Datasheet

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V
IN
GND
EN
FB
SW
TPS62243DRV
L
1
2.2 Hµ
C
IN
4.7 µF
C
OUT
10 Fµ
V
OUT
1.8V
Upto300mA
MODE
V
IN
2.0V to 6V
OUTPUT VOLTAGE SETTING
V
OUT
+ V
REF
ǒ
1 )
R
1
R
2
Ǔ
with an internal reference voltage V
REF
typical 0.6 V.
OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)
Inductor Selection
TPS62240 , TPS62242 , TPS62243
SLVS762B – JUNE 2007 – REVISED SEPTEMBER 2007
Figure 30. TPS62243 Fixed 1.8 V
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 TPS62240 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. Selecting larger capacitors is less critical because the corner
frequency of the L-C filter moves to lower frequencies with fewer stability problems.
The inductor value has a direct effect on the ripple current. The selected inductor must 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 also has an impact on the output voltage ripple in the PFM mode. Higher inductor values
will lead to lower output voltage ripple and higher PFM frequency, and 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 transients the inductor current will rise above the calculated
value.
Copyright © 2007, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Link(s): TPS62240 TPS62242 TPS62243