4.2. A-Star 32U4 Mini ULV regulator
A-Star 32U4 Mini ULV, bottom view with dimensions.
The A-Star 32U4 Mini ULV can be powered from a 0.5 V to 5.5 V external source. The input voltage is regulated to 5 V by a TPS61202 switching step-up (boost) converter from Texas Instruments. (We also make a standalone regulator based on this integrated circuit.)
The regulator’s low minimum input voltage makes it possible to power this A* with 1 to 3 NiMH, NiCd, or alkaline cells or from a single lithium cell. Unlike standard boost regulators, the TPS61202 also features a linear down-regulation mode that is automatically enabled when the input voltage exceeds 5 V, allowing it to handle input voltages as high as 5.5 V.
As shown in the left graph below, the ULV’s switching regulator has an efficiency – defined as (Power out)/(Power in) – of 70% to 90% for most combinations of input voltage and load.
The A-Star’s components, including the microcontroller and LEDs, draw 30 mA to 40 mA in typical applications. The rest of the regulator’s achievable output current, which depends on input voltage as well as ambient conditions, can be used to power other devices. The right graph above shows output currents at which the voltage regulator’s over-temperature protection typically kicks in after a few seconds. These currents represent the limit of the regulator’s capability and cannot be sustained for long periods; a good estimate for the maximum continuous regulator output current is 60% to 70% of the values shown in the graph.