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

APPLICATION INFORMATION

capacitor selection (continued)

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

IO

Ci

(

µF)

C(xF)

(

µF)

Co

(

µF)

VPPTYP

PART

I

(V)

O

(mA)

TANTALUM

CERAMIC

(X7R)

CERAMIC

(X7R)

TANTALUM

CERAMIC

(X7R)

PP

(mV)

TPS60120

150

4.7

47

22

22

4.7

65

TPS60120

TPS60121

24

150

4.7

2.2

22

40

TPS60124

TPS60125

2.4

200

10

4.7

22

22

4.7

80

TPS60125

200

10

2.2

22

35

TPS60122

24

50

2.2

1

10

70

TPS60123

2.4

100

4.7

1

10

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.