Tutorial
Li-Ion Battery Protection ICs
An added requirement for Li-ion battery packs is a protection circuit that limits each cell's peak voltage during charge and prevents the voltage from dropping too low on discharge. The protection circuit limits the maximum charge and discharge current and monitors the cell temperature. This protects against overvoltage, undervoltage, overcharge current, and overdischarge current in battery packs
Ideally, the protection circuit should consume no current when the battery-powered system is turned off. However, the protector always consumes some small current.
Battery Protector IC Examples
1. A single-cell rechargeable Li+ protection IC provides electronic safety functions required for rechargeable Li+ applications including protecting the battery during charge, protection of the circuit from damage during periods of excess current flow and maximization of battery life by limiting the level of cell depletion. Protection is facilitated by electronically disconnecting the charge and discharge conduction path with switching devices such as low-cost N-channel power MOSFETs
The IC provides high-side drive to external N-channel protection MOSFETs from a 9V charge pump, with better on-resistance performance results compared with common low-side protector circuits using the same MOSFETs. The MOSFET on-resistance actually decreases as the battery discharges.
Adding to the uniqueness of this IC is the ability of the system to control the MOSFETs from either the data interface or a dedicated input, thereby eliminating the power-switch control redundancy of rechargeable Li+ battery systems. Also, the command set supports a means of performing simultaneous switching of multiple battery packs, allowing the protector IC to function as a battery selector in these applications.
Through its 1-Wire interface, the IC gives the host system read/write access to status and control registers, instrumentation registers, and general-purpose data storage. Each device has a factory-programmed 64-bit net address that allows it to be individually addressed by the host system, supporting multi-battery operation.
Two types of user-memory are provided in the IC for battery information storage: EEPROM and lockable EEPROM. EEPROM memory saves important battery data in true nonvolatile (NV) memory that is unaffected by severe battery depletion, accidental shorts, or ESD events. Lockable EEPROM becomes ROM when locked to provide additional security for unchanging battery data.
2. This protector IC handles lithium-ion/lithium-polymer (Li+) 3- or 4-series Li+ battery packs. The IC enhances the useful operating life of Li+ batteries by monitoring individual cell voltages and preventing over/undervoltage conditions.
The IC also protects the battery pack against charge current, discharge current, and packshort fault conditions. In case of a fault condition, on-board drivers control external P-channel MOSFETs, which disconnect the cells from the pack external terminals. The external protection MOSFETs are connected in a common-source configuration that does not require external pullup resistors. The IC uses only one current-sense resistor to achieve the protection features. All protection thresholds and delays do not require any external components and are trimmed at the factory.
If any cell voltage drops below the undervoltage threshold, the IC disconnects the pack from the load and power down to prevent deep discharge of the pack. The IC offers a trickle-charge feature, which provides a low-current path to safely charge a deeply discharged pack. The protector IC also has two logic-level inputs, which can be used by a microcontroller to disable the protection MOSFETs and to put the device in shutdown. The IC has low quiescent current (30µA typ) and ultra-low shutdown current (0.8µA typ) to prevent deep-cell discharge.
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