STM32L476 with WLCSP72 package has outpin problem.

Yasin Yelkovan · ‎2021-10-21

Hi everbody,

I am using STM32L476 mcu with WLCSP72 package on my designed board. On this mcu PC5, PC4, PB14, PC13 and PB13 pins are configured as an output-pushpull.

The problem is, when the PB13 pin is set from Low to High, each time short-term pulse occurs on the other mentioned pins. And this event occurs only when PB13 is triggered.

I could not understand the main problem. Is there any one have experience about this type issues ?

Please, if anyone has the same MCU in the same package, check out the some of the these pin outs with triggering PB13 pin and share the results.

Uwe Bonnes · ‎2021-10-21

Give more context. Does this happen on a single board or do you have and test on multiple boards boards to exclude hardware errors? what does "Short pulse" mean in hard measured values? Is the load on PB13 different than on the other pins? Etc...

Yasin Yelkovan · ‎2021-10-21

Hi Uwe,

In advance thanks for your interest. I have tested on multiple boards but result was always same.

I attached a picture of output circuit schematic. On board there are 4 outputs with same circuit.

I noticed that error when I was testing the software. When output -4 ( PB13 ) goes from Low to High state, also other output leds were blinking very shortly. But it is noticeable. This error does not occur when other output states are changed.

TDK · ‎2021-10-21

PC13 has limited current driving capability, although the provided circuit appears to be high impedance at the pin. Perhaps take an analog capture of the pin output and related pin outputs during the even for more information.

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Amel NASRI · ‎2021-10-25

Hi @Yasin Yelkovan ,

Is issue faced only with WLCSP72 package?

Please make sure that you aren't hitting the limitation Some I/Os must not be used as output when VDDA > VDD + 0.6 V or VDDUSB > VDD + 0.6 V or VLCD > VDD + 0.6 V described with details in the product erratasheet.

-Amel

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waclawek.jan · ‎2021-10-25

Try disconnecting C314. Does it make any difference?

JW

Yasin Yelkovan · ‎2021-10-26

Hi Amel,

Thanks for your response. I want to share some extra information about my card.

1) 'Is issue faced only with WLCSP72 package?' :

I have only this package so I could not try other packages.

I have same PCBs from two different PCB manufacturers and this problem occurs on both of them.

2) 'Some I/Os must not be used as output when VDDA > VDD + 0.6 V or VDDUSB > VDD + 0.6 V or VLCD > VDD + 0.6 V' :

I added the power circuit schematic (Power_Sch.jpg) below. As depicted in the schematic, the voltages of VDDA, VDDUSB and VLCD are not higher than VDD.

3) Effect difference on PC13 output pin:

I attached some oscilloscope screen shots to below.

This picture shows the voltage change on the PC13 pin which is configured as output pin, when PB14 pass from low to high.

And picture shows the voltage change on the PC13 pin which is configured as output pin, when PB13 pass from low to high.

This picture shows how PC13 (LED-MCU) is connected.

In addition, fluctuation on PB14 is bigger than the others.

As I mentioned before, PC4, PC5, PB13, and PB14 pins have same circuit structures and same configurations. But this fluctuation on voltage problem occurs only PB13 pin when goes Low to High.

My request is, if anyone has the same MCU in the same package, run the same test and share the results, please.

Yasin Yelkovan · ‎2021-10-26

Hi Waclawek,

Thanks for your interest.

PC4, PC5, PB13, and PB14 pins have same circuit structures But only PB13 pin cause problem.

So I think the problem is not on the schematic side.