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.

The EEPROM

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
Copyright © BatteryEducation.com. All rights reserved.

Dissecting A Smart Battery – Part 2

In part 1 of Dissecting A Smart Battery I mentioned that smart batteries have contained within them specialized hardware that when working in concert provides the power necessary to run a device such as a PDA, digital camera, or ipod player. Continuing the dissection of a smart battery this article of the series will look at the smart battery’s fuse, charge and discharge FETs , the cell pack, and the sense resistor (RSENSE) to discover what role they each play within the smart battery.

Before we begin let’s just recap some of the specialized hardware within the smart battery:

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.
11. and the SMBus

The Smart Battery Fuse

When we discuss fuses in relation to electronics we are speaking directly of a fusible link that is responsible for protecting the device from over current. Fusible links have a metal wire that melts when heated to a predetermined electric current rating. When melted the electrical circuit is opened and thereby protecting the circuit from an over-current condition. The obvious concern here is the selection of the fuse – an improperly selected fuse will not protect from over-current conditions and the result will be a fire or damage due to a short circuits.

In a smart battery a typical fuse has three-terminal components that limit current flow based on the temperature, current, and or power across the heating wire. Besides temperature ratings other important factors when selecting the proper fuse to work with each smart battery is hold current, trip current, maximum battery voltage, and fuse size.

The Smart Battery’s FET (field effect transistor)

Smart batteries must have a series FET (field effect transistor) switch to open and protect the battery’s cells. A FET is a transistor that uses an electric field to control the conductivity of a particular 'channel' in a semiconductor material. FETs at times are used as voltage-controlled resistors. As such field effect transistors are chosen based upon their designed ability to dissipate on demand power.

The Smart Battery’s Cell Pack

The battery cell can be thought of as the holding area of the battery’s chemical. The battery cell pack is critical to the overall capability of the smart battery. Cell packs have to be designed and integrated based upon the vitals of the battery including chemistry type (Li-ion, Li-po, NICD, NIMH, etc.) cycle life, storage-capacity loss, shelf life, impedance, capacity at different rates of discharge and temperature, and mechanical and environmental requirements. It is critical to say the least.

The Smart Battery’s Sense Resistor

The final specialized hardware I want to review in this article is the sense resistor (RSENSE). In electronics, sense, is generally referred to the task of producing the correct voltage. Current not temperered will cause damage so sense resistors need to be integrated in order to control power and temperature.

In my next article on the dissection of a smart battery I will cover secondary protection ICs, the fuel-gauge IC, the thermistor, the pc board, and the EEPROM.

Until next time, Dan Hagopian – www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

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
Copyright © BatteryEducation.com. All rights reserved.

What is Inside A Smart Battery?

If you have a PDA, MP3, MP4, Laptop, Cell Phone, Smartphone, DVD players, or other electronic device then more likely then not the battery within your device is a high capacity smart battery pack. What is a high capacity smart battery pack? A high capacity smart battery pack is a complex battery system designed to power high tech electronic devices.

What differentiates smart batteries from standard batteries is the specialized hardware that provides calculated 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 or firmware for the fuel-gauge IC.

In addition to the above advanced chip components, I mentioned that information flows from these components to another advanced component of the smart battery and that is the smart battery’s System Management Bus (SMBus) control – a two-wire interface through which simple power-related chips can communicate with rest of the system. Typically a SMBus uses I2C as its backbone so that multiple chips can be connected to the bus. The SMBus allows a device to transfer manufacturer information, transfers model or part number to and from the device and battery, save its state for a suspend event, report different types of errors, accept control parameters and return its status.

All in all the smart battery is a highly specialized battery that functions within its intended design. Used outside its design the smart battery really won’t work too well!

Until next time, Dan Hagopian – www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

Batteries – One Size Does Not Fit All

I have a Palm Zire 72 and a Palm m505 PDA. If I buy a Palm Zire 72 Battery that is 3.7 volts can I plug it into a Palm m505 and have that battery power both devices as needed?

In a nut shell the question above seeks to ascertain if all 3.7 volt batteries are the same?

The quick answer is no – all 3.7 volt batteries are “not” the same – and a battery specifically designed for a Palm Zire 72 will not be compatible with a Palm m505 PDA.

Let me explain.

It is true that all batteries share similar components and share common electrical measurements. But just because all batteries have some common components and measurements does not mean at all that you can interchange batteries with various devices even if the technical ratings are the same. Note that a component is something tangible and a measurement is intangible – a result of an action contained within the battery system.

Quick Review: What is a Battery and how does it work?

A battery in its most basic definition is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positve and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Somtimes the opposite is true depending on battery technology.

In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either liquid or solid). This battery consisting of two electrodes is called a voltaic cell.

Electrical measurements that can be gleaned from battery operations inclued the measurements of:

Volts – or V – is the electrical measure of battery’s energy potential. For example you can think of energy potential as the pressure being exerted by all the electrons of a PDA Battery’s negative terminal as they try to move to the positive terminal.

Amps – or A – which is a measure of the volume of electrons passing through a wire in a one second. One Amp equals 6.25 x 1018 electrons per second.

Watts: Volts x Amps = Watts. Watts are important because a watt represents the electrical energy spent by a battery (power generator) and used by an electrical device. Watts in effect is the measure of the amount of work done by certain amperage (amount) of electric current at a certain pressure or voltage.

Now beyond that basic review of the common components and measurements of batteries begins the radical differences between batteries. If you have a PDA, MP3, MP4, Laptop, Cell Phone, Smartphone, DVD players, or other electronic devices then more likely then not the battery within your device is a high capacity smart battery pack.

What is a high capacity smart battery pack? A high capacity smart battery pack is a complex battery system designed to power high tech electronic devices.

To construct a smart battery the battery manufacturer must carefully plan the internal battery design environment by considering the:

• design parameters
• current requirements
• capacity and runtime requirements
• temperature requirements
• safety requirements
• ambient operational/non-operational temperatures

As a design for a smart battery pack is considered manufacturers must evaluate the differences in components in relation to their design environment. Proper component evaluation and specification selection based on the intended application will determine the ultimate performance of the entire battery.

To give you an example of why smart batteries are carefully designed consider a PDA that when turned on explodes (don’t think it can’t happen) thankfully it occurs very rarely. To be a more reassuring the US Consumer Product Safety Commission has noted that 339 battery-related overheating incidents have occurred since 2003. Since conservative estimates puts the sale and use of devices containing smart batteries in excess of 100 million battery related devices during the same period makes the 339 incidents reported by the Saftey Commission at .000003% (a very small percent) of all battery related devices on the market. What is preventing more battery related fires -reliable and safe design under worst-case conditions is especially critical when designing with lithium based batteries. Specifically over-voltage and under-voltage of the cells and over-current of the battery pack.

Now with all this said I can tell you again, almost emphatically, that not all batteries are the same. From battery to battery the internal design will be different depending on the device the battery was specifically built to work within.

Until next time, Dan Hagopian – www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.