Dissecting A Smart Battery – Part 3

In my first two articles of the series Dissecting A Smart Battery I discussed the specialized hardware contained in the smart battery including the connector, the fuse, the charge and discharge FETs, the cell pack, and the the sense resistor (RSENSE).  In my final article of the series “Dissecting A Smart Battery” I would like discuss some of the other important hardware features contained in a smart battery.

As we have done in the first two parts of Dissecting A Smart Battery let’s recap the specialized hardware we have talked about. Included in the smart battery are the following specialized hardware:

  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 or firmware for the fuel-gauge IC.

The Primary and Secondary Protection IC

Integrated Power Management Circuits protects against over-voltage, and under-voltage conditions and they maximize battery life between charges, minimize charging times, and improve overall battery life. Batteries for PDAs, MP3s, Digital Cameras, and Laptops for example have designed within them integrated power management circuits that insure that the deliverance of reliable power is properly managed. Without these power management integrated circuits even fine tuned handhelds will exhibit problems such as over-voltage, and under-voltage conditions. Incidentally, overcharging is potentially a very dangerous problem. Overcharging is the state of charging a battery beyond its electrical capacity, which can lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the charger or device in which the overcharged battery is later used.

An integrated circuit in general is a miniaturized electronic circuit. An electrical circuit is a network that has a closed loop, giving a return path for current. The goals of integrated circuits are multifaceted, for example when designing for signal processing integrated circuits apply a predefined operation on potential differences (measured in volts) or currents (measured in amperes). For batteries the use of integrated circuits with the goal of power management is integrated battery management which include voltage regulation and charging functions. Power management integrated circuits offer other key benefits as well including maximizing battery life between charges, minimize charging times, and improve battery life. The other critical aspect of power management integrated circuits is their functioning design to detect and monitor voltage levels in batteries. When certain parameter thresholds are exceeded or dangerous conditions exist, these “supervisory circuits” react through a programmable logic design to protect the monitored system and correct problems as programmed. Supervisory circuits are known by a variety of names, including battery monitors, power supply monitors, supply supervisory circuits and reset circuits. They perform critical functions including power-on-reset (POR) protection to ensure that processors always start at the same address during power-up. Without POR, even well-functioning systems can exhibit problems during power-up, power-down, over-voltage, and under-voltage conditions.   

The Fuel-gauge IC

We may all be familiar with the battery charge indicator on our device. The little blinking light or bar meter indicator that let’s us know when we need to recharge our battery. But did you know that the calculation of the remaining battery capacity (power) is performed within the battery and that calculation is transmitted to the device from within the battery to the device through the connector. The calculation of remaining battery capacity is performed by the fuel-gauge integrated circuit. The fuel-gauge stores cell characteristics and application parameters used in the calculations within the on-chip EEPROM (which we will discuss shortly). The available capacity registers report a conservative estimate of the amount of charge that can be removed given the current temperature, discharge rate, stored charge and application parameters. Capacity estimation is then reported in mAh remaining and percentage of full charge.

The Thermistor

A thermistor is a temperature-sensing element. The thermistor is used to determine starting temperature and prevent charging if the battery temperature is too low or too high. The battery charger also uses the thermistor as an external thermal sense that provides input to temperature sense for the fuel gauge.

The PC Board

All the components that we have discussed throughout the series on Dissecting A Smart Battery (the connector the fuse the charge and discharge FETs, the cell pack, the sense resistor, the primary and secondary protection ICs, the fuel-gauge IC, the thermistor) is at one point within the battery connected to a PC Board. The PC Board or printed circuit board is used to mechanically support and electrically connectthe aforementioned specialized hardware using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate.


Lastly I want to discuss the EEPROM, which stands for the electrically erasable programmable read only memory of the smart battery. It is a reference in effect to the user programmable integrated circuits memory devices which retain stored information in the absence of electrical power and in which the information may be altered electrically.

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