Idd Measurement Principle - ST STM32L1 Series Application Note

AN3413
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
Manufacturing test
different test modes.
1.4.2 I measurement principle
DD
The STM32L1xx DISCOVERY I
side shunt voltage value V at the terminals of a high precision serial resistor (1%) inserted
between the +3V3 power supply and the V
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
for details regarding the test activation and for an explanation of the
Figure 2. I
DD
K1
Q14 Q13
Counter
PC13
EN
DocID018933 Rev 2
measurement circuitry consists of measuring the high
DD
pin of the MCU. Depending on the device
DD
measurement equivalent circuitry
+3V3
I
DD
2R
V
2k
V
DD
PA4
I meas
DD
STM32L15x
PA0
LP wake-up
GND
Application description
Section 1.5.3:
Gain = 50
A
S
C
+3 V3
K2
MS19811V1
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