AS1302
Datasheet - Application Information
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
C
TC Code
X5R
Rated Voltage
Dimensions
0603
Manufacturer
Murata
www.murata.com
GRM188R61C225KE15
GRM21BR71E225KA73
GRM188R60J475KE19
GRM188R60J106ME47
2.2µF
2.2µF
4.7µF
10µF
16V
25V
6.3V
6.3V
X7R
0805
X5R
0603
X5R
0603
Figure 35. Load Regulation Comparision with different
Capacitors
Figure 36. Output Ripple vs. Output Current
Comparision with different Capacitors
5.15
5.1
5.05
5
100
2.2µF16V 0603
2.2µF25V 0805
4.7µF6.3V 0603
49kHz 1.2MHz
80
60
40
20
0
10µF6.3V 0603
4.95
2.2µF16V 0603
4.9
2.2µF25V 0805
4.7µF6.3V 0603
10µF6.3V 0603
4.85
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Load Current (mA)
Load Current (mA)
www.austriamicrosystems.com/DC-DC_Step-Up/AS1302
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