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AS1302

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

External Component Selection

The high internal oscillator frequency of 1.2MHz permits the use of small capacitors for both, the flying capacitors and

the output capacitors. For any given load the value of the flying- and output capacitors as well as their ESR are

affecting the output voltage performance.

In general, the capacitor’s ESR is inversely proportional to its physical size. Larger capacitances and higher voltage

ratings tend to reduce ESR. The ESR is a function of the frequency too, so it must be rated at the devices operating

frequency. Another factor affecting capacitor ESR is temperature.

Note:

Many capacitors have a huge capacity variation over temperature. This can be compensated by choosing a

capacitor with a better thermal coefficient or by choosing a larger nominal value to ensure proper operation

over temperature.

It is not critical which type of input bypass capacitor CBAT and output filter capacitor COUT is used, but it will affect the

performance of the charge pump. Low ESR capacitors should be used to minimize VOUT ripple. Multi-layer ceramic

capacitors are recommended since they have extremely low ESR and are available in small footprints.

Input Capacitor

A 2.2µF input bypass low ESR capacitor such as tantalum or ceramic is recommended to reduce noise and supply

transients. During startup and mode change it supplies a part of the peak input current drawn by the device.

Output Capacitor

The output capacitor is charged to VOUT during the pumping phase. The ESR of the output capacitor introduces spikes

in the output voltage waveform whenever the charge pump charges COUT. These spikes contribute to the ripple volt-

age of VOUT. Therefore, ceramic or tantalum low ESR capacitors are recommended for COUT to minimize the output

voltage ripple.

Table 4. Recommended Input and Output Capacitors

Part Number

TC Code

Rated Voltage

Dimensions

Manufacturer

GRM188R61C225KE15

2.2µF

X5R

16V

0603

Murata

www.murata.com

GRM21BR71E225KA73

2.2µF

X7R

25V

0805

GRM188R60J475KE19

4.7µF

X5R

6.3V

0603

GRM188R60J106ME47

10µF

X5R

6.3V

0603

Figure 35. Load Regulation Comparision with different

Capacitors

Figure 36. Output Ripple vs. Output Current

Comparision with different Capacitors

4.85

4.9

4.95

5.05

5.1

5.15

Load Current (mA)

2.2µF16V 0603

2.2µF25V 0805

4.7µF6.3V 0603

10µF6.3V 0603

100

Load Current (mA)

2.2µF16V 0603

2.2µF25V 0805

4.7µF6.3V 0603

10µF6.3V 0603

1.2MHz

49kHz

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