Idd Measurement; Figure 4. Stm3210C-Eval Idd Measurement Circuit - ST STM3210C-EVAL User Manual

Hardware layout and configuration
2.18
VDD_MCU
JP23
R156
+3V3
1[1%]
S
T2
STT5PF20V
20/54
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IDD measurement

Figure 4. STM3210C-EVAL IDD measurement circuit

U21
MAX9938FEUK+
5
3
4
R157 1K[1%]
5 3
+3V3
D
G
The circuit above is implemented on STM3210C-EVAL for IDD measurement.
In Run mode, IDD current is measured using MAX9938FEUK+ (U21) connected to the
1ohm shunt resistor. In this case IDD_CNT_EN remains high during measurement and
JP23 jumper must be set to 2<->3.
In Stop or Standby mode, the operational amplifier MAX9938FEUK+ (U21) is connected on
the 1 Kohm shunt resistor.
To measure a current corresponding to the Stop or Standby modes the procedure is:
1. Configure ADC to measure voltage on IDD_measurement pin.
2. Configure PA0 as interrupt input on falling edge.
3. Enter in Stop or Standby modes with IDD_CNT_EN Low.
4. LP_WAKEUP falling edge wakeup the MCU after 100 ms.
5. Start ADC conversion as soon as possible after wakeup in order to measure the
voltage corresponding to Low power mode on 1 uF capacitor.
6. Reset the counter by programming IDD_CNT_EN High in less than 50 mS after the
wakeup to avoid 1 Kohm to be connected later on VDD_MCU.
In Stop or Standby modes, the 1K resistor is connected when T2 goes off after entering the
Stop or Standby mode. Q13 output of the counter allows connection of the 1K resistor when
the current IDD becomes very low.
U22
R149
2
1
I/O O/I
4
4K7
C
VCC 5
3
+3V3
GND
74HIG66STR
U23
74LX1G04CTR
U24
1
Q12 VCC
2
Q13 Q10
3
Q14 Q8
4
Q6 Q9
5
Q5 CLR
6
Q7 CI
7
Q4 CO
8
GND CO
M74HC4060TTR
Figure 5 shows the measurement timing.
DocID15082 Rev 5
R79
PA6
IDD_Measurement
0
C78
4
T1 +3V3
0.47uF
3
5
1
2
+3V3
PA0
6
LP_WAKEUP
STT5PF20V
C48
+3V3
100nF
16
15
R152
14
10K
13
PC13
12
IDD_CNT_EN
11
10
9
C88 R158 R153
1nF 15K 30K
Oscillator frequency 30KHz
UM0600
MS32845V1