bq24075 锂电池 充电电路分析

　　本文主要是分析bq24075锂电池充电芯片电路，知道其大致是怎么工作的，其中的一些电阻该如何配置。

　　　　　　　　　　　　　　　　　　　　　　　　　　　　2016-1-22 深圳 南山平山村 曾剑锋

一、参考文章：

    1. NTC热敏电阻器
　　　　http://baike.baidu.com/link?url=gD9Ikiv4C21Nhx2WlJwX5_b5vPeMztc4SwwsY5R0Bw-9sHrQFx8CZJBuU9EgMNABz4zgLEKF_j-bsP1qu2QcBa
　　2. 103AT-2
　　　　http://www.mouser.cn/ProductDetail/Semitec/103AT-2/?qs=wgO0AD0o1vvcDzsKguD%252bew%3D%3D
　　3. bq24075输出问题
　　　　http://www.deyisupport.com/question_answer/analog/battery_management/f/35/t/77294.aspx
　　4. bq24075
　　　　http://wenku.baidu.com/link?url=rq7MvZFy49pOHZnRpCO43PXGmLM46ty99skxKXxDalLsVq9zZj92SAGzoPTs28T8ZRRgHDXKYBCVb27oFB5eqncJWAyo7sdFK0_wjDGamV3

二、电路典型接法：

三、引脚功能说明：

四、芯片内部结构：

五、实际原理图：

　　1. Program the Input Current Limit (ILIM)
　　　　RILIM = KILIM / II_MAX
　　　　KILIM = 1550 AΩ from the electrical characteristics table.
　　　　RISET = 1550AΩ / 1.3A = 1.192 kΩ
　　　　Select the closest standard value, which for this case is 1.18 kΩ. Connect this resistor between ILIM (pin 12) and VSS.
　　2. Program 6.25-hour Fast-Charge Safety Timer (TMR)
　　　　RTMR = tMAXCHG / (10 × KTMR)
　　　　KTMR = 48 s/kΩ from the electrical characteristics table.
　　　　RTMR = (6.25 hr × 3600 s/hr) / (10 × 45 s/kΩ) = 46.8kΩ
　　　　Select the closest standard value, which for this case is 46.4 kΩ. Connect this resistor between TMR (pin 2) and VSS.
　　3. TS Function
　　　　Use a 10kΩ NTC thermistor in the battery pack (103AT-2). For applications that do not require the TS monitoring function, connect a 10kΩ resistor from TS to VSS to set the TS voltage at a valid level and maintain charging.
　　　　103AT-2热敏电阻图：

　　4. CHG and PGOOD
　　　　LED Status: connect a 1.5kΩ resistor in series with a LED between OUT and CHG to indicate charging status. Connect a 1.5kΩ resistor in series with a LED between OUT and PGOOD to indicate when a valid input source isconnected.
　　　　Processor Monitoring Status: connect a pullup resistor (on the order of 100 kΩ) between the processor’s power rail and CHG and PGOOD
　　5. System ON/OFF (SYSOFF) (bq24075 or bq24079 only)
　　　　Connect SYSOFF high to disconnect the battery from the system load. Connect SYSOFF low for normal operation