Datasheet
( )
f
OUT
IN max
RIPPLE1 MIN
SW
V V
1 14 3.3 1
I D 0.236 0.513 A
L1 8.2 H 600 kHz
-
-
» ´ ´ = ´ ´ =
m
( )
f
OUT
IN max
RIPPLE2 MIN
SW
V V
1 14 1.2 1
I D 0.086 0.556A
L2 3.3 H 600kHz
-
-
» ´ ´ = ´ ´ =
m
( ) ( ) ( )
( ) ( )
2 2
2 2 2 2
1 1 1
RIPPLE RIPPLE
L rms L avg OUT max
12 12 12
I I I I I 1.5 0.513 A 1.51A= + » + = + =
( ) ( ) ( )
( ) ( )
2 2
2 2 2 2
1 1 1
RIPPLE RIPPLE
L rms L avg OUT max
12 12 12
I I I I I 2.5 0.556 A 2.51A= + » + = + =
( ) ( )
1 1
RIPPLE
L peak OUT max
2 2
I I I 1.5 A 0.513A 1.76 A» + = + =
( ) ( )
1 1
RIPPLE
L peak OUT max
2 2
I I I 2.5 A 0.556A 2.78 A» + = + =
( )
( )
( )
2
2
TRAN max
OUT1 min
OUT OVER
I L
1A 8.2 H
C 12.4 F
3.3 V 0.2 V
V V
´
´ m
= = = m
´
´
( )
( )
( )
2
2
TRAN max
OUT 2 m in
OUT OVER
I L
1A 3.3 H
C 13.7 F
1.2 V 0.2 V
V V
´
´ m
= = = m
´
´
f
RIPPLE
RIPPLE(total)
OUT SW
MAX
RIPPLE
I
0.513 A
V
0.050 V
8 C
8 12.4 F 600kHz
ESR 0.081
I 0.513 A
æ ö
æ ö
-
-
ç ÷
ç ÷
´ ´
´ m ´
è ø è ø
= = = W
f
RIPPLE
RIPPLE(total)
OUT SW
MAX
RIPPLE
I
0.556 A
V
0.024 V
8 C
8 13.7 F 600kHz
ESR 0.028
I 0.556 A
æ ö
æ ö
-
-
ç ÷
ç ÷
´ ´
´ m ´
è ø è ø
= = = W
TPS54290, TPS54291, TPS54292
SLUS973 –OCTOBER 2009
www.ti.com
(22)
(23)
The RMS current through the inductor is approximated by Equation 24 and Equation 25.
(24)
(25)
A DC current with 30% peak-to-peak ripple has an RMS current approximately 0.4% above the average current.
The peak inductor current is estimated by Equation 26 and Equation 27.
(26)
(27)
A 8.2-µH inductor with a minimum RMS current rating of 1.51 A and minimum saturation current rating of 3.7 A
must be selected. A Coilcraft MSS1048-822ML 8.2-µH, 4.38-A inductor is chosen for Channel 1 and a Coilcraft
MSS1048-332 3.3-µH inductor is chosen for Channel 2.
Output Capacitor Selection
Output capacitors are selected to support load transients and output ripple current. The minimum output
capacitance to meet the transient specification is given by Equation 28 and Equation 29.
(28)
(29)
The maximum ESR to meet the ripple specification is given by Equation 30 and Equation 31.
(30)
(31)
A single 22-µF ceramic capacitor with approximately 2.5 mΩ of ESR is selected to provide sufficient margin for
capacitance loss due to DC voltage bias.
Input Capacitor Selection
A minimum 10-µF ceramic input capacitor on each PVDD pin is recommended. The ceramic capacitor must
handle the RMS ripple current in the input capacitor.
The RMS current in the input capacitors is estimated by Equation 32 and Equation 33.
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