AS1301
Data Sheet - Application Information
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 still 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 1.2µF/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.
Table 4. Recommended Input Capacitor
Part Number
C
TC Code Rated Voltage Dimensions (L/W/T)
X7R 10V 2x1.2x1.35mm
Manufacturer
Murata
www.murata.com
GRM21BR71A225KA01
2.2µF
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.
Table 5. Recommended Output Capacitor
Part Number
C
TC Code Rated Voltage Dimensions (L/W/T)
X7R 10V 2x1.2x1.35mm
Manufacturer
Murata
www.murata.com
GRM21BR71A225KA01
2.2µF
Charge-Pump 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 120nF capacitor is sufficient for most applications. Dependent on the operation mode the AS1301
alternately charges and discharges the CFLY1/2 . While the ESR of the output capacitor produces part of the output
voltage ripple, the voltage drop caused by the ESR of the flying capacitors affects the maximum available output
voltage. Therefore low ESR capacitors, e.g. tantalum or ceramic, are recommended for the flying capacitors as well.
Table 6. Recommended Charge-Pump Capacitor
Part Number
C
TC Code Rated Voltage Dimensions (L/W/T)
Manufacturer
Murata
www.murata.com
GRM188R71E224KA88
220nF
X7R
25V
1.6x0.8x0.87mm
www.austriamicrosystems.com
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