STM32F103CBT6 power consumption

[shin212]

Hello, 

I recently designed STM32F103CBT6 based PCB for motor controller and I wanted to ask about power consumption at the default state of STM32F103CBT6. What is expected current consumption for just STM32F103CBT6 when I power up the board when not programmed to anything? I am using DC/DC from 5V to 3.3V and 3.3V is used to power up the STM32F103CBT6. I am getting 5V from lab bench power supply and directly soldered onto the input of DC/DC converter. I see current consumption about 40mA at the bench power supply. 3.3V is used for some LEDs and an ADC but still higher than I expected. I have attached related schematics here. Please let me know 

Thank you 

Regards,

Mike 

[TDK]

The data sheet lists power consumption characteristics. 40mA after including external LED and ADC seems in line with what it suggests, for undisclosed clock speeds quite high, for an unprogrammed part. Lower clock speeds will use less current. You can hold the chip in reset to see what the relative consumption is at idle vs with code running.

[shin212]

Hi, thanks for your reply. 

I will certainly check while holding the chip in reset to see what the relative consumption is. However, it still seems to me that current consumption is high. I was actually wrong. This is DC/DC Buck converter and efficiency is about 85% at light load. So output current of the buck converter is actually higher than that I see on the bench power supply (40mA)... (5V * 40mA * 85%)/3.3V = 51.5mA. It still seems too high.. is this reasonable amount of current consumption? Current consumption of LED and ADC is pretty low according to the datasheet. Again, I will check after configuring the chip with some code but the current consumption seems to be still too high. What would be the best way to validate your PCB is okay without programming the chip? Is there any app notes that explains about the chip's default state and current consumption? Otherwise, it's hard to validate the PCB design. 

[shin212]

Hi, I think I solved the problem. It seems that the problem was relevant to VA pin of ADC floating. When I enable both 5VA and +3.3V, current consumption on +3.3V seem to be ~5mA. It seems that ADC needs to have VA and VD pin supplied. Is this reasonable amount for unprogrammed chip? I don't see 40mA anymore but 5mA! 

[TDK]

5mA seems quite reasonable for an unprogrammed chip.

[shin212]

I see. Thank you. I will check out after programming the chip. Btw I have an external crystal. Am I expected to see output of crystal after programming the chip? I don't see anything now. 

[TDK]

Does your code initialize and use the external crystal? Probably does, in which case you would see a signal there. It would be silly to put an external crystal on the board if it were not used, but that is also a possibility.

[shin212]

Code has not been flashed onto the chip yet. I am asking if i still should still some waveform out of crystal even though chip is not programmed with anything. 

[TDK · Accepted solution]

Here's the question you asked:

> Am I expected to see output of crystal after programming the chip?

If you meant before programming the chip, no you will not see a waveform.

[shin212]

Z