Data Sheet

5.4. A-Star 32U4 Prime SV regulator

The A-Star 32U4 Prime SV can be powered from a 5 V to 36 V

external source. The input voltage is regulated to 5 V by a 1 A

ISL85410 switching step-down (buck) converter from Intersil. (We

also make a standalone regulator [http://www.pololu.com/product/2831]

based on this integrated circuit.)

As shown in the left graph below, the SV’s switching regulator has

an efficiency – defined as (Power out)/(Power in) – of 80% to 95%

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 the

output currents where the regulator’s output voltage drops below 4.75 V. These currents are close to the limits of the

regulator’s capability and generally cannot be sustained for long periods; under typical operating conditions, a safe

limit for the maximum continuous regulator output current is approximately 1 A.

The dropout voltage of a step-down regulator is defined as the minimum amount by which the input voltage much

exceed the regulator’s target output voltage in order to assure the target output can be achieved. As can be seen in the

graph below, the dropout voltage of the Prime SV’s regulator increases approximately linearly with the output current.

For light loads where the dropout voltage is small, the board can operate down to 5 V. However, for larger loads, the

dropout voltage should be taken into consideration when selecting a power supply; operating above 6 V will ensure

the full output current is available.

5. A-Star 32U4 Prime Page 28 of 47