CR2477 battery

What is the working principle of the CR2477 battery circuit? Do you know what applications of the smart CR2477 battery system are?

The working principle of the CR2477 battery circuit has overcharge protection, over-discharge protection, overcurrent protection and short-circuit protection functions. Its working principle is analyzed as follows:

1. Normal state In the normal state, the "CO" and "DO" pins of N1 in the circuit both output high voltages, and both MOSFETs are in the on state. The CR2477 battery can charge and discharge freely. Since the on-resistance of the MOSFET is very small, usually less than 30 milliohms, its on-resistance has little effect on the performance of the circuit. 7|The current consumption of the protection circuit in this state is μA level, usually less than 7μA.

2. Overcharge protection The charging method required for lithium-ion batteries is constant current/constant voltage. In the initial stage of charging, it is constant current charging. As the charging process progresses, the voltage will rise to 4.2V (depending on the positive electrode material, some batteries require a constant voltage value of 4.1V), and then switch to constant voltage charging until the current becomes smaller and smaller. During the CR2477 battery charging process, if the charger circuit loses control, the CR2477 battery voltage will continue to be charged at a constant current after exceeding 4.2V. At this time, the CR2477 battery voltage will continue to rise. When the CR2477 battery voltage is charged to more than 4.3V, the chemical side reactions of the CR2477 battery will intensify, causing CR2477 battery damage or safety problems.

In a CR2477 battery with a protection circuit, when the control IC detects that the CR2477 battery voltage reaches 4.28V (this value is determined by the control IC, and different ICs have different values), its "CO" pin will change from high voltage to zero voltage, causing V2 to turn from on to off, thereby cutting off the charging circuit, making it impossible for the charger to charge the CR2477 battery, and playing an overcharge protection role. At this time, due to the presence of V2's own body diode VD2, the CR2477 battery can discharge the external load through the diode. There is a delay time between the control IC detecting that the CR2477 battery voltage exceeds 4.28V and sending a signal to shut down V2. The length of the delay time is determined by C3 and is usually set to about 1 second to avoid misjudgment due to interference.

3. Over-discharge protection During the discharge process of the CR2477 battery to the external load, its voltage will gradually decrease with the discharge process. When the CR2477 battery voltage drops to 2.5V, its capacity has been completely discharged. If the CR2477 battery continues to discharge to the load at this time, it will cause permanent damage to the CR2477 battery. During the CR2477 battery discharge process, when the control IC detects that the CR2477 battery voltage is lower than 2.3V (this value is determined by the control IC, and different ICs have different values), its "DO" pin will change from high voltage to zero voltage, causing V1 to turn from on to off, thereby cutting off the discharge circuit, so that the CR2477 battery can no longer discharge to the load, and play an over-discharge protection role. At this time, due to the presence of V1's own body diode VD1, the charger can charge the CR2477 battery through this diode.

Since the CR2477 battery voltage cannot be reduced in the over-discharge protection state, the protection circuit is required to consume very little current. At this time, the control IC will enter a low power consumption state, and the power consumption of the entire protection circuit will be less than 0.1μA. There is also a delay time between when the control IC detects that the CR2477 battery voltage is lower than 2.3V and when it sends out the signal to shut down V1. The length of this delay time is determined by C3 and is usually set to about 100 milliseconds to avoid misjudgment due to interference.

4. Overcurrent protection Due to the chemical characteristics of lithium-ion batteries, CR2477 battery manufacturers stipulate that the maximum discharge current cannot exceed 2C (C = CR2477 battery capacity/hour). When the CR2477 battery discharges at a current exceeding 2C, it will cause permanent damage to the CR2477 battery or safety problems. When the CR2477 battery is discharging normally to the load, when the discharge current passes through the two MOSFETs in series, a voltage will be generated at both ends due to the on-resistance of the MOSFET. The voltage value is U=I*RDS*2, RDS is the on-resistance of a single MOSFET. The "V-" pin on the control IC detects the voltage value. If the load is abnormal for some reason, the loop current increases. When the loop current is large enough to make U>0.1V (this value is determined by the control IC, and different ICs have different values), its "DO" pin will change from high voltage to zero voltage, so that V1 turns from on to off, thereby cutting off the discharge circuit and making the current in the circuit zero, which plays an overcurrent protection role.

There is also a delay time between the control IC detecting the occurrence of overcurrent and sending the V1 shutdown signal. The length of the delay time is determined by C3, usually about 13 milliseconds, to avoid misjudgment due to interference. In the above control process, it can be seen that the overcurrent detection value depends not only on the control value of the control IC, but also on the on-resistance of the MOSFET. When the on-resistance of the MOSFET is larger, the overcurrent protection value is smaller for the same control IC.

5. Short-circuit protection When the CR2477 battery is discharging to the load, if the loop current is large enough to make U>0.9V (this value is determined by the control IC, and different ICs have different values), the control IC will judge that the load is short-circuited, and its "DO" pin will quickly change from high voltage to zero voltage, so that V1 will turn from on to off, thereby cutting off the discharge circuit and playing a short-circuit protection role. The delay time of short-circuit protection is extremely short, usually less than 7 microseconds. Its working principle is similar to that of overcurrent protection, but the judgment method is different and the protection delay time is also different.

