A brief description of the smart battery system

In the computer industry, lithium-ion batteries are a love-hate affair. The incidents that occurred in the early days of lithium-ion battery use are still fresh in the minds of the companies involved. They learned an impressive lesson: under no circumstances should you exceed the rated parameters of a lithium-ion battery, or you are sure to cause an explosion or fire.

In addition to the chemical composition of the battery or the parameters of the electrode, there are several certain parameters for the lithium ion battery, and if it exceeds, the battery will enter an uncontrolled state. In the chart explaining these parameters (refer to the lithium ion parameter map), any point outside the corresponding threshold curve is out of control. As the battery voltage increases, the temperature threshold drops. On the other hand, any behavior that causes the battery voltage to exceed its design value will cause the battery to overheat.

Beware of the danger caused by the charger

The battery pack manufacturer has set several layers of battery and package protection to prevent dangerous overheating. However, there is a component in the battery that may cause these measures to fail and cause harm. This device is a charger.

There are three ways to cause damage to a rechargeable lithium-ion battery: the battery voltage is too high (the most dangerous situation); the charging current is too large (the excessive charging current causes the lithium plating effect, which causes heat); the charging process cannot be terminated correctly, or Charging at too low a temperature.

Designers of Li-Ion battery chargers take additional precautions to avoid exceeding the allowable range of these parameters. It is absolutely safe to ensure that the relevant parameters of the system work within the safe range.

For example, the smart battery charger specification allows a negative bias of -9%, but emphasizes that the positive deviation must not exceed 1%. It is guaranteed to meet the smart battery safety standards. Of course, in actual design, the positive and negative deviations are random. Therefore, the design conforming to this specification often sets the target voltage value of the charger to be near -4% of the rated value.

Due to the inaccuracy of the charging voltage (whether -4% or -9%), the battery is always undercharged. The fear of the potential danger of lithium-ion batteries results in a very low utilization of battery capacity. According to the experience of industry experts, even after charging, the voltage is only 0.55% lower than the rated value, and the capacity drop is as high as 15%.

Battery built into the computer

The principle of smart battery technology is very simple. The battery is built into a small computer to monitor and analyze all battery data to accurately predict the remaining battery capacity. The remaining battery capacity can be directly converted to the remaining working time of the portable computer. The working time can be immediately extended by 35% compared to the original capacity monitoring method based on voltage monitoring alone.

Unfortunately, smart 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 a "smart battery system" environment, the battery asks the smart charger to charge it under certain voltage and current conditions. The smart charger is then responsible for charging the battery based on the requested voltage and current parameters.

The charger adjusts its output with its own internal voltage and current reference to match the value requested by the smart battery. Since the inaccuracy of these benchmarks can be as high as -9%, the charging process may end with the battery only partially charged.

A more detailed understanding of the charging environment can reveal more problems affecting the charging efficiency of lithium-ion batteries. Even in the most ideal case, assuming that the accuracy of the charger is 100%, the resistive element between the cells of the charger in the charging path introduces an additional voltage drop, especially during the constant current charging phase. These additional voltage drops cause the charging process to enter the constant voltage phase prematurely from constant current.

As 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 transfer efficiency of energy during constant current charging is higher.

Eliminate the resistance drop

Ideally, the output of the charger accurately eliminates the effects of the voltage drop across the resistor. Someone may come up with a solution in which the smart charger monitors and corrects its output using intelligent battery monitoring circuit data at all stages of the charging process. This is possible for a single battery system, but not for dual or multi-battery systems.

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

Smart Battery System (SBS) Manager

In addition to providing multiple SMBUS ports, technology of SBS Manager can also significantly improve the performance of lithium-ion smart batteries. The SBS Manager is part of the SBS and is defined by the SBS 1.1 specification. It replaces the Smart Selector defined in the previous version.

The SBS Manager provides an interface to the drive and the system side of the drive, and on the other hand manages the smart battery and charger. The drive can read and request to send information about the battery, charger, and manager itself. The interface associated with this information transfer is defined in the specification. In a multi-battery system, the SBS manager is responsible for selecting the system power supply and deciding which battery to charge or discharge at a particular time. In short, the SBS Manager determines which battery to charge, which one to discharge, and when.

A well-implemented SBS management has several advantages: a more complete and faster charging process, simultaneous efficient charging and discharging, and the ability to detect and react quickly to dangerous conditions such as potential voltage overruns.

The SBS Manager, which monitors the voltage of the battery itself, charges the battery to its true capacity. Insufficient charging due to the inaccurate monitoring voltage of the smart charger (generally -4% to -9% as described above) can be avoided. In addition, this process does not require a particularly accurate reference voltage (precise voltage references are expensive).

The strategy to avoid using a precise voltage reference is to measure the battery voltage using a measurement circuit inside the smart battery with an accuracy of 1%. In this way, the SBS manager can command the charger to increase the voltage appropriately until the monitored voltage reaches a suitable value.

A well-implemented SBS manager allows the battery to be charged 16% faster than conventional chargers. Safely increase the output voltage of the charger above the rated voltage of the battery to compensate for the voltage drop due to the internal resistance of the battery and the loop resistance. This can be done by monitoring the internal voltage of the battery and quickly adjusting the charger voltage.

When and how to charge

The SBS Manager can determine when to charge the battery pack at the same time. Simultaneous charging allows for better utilization of the charger's current for charging. In a single cell system, when entering the constant voltage charging mode, the charging current provided by the charger decreases as the battery is fully charged. The unused current is wasted. This is not the case in a dual battery system that utilizes the SBS manager, and the current that is not used when charging a battery can be used for another.

Moreover, the SBS manager can determine which battery state can be energy transferred faster. The battery that can increase the system capacity fastest is charged first, and the battery that can charge more energy is quickly discharged. This speeds up the charging process by up to 60%. The SBS Manager can also determine when the simultaneous discharge function is enabled. Proper simultaneous discharge can increase system capacity by as much as 16%.

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

As the performance of computers and other devices continues to increase, the demand for energy is growing rapidly, and the improvement of chemical batteries cannot keep up with this growth rate. Although SBS technology is very helpful, there will always be a day when SBS technology cannot provide the power required by high-performance systems, and a more intelligent power management solution is needed.

If that OEM can keep the laptop running for six hours without significantly affecting performance, it will quickly take over the market. The SBS Manager has taken a big step towards this goal.

The page contains the contents of the machine translation.