In recent years, due to the rapid development of lithium batteries, many portable products use the voltage measurement value to estimate the residual capacity of the battery, but the relationship between the battery voltage and the residual capacity will change with the discharge rate, temperature and the degree of battery aging, and the error rate of this method is up to 50%. Due to the increasing market demand for products with longer service life, more accurate solutions are needed in design. Using smart power meter IC to measure the charge or consumption of battery can provide more accurate battery power estimation in a wide range of application power levels.
1. POS intelligent battery design requirements:
According to the customer's requirements and specifications, the POS intelligent battery pack is designed, which integrates the intelligent electricity meter with communication protocol, lithium battery and security protection performance into the solution, so as to achieve the information sharing between the intelligent lithium battery pack and the POS host, and finally achieve a reasonable, efficient and safe battery management scheme. In the whole design process, to achieve the most perfect integration with the host as the direction, to ensure the safety of the battery, battery pack and the whole system as the premise, to meet the corresponding design regulations and certification regulations as the preferred consideration. At the same time, in order to ensure the safety and reliability of the lithium battery, multi-layer protection should be taken inside the battery pack to prevent the lithium battery from being damaged due to overcharge, over discharge or short circuit.
2. POS intelligent battery design scheme:
1) Protection board (PCM): it is mainly a protection circuit designed for rechargeable intelligent battery pack. Due to the chemical characteristics of lithium battery itself, it needs to provide intelligent power calculation, overcharge, over discharge, short circuit, and overcurrent and over temperature protection functions. In order to avoid the danger of combustion and explosion.
2) Protection IC: the main protection function chip of the design scheme, which can monitor the overcharge, over discharge, over current, short circuit and other functions of the cell online and constantly. Make the cell work in a safe, stable and efficient range.
3) Over current protection chip (PTC): mainly designed for secondary protection function. PTC recoverable fuse has double functions of over-current protection and automatic recovery. PTC in battery products can prevent high temperature discharge and unsafe high current.
4) 103450 Li ion cell / 103450 Li ion cell (Sanyo).
5) Field effect transistor (MOSFET): MOSFET, in the protection circuit to play a switching role, always make the voltage at both ends of the load will not rise or fall, to ensure voltage stability.
6) Power management control chip (BQ26500): a fully functional power detector, with an analog-to-digital converter (ADC) for measuring voltage and temperature and an analog-to-digital converter for measuring current and charging sensing. The electric quantity detector has a microprocessor, which is responsible for executing the electric quantity detector, and can provide the remaining state of capacity and other information. The BQ26500 product also provides the remaining time to empty. The host can query the information from the electricity detector at any time and inform the user of the battery information. The use of electric quantity detector is very convenient. Let the user master the battery power at any time.