Appliance Design - March 2008 - (Page 31)

POWER tion such as a robotic vacuum. This design supports control of both charge and discharge currents using a single path with two MOSFETs. It also provides pack-current monitoring for over-current and short-circuit events; individual cell-voltage monitoring; pack-temperature monitoring; and fast, cell balancing with up to 200 mA of balance current. In this example, an Intersil ISL9208, functions as an Analog Front End (AFE) and operates in conjunction with an external microcontroller. The AFE performs level-shifting of the cell voltages and outputs the actual cell voltage on the analog output pin (AO) to the microcontroller. The microcontroller uses this information to monitor the status of each cell during charge and discharge, as well as for cell balancing. Along with the analog voltage of each cell, the AFE also reports any error conditions to the microcontroller. The charge and discharge FETs may be controlled directly by the AFE and provide an automatic protection mechanism to minimize any possibility of delays in protection being introduced by the microcontroller when critical error states such as overcurrent or short-circuit conditions exist. It is possible to disable this automatic protection feature if designers have some proprietary battery-management algorithms they prefer to use. In cases where the automatic protection feature is disabled, the AFE will continue to monitor the current and will report an error condition to the microcontroller, which will then direct the AFE to disable the MOSFETs or execute the proprietary algorithms. For battery packs that require more than seven cells in series, as shown in Fig. 2, a chipset approach that incorporates a single microcontroller and multiple AFE’s can be easily implemented using Intersil’s ISL9216 and ISL9217 chipset. In a well-designed battery pack, error conditions will be qualified in time and amplitude to avoid spurious shutdowns. For example, the ISL9208 provides multiple voltage, current, and timing thresholds that are programmable by designers for their specific applications. These include: Four discharge over-current thresholds. Four short-circuit thresholds. Four charge over-current thresholds. Eight over-current delay times (Charge). Eight over-current delay times (Discharge). Two short-circuit delay times (Discharge). These multiple thresholds provide the applianceDESIGN March 2008 31 Fig. 1. Example of a Li-ion battery pack managed by an ISL9208 chip. The design supports control of both charge and discharge currents using a single path with two MOSFETs. Fig. 2. The ISL9216 and ISL9217 chipset can be used to manage battery packs with more than seven cells in series. www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - March 2008

Appliance Design - March 2008 Contents Editorial Shipments/Forecasts News Watch A New Appliance is Set to Break into Homes Soon - the Micro CHP Unit, which Generate both Heat and Power. Thermally Enhanced Varistors Help Protect Low-Power Systems Against Damage Caused by Over-Current, Over-Temperature and Over-Voltage Faults. Hybrid Controller Reduces Standby Power Consumption and Improves Active-Mode Efficiency. Battery-Management ICs Solve Design Challenges for Cordless Appliances Using High-Voltage, Lithium-Ion Battery Technology. A Semiconductor Solution Protects the Relay in a Temperature Controller for a Cooking Appliance. New Polyurethane Foam Insulation System Optimizes both Insulation Performance and Productivity. Innovations in Decorative, Pre-Finished Metals Expand Range of Design Options for Appliance Designers. Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - March 2008

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