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Today, Li-ion batteries are widely used in many electrical devices such as cell phones, tablet PCs and portable video games. Although Li-ion batteries are convenient thanks to their rechargeability, they could go out of control without proper protection. To support designing Li-ion-battery-powered systems of high safety, we provide Li-ion battery protection ICs equipped with variety of optional protection functions.
Short-circuit state between external electrodes causes Li-ion battery cells to discharge to the limit of their capacity and generate heat. If the temperature increases and the battery becomes overheated, the internal structure (especially a separator) of a Li-ion battery can be damaged, which may lead to dangerous situations such as toxic-fume emission, fire and explosion.
A short-circuit current protection can cut off a discharge current within 1 micro second after detecting a short-circuit current. Though it is functionally similar to a discharge overcurrent protection, this short-circuit protection features its fast response to a large discharge current.
Adopted Products:：all the 1-/2-/multi-cell protection ICs except the R5433
Whether recharge of 0 V cells (fully discharged cells) is accepted or not is determined by product version.
0-V-charge prohibited Version:
Charging operation is prohibited if the cell voltage decreases to a voltage level below the overdischarge detection voltage.
A Li-ion battery without guarantee for 0-V charging may be under internal short-circuit state by metal deposition penetrating its separator when its voltage is lower than or equal to a certain value.
Charging a Li-ion battery under internal short-circuit state can raise the battery’s internal temperature, which leads to dangerous chemical reactions causing gas emission, self-ignition, and, even worse, explosion.
Li-ion battery protection ICs with 0-V-charge prohibition can protect batteries, devices and systems from these risks by prohibiting dangerous charging operation.
0-V-charge Acceptable Version:
This version allows charging 0-V cells. It is suitable for Li-ion batteries which guarantee secure 0-V charge. This version enables an exhausted Li-ion battery to regain its original performance as much as possible.
・ selectable： R5405, R5494, R5487, R5497, R5471
・ Prohibited Only： R5463
A cell balancing function equalizes cell voltages of multi-cell Li-ion batteries by bypassing a charge current or by discharging cells with a higher voltage.
Cell voltages of multi-cell Li-ion batteries become out of balance due to individual cell differences such as capacity and leak current. The unbalance stops charging operation when the highest-voltage cell reaches its charge-end voltage regardless of the state of the other lower-voltage cells. On the other hand, the lowest-voltage cell reaches its discharge-end voltage faster than the other higher-voltage cells. The unbalancing state narrows the specification range substantially, reduces the actual capacity of a multi-cell Li-ion battery, and deteriorates the lifetime of the system and the battery.
By monitoring and equalizing the voltage state of each cell with a cell balancing function, it is possible to maintain the actual capacity of a multi-cell Li-ion battery.
Some of our multi-cell Li-ion battery protection ICs adopt cascade connection, which makes it possible to protect batteries with 6 or more cells.
For example, by connecting two 5-cell Li-ion battery protection ICs with their COUT and DOUT pins, those ICs can protect a 10-cell Li-ion series battery. Cascade connection enables protection ICs to support multi-stage batteries even though there are no ICs capable of monitoring those batteries with a single chip.
Besides, in some cases, multiple ICs with cascade connection can be less expensive than a multi-cell battery protection IC with high-voltage resistance.
A temperature protection function detects the abnormal temperature increase of a Li-ion battery and stops charging / discharging operation to prevent dangerous situations.
Basically, our temperature protection function adopts a method of connecting an NTC thermistor and a resistor as a voltage divider in series to detect abnormal temperatures.
A Li-ion battery protection IC with an alarm function monitors temperature and a cell voltage with an external thermistor and the alarm pin. In detecting the cell voltage exceeding the alarm detection voltage, the IC outputs an alarm signal to a charger. This detection voltage switches over from the one at normal temperature to the other at high temperature when the thermistor detection temperature exceeds 45℃.
Overcharging a Li-ion battery at high temperature may shrink and damage the separator inside the battery. This leads to internal short-circuit state causing dangerous accidents such as gas emission, self-ignition, and explosion. By using a Li-ion battery protection IC with an alarm function, a system can notice overcharge state against temperature before the real danger occurs and take countermeasures such as stopping charging operation.
In Japan, two-stage overcharge protection for Li-ion Batteries is prescribed by Electrical Appliance and Material Safety Act*. Protection ICs with this alarm function can meet the requirements in just a single chip.
* Other countries have similar regulations.
Adopted Products： R5461K, R5464K, (R5466K)
An open-wire detection function detects open wires between cells and protection circuits in a multi-cell Li-ion battery.
As for products such as electric power tools, there are risks of becoming open-wire by vibration. Under open-wire condition, protection ICs cannot monitor the state of Li-ion battery cells and therefore cannot judge whether the battery is safe or not.
Protection ICs with an open-wire detection function monitor the connection with battery cells periodically. In detecting an open wire, the protection circuit prohibits charging / discharging operation to avoid dangerous situations.