Susie Maestre

user Electronics Engineer

city Innovuze Solutions Inc.

  • Low Power Protector for Lithium-Ion Battery

  • Created: Oct 05, 2016

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Battery protectors are essential to electronic systems to enhance the operating life of batteries. It does this by monitoring the individual cell voltages and by preventing overtemperature condition. This design utilizes Texas Instruments bq77905, which is an ultra low-power stackable lithium-ion battery protector IC. This device implements a suite of voltage, current, and temperature protections without microcontroller (MCU) control. Protection thresholds and delays are factory-programmed and available in a variety of configurations. Separate overtemperature and undertemperature thresholds for discharge (OTD and UTD) and charge (OTC and UTC) are provided for added flexibility.

The design consists of one bq77905 and FETs to control current in a configuration typical for switching current in a lithium-ion battery pack. The circuit also includes a sense resistor, thermistor, two CSD18534Q5A FETs, and all other onboard components necessary to switch charge and discharge current. The supply in this circuit is connected to screw terminal (ST1). These are the supply terminals for the board. The BATT+ or CELL5 (C5) is the positive terminal of the power supply and BATT- is the negative terminal of the power supply. The inputs CELL1 through CELL4 are divided between the BATT+ and BATT- voltages. In addition to the current and voltage applied to the module, the user can remove onboard jumpers to simulate over/undertemperature conditions to observe FET control under different charge and discharge conditions. The integrated independent CHG and DSG low-side MOSFET drivers, may be disabled via two control pins. This provides pack protection. These control pins may also be used to achieve cell protection solutions for higher series (6S and beyond) in a simple and economical manner by cascading a higher device CHG and DSG outputs to the immediate lower device control pins. For reduced component count, all protection faults use internal delay timers.

This design is very useful among battery-monitoring circuits specifically for Li-ion batteries. This is also very suitable battery protector in power tools, start-stop battery packs, light electric vehicles, energy storage systems, UPS, and in other consumer electronics products.