Datasheet
L1=
( - 1)V V
IN(max) O
I f
L (ripple) SW1
·
·
V
O
V
IN(max)
=
3 ( - 1)· V V
IN(max) O
I f
O SW
1 ·
·
V
O
1
V
IN(max)
¾
¾
¾
¾
1
I
L (ripple)1
=
V V
IN(max) O
- 1
L f1 ·
SW
·
V
O
1
V
IN(max)
¾
¾
I
L (peak)1
=
V
TRIP
R
DS(ON)
+
I
L (ripple)1
¾
I
L (RMS)1
=
ÖI I
O L (ripple)
1+( )
2 2
1
1
¾
12
¾
C1=
D
I L
load
2
1·
¾
2 1· ·V
O
D
V
OS
C1=
D
I L
load
2
1·
¾
2 · ·K D
V
US
K V V=( - 1)
IN O
·
T
on
1
¾
T T
ON min(off)
1+
C1=
I
L (ripple)1
8 1· V
O (ripple)
·
1
¾
f
SW
¾
TPS53114
SLVS887B –APRIL 2009–REVISED OCTOBER 2010
www.ti.com
COMPONENT SELECTION
CHOOSE INDUCTOR
The inductance value is selected to provide approximately 30% peak to peak ripple current at maximum load.
Larger ripple current increases output ripple voltage, improve S/N ratio and contribute to stable operation. L1 can
be calculated using Equation 3.
(3)
The inductors current ratings needs to support both the RMS (thermal) current and the peak (saturation) current.
The RMS and peak inductor current can be estimated as follows:
(4)
(5)
(6)
Note:
The calculation above shall serve as a general reference. To further improve transient response, the output
inductance could be reduced further. This needs to be considered along with the selection of the output
capacitor.
CHOOSE OUTPUT CAPACITOR
The capacitor value and ESR determines the amount of output voltage ripple and load transient response.
Recommend to use ceramic output capacitor.
(7)
(8)
Where:
(9)
(10)
Select the capacitance value greater than the largest value calculated from Equation 7, Equation 8 and
Equation 10. The capacitance for C1 should be greater than 66 mF.
Where:
• Δ V
OS
= The allowable amount of overshoot voltage in load transition
• ΔV
US
= The allowable amount of undershoot voltage in load transition
• T
min(off)
= Minimum off time
CHOOSE INPUT CAPACITOR
The TPS53114 requires an input decoupling capacitor and a bulk capacitor is needed depending on the
application. A minimum 10-mF high-quality ceramic capacitor is recommended for the input capacitor. The
capacitor voltage rating needs to be greater than the maximum input voltage.
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