AN-1052: Operating the EnerChip™ in High Temp. Environments

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Doc AN-72-1052 Rev A

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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.

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.

Figure 2: State of Charge can be Adjusted by Varying the Charge Voltage