Ibias Current Measurement Procedure - ST STM32L152-EVAL User Manual

Hardware and layout
2.16.3
Note:
Note:
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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.
Table 12. IDD measurement related jumpers
Jumper
PA5 is connected to IDD_measurement, the output of IDD measurement circuit
when JP14 is closed (default).
JP14
PA5 is disconnected from IDD_measurement but remains connected to BNC
connector CN13 when JP14 is open.
STM32L is powered through IDD measurement circuit (default)
JP4
STM32L is powered directly by +3V3, IDD measurement circuit is bypassed.
Please refer to Section 2.2: Power supply
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.
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.
Description
for details.
Doc ID 18141 Rev 1
UM1018
Setting
1 2 3
1 2 3