Datasheet

APPLICATION INFORMATION
V
IN
GND
EN
FB
SW
R2
360kΩ
R1
540kΩ
MODE
V =2Vto6V
IN
C
4.7 F
IN
m
TPS62250DRV
L1
2.2 Hm
C1
22pF
C
10 F
OUT
m
V 1.5V
Upto600mA
OUT
OUTPUT VOLTAGE SETTING
V
OUT
+ V
REF
ǒ
1 )
R
1
R
2
Ǔ
with an internal reference voltage V
REF
typical 0.6V.
OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)
Inductor Selection
TPS62250
www.ti.com .......................................................................................................................................................................................... SLVS842 – SEPTEMBER 2008
Figure 35. TPS62250DRV Adjustable 1.2-V Output
Figure 36. TPS62250 adjustable 1.5-V Output
The output voltage can be calculated to:
To minimize the current through the feedback divider network, R
2
should be 180 k Ω or 360 k Ω . The sum of R
1
and R
2
should not exceed ~1M Ω , to keep the network robust against noise. An external feed forward capacitor
C
1
is required for optimum load transient response. The value of C
1
should be in the range between 22pF and
33pF.
Route the FB line away from noise sources, such as the inductor or the SW line.
The TPS62250 is designed to operate with inductors in the range of 1.5 µ H to 4.7 µ H and with output capacitors in
the range of 4.7 µ F to 22 µ F. The part is optimized for operation with a 2.2 µ H inductor and 10 µ F output capacitor.
Larger or smaller inductor values can be used to optimize the performance of the device for specific operation
conditions. For stable operation, the L and C values of the output filter may not fall below 1 µ H effective
inductance and 3.5 µ F effective capacitance.
The inductor value has a direct effect on the ripple current. The selected inductor has to be rated for its dc
resistance and saturation current. The inductor ripple current ( Δ I
L
) decreases with higher inductance and
increases with higher V
I
or V
O
.
The inductor selection has also impact on the output voltage ripple in PFM mode. Higher inductor values will lead
to lower output voltage ripple and higher PFM frequency, lower inductor values will lead to a higher output
voltage ripple but lower PFM frequency.
Equation 1 calculates the maximum inductor current in PWM mode under static load conditions. The saturation
current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 2 .
This is recommended because during heavy load transient the inductor current will rise above the calculated
value.
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