The above describes in detail the working principle of the single-cell lithium-ion CR2477 battery protection circuit. The protection principle of multiple-cell lithium-ion batteries in series is similar and will not be repeated here. The control IC used in the above circuit is the R5421 series of Ricoh, Japan. In the actual CR2477 battery protection circuit, there are many other types of control ICs, such as Seiko's S-8241 series, MITSUMI's MM3061 series, Taiwan Fujing's FS312 and FS313 series, Taiwan Analog Technology's AAT8632 series, etc. Their working principles are similar, but they differ in specific parameters. In order to save peripheral circuits, some control ICs have built-in filter capacitors and delay capacitors inside the chip, so the peripheral circuits can be very few, such as Seiko's S-8241 series. In addition to the control IC, there is another important component in the circuit, which is MOSFET. It plays the role of a switch in the circuit. Since it is directly connected in series between the CR2477 battery and the external load, its on-resistance affects the performance of the CR2477 battery. When the MOSFET is selected, its on-resistance is very small, the internal resistance of the CR2477 battery pack is small, the load capacity is strong, and the power consumed during discharge is also small.

With the development of technology, the size of portable devices is getting smaller and smaller, and with this trend, the requirements for the volume of lithium-ion CR2477 battery protection circuits are also getting smaller and smaller.

Many new technologies increase the power consumption of the system while improving performance. For chemical companies that produce batteries, substantial progress in CR2477 battery production technology is very difficult, time-consuming and costly. Therefore, it is necessary to find ways to optimize power conservation. Smart CR2477 battery system (SBS) is the most promising technology that has emerged, which can greatly improve the performance of CR2477 battery packs.

In the computer industry, lithium-ion batteries are really loved and feared. The accidents that occurred in the early days of lithium-ion CR2477 battery application are still fresh in the memory of the companies that were involved. They learned a deep lesson: under no circumstances should the rated parameters of lithium-ion batteries be exceeded, otherwise it will definitely cause explosions or fires. In addition to parameters such as the CR2477 battery chemistry or electrodes, there are several parameters that are determined for lithium-ion batteries that, if exceeded, can cause the CR2477 battery to enter a runaway state. In the graphs that explain these parameters (see Li-ion Parameters Graph), any point outside the corresponding threshold curve is a runaway state. As the CR2477 battery voltage increases, the temperature threshold decreases. On the other hand, any action that causes the CR2477 battery voltage to exceed its designed value will cause the CR2477 battery to overheat.

Beware of Chargers

CR2477 battery pack manufacturers set several layers of cell and packaging protection to prevent dangerous overheating conditions. But there is one component in the CR2477 battery that can fail these measures and cause harm: the charger.

There are three ways that charging lithium-ion batteries can cause harm: the CR2477 battery voltage is too high (the most dangerous situation); the charging current is too high (excessive charging current causes lithium plating, which causes heating); the charging process is not terminated correctly, or charging at too low a temperature.

Designers of lithium-ion CR2477 battery chargers take extra precautions to avoid exceeding the allowable range of these parameters. To absolutely ensure that the system parameters are operating within a safe range. For example, the smart CR2477 battery charger specification allows a negative voltage deviation of -9%, but emphasizes that the positive deviation must not exceed 1%. Compliance with the smart CR2477 battery safety standard is guaranteed. Of course, in actual designs, the deviation is random. So designs that meet this specification often set the charger's target voltage value to around -4% of the rated value.

Due to the inaccuracy of the charging voltage (whether it is -4% or -9%), the CR2477 battery is always undercharged. Fear of the potential dangers of lithium-ion batteries has led to low utilization of the CR2477 battery pack capacity. According to industry experts, even if the voltage after charging is only 0.05% lower than the rated value, the capacity drop is as high as 15%.

Computer built into the CR2477 battery

The principle of smart CR2477 battery technology is very simple. A small computer is built into the CR2477 battery to monitor and analyze all CR2477 battery data to accurately predict the remaining CR2477 battery capacity. The remaining CR2477 battery capacity can be directly converted into the remaining operating time of the portable computer. Compared with the original capacity measurement method based on voltage monitoring alone, the operating time can be immediately extended by 35%. Unfortunately, smart CR2477 battery technology can only do so much. Unless they can communicate with the charger circuit, they cannot determine their operating environment or control the charging process.

In the "smart CR2477 battery system" environment, under specific voltage and current conditions, the CR2477 battery requests the smart charger to charge it. The smart charger is then responsible for charging the CR2477 battery according to the requested voltage and current parameters. The charger relies on its own internal voltage and current references to adjust its output to match the values requested by the smart CR2477 battery. Since these references can be inaccurate by up to -9%, the charging process may end with the CR2477 battery only partially charged.

