Power Consumption STM32

[thetectivestm]

Hello everyone,

I need to get some information about the power consumption of the STM32 Nucleo-64 with STM32F401RE MCU.
The board is powered from the computer's USB port.
I created a project in which the main while loop is empty, all peripherals are disabled and the HCLK frequency (from PLLCLK with HSI PLL source mux) is 84 MHz.

I used a USB Digital Tester J7-c (between the board and the pc's USB port) and I obtained this values:
5.04 V; 0.05 A; 0.29 W; 92 Ω.

Changing the HCLK frequency from 84 MHz to 42 MHz, I obtain this values:
5.04 V; 0.04 A; 0.25 W; 108 Ω.

But if I use the PCC (Power Consumption Calculator) tool with these step parameters (RUN mode, power scale: scale2, memory fetch type: flash, VDD: 3.3 V, voltage source: battery, CPU freq.: 84 MHz, all peripherals disabled) I get a step consumption of 20.2 mA (= 0.0202 A).
Instead, with these step parameters (RUN mode, power scale: scale3, memory fetch type: flash, VDD: 3.3 V, voltage source: battery, CPU freq.: 42 MHz, all peripherals disabled) I get a step consumption of 11.03 mA (= 0.01103 A).
I read from the datasheet that the MCU is placed under the conditions of TA=25°C and VDD=3.3 V. The USB provides 5V which is stepped-down to 3.3V for the MCU, right?

So, why did the USB tester give me that values?
Shouldn't I get a value close to 0.0202 A (with 84 MHz) and 0.01103 (with 42 MHz)?

Could anyone please help me?

[KnarfB · Accepted solution]

Haven't used your specific model of USB tester, but in my experience those testers are quite crude devices, especially for lower currents.

And, you are measuring the board power consumption, not only the MCU chip. As you wrote, there are voltage converters, LEDs and the ST-LINK on a Nucleo board.

The Nucleos have a IDD jumper for MCU current measurement, see board schematics (under CAD  Resources). You need to open that and attach an (milli)ampere meter, see User Manual.

hth

KnarfB

[thetectivestm]

Hi @KnarfB , thank you for the reply.

As you wrote, the board has a IDD jumper (JP6) for MCU current measurement so I've attached a multimeter to get the current. But in some cases the value of the current shown on the display of the multimeter is variable. 

Can you tell me more about this? Further details here:  Power Consumption Measurement