STMicroelectronics UM1079, User Manual

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UM1079 Hardware and layout
37
Figure 10. I
DD
measurement circuit
4.7.1 High I
DD
range mode
In high I
DD
range mode, the I
DD
current is measured using the operational amplifier
MAX9 (U5) connected to the 2 Ω shunt resistor (R21). In this case IDD_CNT_EN
remains high during the measurement. R22 remains in short-circuit during the measurement
because the FET transistor 1 of U20 remains ON permanently.
4.7.2 Low I
DD
range mode
In low I
DD
range mode, the operational amplifier MAX9 (U5) is connected to the
1 K
Ω
shunt resistor (R22), controlled by the FET transistor 1 of U20. In this case the counter
74HC4060 (U3) enabled by IDD_CNT_EN manages the measurement timing according to
Figure 11 .
Low I
DD
range measurement principle
The principle used to measure the consumption current when the STM32L152RCT6 is in
low I
DD
range mode is as follows:
1. Configure ADC to measure voltage on the IDD_Measurement pin.
2. Configure PA0 to serve as wakeup pin.
3. Enter low I
DD
range mode after setting IDD_CNT_EN (PC13) signal low.
4. IDD_WAKEUP rising edge wakes up the MCU after around 300 ms.
5. Start ADC conversion as soon as possible after wakeup in order to measure the
voltage corresponding to Low-power mode on capacitor C13.
6. Reset the counter by programming IDD_CNT_EN high (in less than 150 ms after the
wakeup) to avoid the R22 1 K
Ω
resistor being connected later in Run mode.
The measurement timing is given in Figure 11 . In low I
DD
range mode, the 1 K Ω resistor is
connected when the FET transistor 1 of U20 goes OFF, after entering low I
DD
range mode.
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