Data Sheet

5.3. A-Star 32U4 Prime LV regulator

The A-Star 32U4 Prime LV can be powered from a 2.7 V to 11.8 V

external source. The input voltage is regulated to 5 V by a

TPS63061 switching step-up/step-down (buck-boost) converter

from Texas Instruments. (We also make a standalone regulator

[http://www.pololu.com/product/2123] based on this integrated circuit.)

The regulator’s flexibility in input voltage is especially well-suited

for battery-powered applications in which the battery voltage begins

above 5 V and drops below 5 V as the battery discharges. Without

the typical restriction on the battery voltage staying above 5 V

throughout its life, a wider range of battery types can be considered.

For example:

• A 4-cell battery holder, which might have a 6 V output with fresh alkalines or a 4.0 V output with partially

discharged NiMH cells, can be used to power this A*.

• A disposable 9 V battery powering the board can be discharged to under 3 V instead of cutting out at 6 V, as

with typical linear or step-down regulators.

As shown in the left graph below, the LV’s switching regulator has an efficiency – defined as (Power out)/(Power in)

– of 80% 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

(without the buzzer, microSD card, or an LCD). 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; under typical

operating conditions, a safe limit for the maximum continuous regulator output current is 60% to 70% of the values

shown in the graph.

5. A-Star 32U4 Prime Page 27 of 47