Pumping Milliamps

When putting together the power tree for a complicated system, such as a smartphone or tablet, very often specific integrated circuits are used because they support a wide input voltage range or because they run off of a common input voltage, such as 5V or 3.3V. This greatly simplifies the power architecture of the system, as one power supply can be used to supply all devices that require a given voltage. Even though hundreds of integrated circuits may be used in such systems, the number of power supplies is typically only a fraction of that amount. This allows high levels of integration, saving cost and precious board space.

For smaller, less-complicated systems such as many medical devices (insulin pumps, thermometers, blood glucose meters, etc.), the system engineer may be unable to combine all the required integrated circuits’ power needs into a few common power rails. There may be one odd ball device, critical to the system’s functionality, which requires 2.9V or 4.3V. This single device would then require an entire power supply circuit to power just it. Adding insult to injury, this one device, commonly a reference voltage, typically only requires mA of load current. This creates an extremely lop-sided cost/space per mW of output power tradeoff for this one integrated circuit that is an inefficient use of the system’s resources.

Enter the auxiliary charge pump circuit to do this light lifting and save the day. Using the switching of existing power supply circuits and only needing two capacitors and two diodes, it can simply, easily, and cost effectively deliver the mA of current for such low power devices. Add a low-cost, small size linear regulator and a regulated output voltage is now created, as in this paper. The following schematic shows an auxiliary charge pump circuit with the TPS62231 (D1/D2 and C3/C4).


How have auxiliary charge pump circuits helped you overcome system design challenges?

Additional resources:

  • TPS62231 3-MHz ultra-small step down converter in 1x1.5 SON package
  • Evaluation module for TPS62231 charge pump converter
  • TLV70025 200mA, low IQ, low dropout regulator for portable applications
  • TI's full line of charge pump circuits (boost, step-down, buck-boost, inverting)