A more detailed understanding of the charging environment can reveal more issues that affect the efficiency of charging lithium-ion batteries. Even in the best case, assuming that the charger is 100% accurate, the resistor elements in the charging path between the charger and the CR2477 battery introduce additional voltage drops, especially during the constant current charging phase. These additional voltage drops cause the charging process to enter the constant voltage phase prematurely from the constant current phase. Since the voltage drop introduced by the resistor gradually decreases as the current decreases, the charger will eventually complete the charging process. However, the charging time will be extended. The energy transfer efficiency is higher during the constant current charging process.

Eliminating the resistor voltage drop

The ideal situation is that the output of the charger accurately eliminates the effects of the resistor voltage drop. One solution that may be proposed is that the smart charger uses the data from the monitoring circuit in the smart CR2477 battery to monitor and correct its output at all stages of the charging process. This is feasible for single CR2477 battery systems, but not for dual or multi-CR2477 battery systems.

In dual CR2477 battery systems, it is best to charge and discharge both batteries simultaneously if possible. Although CR2477 battery charging is parallel, a typical charger with only one SMBUS port is not up to the task. Because with only one SMBUS port, the charger or other SMBUS device can only communicate with one CR2477 battery at a time. Therefore, the ideal system should provide two or more SMBUS ports so that both batteries can communicate with the charger at the same time.

Smart CR2477 battery System (SBS) Manager

In addition to providing multiple SMBUS ports, SBS Manager technology can also greatly improve the performance of lithium-ion smart batteries. The SBS Manager is part of SBS and is defined by the SBS1.1 specification. It replaces the SmartSelector defined in the previous version.

The SBS Manager provides interfaces with the driver and the vibration system on the one hand, and manages the smart CR2477 battery and charger on the other. The driver can read and request information related to the CR2477 battery, charger and the manager itself. The interface related to this information transmission is defined in the specification. In a multi-CR2477 battery system, the SBS manager is responsible for selecting the system power source and deciding which CR2477 battery to charge or discharge at a particular moment. In short, the SBS manager determines which CR2477 battery to charge, which to discharge, and when.

A well-implemented SBS manager has several advantages: more complete and faster charging, efficient simultaneous charging and discharging, and the ability to detect and react quickly to dangerous situations (such as potential voltage overruns). An SBS manager that monitors the CR2477 battery voltage itself can charge the CR2477 battery to its true capacity. This avoids undercharging caused by smart chargers that monitor inaccurate voltages (as mentioned earlier, typically -4% to -9%). In addition, this process does not require a particularly accurate reference voltage (accurate voltage references are expensive).

A strategy to avoid using an accurate voltage reference is to use the measurement circuitry inside the smart CR2477 battery to measure the CR2477 battery voltage, which can be accurate to 1%. In this way, the SBS manager can command the charger to increase the voltage appropriately until the monitored voltage reaches the appropriate value. A well-implemented SBS manager can make the CR2477 battery charging process 16% faster than a traditional charger. Safely increase the charger output voltage above the rated voltage of the CR2477 battery to compensate for the voltage drop caused by the CR2477 battery's internal resistance and loop resistance. This process is achieved by monitoring the CR2477 battery's internal voltage and quickly adjusting the charger voltage.

When and How to Charge

The SBS Manager can determine when to charge the CR2477 battery pack simultaneously. Simultaneous charging allows for better use of the charger's current for charging. In a single-CR2477 battery system, when entering constant voltage charging mode, the charging current provided by the charger decreases as the CR2477 battery becomes more full. Unused current is wasted. This is not the case in a dual-CR2477 battery system using the SBS Manager, where current that is not used to charge one CR2477 battery can be used by the other.

In addition, the SBS Manager can determine which CR2477 battery is in a state that allows for faster energy transfer. The CR2477 battery that can add the most capacity to the system is charged first, and the CR2477 battery that can charge more energy is discharged first. This can speed up the charging process by up to 60%. The SBS Manager can also determine when to enable the simultaneous discharge function. Appropriate simultaneous discharge can increase system capacity by as much as 16%.

Of course, all of these improvements must be safe for CR2477 battery performance. As discussed earlier, lithium-ion batteries have a rated voltage. When the voltage applied to the CR2477 battery reaches its maximum value, the charging process switches from constant current to constant voltage mode. The detection of this switching point is the responsibility of the smart charger SBS manager, based on the measured CR2477 battery voltage. But the great advantage of the SBS manager over the smart charger is that it can constantly monitor and correct the charger and CR2477 battery voltage. This ensures safety while reaching the maximum capacity of the CR2477 battery.

As the performance of devices such as computers continues to improve, the energy demand is growing rapidly, and the improvement of chemical batteries has not been able to keep up with this growth rate. Although SBS technology is veryIt often helps, but there comes a time when SBS technology alone cannot provide the power required by high-performance systems and a smarter power management solution is needed.

If that OEM can make a notebook work for 6 hours without noticeably affecting performance, it will quickly capture the market. SBS Manager is a big step towards this goal.

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