User manual for APPEB1012 Revision 1.2, Oct 2019
Solar Energy Harvesting Supercapacitor Evaluation Board using a
PMIC with MPPT
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Page
10
of
11
PMIC controlled output voltage
When the PMIC controlled output mode (CTRL) is selected, the voltage range of which output
enables is determined by the charge management configuration. The upper threshold is Vchrdy
which enables the output voltage to the load whilst the output is disabled typically 600ms after the
supercapacitor voltage drops below Vovdis.
Figure 9: Example output voltage operation
In figure 9, HA102 is connected to the APPEB1012 and the supercapacitor voltage and output
voltage was observed. The system configuration was connected as CFG[2:0] = [0 0 0] such that
the PMIC entered custom mode as described in table 3. Custom external resistors were chosen to
create the charge management equal to the first row of table 4.
In this example, Vovch = 2.7; Vchrdy = 2.57V; Vovdis = 2.2V and a constant current of 100mA was
drawn as the load. Furthermore, a power supply limited at 50mA was used as a representation of a
solar cell.
Since the lower threshold of the output voltage is 600ms after the Vscap falls below Vovdis we can
calculate the lower threshold from
𝑖
=
𝐶
∆
𝑣
∆
𝑡
Where
𝑖
is the load current,
𝐶
is the capacitance of the supercapacitor,
∆
𝑣
is the voltage drop and
∆
𝑡
is the time taken. Since a HA102 is 0.24F, using the above equation, we can calculate the lower
threshold voltage to be
𝑉
!"#$%
=
𝑉
!"#$%
−
𝑖
𝐶
∆
𝑡
=
2
.
2
𝑉
−
0
.
1
𝐴
0
.
24
𝐹
×
0
.
6
𝑠
=
1
.
95
𝑉
Hence, the lower and upper output voltage thresholds are at 1.95V and 2.57V as seen in figure 9.
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0
0.5
1
1.5
2
2.5
3
-2.5
2.5
7.5
12.5
17.5
22.5
Cu
rre
nt
(A
)
V
oltage
(V)
Time (s)
APPEB1012 100mA discharge
Vout
Vscap
Current
MPP
[1:0]
Vmpp / Voc
Output is
enabled back
Output is disabled
600ms after
Vscap falls below
Vovdis
Boost mode
