Datasheet

Inductor Selection
´
´
´
IN OUT IN
OUT
V (V - V )
1
L =
f 200 mA V
(2)
´
ì
ï
´
í
ï
î
OUT OUT
IN
L,MAX
V I
+ 100 mA; continous current operation
0.8 V
I =
200 mA; discontinuous current operation
(3)
´
> ´
OUT OUT
IN
V I
0.8 100 mA
V
(4)
Capacitor Selection
Input Capacitor
Output Capacitor
TPS61220
TPS61221
TPS61222
SLVS776 – JANUARY 2009 ............................................................................................................................................................................................... www.ti.com
To make sure that the TPS6122x devices can operate, a suitable inductor must be connected between pin VIN
and pin L. Inductor values of 4.7 µ H show good performance over the whole input and output voltage range .
Choosing other inductance values affects the switching frequency f proportional to 1/L as shown in Equation 2 .
Choosing inductor values higher than 4.7 µ H can improve efficiency due to reduced switching frequency and
therefore with reduced switching losses. Using inductor values below 2.2 µ H is not recommended.
Having selected an inductance value, the peak current for the inductor in steady state operation can be
calculated. Equation 3 gives the peak current estimate.
For selecting the inductor this would be the suitable value for the current rating. It also needs to be taken into
account that load transients and error conditions may cause higher inductor currents.
Equation 4 provides an easy way to estimate whether the device will work in continuous or discontinuous
operation depending on the operating points. As long as the inequation is true, continuous operation is typically
established. If the inequation becomes false, discontinous operation is typically established.
The following inductor series from different suppliers have been used with TPS6122x converters:
Table 1. List of Inductors
VENDOR INDUCTOR SERIES
EPL3015
Coilcraft
EPL2010
Murata LQH3NP
Tajo Yuden NR3015
Wurth Elektronik WE-TPC Typ S
At least a 10- µ F input capacitor is recommended to improve transient behavior of the regulator and EMI behavior
of the total power supply circuit. A ceramic capacitor placed as close as possible to the VIN and GND pins of the
IC is recommended.
For the output capacitor C
2
, it is recommended to use small ceramic capacitors placed as close as possible to
the VOUT and GND pins of the IC. If, for any reason, the application requires the use of large capacitors which
can not be placed close to the IC, the use of a small ceramic capacitor with an capacitance value of around
2.2 µ F in parallel to the large one is recommended. This small capacitor should be placed as close as possible to
the VOUT and GND pins of the IC.
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