Datasheet

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Output Capacitor Selection
I
RMSCout
+ Vout
1 *
Vout
Vin
L ƒ
1
2 3
Ǹ
(3)
DVout + Vout
1 *
Vout
Vin
L ƒ
ǒ
1
8 Cout ƒ
) ESR
Ǔ
(4)
Input Capacitor Selection
LAYOUT CONSIDERATIONS
TPS62290 , TPS62291 , TPS62293
SLVS764C – JUNE 2007 – REVISED MARCH 2008
Table 2. List of Inductors
DIMENSIONS [mm
3
] INDUCTOR TYPE SUPPLIER
3 × 3 × 1.5 LPS3015 Coilcraft
3 x 3 x 1.5 LQH3NPN2R2NM0 MURATA
3.2 x 2.6 x 1.2 MIPSA3226D2R2 FDK
The advanced fast-response voltage mode control scheme of the TPS6229x allows the use of tiny ceramic
capacitors. Ceramic capacitors with low ESR values have the lowest output voltage ripple and are
recommended. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors,
aside from their wide variation in capacitance over temperature, become resistive at high frequencies.
At nominal load current, the device operates in PWM mode and the RMS ripple current is calculated as:
At nominal load current, the device operates in PWM mode and the overall output voltage ripple is the sum of the
voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the
output capacitor:
At light load currents the converter operates in Power Save Mode and the output voltage ripple is dependent on
the output capacitor and inductor value. Larger output capacitor and inductor values minimize the voltage ripple
in PFM mode and tighten dc output accuracy in PFM mode.
The buck converter has a natural pulsating input current; therefore, a low ESR input capacitor is required for best
input voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. For
most applications, a 10- µ F ceramic capacitor is recommended. The input capacitor can be increased without any
limit for better input voltage filtering.
Take care when using only small ceramic input capacitors. When a ceramic capacitor is used at the input and the
power is being supplied through long wires, such as from a wall adapter, a load step at the output or V
IN
step on
the input can induce ringing at the V
IN
pin. The ringing can couple to the output and be mistaken as loop
instability or could even damage the part by exceeding the maximum ratings.
Table 3. List of Capacitor
CAPACITANCE TYPE SIZE SUPPLIER
10 µ F GRM188R60J106M69D 0603 1.6x0.8x0.8mm3 Murata
As for all switching power supplies, the layout is an important step in the design. Proper function of the device
demands careful attention to PCB layout. Care must be taken in board layout to get the specified performance. If
the layout is not carefully done, the regulator could show poor line and/or load regulation, stability issues as well
as EMI problems. It is critical to provide a low inductance, impedance ground path. Therefore, use wide and
short traces for the main current paths. The input capacitor should be placed as close as possible to the IC pins
as well as the inductor and output capacitor.
Connect the GND Pin of the device to the Power Pad of the PCB and use this Pad as a star point. Use a
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Product Folder Link(s): TPS62290 TPS62291 TPS62293