Figure 17. Schematic Diagram Of The Analog Part Of Idd Measurement - ST STM32L476ZG User Manual

Hardware layout and configuration
R135 and R123. The former state is used for measuring the current consumption in
Dynamic-Run mode, the latter in Low-power mode.
The differential amplifier uses three stages U15B, U15C, and U15D of the quadruple
operational amplifier device U15, TSZ124. The gain is set to 50, so an additional 50 mV at
the U15C output, terminal 8 of U15 represents every 1 mA of supply current.
The resistance formed with the series of R135 and R123, when T2 is in a high-impedance
state, is 1001 Ω. It makes the voltage on terminal 8 of U15 increase by approximately 50 mV
for every µA of MCU power consumption. The full-scale range, with VDD at 1.8 V is about
30 µA.
Even with precision resistors R136, R125, R129, and R132 to set the gain of the differential
amplifier, the output voltage might theoretically become negative. To avoid the need for a
negative power supply, a positive offset of about 220 mV is created at the output, at zero
current consumption of the MCU. This offset does not need to be precise. Any dispersion is
compensated through a calibration procedure detailed in
For allowing the IDD measurement, the jumper in the JP11 header must short its terminals 3
and 4.
bypass path
58/80

Figure 17. Schematic diagram of the analog part of IDD measurement

VDD from
power
supply
VDD
Current
direction
T2
4
Shunt_x1000 3 5
1
2
6
FDC606P
current
measurement
path
JP11
Current
direction
U15B
TSZ124IPT
5
R136
7
6
3K6 0.1%
R135
1[1%]
shunts
R123
1K[1%]
differential
amplifier
U15D
12 TSZ124IPT
R125
14
13
3K6 0.1%
VDD_MCU
to MCU
UM1855 Rev 6
Section 6.30.4.
+5V
decoupling capacitor
C75
close from TSZ124 part
100nF
R128
22K U15A
GND
TSZ124IPT
3
1
V+
R124
2
V-
C144 1K
100nF
GND
GND GND
R129
180K 0.1%
U15C
TSZ124IPT
10
8
9
R132
180K 0.1%
UM1855