Datasheet

2R
2C
Ω3.0C
ff
××=
TPS61260, TPS61261
www.ti.com SLVSA99A –MAY 2011–REVISED FEBRUARY 2013
In Equation 3, the minimum inductance value required for accurate average output current regulation is
calculated. V
IN
is the input voltage. For typical applications which require voltage regulation, the recommended
inductor value is 4.7 μH. Applications with higher inductance values have lower light load efficiency. The
recommended range for the inductor value is from 2.2 μH up to 22 μH. The current rating required for this
inductor is I
LIM
and depends on the programmed output current I
OUT
. Please refer to the ELECTRICAL
CHARACTERISTICS table. Table 2 contains a list of inductors recommended for the TPS6126x:
Table 2. List of Inductors
VENDOR INDUCTOR SERIES
Murata LQM2HP_G0
Toko DFE252012C
Hitachi Metals KSLI-252010AG
CAPACITOR SELECTION
Input Capacitor
At least a 4.7-μF input capacitor is recommended to improve transient behavior of the regulator and EMI
behavior of the total power supply circuit. An X5R or X7R ceramic capacitor placed as close as possible to the
VIN and GND pins of the IC is recommended.
Output Capacitor
For the output capacitor, use of a small X5R or X7R ceramic capacitor placed as close as possible to the VOUT
and GND pins of the IC is recommended. If, for any reason, the application requires the use of large capacitors
which can not be placed close to the IC, use a smaller ceramic capacitor in parallel to the large capacitor. The
small capacitor should be placed as close as possible to the VOUT and GND pins of the IC.
The output capacitor should be at least 2.2 μF. There are no additional requirements regarding minimum ESR.
There is also no theoretical upper limit for the output capacitance value. The device has been tested with
capacitors up to 100 μF. In general, larger capacitors cause lower output voltage ripple as well as lower output
voltage drop during load transients. To improve control performance, especially when using high output
capacitance values, a feedforward capacitor in parallel to R1 is recommended. The value should be in the range
of the value calculated in Equation 4:
(4)
LAYOUT CONSIDERATIONS
For all switching power supplies, the layout is an important step in the design, especially at high peak currents
and high switching frequencies. If the layout is not carefully done, the regulator could show stability problems as
well as EMI problems. Therefore, use wide and short traces for the main current path and for the power ground
tracks. The input capacitor, output capacitor, and the inductor should be placed as close as possible to the IC.
Use a common ground node for power ground and a different one for control ground to minimize the effects of
ground noise. Connect these ground nodes at any place close to the ground pin of the IC.
The feedback divider should be placed as close as possible to the control ground connection. To lay out the
control ground, short traces are recommended as well, separated from the power ground traces. This avoids
ground shift problems, which can occur due to superimposition of power ground current and control ground
current. See Figure 20 for the recommended layout:
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