22)
( )
OUT1 FD
MIN1
FD
IN max
V V
5.0 0.4
D » 0.397
V V 13.2 0.4
+
+
= =
+ +
(23)
( )
OUT2 FD
MIN2
FD
IN max
V V
3.3 0.4
D » 0.272
V V 13.2 0.4
+
+
= =
+ +
(24)
( ) ( )
Lrip max OUT max
I 0.25 I 0.25 3.0 A 0.750 A= ´ = ´ =
(25)
( )
OUT1
IN max
min1 m in1
Lrip1(max) SW
V V
1 13.2 5.0 1
L D 0.397 7.23 H
I f 0.75 A 600 kHz
-
-
» ´ ´ = ´ ´ = m
(26)
( )
OUT2
IN max
min 2 min2
Lrip2(max) SW
V V
1 13.2 3.3 1
L D 0.272 6.0 H
I f 0.75 A 600kHz
-
-
» ´ ´ = ´ ´ = m
(27)
( )
OUT1
IN max
RIPPLE1 min1
1 SW
V V
1 13.2 5.0 1
I D 0.397 0.661A
L f 8.2 H 600kHz
-
-
» ´ ´ = ´ ´ =
m
(28)
( )
OUT2
IN max
RIPPLE2 min 2
2 SW
V V
1 13.2 3.3 1
I D 0.272 0.547 A
L f 8.2 H 600kHz
-
-
» ´ ´ = ´ ´ =
m
(29)
( ) ( )
(
)
( )
( )
(
)
( ) ( ) ( )
2 2
2 2 2 2
1 1 1
RIPPLE1 RIPPLE1
L1 rms L1 avg OUT1 max
12 12 12
I I I I I 3.0 0.661 A 3.0 A= + » + = + =
( ) ( )
(
)
( )
( )
(
)
( ) ( ) ( )
2 2
2 2 2 2
1 1 1
RIPPLE2 RIPPLE2
L2 rms L2 avg OUT2 max
12 12 12
I I I I I 3.0 0.547 A 3.0 A= + » + = + =
TPS55383 , , TPS55386
www.ti.com
......................................................................................................................................................................................... SLUS818 – SEPTEMBER 2008
The bill of materials for this application is shown below in Table 3 . The efficiency, line and load regulation
measurements from boards built using this design are shown in Figure 34 and Figure 35 .
Duty Cycle Estimation
The duty cycle of the main switching FET of each channel is estimated by:
Inductor Selection
The peak-to-peak ripple is to be limited to 25% of the max output current, so that
The minimum inductor size is estimated by:
The standard inductor value of 8.2 µ H is selected for both Channel 1 and Channel 2. The resulting ripple
currents are estimated by:
RMS current through the inductor is approximated by:
(30)
(31)
The RMS inductor current is 3.0 for both channels.
Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 31
Product Folder Link(s): TPS55383 TPS55386