Datasheet

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     
   
SLVS354A − FEBRUARY 2001 − REVISED SEPTEMBER 2001
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
capacitor selection
The TPS6020x devices require only four external capacitors to achieve a very low output voltage ripple. The
capacitor values are closely linked to the required output current. Low ESR (<0.1 Ω) capacitors should be used
at input and output. In general, the transfer capacitors (C1 and C2) will be the smallest; a 1-µF value is
recommended for maximum load operation. With smaller capacitor values, the maximum possible load current
is reduced and the LinSkip threshold is lowered.
The input capacitor improves system efficiency by reducing the input impedance. It also stabilizes the input
current of the power source. The input capacitor should be chosen according to the power supply used and the
distance from the power source to the converter IC. C
i
is recommended to be about two to four times as large
as the flying capacitors C1 and C2.
The output capacitor (C
o
) should be at minimum the size of the input capacitor. The minimum required
capacitance is 2.2 µF. Larger values will improve the load transient performance and will reduce the maximum
output ripple voltage.
Only ceramic capacitors are recommended for input, output, and flying capacitors. Depending on the material
used to manufacture them, ceramic capacitors might lose their capacitance over temperature and voltage.
Ceramic capacitors of type X7R or X5R material will keep their capacitance over temperature and voltage,
whereas Z5U- or Y5V-type capacitors will decrease in capacitance. Table 2 lists the recommended capacitor
values.
Table 2. Recommended Capacitor Values (Ceramic X5R and X7R)
LOAD CURRENT,
I
L
(mA)
FLYING
CAPACITORS,
C1/C2
(µF)
INPUT
CAPACITOR,
C
i
(µF)
OUTPUT
CAPACITOR,
C
o
(µF)
OUTPUT VOLTAGE
RIPPLE IN LINEAR MODE,
V
(P-P)
(mV)
OUTPUT VOLTAGE
RIPPLE IN SKIP MODE,
V
(P-P)
(mV)
0−100 1 2.2 2.2 3 20
0−100 1 4.7 4.7 3 10
0−100 1 2.2 10 3 7
0−100 2.2 4.7 4.7 3 10
0−50 0.47 2.2 2.2 3 20
0−25 0.22 2.2 2.2 5 15
0−10 0.1 2.2 2.2 5 15
Table 3. Recommended Capacitor Types
MANUFACTURER PART NUMBER SIZE CAPACITANCE TYPE
Taiyo Yuden
UMK212BJ104MG 0805 0.1 µF Ceramic
Taiyo Yuden
EMK212BJ224MG 0805 0.22 µF Ceramic
EMK212BJ474MG 0805 0.47 µF Ceramic
LMK212BJ105KG 0805 1 µF Ceramic
LMK212BJ225MG 0805 2.2 µF Ceramic
EMK316BJ225KL 1206 2.2 µF Ceramic
LMK316BJ475KL 1206 4.7 µF Ceramic
JMK316BJ106ML 1206 10 µF Ceramic
AVX
0805ZC105KAT2A 0805 1 µF Ceramic
AVX
1206ZC225KAT2A 1206 2.2 µF Ceramic