Secondary battery protection for notebook PCs
Ablic has launched secondary protection devices for notebook PCs with overcharge protection, temperature protection, and constant-voltage output in a single chip.
The S-82M3/M4 Series from Ablic, part of the MinebeaMitsumi group, supports serially connected 3 cell packs and the S-82L4 Series protects serially connected 3 to 4 cell packs.
The devices protect lithium-ion batteries from overcharging when combined with a protection fuse which blows when an external signal is received.
For notebook PCs and tablet PCs in particular, temperature protection and RTC drive are required, so the secondary protection chips can be equipped with both a function to protect battery packs from abnormal temperatures and a function to output the constant-voltage required for RTC drive by connecting an external PTC thermistor.
A CTL pin enables temperature protection through connection with a PTC thermistor and a constant-voltage 1.5V output pin for driving an external RTC real-time clock, all on a single chip.
This makes it possible to detect temperatures when a battery pack reaches abnormal temperatures, thereby achieving both overcharge protection and temperature protection in a single IC. In addition, the back of the DFN-8(2020)A package is used as a pin in order to mount the 9 pin IC in a compact package. This contributes to a smaller footprint on circuit boards.
The RTC supply allows for power to be supplied from the main battery, even when the PC is shutdown, eliminating the need for a coin-type battery for RTC backup, and contributing to a smaller footprint on circuit boards.
The constant-voltage circuit stops operating when the battery voltage reaches shutdown voltage, and the IC enters low current consumption mode (S-82L4 Series: 0.4µA max.), making it possible to reduce current consumption.
Example of a protection circuit using the S-82M3 Series
Example of a protection circuit using the S-82L4 Series
Both the M3 and M4 series devices have a wake-up function to prevent protection fuses from blowing during battery pack assembly in the manufacturing process. This monitors whether all batteries have been connected, and prevents the protection fuse blowing signal from being output until all batteries are connected, no matter what order the batteries and protection circuit board are connected in. This function allows for the protection circuit board and batteries to be connected in any order, which contributes to improved work efficiency in the assembly process.
The S-82L4 Series however is not equipped with a wake-up function, but is compatible with both serially connected 3 cell and 4 cell packs.
The S-82K3B/K4B Series, which is not equipped with a CTL pin but is equipped with a wake-up function, and the S-82H4B Series for serially connected 3 and 4 cell packs are also available with the same specifications.
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