Download Energy Calculation for Energy Harvesting with S6AE101A,2A,3A

AN210772
Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and
S6AE103A
Author: Hiroyuki Takada
Associated Part Family:S6AE101A, S6AE102A, S6AE103A
Related Documents: S6AE101A, S6AE102A, S6AE103A Datasheets
This application note describes system energy calculations for an energy harvesting system where the amount of
energy from an energy harvester is very small.
1
Introduction
Systems that are dependent on an energy harvesting solution must be designed for a low-power operation based on
an energy budget calculation because the amount of energy from the energy harvester such as indoor solar cell is
very small.
1.1
Energy Harvesting System
S6AE101A/2A/3A is a power management IC (PMIC) for energy harvesting operated with super-compact solar cells.
Figure 1 shows an example of an energy harvesting system with S6AE101A/2A/3A.
Figure 1. Example of Energy Harvesting System with S6AE101A/2A/3A
Enveronmental Energy (Light)
S6AE101A/2A/3A
VDD
Harvester
Block
(Solar Cell)
PMIC Block
SW2
SW1
Control
Block
VOUT1
VSTORE1
CVSTORE1
Application Block
MCU
RF
Sensor
Because the energy from a harvester is limited, it should be stored in a capacitor (CVSTORE1). A large-value capacitor
would take too much time to store the energy into the capacitor; this means that the system cannot be operated
frequently. On the other hand, if the capacitor were too small, enough energy cannot be stored on the capacitor for
the application block. Therefore, the sizing of the capacitor is very important.
This PMIC has a power gating switch, SW1, for the application block. Once the VSTORE1 pin voltage reaches the
VOUT maximum voltage (VVOUTH), the path between the VSTORE1 pin and the VOUT1 pin is connected by the SW1
until the VSTORE1 pin voltage reaches the VOUT minimum voltage (VVOUTL) (see Figure 2).
This PMIC has a switch, SW2, for charging the capacitor efficiently. After starting up the internal circuit of the PMIC,
the path between the VDD pin and the VSTORE1 pin is connected by the SW2. When the VSTORE1 pin voltage
reaches the VVOUTH, the SW2 disconnects the path. When the VSTORE1 pin voltage reaches the input power
reconnect voltage (VVOUTM), the SW2 reconnects the path (see Figure 2).
For more information, see S6AE101A, S6AE102A, and S6AE103A datasheets.
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Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
Figure 2. Relationship between SW1, SW2 and VSTORE1 Pin
VVOUTH
VVOUTM
VVOUTL
VSTORE1
VOUT1
VOUT1
Load
off
SW1
SW2
off
on
off
on
on
Starting up
2
Energy Calculation for Energy Harvesting
2.1
Calculation of Energy Consumption
Figure 3. Measurements of Voltage, Current, and Operation Time
S6AE101A/2A/3A
VDD
Power
Source
PMIC Block
Control
Block
SW2
SW1
IAPP_IN
VOUT1
VSTORE1
CVSTORE1
A
APP_IN
V
VAPP_IN
Application Block
MCU
RF
Sensor
First of all, the voltage (VAPP_IN), the current (IAPP_IN), and the operation time (tAPP_IN) of APP_IN pin in the application
block are measured (see Figure 3 and Figure 4). The energy consumption in the application is calculated from
Equation 1.
Equation 1
However, when checking the waveform of VAPP_IN and IAPP_IN in the Figure 4, the waveform is divided into three parts,
(1), (2), and (3). Therefore, the energy consumptions of each part should be calculated, and then three energy
consumptions are added together.
In this example, the energy consumption for the application block is calculated as 233.4 µJ.
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Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
Figure 4. Waveform of VAPP_IN, IAPP_IN, and tAPP_IN
VVOUTH = 3.3 V, VVOUTM = 3.135 V, VVOUTL = 2.0 V
V(1) ≈ 3.28 V (Average) V ≈ 3.15 V (Average)
(2)
V(3) ≈ 2.80 V (Average)
VAPP_IN
1 V/div
(1)
(2)
(3)
(3) RF transmission
I(3) ≈ 10 mA
(1) MCU
IAPP_IN
5 mA/div
(2) MCU & Sensor
I(2) ≈ 3 mA
I(1) ≈ 1 mA
5 ms/div
t(1) ≈ 5 ms
t(2) ≈ 20 ms
t(3) ≈ 1 ms
tAPP_IN ≈ 26 ms
2.2
SW1
off
SW2
on
on
off
on
Calculation of Capacitance
Next, the capacitance is calculated based on the energy consumption of the application. Figure 5 shows the capacitor
in the system.
Figure 5. Capacitor in the System
S6AE101A/2A/3A
VDD
Power
Source
PMIC Block
SW2
SW1
VSTORE1
Control
Block
: Available Energy (EAVAILABLE)
VVOUTH : VOUT maximum voltage
VVOUTL : VOUT minimum voltage
VOUT1
CVSTORE1
EAVAILABLE
Application
EAPP_IN = 233.4 µJ
VVOUTH
VVOUTL
0V
The energy stored on a capacitor is calculated by Equation 2 (E: Energy [J], C: capacitance [F], V: Voltage [V]).
