Application description

AN3413

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DocID018933 Rev 2

resulting voltage, image of the consumption current.

In low power modes only, a counter enabled by STM32L15x (PC13 pin) manages the

measurement timing while the microcontroller is idle. The microcontroller is woken-up after

a 150 ms delay when the rising edge is triggered on a wake-up pin (PA0) controlled by the

K2 switch.

While the microcontroller is in one of the power saving modes, a capacitor (C) is charged

with the voltage amplified by the operational amplifier. The microcontroller can later sample

(during its wake-up phase - 50 ms) the value of capacitor voltage proportional to the current

consumption of MCU in low power mode. Switch S is opened at device start-up in order to

keep the charge collected in capacitor (C) intact while the microcontroller is in low power

mode.

The current measurement precision is enhanced by taking into account the current bias of

measurement circuitry disabled), a special test invoked by the user at device start-up

measures this current value and stores it in the non-volatile memory. Once this value is

due to I bias current (see Section 1.5.2: Bias current record).

section 4.7, Built-in IDD measurement circuit of the STM32L1 discovery kits: STM32L-

DISCOVERY and 32L152CDISCOVERY user manual (UM1079).

1.5

Getting started with the application

This STM32L1xx DISCOVERY example application has 3 application modes that can be

run:

•

•

Bias current record

•

Manufacturing test

Demo mode is available at application power-up while the two others are invoked by the

user using a specific procedure that is described in detail later in this chapter. However, for

best performance, it is recommended to measure and record the bias current before starting

1.5.1

Once the application is powered-up via the USB cable (or by external power supply), it starts

applied to the STM32L1x device.

are displayed, both LEDs are turned off.

The User push-button allows you to change the functions as described in the state diagram

in Figure 3.

The first step is a demonstration of the linear touch sensor function followed by a touchkey

demo activated by pressing the user button.