DocID018933 Rev 2

5/18

AN3413

Application description

17

The firmware associated with this application note also provides a demonstration of the

touch sensing functionality available on STM32L1xx DISCOVERY. The touch sensing

electrodes can be configured either as a linear touch sensor to perform linear sensing of

finger position displayed as a percentage on the LCD, or, it can be configured as a group of

four independent touchkeys.

It also includes a manufacturing test mode for performing a quick diagnosis of the

STM32L1xx DISCOVERY related to this application example. See Section 1.5.3:

Manufacturing test for details regarding the test activation and for an explanation of the

different test modes.

1.4.2

side shunt voltage value V at the terminals of a high precision serial resistor (1%) inserted

power modes, the application uses R or [2000 + 2] x R as the equivalent resistor value by

closing or opening K1. In Run mode, the current is in the range of mA, K1 is closed, and the

equivalent resistor is R. In low power modes, the current is in the µA range, K1 is opened,

and the equivalent resistance is 2002 x R.

This resistor is connected between the differential inputs of a high-side current sense

operational amplifier (A) with a fixed gain that amplifies the voltage (V) present on the

resistors. A sample and hold stage is placed at the operational amplifier output and is then

MS19811V1

A

2R

2k

+3V3

STM32L15x

GND

+3 V3

Q14 Q13

EN

Counter

PC13

PA0

LP wake-up

PA4

Gain = 50

C

K1

K2

V

S