My custom pcb cannot reach the power specifications of the nucleo

[Aurélien f]

Posted on November 16, 2017 at 13:06

Hello,

On my nucleo-l073 board, my software can run in stop mode and consumes only 3uA. I decided to make my own PCB but i can't figure out why the consumption can't reach 3uA. Actually, i'm running around 25uA with the same software. I'm using a stencil and a reflow oven to solder the components (T-962) and the solder paste is a Sn63 Pb37. I'm making the pcb by PCBway and i take the cheapest quality (5$ for 10 pieces : TG 130-140 (i don't what it means)), do you think it could come from that ?

I have also noticed when i put my finger directly on the stm32, consumption often decreases.

If you have any ideas, please feel free to share

Thank you in advance.

Edit : I join in attached file my schematic and my PCB (the ground planes are not displayed)

Best regards,

Aur�lien

#stop-mode #low-power #stm32 #pcb #nucleo-l073rz #pcbway

[Aurélien f]

Posted on November 23, 2017 at 15:33

Hi,

Thank you for the reply. 

I tried what you proposed but unfortunatly it didn't change anything. I have also tried to not use RTC but without success, i'm still having this extra current consumption if i don't connect PC13 to the ground !

Regards,

Aurélien

[Michael Stevens]

Posted on November 27, 2017 at 16:46

I'm still sorting out some of the intricacies of STM32s, how the parts come out of reset, and the software framework, but I suspect, based on what you've said thus far, that PC13 is still configured as an input.  Even though the actual peripheral functionality may be deactivated, if the input buffer is still on, leaving this floating would result in internal oscillations and shoot-through currents in the input totem.  

Looking at the Nucleo schematic, PC13 is used by the the blue pushbutton and has a PU to VDD, so it's being held in a known logic state.  If you cut the solder bridge, you would probably see similar current consumption on the Nucleo.

[Aurélien f]

Posted on November 28, 2017 at 13:51

Hi,

Exactly, when i cut the solder bridge SB17, i have the same bahavior with unregular current consumption, even if i set this pin with an internal pull up or pull down ...

So my question is : is it preferable to put a pull up with a 100k resistor or directly connected to the ground ?

Regards,

Aurélien

[Michael Stevens]

Posted on November 29, 2017 at 18:53

Hi Aurélien,

Peculiar... I would whitewire a PU to VDD and see what happens. 

If the internal PU or PD are enabled and no external PU or PD is present, you should only see additional currents that correlate to the IO leakage currents as specified in the datasheet unless you have another path for current to flow.  If you enable both the PU and PD, then the current would be considerably higher than just the IO leakage.

How is PC13 configured by firmware?

[Aurélien f]

Posted on November 29, 2017 at 20:06

Hi,

Thank you very much for the investigation

My firmware puts every pins as analog inputs, even PC13. On nucleo board (with the same firmware) :

- if the

external

PU is present, all is ok, no extra consumption observed. The current consumption is around 3uA

- if i cut SB17 (no PU or PD), i can observe an 

unregular current consumption (even if i configure PC13 as analog input or digital input with an 

internal

PU or PD with PUPDR register)

- if i pull this pin to the ground, i observe the same thing as the 1st case :the current consumption is very stable and around 3uA.

I will take a look at my software to see if i missed something but i'm suspecting a different behavior on this pin ...

Edit : I displayed MODER register of GPIOC at runtime, and this register is at 0xFFFFFFFF, it means all my GPIO on this port are configured as analog input, but i'm still having this current consumption if i cut SB17 ... I did the same thing with PUPDR to see if my pull up/pull down were well configured.

Regards,

Aurélien