UM1481 Datasheet, PDF (11/55 Pages) STMicroelectronics – This document describes an easy and compact solution

UM1481
System overview
● In a similar manner, another MOSFET is provided between an external load and
battery. When battery voltage falls below the cut-off value (3.15 V), it disconnects the
external load from the battery.
● Whenever the microcontroller accesses the STC3105 registers, the LED (D3) blinks
and the values are updated.
● LED D2 toggles if the battery is in a charging position with either an internal or external
charger. This LED is turned off if the battery is being discharged and is turned on if the
battery voltage is below 3.2 V.
● LED D13 turns on if any alarm condition occurs i.e. battery voltage or SOC goes below
the threshold set by the user. A related message also appears on the LCD. Similarly, if
the battery is absent or deeply discharged, this LED turns on and a warning message
appears on the screen.
3.2
Automatic battery capacity learning
Whenever a new battery is connected to the board it automatically estimates the present
SOC percentage depending on the open circuit voltage (refer to step 3 below). Initially, the
total capacity of the battery is assumed to be default, i.e. 1500 mAh here. The user can
change the total capacity of the battery to the required value as mentioned in Section 5.1.
In order to learn the actual capacity of the battery we need to first discharge it completely
and then charge it back to 100%. To achieve this, follow the steps below:
1. Do not connect external charger with the board and change switch position SW8
towards external charger. This ensures that the battery is not charged on first
connection. Place the jumper between pin 1 and 2 of J3.
2. Connect power source (USB/wall adapter) to the board and then connect the battery.
3. Steps 1 and 2 ensure the battery is neither being charged nor discharged and so it
measures OCV in order to estimate initial SOC of the battery.
4. Now, in order to discharge the battery we must disconnect the external power source,
the board acts as a load and consumes power from the battery.
5. Similarly, if the user wants to charge the battery, either an internal or external charger
can be used by adjusting SW8 accordingly.
6. Battery parameters appear on the LCD screen as shown in Figure 5.
Figure 5. Data screen
7. Change the jumper position to pin 2 and 3 of J3.
8. When battery voltage falls below 3.2 V, LED D2 turns on and indicates that battery is
low. Now, it is recommended to start charging the battery using an internal or external
charger in order to avoid a deep discharge of the battery.
Doc ID 022389 Rev 1
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