Discussing internal battery design would be incomplete if we did not write on the subject of integrated circuits. Batteries for PDAs, MP3s, Digital Cameras, and Laptops 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.

Taking a step back a moment lets build a platform with which to discuss power management integrated circuits. At its most basic level 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). Typical functions for such electrical networks are amplification, oscillation and analog linear algorithmic operations such as addition, subtraction, multiplication, division, differentiation and integration.

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, overvoltage, and undervoltage conditions.

A real example of a battery pack protector circuit is a Texas Instrument two-cell lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) battery pack protector device. The devices primary function is to protect both Li-Ion and Li-Pol cells in a two-cell battery pack from being either over-charged (over-voltage) or over-discharged (under-voltage). It employs a precision band-gap voltage reference that is used to detect when either cell is approaching an over-voltage or under-voltage state. When on-board logic detects either condition, the series FET (field effect transistor) switch opens to protect the cells.

I wont be getting anymore technical as this topic is better left to engineers. But suffice to say power management integrated circuits are a critical design aspect of your handheld battery. Without these integrated circuits your handheld device would have died along while back.