Battery-Based Power Supply Controller ICs

Virtually all battery-based systems are intended for portable operation. As such, their power supplies have unique requirements:

  • Operate from one- or two-cell Li-ion batteries or three- or four-cell NiCd or NiMH packs.
  • Provide the appropriate voltage and current for load
  • Provide high efficiency for maximum battery run time
  • Allow light weight and small physical size supplies to minimize overall system size
  • Be thermally efficient to prevent overheating
  • Minimize assembly and component cost for consumer-based systems
  • Provide high reliability, care-free service

These requirements dictate the associated power supply controller IC configurations. This also means that the controller ICs should require very few external components and any that are used should be low-cost types. Also, to minimize size and weight, the IC should be packaged in some form of small outline package. In addition, the application will determine whether the controller should provide step-up, step-down or some other topology.

One tradeoff in selecting a controller IC is whether it employs external or on-chip power MOSFET switches. On-chip devices minimize external components, but have the potential for increasing the junction temperature and degrading thermal performance. Depending on the package employed, this could also reduce the current carrying capacity of the IC. Some controller ICs described below have on-chip power MOSFETs, others require external MOSETs.

One design consideration is reducing power dissipated by the power supply, which in turn increase battery run time. All controller ICs described below have a shutdown pin that disables the power supply, cutting battery drain. This can be done in many systems that have a normal "sleep" mode. When the IC comes out of the shutdown mode, it has to do so without upsetting the system.

Also available in most battery-based controller ICs is undervoltage lockout (UVLO) that shuts down the power supply if the input voltage drops below a specific threshold. Therefore, if the battery output voltage drops too far, the power supply will shut down.

Another characteristic of these controller ICs is protection against overcurrent, which protects both the controller IC and the system components. This is accomplished by sensing current to the load and cutting power for an overload condition.

For all switching power supplies, the layout is an important step in the design, especially at high peak currents and high switching frequencies. If the layout is not carefully done, the regulator could show stability as well as EMI problems. Therefore, use wide and short traces for the main current path and for the power ground tracks. The input capacitor, output capacitor, and the inductor should be placed as close as possible to the IC. Use a common ground node for power ground and a different one for control ground to minimize the effects of ground noise. Connect these ground nodes at any place close to one of the ground pins of the IC.

The feedback divider should be placed as close as possible to the control ground pin of the IC. To lay out the control ground, it is recommended to use short traces as well, separated from the power ground traces. This avoids ground shift problems, which can occur due to superimposition of power ground current and control ground current.

Battery-based power supply IC applications:

  • Cellular telephones
  • Digital cameras
  • MP3 players
  • Mobile communication devices
  • Pagers
  • Handheld games
  • PDAs
  • Medical monitors
  • Notebooks & sub-notebook computers
  • Palmtop computers
  • PCMCIA cards
  • Portable instruments
  • GPS receivers

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