The hottest intelligent battery system SBS simplif

2022-08-14
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Intelligent battery system SBS simplifies the design of independent battery system

the emergence of intelligent battery system (SBS) greatly simplifies the design of independent battery system, so its application has gone beyond the field of notebook computer, and appears in other applications, such as backup power system, high reliability military and aerospace applications. Other key applications include automobiles, security/surveillance/anti-counterfeiting systems, medical devices, blade servers, telecommunications and portable electronic products

smart batteries use internal electronic circuits to measure, calculate and store battery data, which makes the use of power more predictable. Moreover, smart batteries have another important advantage, which is to prevent accidental system downtime

a basic SBS system consists of the following parts: system management bus (SMBus), smart battery charger and smart battery

The modularity of SBS makes it very easy to design a closed-loop battery charging system. Such a system allows the use of independent battery chargers (smart chargers), which minimizes the non repetitive Engineering (NRE) cost of hardware and software, and promotes a solid system, which is particularly important for high reliability battery backup applications. The high accuracy barometer integrated into the battery pack can always accurately monitor the battery, even when the battery is not in the system. The barometer is calibrated according to the actual capacity value of the battery, so the deviation is eliminated and the accuracy is ensured

the main function of smart battery charger is to provide voltage source and current source for charging the smart battery accumulated into an average thin layer. The smart battery communicates with the smart charger through the SMBus Interface, and can optionally communicate with the host. In order to prevent overcharging due to the loss of SMBus function, the monitoring timer runs continuously to monitor the call frequency between the smart battery and the charger. If the battery does not operate for more than 3 minutes, the charger will pause and wait for the battery to request charging again. In addition, the battery can also control the charger through the forced shutdown function, which can bypass SMBus to provide redundancy level and let the charger know that the battery is indeed present

compared with the fixed independent charger, the smart battery charger has the following advantages:

① it is truly plug and play and is not affected by the chemical characteristics of the battery and the battery configuration. Any smart battery pack can be matched with any smart battery charger. Batteries with different chemical characteristics, configurations, and even different charging algorithms can be replaced with charger circuits without modification

② the built-in safety function of the equipment must be turned off first. SBS standard provides a monitoring timer and a special "safety signal" interface between battery and charger

③ reliable battery detection system

④ automatic charging management without host

⑤ closed loop charging system without host intervention. The host can collect electricity measurement information as needed

ltc1760 dual smart battery system manager

ltc1760 is a highly integrated three-level battery charger and selector for products using dual smart batteries. It is a step-down switching topology battery charger, which has a variety of functions in line with the definition of smart battery standards and other new functions, such as input current limit and safety limit, and so on. The three SMBus interfaces enable the ltc1760 to realize servo functions such as tracking the internal voltage and current of two batteries, and allow one SMBus host to monitor the status of any battery. This servo technology can make the accuracy of the charger only have ± 0.2% error with the measured value of the internal voltage and current of the battery

traditionally, the dual battery system is a sequential discharge system, which allows the sequential consumption of battery power to simply extend the total battery working time. Ltc1760 adopts proprietary analog control technology, which allows two batteries to be safely charged or discharged in parallel. This structure increases the charging speed by 50% and the battery working time by 10%. In addition, parallel discharge not only enhances the current capacity, but also reduces the I2R loss and improves the voltage regulation ability under extremely high load conditions. Reducing I2R loss and improving voltage regulation have extended the total discharge time of the timing solution

● main features of ltc1760:

① independent three-level charger polls the charging requirements of the battery and monitors the actual current and voltage determined by the internal electric quantity measurement of the battery (error is ± 0.2%), so as to realize fast, safe and complete charging

② the fast charging mode can be used to further shorten the charging time

③ support battery inspection to realize barometer calibration

④ the three power path FET diodes allow safe and low loss discharge from dcin and the two batteries, which are the eighth city in China with an annual output of more than 100 vehicles

⑤ two FET diodes realize the safe and low loss discharge of two batteries at the same time

⑥ hardware programmable current and voltage safety limits and many other safety functions are used to supplement the internal protection circuit of the battery

ltc1760 is very precise, but it is very easy to use. In any given design, only four key parameters need to be determined: input current limiting detection resistance RICL, current limiting resistance rilim and matching charging current detection resistance RSENSE, voltage limiting resistance rvlim and short-circuit protection resistance RSC. Ltc1760, together with some smart batteries and an AC adapter, can form a simple system

Figure 1 ltc1760 dual battery charger/selector system architecture

● input current limiting detection resistance rcl

as shown in Figure 2, this circuit limits the charging current to prevent AC adapter overload when the system power increases. To set the input current limit, the most important thing is to minimize the rated current of the wall adapter. The current limiting resistance can be calculated by the following two equations

Figure 2 input current limiting inductive resistance circuit

ilim = minimum current value of adapter - (minimum current value of adapter × 5%) (1)

rcl = 100mv/ilim (2)

however, the AC adapter can have a current limiting margin of at least +10%, so it is often easy to set the adapter current limiting value to the actual adapter rating

● current limiting resistor rilim

rilim resistor has two functions. First, it tells the SMBus Interface of ltc1760 that the charger can supply the maximum allowable current of the battery, and any value exceeding this limit will be replaced by the limit value. The second function is to synchronize the full-scale current of PWM charger with the full-scale current limit of SMBus Interface

● the external resistance value connected between the voltage limiting resistor rvlim

vlim pin and GND can determine any of the five charger output voltage limits (see Table 3). This method of using hardware to limit the pressure value with the continuous enhancement of human environmental awareness is a relatively safe measure, which cannot be replaced by software

● short circuit protection resistance RSC

each power path is composed of two back-to-back PFETs, which are connected in series with the short circuit detection resistance RSC. The equivalent circuit of powerpathtm switch driver is shown in Figure 3

Figure 3 ltc1760 power path circuit

● no software required

no software required for ltc1760 based chargers. Putting the integrated circuit in the initial hardware prototype will allow the system to charge and discharge the battery. However, in some cases, some software can be written so that the host can complete the following actions

① collect "charger status" information directly from the smart battery (that is, as a barometer)

② support battery inspection

conclusion

intelligent battery system provides advanced functions, requiring only minimal design work. Ltc1760 is the representative of a very comprehensive single-chip dual intelligent battery system. It is simple and easy to use. It only needs to determine 4 parameters to complete a complete design, and it does not need software code. The device can form a complete independent battery charger system and work normally with only the minimum NRE work. (end)

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