MB39C811 Datasheet, PDF (16/36 Pages) Cypress Semiconductor – Ultra Low Power Buck PMIC Solar/Vibrations Energy Harvesting

MB39C811
Sizing of Input and Output Capacitors
Energy from harvester should be stored on the Cin and Cout to operate the application block. If the size of these
capacitors were too big, it would take too much time to charge energy into these capacitors, and the system cannot be
operated frequently. On the other hand, if these capacitors were too small, enough energy cannot be stored on these
capacitors for the application block. The sizing of the Cin and Cout is important.
Common capacitors are layered ceramic capacitor, electrolytic capacitor, electric double layered capacitor, and so on.
Electrostatic capacitance of layered ceramic capacitors is relatively small. However, layered ceramic capacitors are
small and have high voltage resistance characteristic. Electrolytic capacitors have high electrostatic capacitance from
µF order to mF order. The size of capacitor becomes large in proportion to the size of capacitance. Electric double
layered capacitors have high electrostatic capacitance around 0.5F to 1F, but have low voltage resistance
characteristics around 3V to 5V. Be very careful with a voltage resistance characteristic. Also, leak current, equivalent
series resistance (ESR), and temperature characteristic are criteria for selecting,
Table 14. Manufactures Of Capacitors
Part number/Series name
EDLC351420-501-2F-50
Type, Capacitance
EDLC, 500mF
Manufacture
EDLC082520-500-1F-81
EDLC, 50mF
TDK Corporation
EDLC041720-050-2F-52
EDLC, 5mF
Gold capacitor
EDLC
Panasonic Corporation
First of all, apply the following equation and calculate energy consumption for an application from voltage, current, and
time during an operation.
The energy stored on a capacitor is calculated by the following equation.
Since the energy in a capacitor is proportional to the square of the voltage, it is energetically advantageous for the
buck DC/DC converter to make the Cin larger.
An example of an application using the power gating by the OPGOOD signal is shown in the Figure 10. The Cin and
the Cout are sized so as to satisfy the following equation. The η, the efficiency of the MB39C811, is determined from
the current of application and the graph shown in Figure 12, Efficiency vs IOUT.
dECin and dECout are the available energies for the application.
Document Number: 002-08401 Rev *A
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