Smart watch is a multi-function watch which is connected to the network with built-in intelligent system and smart phone system. It can synchronize the phone, SMS, e-mail, photos, music, etc. Smart watches are usually powered by high-performance polymer batteries to ensure the continuous, efficient and stable operation of the products. To meet the users long-term reliable and safe use requirements.

1. Design requirements of smart watch battery

According to the customer's requirements and specifications, design the battery pack matching with the host, and integrate the polymer battery and safety protection performance into the solution. 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 polymer 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.

1) Model of polymer battery pack: 403040PL 3.7V 450mah

2) Circuit design requirements:

• Single section overcharge protection voltage: 4.30 ± 0.25V

• Single section overcharge recovery voltage: 4.15 ± 0.50v

• Single section over discharge protection voltage: 2.8 ± 0.08v

• Recovery voltage of single section over discharge: 3.00 ± 0.08v

• Over current protection value of combined battery (10ms): 2 ~ 4A

• The finished battery also has short circuit and reverse charge protection.

• Battery cycle life design requirements: 300 ~ 500 times (national standard for charging and discharging)

• Battery size design requirements: Refer to the host shell

2. Battery design of smart Watch

1) Protection board (PCM): it is mainly a protection circuit designed for polymer battery. Due to the chemical characteristics of lithium battery, it is necessary to provide protection functions such as overcharge, over discharge, short circuit and overcurrent, so as to avoid the danger of combustion and explosion.

2) Protection IC (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, so that the cell can work in a safe, stable and efficient range. At the same time, the capacity, temperature, remaining time alarm and other parameters of the battery pack are measured.

3) Polymer Li ion cell: 403040pl 3.7V 450mah Li polymer cell.

4) 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.

5) Battery package: sealed and fixed with the host