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

[S.Ma]

Posted on November 16, 2017 at 14:42

Is it the same package? More GPIOs? Are they polarized properly? Oscillators are all same and off? Reset signal? If there are some pull-ups and pull-down, you could have few uA there. Example would be I2C Pull-ups and SW is stopped while I2C bus lines were used and are low level.

[Aurélien f]

Posted on November 16, 2017 at 15:40

Thank you very much for the reply.

No, it is not the same package, i'm using a stm32l073cbt6 (48pin) whereas it is a 64pin on nucleo-l073.

To test, on my own board, i'm only soldering the stm32, the pull down resistor (10k) on boot0 and all decoupling capacitors.

I m also loading the same firmware on my nucleo board or my custom board (so all peripherals are deactivated, only RTC (running on LSI) is on and ADC).

[Antonio Vilei]

Posted on November 17, 2017 at 16:22

Hi Aurélien,

since the package and the pinout is different, maybe there are some slight differences in the way the GPIOs have been configured. Did you check whether all the pins that you don't need are actually configured as analog with no pull on your custom board?

Best regards,

Antonio

[Aurélien f]

Posted on November 17, 2017 at 23:35

Hi Antonio,

The difference between STM32L073RZT6 (the LQFP 64 cpu on nucleo board) and STM32L073CZT6 (LQFP 48 i have chosen for my custom board) is that only GPIO have been removed. The remaining GPIO of LQFP48 package should be handled by my software in the same way they were on the LQFP64 package. I will check again my software but on my side i d rather suspect a soldering issue or the finition of the PCB that is not sufficient to meet my requirements !

Regards,

Aurélien

[S.Ma]

Posted on November 18, 2017 at 04:21

Time for debug: If you have more than one board, are the results the same? If no, it's a PCB issue.

If yes, have you checked the oscillator and regulators (if powered by 5V)?

Check the reset pin.

Is your board having a JTAG programmer connected?

Put all pins with pull-up and then pull-down to inspect the current, then adjust by groups of pins.

If using ADC, did you power it up and turned it off?

If using I2C, how about the SDA/SCL? If they are low, it's surely not good.

If you have a board without the MCU, check the consumption of the rest of the components.

A resistor divider somewhere can cause the xtra leak.

[Aurélien f]

Posted on November 21, 2017 at 23:57

Time for debug: If you have more than one board, are the results the same? If no, it's a PCB issue.

If yes, have you checked the oscillator and regulators (if powered by 5V)?

The result is the same with all boards but each time with a different current consumption. With the last one, soldered with SAC305 solder paste and a reflow oven, juste after cleaning it with acetone, the current consumption decreased down to 6uA and then after a while (it seems after acetone evaporation), it increase to 120uA. Same result after a second cleaning. I don't think it is an issue with oscillator and regulator because all is working fine on my nucleo board on which i consume less than 3uA with the same software.

Check the reset pin.

It seems to be floating. Do i need to put a pull up ? On nucleo there is no pull up or pull down connected to NRST pin.

EDIT: i put a 100k pull up resistor and it didn't change anything

:(

Is your board having a JTAG programmer connected?

No (only a UART TX connector)

Put all pins with pull-up and then pull-down to inspect the current, then adjust by groups of pins.

Normally, i put all pins in analog input. But when i put them in input with pull-up, the current consumption starts normally at 1uA and increases, then it stabilize at 21uA. I don't know why ... (with pull down it stabilizes at 50uA)

I have checked supply pins (1 9 24 36 48) and ground pins (8 23 35 47 connection to the board by using beeping function of my multimeter. Only these pins should matter for current consumption in my case, no ?

If using ADC, did you power it up and turned it off?

Yes

If using I2C, how about the SDA/SCL? If they are low, it's surely not good.

No, i'm not using I2C line (even if you can see the corresponding pull up on the schematic)

If you have a board without the MCU, check the consumption of the rest of the components.

I have tried to do that but there is only my MCU and 5 decoupling capacitors (C35 C36 C37 C38 C39) and one pull up resistor on BOOT0, so the consumption is clearly coming from the MCU or the way it is soldered.

I have attached schematic and PCB file if someone would like to check 

[Aurélien f · Accepted solution]

Posted on November 22, 2017 at 16:10

Hello,

I have noticed when i connect the pin 2 (PC13) to the ground, my current consumption is around 2.9uA (exactly what i want and this is exactly the same current consumption as the nucleo board). But it is not indicated in the datasheet that this pin should be put to the ground and on the nucleo board, this pin is not put to the ground. 

Did i miss something in the datasheet ? Or Am i doing something wrong ?

I have tested this on three of my custom boards and in the three cases, the current consumption falls down to 2.9uA.

Regards,

Aurélien

[Brow Joey]

Posted on November 23, 2017 at 07:47

I've heard about pcbway service.

I've recently used Seeed Studio's

https://www.seeedstudio.com/fusion_pcb.html

to try them out - I'm very impressed with them, it was the lowest overall price I could find anywhere but still had excellently short manufacturing and shipping time (I paid for DHL).

[alexandre239955_stm1]

Posted on November 23, 2017 at 13:11

As the datasheet says, PC13 is used for RTC_TAMP1/RTC_TS/RTC_OUT/WKUP2, and you said previously that you are using the RTC. Try to enable the pull-down on this pin.