Datasheet

C2 +
1
2 p ƒ
P
R2
+
1
2 p 8 kHz R2
V
I
GND
EN
SW
FB
C3
4.7 µF
L1
4.7 µH
C4
10 µF
TPS62220
V
I
2.5 V − 6 V
V
O
1.8 V / 400 mA
R1
470k
R2
180k
C1
15 pF
C2
100 pF
INDUCTOR SELECTION
DI =V x
L O
I max=I max+
L O
1-
V
O
DI
L
V
I
2
L xf
TPS62220 , , TPS62221 , , TPS62222
TPS62223 , TPS62224 , TPS62225
TPS62227 , TPS62228 , TPS62229
SLVS491E SEPTEMBER 2003 REVISED FEBRUARY 2009 .......................................................................................................................................
www.ti.com
The pole is calculated as:
with R2 = lower resistor of voltage divider and C2 = lower capacitor of voltage divider.
For an output filter combination of L = 4.7 µ H and C
O
= 10 µ F, C1 and C2 must be selected to place a zero at 22
kHz, and a pole at 8 kHz. Choose components close to the calculated values.
Table 2. Compensation Selection
L C
O
f
Z
f
P
4.7 µ H 10 µ F, 22 µ F 22 kHz 8 kHz
Figure 15. Typical Application Circuit for the TPS62220 With Adjustable Output Voltage
For high efficiencies, the inductor should have a low dc resistance to minimize conduction losses. Especially at
high-switching frequencies the core material has a higher impact on efficiency. When using small chip inductors,
the efficiency is reduced mainly due to higher inductor core losses. This needs to be considered when selecting
the appropriate inductor. The inductor value determines the inductor ripple current. The larger the inductor value,
the smaller the inductor ripple current and the lower the conduction losses of the converter. Conversely, larger
inductor values cause a slower load transient response. To avoid saturation of the inductor, the inductor should
be rated at least for the maximum output current of the converter plus the inductor ripple current that is
calculated as:
where:
f = switching frequency (1.25-MHz typical, 800-kHz minimal)
L = inductor value
Δ I
L
= peak-to-peak inductor ripple current
I
L,max
= maximum inductor current
The highest inductor current occurs at maximum Vin. A more conservative approach is to select the inductor
current rating just for the maximum switch current of 880 mA. SeeTable 3 for inductor selection.
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Product Folder Link(s): TPS62220 TPS62221 TPS62222 TPS62223 TPS62224 TPS62225 TPS62227 TPS62228
TPS62229