Hardware layout and configuration
UM1521
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Doc ID 022868 Rev 1
2.20 I
DD
measurement
The built-in I
DD
measurement circuit implemented allows the consumption measurement of
the STM32L152ZDT6 while the MCU is in Run or Low power saving modes.
For I
DD
measurement the circuit below is implemented on the STM32L152D-EVAL.
Figure 9.
STM32L152D-EVAL I
DD
measurement circuit
2.20.1 Run
mode
In Run mode, I
DD
current is measured using operational amplifier MAX9 (U19)
connected to the 1 Ohm shunt resistor (R62). In this case IDD_CNT_EN remains high
during measurement, so R81 remains in short-circuit during measurement because of
transistor T1 which remains ON permanently. JP10 must be connected between pins 2 & 3.
2.20.2 Low
power
mode
In Low power modes (Stop or Standby), the operational amplifier MAX9 (U19) is
connected to the 1 KOhm shunt resistor (R81), controlled by the analog switch T1. In this
case the counter 74HC4060 (U15) enabled by IDD_CNT_EN manages the measurement
timing according to
.
The principle used to measure a current when the STM32L is in Low power mode is:
1.
Configure ADC to measure voltage on the IDD_Measurement pin (PF11).
2.
Configure PA0 to serve as wakeup pin.
3.
Enter Low power 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 C82.
6.
Reset the counter by programming IDD_CNT_EN high (in less than 70 ms after the
wakeup) to avoid the R81 (1 KOhm) resistor being connected later in Run mode.
In Low power modes, the 1 K resistor is connected when T1 goes off after entering Low
power mode. Q12 output of the counter allows connection of the 1 K resistor when the
current I
DD
becomes very low.
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