AN4085 Datasheet, PDF (6/16 Pages) STMicroelectronics – STMicroelectronics has developed micro battery products

Discharging the EFL700A39 battery
AN4085
were performed at 30 °C on 4.2 V fully charged batteries and with a cut-off protection set to
3.0 V.
The initial EnFilm™ micro battery voltage value is 4.2 V for a battery at full charge in open
circuit conditions (OCV). When a load is connected, the battery voltage drops to a lower
value (the higher is the load current, the higher is the drop voltage), and progressively the
battery discharges until the voltage decreases down to the protection cut-off level. In any
case, the cut-off voltage must not be fixed below 3.0 V.
Figure 4 curves show that when the discharged capacity increases, the EFL700A39
terminal voltage decreases.
Figure 4. EFL700A39 typical discharge curves

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The time between the beginning and the end of a discharge depends on:
• the initial state of charge,
• the discharge current,
• the temperature,
• the minimum operating voltage of the application (cut-off voltage setup).
For example, extracting information from the Figure 4, with a constant load current of 1 mA,
the charge used by the load starts at 0 mA.h and reaches a maximum of 0.81 mA.h. This
means that 1 mA was supplied to the load by the battery during 0.81 h (48 min 36 s) before
the 3.0 V cut-off threshold voltage was reached. For a 3.5 mA load current, the cut-off
occurs at 0.68 mA.h. The discharge duration can then be calculated as follow:
0.68/3.5 = 0.19 h (11 min 40 s).
EFL700A39 survival time in battery disconnect protection mode
The EFL700A39 open-circuit voltage should not go below 3.0 V in continuous discharge
operating conditions.
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