Author Topic: Custom board with unusual power consumption  (Read 543 times)

Marc-Aurele

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Custom board with unusual power consumption
« on: November 16, 2017, 02:27:00 PM »
Hello,
 
On my nucleo-l073 board from st microelectronic (that embeds a stm32l073), 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 (one of the cheapest on aliexpress). I'm making the pcb by PCBway and i take the cheapest quality (5$ for 10 pieces : TG 130-140), do you think it could come from that ?
I have also noticed when i put my finger directly on the stm32, consumption often decreases. I'm also suspecting the solder paste i'm currently using ...
If you have any ideas, please feel free to share  ;)
Thank you in advance.
 
Best regards,
 
Aurélien

Edit : I join in attached file my schematic and my PCB (the ground planes are not displayed)
« Last Edit: November 18, 2017, 09:19:24 PM by Felix »

Felix

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Re: Custom board with unusual consumtion
« Reply #1 on: November 16, 2017, 04:23:34 PM »
my software can run in stop mode and consumes only 3uA
Is that an assumption? How do you know that? From datasheet?
« Last Edit: November 17, 2017, 09:00:44 AM by Felix »

TomWS

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Re: Custom board with unusual consumtion
« Reply #2 on: November 16, 2017, 06:56:48 PM »

I have also noticed when i put my finger directly on the stm32, consumption often decreases. I'm also suspecting the solder paste i'm currently using ...
If you have any ideas, please feel free to share  ;)
Unterminated GPIOs might do it...

perky

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Re: Custom board with unusual consumtion
« Reply #3 on: November 16, 2017, 08:48:59 PM »
I agree with Tom. If the current goes down when you add capacitance with a finger it's likely to be floating inputs. You need to ensure all digital inputs are either close to GND or close to VCC (including all unused pins), anything inbetween can increase current. Also ensure that if a signal is low there isn't a pull-up sourcing current, or vice versa with a pull-down and a high signal, a classic source of this can be switches with pull-ups.
Edit: That also applies to ADC inputs that can also be digital inputs, if you forget to disable the digital input buffer the input may be sitting somewhere between GND and VCC and will increase current. I assume by 'stop' you mean not running the code which is equivalent I guess to idle sleep of an AVR.

Mark.
« Last Edit: November 16, 2017, 09:20:49 PM by perky »

Marc-Aurele

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Re: Custom board with unusual consumtion
« Reply #4 on: November 17, 2017, 05:09:21 PM »
Hello,

Thank you all for your replies.
I have loaded my software on a nucleo-l073 (STM32L073RZT6 : which is a LQFP 64 CPU) that is an evaluation board from st microelectronic, and on this board, i consume less than 3uA with stop mode activated (CPU is stall and is waken up at regular intervals, only RAM is maintained)
I have decided to make my own board but on this custom board i'm using a STM32L073CZT6, that is a LQFP 48 package (two GPIO ports have been removed). So on this new package, my software should handled the GPIO as they were on the previous package because they were previously present. There shouldn't be new GPIO to be handled.
So, that's why i'm not suspecting a missing GPIO configration but rather a soldering issue or the finition of my PCB but i will take a look at the software to know if i can find something.
Thank you again for all your replies.
Best regards,
Aurélien
« Last Edit: November 17, 2017, 05:53:06 PM by Marc-Aurele »