AN-1052: Operating the EnerChip™ in High Temp. Environments
As a starting point, it’s important to understand how the state of charge of the EnerChip can be adjusted by
regulating the charge voltage and allowing the charging or discharging current to settle to a steady state value.
Figure 2 represents the relative state of charge as a function of this charge voltage.
Figure 2: State of Charge can be Adjusted by Varying the Charge Voltage
The EnerChip CC has a charge voltage temperature coefficient with a slope of --2.2mV/°C so as to lower the
charge voltage as the temperature increases. The charging source can also be enabled or disabled by way of
an external control line. The advantage of activating/deactivating the charge pump will become apparent in the
next section. As shown in Figure 3, a lower state of charge improves capacity retention at higher temperatures.
In applications where high temperature excursions are likely, the cumulative life-cycle capacity can be improved
by keeping the EnerChip at a lower state of charge, thereby retaining that capacity over a greater number of
charge-discharge cycles. The experimental results of Figure 3 were derived by charging the cells to 4.1V (100%
SoC) at room temperature and discharging each cell to establish the baseline discharge capacity. The cells
were then charged to either 60% or 100% SoC and subjected to the temperature shown in the charts. After the
prescribed time at temperature, the cells were discharged (top quad chart), then fully charged and discharged
again (bottom quad chart). Note the higher discharge capacity in the cycle 3 discharge vs. cycle 2 for the 100%
SoC cells, as the third discharge cycle includes the recoverable portion of the capacity that was lost during the
previous (cycle 2) charge-discharge cycle.
Doc AN-72-1052 Rev A
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