Datasheet

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       
 
SLVS258A − NOVEMBER 1999 − REVISED DECEMBER 1999
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 22
−0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
−0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
t − Time − ms
OUTPUT VOLTAGE
vs
TIME
(START-UP TIMING)
V
O
− V
V
I
= 3.6 V
R
LOAD
= 16.7 Ω
ENABLE − V
V
O
− Output Voltage and Enable − V
APPLICATION INFORMATION
capacitor selection
The TPS6013x charge pumps require only four external capacitors as shown in the basic application circuit.
Their capacitance values and types are closely linked to the output current and output noise/ripple
requirements. For lowest noise and ripple, low ESR (< 0.1 Ω) capacitors should be used for input and output
capacitors.
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 power source to the converter IC. The input capacitor also has an impact on the output voltage
ripple. The lower the ESR of the input capacitor C
i
, the lower is the output ripple. C
i
is recommended to be about
two to four times as large as C
(xF)
.
The output capacitor C
o
can be selected from 5-times to 50-times larger than C
(xF)
, depending on the ripple
tolerance. The larger C
o
, the lower will be the output voltage ripple. C
i
and C
o
can be either ceramic or low-ESR
tantalum; aluminum capacitors are not recommended.
Generally, the flying capacitors C
(xF)
will be the smallest. Only ceramic capacitors are recommended, due to
their low ESR and because they retain their capacitance at the switching frequency. Because the device
regulates the output voltage using the pulse-skip technique, a larger flying capacitor will lead to a higher output
voltage ripple if the size of the output capacitor is not increased. Be aware that, depending on the material used
to manufacture them, ceramic capacitors might lose their capacitance over temperature. 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 recommended capacitor values.