Dissecting A Smart Battery – Part 1

Smart Batteries – they are used in PDAs, MP3s, MP4s, Laptops, Cell Phones, Smartphones, DVD players, and other electronic devices.  When we buy new batteries we want them to work. We really don’t care how they work just as long as the do. But since PDA Batteries are a unique interest for me and since pda batteries are smart batteries I’m going to dig a little deeper to discover what lies within PDA batteries. So follow along as I dissect a pda battery to learn what it is made of!

Contained within a smart battery is specialized hardware. Hardware that has a specific purpose: to deliver calculated and on demand current as well as predicted information.

This specialized hardware includes:

1. the connector
2. the fuse
3. the charge and discharge FETs
4. the cell pack
5. the sense resistor (RSENSE)
6. the primary and secondary protection ICs
7. the fuel-gauge IC
8. the thermistor
9. the pc board
10. the EEPROM
11. the SMBus

But what are each of these components and what do they do? Let’s find out?

The connector is a device that joins electric circuits together. Most battery packs require more than one connector. The main battery connector is both the mechanical and electrical part that interfaces the battery to the PDA or other electronic device. If you have ever installed a battery in your PDA then you probably have plugged your battery in by plugging/snapping in the main battery connector to the device’s PC board. Features that have to be considered when selecting a connector of a particular battery is operating temperature (range/limits) since high capacity batteries discharge excessive heat – having a connector that can withstand such temperature extremes will prevent a short circuit. Connectors also have to proper pin assignments so that current and performance capacity can be met and short-circuit thresholds are predetermined. Pin orientation within the connector has to be designed in order to fit the device. If it doesn’t well you won’t be able to connect the battery to the PDA or other electronic device. Finally the connectors has to be handle time-varying current therefore the ratio of the phasor voltage across the element to the phasor current through the element (otherwise known as impedance) has to be preset or else expect connector to not function in the way it was supposed to!

In the next article of this series I will cover the smart battery’s fuse, charge and discharge FETs , the cell pack, and the sense resistor (RSENSE). The article after the next will cover the primary and secondary protection ICs, the fuel-gauge IC, the thermistor, the pc board, the EEPROM, and the SMBus.

Until next time, Dan Hagopian – www.batteryship.com
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