PowerManagement ICs
charge-pump chips for powering portable devices, supervisory and power-sequencing ICs for linear and switching power supplies, larger self- contained DC/DC converter ICs, semiconductor power devices (e.g., MOSFETs), AC/DC chips for mains- connected power applications, and LED and LCD displays.
Each segment is a large area unto
itself. Here's a basic overview of how they all fit together.While the specific requirements for each area vary, typical PMICs share a common ground. The ideal chip, which most often contains some form of power switch or converter (e.g., regulator, low-dropout regulator):
• Is itself a low-power, low-noise device
• Minimizes the number of external components to preserve PCB real estate
• Includes thermal-management circuitry to minimize related high- current, heat, and safety issues
• Includes automated, proactive circuitry to detect trouble before it happens
• Lends itself to microprocessor-based control for integrated applications and quick decision-making
How much battery?
With so-called battery management charger and regulator chips a mature yet still very active area (see ESNA, February 2011 issue for an overview of battery charger ICs), so-called fuel- gauge or gas-gauge ICs for lithium-ion batteries have captured most of the
innovation.More than ever, users need to know precisely how much battery power, or time, is left before their
22 | April 2011
portable device conks out. These power management devices are also at the focal point of a battery's cell-balancing systems, which in turn is related to several performance and safety issues.
Cost considerations aside, today's
users expect to know how much power is "left in the tank" to within one percent of actual battery capacity or the time to loss of operating power. That's about a tenfold improvement in the capability of last decade's "battery monitors," the best of which provided perhaps down to eight percent accuracy.
What do you look for in a gas-gauge?
A good one should at least be able to take into account the user's power- usage profile, the age of the battery, and the operating temperature. Today's ICs tend to incorporate the equivalent of a so-called coulomb counter for measuring charge/current (as opposed to earlier types that rely on measuring voltage); some sort of learning algorithm to track battery parameters; and sensors to keep a tab on operating temperature. Most gauges today will likely be compatible with the smart battery specification (SBS), which open the door to SMBus and linking up with microcontroller- based systems.
The bq20z80 from Texas Instruments
(Dallas, Texas), released in 2004, was among the first that arrived for these high-accuracy devices. TI's "Impedance Track" algorithm calculates the impedance of the battery in real-time. Maxim Integrated Products' (Sunnyvale, Calif.) DS2780 device came along about the same time in a parallel development, for non-SBS systems. Subsequent chips fromMaximhave
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