Equation 2
Calculation of CVSTORE1
The VOUT maximum voltage (VVOUTH) and the VOUT minimum voltage (VVOUTL) of S6AE101A/2A/3A are set by
changing the external resistances. As a premise, the recommended operating voltage range for the application block
is set from 1.8 V to 3.6 V. Then, VVOUTH is set to 3.3 V and VVOUTL is set to 2.0 V within the range. The stored energy
from VVOUTL to VVOUTH is the available energy for the application. (EAVAILABLE: Available energy, see Figure 5).
EAVAILABLE should be larger than the EAPP_IN (233.4 µJ). (Equation 3 is derived from Equation 2)
Equation 3
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Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
In this example, the capacitance of CVSTORE1 should be larger than 67.8 µF. Moreover, at least 100-µF or larger
capacitor is required for this PMIC (see the recommended operating conditions in S6AE101A, S6AE102A, and
S6AE103A datasheets). The capacitance is set to 100 µF in this example.
Note:
The calculated capacitance in this example is the ideal value. There is a wide difference between an actual
capacitance and a capacitance described in a datasheet. Also, there is a potential for a decrease in a capacitance by
DC bias characteristics and temperature characteristics. When selecting a capacitor, please check datasheets for
each manufacturer and check the actual capacitances under actual use conditions.
The type of capacitors and the characteristics for the energy harvesting are shown in Table 1. Ceramic capacitors
with low leakage current are suitable for energy the harvesting.
Table 1. Capacitor Characteristics
Type of Capacitor
Capacitance Range
Benefit
Drawback
Low leakage current (nA),
Ceramic capacitor
0.1 µF to 470 µF
Small size,
Small capacitance
Low cost
Aluminum electrolytic capacitor
0.1 µF to 1.5 F
Tantalum electrolytic capacitor
33 nF to 6 mF
Electric double-layer capacitor
(e.g., Supercapacitor)
2.3
High capacitance,
High leakage current (µA)
Low cost
Low leakage current (nA),
High cost
High capacitance
Up to 50 F
High leakage current (µA)
Ultrahigh capacitance
High cost
Calculation of Charging Time
The parameters for calculating charging time for the capacitor are shown in Figure 6.
Figure 6. Calculating the Parameters for Charging Time
Light Energy
PSOLAR
= 200 µW
S6AE101A/2A/3A
VDD
Solar
Cell
PMIC Block
SW1
: Available Energy (EAVAILABLE)
: Initial Energy (EINITIAL)
VOUT1
VSTORE1
PVSTORE1
CVSTORE1 = 100 µF
Control
Block
IQIN1 = 250 nA or 280 nA
(Consumption current 1)
+
SW2
VVOUTH = 3.3 V
VVOUTL = 2.0 V
0V
Application
EAPP_IN
= 233.4 µJ
Repeat charge energy
Initial charge energy
This calculation assumes that the power from a solar cell (PSOLAR) is 200 µW. The charge power (PVSTORE1) to be
supplied to the VSTORE1 pin capacitor (CVSTORE1) is the value PSOLAR minus the power consumption (VVOUTH × IQIN1)
of the PMIC (Equation 4) Values of consumption current 1 (IQIN1) of S6AE101A/2A/3A are shown in Table 2. In this
example, the value of S6AE101A is used.
Equation 4
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Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
Table 2. Consumption Current 1 (IQIN1)
Product Name
Consumption Current 1 (IQIN1)
S6AE101A
250nA
S6AE102A
280nA
S6AE103A
Calculation of Initial Charging Time (tCHARGE)
The capacitor is charged from 0 V to VVOUTH at the time of initial charging. The initial energy (EINITIAL) is calculated by
Equation 2.
Equation 5 is derived from Equation 1 (E: Energy [J], P: Power [W], and t: time [s]). Equation 6 for the charging time
is derived from Equation 5.
Equation 5
Equation 6
Calculation of Repeat Charging Time (tCHARGE_R)
In this example, the initial charging time is 2.73 s, and the repeat charging time is 1.17 s. The repeat charging time is
shorter than the initial one.
3
Summary
This application note explored the basic calculation of energy, capacitance, and charging time for an energy
harvesting application based on Cypress’s S6AE101A/2A/3A PMIC. The most important concept to be gained from
this application note is to figure out a balance of charged energy with energy consumption.
S6AE101A/2A/3A has a set of documentation such as other application notes, development tools, and online
resources to assist you during your development process. Visit www.cypress.com/energy-harvesting to find out more.
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Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
Document History
Document Title: AN210772 - Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
Document Number: 002-10772
Revision
ECN
**
5099308
Orig. of Change Submission Date
HIXT
02/17/2016
Description of Change
New application note
Added the following sentences on page 4.
*A
5273891
HIXT
05/17/2016
Moreover, at least 100-µF or larger capacitor is required for this PMIC
(see the recommended operating conditions in S6AE101A, S6AE102A,
and S6AE103A datasheets). The capacitance is set to 100 µF in this
example.
Corrected typo error
*B
5690448
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AESATMP8
04/10/2017
Updated logo, and Copyright.
Document No. 002-10772 Rev. *B
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Energy Calculation for Energy Harvesting with S6AE101A, S6AE102A, and S6AE103A
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