Datasheet

DV
ESR
+ I
OUT
R
ESR
C
min
+
I
OUT
ǒ
V
OUT
* V
BAT
Ǔ
ƒ DV V
OUT
L +
V
BAT
ǒ
V
OUT
–V
BAT
Ǔ
DI
L
ƒ V
OUT
TPS61030 , TPS61031 , TPS61032
SLUS534G –SEPTEMBER 2002–REVISED MARCH 2015 www.ti.com
(5)
Parameter f is the switching frequency and ΔI
L
is the ripple current in the inductor, i.e., 10% × I
L
. In this example,
the desired inductor has the value of 5.5 µH. In typical applications a 6.8 µH inductance is recommended. The
minimum possible inductance value is 2.2 µH. With the calculated inductance and current values, it is possible to
choose a suitable inductor. Care has to be taken that load transients and losses in the circuit can lead to higher
currents as estimated in equation 4. Also, the losses in the inductor caused by magnetic hysteresis losses and
copper losses are a major parameter for total circuit efficiency.
The following inductor series from different suppliers have been used with the TPS6103x converters:
Table 3. List Of Inductors
(1)
VENDOR INDUCTOR SERIES
CDRH124
Sumida CDRH103R
CDRH104R
7447779___
Wurth Electronik
744771___
EPCOS B82464G
(1) See Third-Party Products Disclaimer
11.2.2.4 Capacitor Selection
11.2.2.4.1 Input Capacitor
At least a 10-µF input capacitor is recommended to improve transient behavior of the regulator and EMI behavior
of the total power supply circuit. A ceramic capacitor or a tantalum capacitor with a 100-nF ceramic capacitor in
parallel, placed close to the IC, is recommended.
11.2.2.4.2 Output Capacitor
The major parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of
the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is
possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by
using Equation 6:
(6)
Parameter f is the switching frequency and ΔV is the maximum allowed ripple.
With a chosen ripple voltage of 10 mV, a minimum capacitance of 100 µF is needed. The total ripple is larger
due to the ESR of the output capacitor. This additional component of the ripple can be calculated using
Equation 7:
(7)
An additional ripple of 80 mV is the result of using a tantalum capacitor with a low ESR of 80 mΩ. The total ripple
is the sum of the ripple caused by the capacitance and the ripple caused by the ESR of the capacitor. In this
example, the total ripple is 90 mV. Additional ripple is caused by load transients. This means that the output
capacitance needs to be larger than calculated above to meet the total ripple requirements.
The output capacitor must completely supply the load during the charging phase of the inductor. A reasonable
value of the output capacitance depends on the speed of the load transients and the load current during the load
change. With the calculated minimum value of 100 µF and load transient considerations, a recommended output
capacitance value is in around 220 µF. For economical reasons this usually is a tantalum capacitor. Because of
this the control loop has been optimized for using output capacitors with an ESR of above 30 mΩ. The minimum
value for the output capacitor is 22 µF.
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