DocID17369 Rev 2

5/13

AN3193

Energy-efficient processing

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Figure 1. STM32L1xx performance versus VDD and VCORE range

A typical example is portable healthcare equipment with USB device capability.

As long as it works in standalone mode, 4 MHz are sufficient to acquire and process the

data from the analog front-end. In this case, the internal logic can be supplied with 1.2 V

only.

However, executing a USB software stack when the system is connected to the USB

interface of a PC requires more processing power: in this case, the device can be placed in

"high-performance mode", where the internal voltage is 1.8 V. It can then execute code at 32

MHz while the USB peripheral is supplied by a 48-MHz clock. Voltage scaling is used to deal

with the contradictory requirements of these two operating modes without having to

compromise on the dynamic current consumption.

1

16 MHz

4MHz

MHz

32 MHz

1.2V

1.5V

1.8V

VCORE

1.65V - 3.6V

2V - 3.6V

32

1

F CPU > 2 MHz 1WS

16MHz

8 MHz

2MHz

32

16

8

0WS

4

ai178201

VDD

F CPU > 8 MHz

1WS

0WS

F CPU > 16 MHz

1WS

0WS

178 μA / MHz

195 μA / MHz

240 μA / MHz

2

Range 2

Range 3

Range 1