Hardware and layout
UM1018
18/44
Doc ID 18141 Rev 1
2.16.3 Ibias
current
measurement procedure
In Low power mode the bias current of operational amplifier input (U10 pin 4) is not
negligible compared to IDD current (typical Ibias is ~240 nA). To obtain a reliable MCU IDD
measurement it is possible to subtract the bias current from the IDD low power
measurement since this current is not sinked by the MCU.
The procedure for accurate IDD measurement is:
1.
Set jumper on JP4 pins 1 and 2.
2.
Follow the Low power mode procedure to measure I1 = I bias.
3.
Remove jumper on JP4 pins 1 and 2 and place it on JP4 pins 2 and 3.
4.
Follow the low power mode procedure to measure I2 = IDD + I bias.
5.
Calculate actual IDD: IDD = I2 - I1.
Note:
When jumper JP4 is removed the current consumption of the STM32L can be measured by
connecting an ammeter between jumper JP4 pin 1 and pin 2.
Note:
RDS (on) typical value of analog switch T4 = 50 micro Ohm, so to improve measurement
accuracy it is recommended to take into account the RDS in series with R36 (1 Ohm) in the
Idd Run mode current calculation.
Table 12.
IDD measurement related jumpers
Jumper
Description
Setting
JP14
PA5 is connected to IDD_measurement, the output of IDD measurement circuit
when JP14 is closed (
default
).
PA5 is disconnected from IDD_measurement but remains connected to BNC
connector CN13 when JP14 is open.
JP4
STM32L is powered through IDD measurement circuit (
default
)
STM32L is powered directly by +3V3, IDD measurement circuit is bypassed.
Please refer to
Section 2.2: Power supply
for details.
3
2
1
3
2
1
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