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AS1301

Data Sheet - Ap p lica tio n In fo r m a tio n

9 Application Information

External Component Selection

The high internal oscillator frequency of 1MHz permits the use of small capacitors for both, the flying capacitors and

the output capacitors. For any given load 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.

Input and Output Capacitor Selection

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

An 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 part of the peak input current drawn by the device.

Output Capacitor

The output capacitor is charged to the VOUT voltage during pumping phase. The ESR of the output capacitor intro-

duces steps in the output voltage waveform whenever the charge pump charges COUT. These steps contribute to the

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

output voltage ripple.

Flying Capacitor Selection

To ensure the required output current and avoid high peak currents the values of the flying capacitors CFLY1 and CFLY2

are very critical. A 220nF capacitor is sufficient for most applications. Dependent on the operation mode the AS1301

alternately charges and discharges CFLY1/2. Since the flying capacitors lead a higher current than the output capacitor

the ESR of CFLY1/2 has a greater impact on the performance of the whole system. The voltage drop caused by the ESR

of the flying capacitors directly adds to the output source resistance of the charge pump.

Therefore low ESR capacitors, e.g. tantalum or ceramic, are recommended for the flying capacitors as well.

Table 4. Recommended Input and Output Capacitor

Part Number

TC Code Rated Voltage

Dimensions (L/W/T)

Manufacturer

GRM21BR71A225KA01

2.2µF

X7R

10V

2x1.2x1.35mm

Murata

www.murata.com

Table 5. Recommended Flying Capacitor

Part Number

TC Code

Rated Voltage

Dimensions (L/W/T)

Manufacturer

GRM188R71E224KA88

220nF

X7R

25V

1.6x0.8x0.87mm

Murata

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