KW41Z's current consumption is different than in the datasheet

[dvdsosa]

Hi all,

I need to set the KW41Z uC (mounted in the FRDM-KW41Z REV C2 dev board, Buck Mode) at its lowest power mode configuration.

For this, I tested the Power Manager SDK example, and the lowest current consumption I obtained was 100uA (at J34) in the Very Low Power Stop (VLPS) mode, while 4mA for the whole dev board, which was measured in the J19 connector with 5V input. The 100uA current matches the information given in a previous post by the @paralax user ( https://community.nxp.com/t5/Kinetis-Microcontrollers/Low-power-mode-with-KW41Z/m-p/1044349/highligh... ).

On the one hand, I need to get even less current consumption, and on the other, the maximum VLPS current stated in the datasheet (Table 15) at 25ºC is about 15uA (datasheet MKW41Z/31Z/21Z Data Sheet, Rev. 4, 03/2018). 

Why am I getting 100uA instead 15uA? Am I measuring it wrong?

I need to keep moving forward ASAP with the project, and this stage of power consumption is crucial for its autonomous application.

Kind regards, David.

[dvdsosa]

Hello @EduardoZamora 

I followed the instructions given in the BLE Heart Rate post by @gerardo_rodriguez, where the revision of the board seems older than the latest FRDM-KW41Z dev. released REV C2, which is what I have. I am still obtaining about 100uA when the BLE Heart Rate Sensor demo (FreeRTOS example) enters in LLS3 measured in J34 versus the 4.08uA maximum Idd_LLS3 stated in the datasheet (J34 is to measure at the VDCDC_IN of the MKW41Z512VHT4, Rev. C2 board, seen in SCH-29102 sheet 3 of 5).

I also see that a total of 19 pins are pinMux_PinDisabledOrAnalog_c inside the BOARD_SetPinsLowPower() function, code that is executed in a callback when entering low power mode, found on the board.c file of the demo.

I have also tried other examples where the lowest current I can measure in stop mode is about 100uA at VDCDC_IN.

Do you have any out-of-the-box example that runs with such a low current as the one shown in the datasheet?

If so, where should I measure it? at J34 at VDCDC_IN?

Regards,

David.

[EduardoZamora]

Hi,

Since dynamic current is implied, a complex current analyzer is required. Could you please provide more details about the measurement method (device, procedure) you are using?

Regards,
Eduardo.

[dvdsosa · Accepted solution]

Hi @EduardoZamora ,

I succeeded by following the Application Note AN12459 made for the FRDM-KW38 dev board.

I missed that there is no such document for the FRDM-KW41Z, so I looked at the schematics of both the FRDM-KW38 and the FRDM-KW41Z, noting the similar jumpers and following the instructions.

Finally, I obtained 1mA in the J34 jumper (VDCDC_IN) w/o peripheral (J8 off) while on with the Heart Rate Demo and 5uA while off in LLS3 mode with a $7k Keithley Digit Multimeter.

I hope sharing this information will help others.

Regards,

David Sosa Trejo.

[EduardoZamora]

Hello @dvdsosa

Please note that MKW41Z Data Sheet describes power consumption only for the chipset. Other devices/components may be involved in the FRDM board that may affect power consumption.

Regarding to the power_manager project, this application may not be fully optimized for taking the lowest current measurements. Please test any of the wireless examples such as the BLE Heart Rate Sensor demo, this demo has low power support enabled by default, but the default power mode could be changed.

Also, please take a look at the Power Management for Kinetis MCUs Application Note. This application note discusses how to use the power management systems, provides use case examples and shows real-time current measurement results for these use cases.

Regards,
Eduardo.