![](http://datasheet.mmic.net.cn/370000/TPS60122PWPR_datasheet_16742979/TPS60122PWPR_17.png)
TPS60120, TPS60121, TPS60122, TPS60123, TPS60124, TPS60125
REGULATED 200-mA HIGH EFFICIENCY CHARGE PUMP
DC/DC CONVERTERS
SLVS257B – NOVEMBER 1999 – REVISED AUGUST 2000
17
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
capacitor selection (continued)
Generally, the flying capacitors C
(xF)
will be the smallest. Only ceramic capacitors are recommended because
they are low ESR and because they retain their capacitance at the switching frequency. Because the device
regulates the output voltage with 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 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 recommended capacitor values.
Table 2. Recommended Capacitor Values
PART
VI
(V)
IO
Ci
(
μ
F)
C(xF)
(
μ
F)
Co
(
μ
F)
VPPTYP
(mV)
I
(mA)
TANTALUM
CERAMIC
(X7R)
CERAMIC
(X7R)
TANTALUM
CERAMIC
(X7R)
TPS60120
TPS60121
TPS60124
TPS60125
150
4.7
4 7
4.7
2 2
2.2
22
4.7
65
2 4
2.4
22
40
200
10
4.7
2 2
2.2
22
4.7
80
10
22
35
TPS60122
TPS60123
2 4
2.4
50
100
2.2
4.7
1
10
70
80
The TPS6012x devices are charge pumps that regulate the output voltage using the pulse-skip operating mode.
The output voltage ripple is therefore dependent on the values and the ESR of the input, output and flying
capacitors. The only possibility to reduce the output voltage ripple is to choose the appropriate capacitors. The
lowest output voltage ripple can be achieved with ceramic capacitors due to their low ESR and their frequency
characteristic.
Ceramic capacitors typically have an ESR that is more than 10 times lower than tantalum capacitors and they
retain their capacitance at frequencies more than 10 times higher than tantalum capacitors. Many different
tantalum capacitors act as an inductance for frequencies higher than 200 kHz. This behavior increases the
output voltage ripple. Therefore, the best choice for a minimized ripple is the ceramic capacitor. For applications
that do not need higher performance in output voltage ripple, tantalum capacitors with a low ESR are a possibility
for input and output capacitor, but a ceramic capacitor should be connected in parallel. Be aware that the ESR
of tantalum capacitors is indirectly proportional to the physical size of the capacitor.
Table 2 is a good starting point for choosing the capacitors. If the output voltage ripple is too high for the
application, it can be improved by selecting the appropriate capacitors. The first step is to increase the
capacitance at the output. If the ripple is still too high, the second step would be to increase the capacitance
at the input.
For the TPS60120, TPS60121, TPS60124, and TPS60125, the smallest board space can be achieved using
Sprague’s 595D-series tantalum capacitors for input and output. However, with the trend towards high
capacitance ceramic capacitors in smaller size packages, these types of capacitors may become more
competitive in size. The smallest size for the TPS60122 and TPS60123 can be achieved using the
recommended ceramic capacitors.
Tables 3 and 4 lists the manufacturers of recommended capacitors. In most applications surface-mount
tantalum capacitors will be the right choice. However, ceramic capacitors provide the lowest output voltage
ripple due to their typically lower ESR.