Datasheet

DI
L
+ V
OUT
1 *
V
OUT
V
IN
L f
I
L
max + I
out
max )
DI
L
2
I
RMSC
OUT
+ V
OUT
1 *
V
OUT
V
IN
L f
1
2 3
Ǹ
DV
OUT
+ V
OUT
1 *
V
OUT
V
IN
L f
ǒ
1
8 Cout f
) ESR
Ǔ
TPS62590
www.ti.com SLVS897B –JANUARY 2009– REVISED APRIL 2011
(2)
(3)
With:
f = Switching Frequency (2.25MHz typical)
L = Inductor Value
ΔI
L
= Peak to Peak inductor ripple current
I
Lmax
= Maximum Inductor current
A more conservative approach is to select the inductor current rating just for the maximum switch current of the
corresponding converter.
Accepting larger values of ripple current allows the use of low inductance values, but results in higher output
voltage ripple, greater core losses, and lower output current capability.
The total losses of the coil have a strong impact on the efficiency of the dc/dc conversion and consist of both the
losses in the dc resistance (R
(DC)
) and the following frequency-dependent components:
• The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)
• Additional losses in the conductor from the skin effect (current displacement at high frequencies)
• Magnetic field losses of the neighboring windings (proximity effect)
• Radiation losses
Table 4. 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
Output Capacitor Selection
The advanced fast-response voltage mode control scheme of the TPS62590 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:
(4)
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:
(5)
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.
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