Datasheet

I
L(PK)
=I +
OUT(MAX)
()
V V V
OUT IN(MAX) OUT
x -
1.6 xV xL xF
IN(MAX) OUT SW
I
L(RMS)
+ I
2
OUT(MAX)
)
1
12
ǒ
V
OUT
ǒ
V
IN(MAX)
* V
OUT
Ǔ
V
IN(MAX)
L
OUT
F
SW
0.8
Ǔ
2
Ǹ
L
MIN
=
()
V
OUT IN(MAX) OUT
xV -V
V
IN(max) IND OUT SW
xK xI xF x0.8
TPS5410
SLVS675C –AUGUST 2006–REVISED SEPTEMBER 2013 www.ti.com
CAUTION
The maximum ratings for voltage and current are not to be exceeded under any
circumstance.
Additionally, some bulk capacitance may be needed, especially if the TPS5410 circuit is not located within
approximately 2 inches from the input voltage source. The value for this capacitor is not critical but it should be
rated to handle the maximum input voltage including ripple voltage and should filter the output so that input ripple
voltage is acceptable.
Output Filter Components
Two components need to be selected for the output filter, L1 and C3. Since the TPS5410 is an internally
compensated device, a limited range of filter component types and values can be supported.
Inductor Selection
To calculate the minimum value of the output inductor, use Equation 4:
(4)
K
IND
is a coefficient that represents the amount of inductor ripple current relative to the maximum output current.
Three things need to be considered when determining the amount of ripple current in the inductor: the peak to
peak ripple current affects the output ripple voltage amplitude, the ripple current affects the peak switch current,
and the amount of ripple current determines at what point the circuit becomes discontinuous. For designs using
the TPS5410, K
IND
of 0.2 to 0.3 yields good results. Low output ripple voltages is obtained when paired with the
proper output capacitor, the peak switch current is below the current limit set point, and low load currents can be
sourced before discontinuous operation.
For this design example, use K
IND
= 0.3, and the minimum inductor value is 66 μH. The next highest standard
value used in this design is 68 μH.
For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded.
The RMS inductor current can be found from Equation 5:
(5)
and the peak inductor current can be determined using Equation 6:
(6)
For this design, the RMS inductor current is 1.004 A, and the peak inductor current is 1.147 A. The chosen
inductor is a Coilcraft MSS1260-683 type. The nominal inductance is 68μH. It has a saturation current rating of
2.3 A and a RMS current rating of 2.3 A, which meets the requirements. Inductor values for use with the
TPS5410 are in the range of 10 μH to 100 μH.
Capacitor Selection
The important design factors for the output capacitor are dc voltage rating, ripple current rating, and equivalent
series resistance (ESR). The dc voltage and ripple current ratings cannot be exceeded. The ESR is important
because along with the inductor ripple current it determines the amount of output ripple voltage. The actual value
of the output capacitor is not critical, but some practical limits do exist. Consider the relationship between the
desired closed loop crossover frequency of the design and LC corner frequency of the output filter. Due to the
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