K32w128 Switch Wakeup-B Switching not fully off

[Dannii]

Hello,

we are currently developing a product where the MCU gets turned off via the internal Mosfet and this switch B pin should wake it up again. This works quite fine, only problem is, that when the mcu is in this powerd off state the GPIO Pins are pulling low internally so external datalines with pull up resistors appear at a voltage Level. In our case around 2,3V this happens when pins are not used and also when before declared as an input. 

In my findings they should be at high impedance but they aren't.

Is this a known problem? I2C lines also float around this 2,3V voltage when using a 4k7 Pull up resistor to in our case 3V supply voltage. The pullup are allways powerd btw.

This happens on multible boards.

Thanks and happy Holidays

[Christine_Li]

Hi, @Dannii 

Thanks for creating case to us.

Are you using our K32W148-EVK? or you are using your customized COB designs?

If you are using COB designs, would you mind share your schematics to my private email to check further? My private Email: christine.li@nxp.com. As you may know, here is a public community, share it directly here, it not safe for you and is also not recommened.

If you are using our K32W148-EVK, please point out which part with a screenshot, so that I can better understand your meanings.

Best regards,

Christine.

[Christine_Li]

Hi, @Dannii 

Thanks for sending me your schematics. 

I checked it and compared with our reference design, found below suspects:

1. You connect  SWITCH_WAKEUP_B  to  PTC4 through  NetR21_2  and using  R22(0 Ohm)  as pull-up resistor. You are using GPIO as wakeup source, am I right? If so, then after MCU enter deep sleep mode, the GPIO could not wakeup it because GPIO is a power level, not a power supply.

2.Please refer to our reference design(K32W148-EVK) schematics, SWITCH_WAKEUP_B connects to 10K resistor with 3V_LDO. You can also try to connect in this way, then use a Button to test wake-up function. 

SWITCH_WAKEUP_B pad is internally pulled up to the switch input through a resistor, it can be pulled down to wake up the smart power switch.  The external SWITCH_WAKEUP_B pin, once driven low, it can turn on power switch; 

For your convenience, I paste our K32W148-EVK link here and also its K32W148 Evaluation Kit Board Schematics download link.

Best regards,

Christine.

[Dannii]

Thanks for the Reply.

1. No we are triggering the waking up from an external button like in the EVK with an 10k Pullup (Sorry its on a different Schematic Page so you didnt see it). This works fine and PTC4 is just there to read the button as well as a backup because we havent been sure in the beginning if the wakeup_B works properly.

But when the MCU Is in this turned off state we are getting some weired voltages on the other GPIO Pins of the MCU if they are pulled high by external Pullup Resistors egg. I2C Lines with 4k7.

When the MCU is in this powerd off state are the other GPIO Pins Pulled Low/High/High impedance or how do they behave? Bc ours behave weired with this 2,3V Floating sawtooth signal.  

[Christine_Li]

Hi， @Dannii 

Thanks for your feedback.

I checked our Datasheet and also RM, could not the answer even personally I agree with your point. But to better support you and give you a confirmed answer, I have escalated to our internal expert team to ask help.

Once receive our internal team's feedback, I will let you know.

By the way, as you mentioned, you are triggering the waking up from an external button like in the EVK with an 10k Pullup (Sorry its on a different Schematic Page so you didnt see it)..  Would you mind send this part of schematics also to my private email? So that we can give more details to our internal team and get a answer ASAP.

Best regards,

Christine.

[Christine_Li]

Hi, @Dannii 

Besides, Can you provide your code to enter/exit Smart Power Switch DPD mode?

Best regards,

Christine.

[Christine_Li]

Hi, @Dannii 

Please see our internal team's feedback as below:

In customer's schematic, the LDO+3v connect to VDD-Switch , and VOUT_SWITCH is the output of VDD-Switch. When k32w148 is in power off, the VCC for K32W148 internal power supply is off, but in customer's schematic, there are two GPIOs(PTA18, PTD2) connected  to LDO+3v, the protection diode in k32w148 would connect to LDO+3v, this would cause voltage leakage. 

Here is the way to turn on power switch, You can refer to K32W1480 Reference Manual page 742.

Please let me know whether have any concerns on this case.

Best Regards,

Christine.

[Dannii]

Sorry for the late reply, it seems that this could be the case with the leakage and the internal Protection Diode, we didn't think about this but I have to double check this with my engineers.

Thank you for the W71 recommendation we will take a deep look at it as well.

But concerning our Problem. When connecting VDD_IO_ABC to +3V_LDO and therefore the ABC registers will always be powerd will they retain their voltage Potential even when the MCU is switched off would this fix our issue? I mean to Use the design like on page 742 of the reference Manual but connecting VDD_IO_ABC to the Blue 3V3 Circuit?
But a huge Thank you for the Help with our issue till now!

[Christine_Li]

Hi， @Dannii 

Thanks for your reply.

No, We still recommend you to refer to our reference designs on Page 742 of RM.

Connect VDD_IO_ABC to the Red part(Power switch), but not to the Blue 3V3 Circuit.

If connect VDD_IO_ABC to +3V_LDO, it might have current leakage when device is switching off all or part of MCU power.    You can disconnect R48 to test in your case to see voltage is still existed.

And also, We suggest you to ask your Hardware colleague help to check for you further.

Best regards,

Christine.

[Christine_Li]

Hi, @Dannii 

By the way, I highly recommend you to move to our MCX W71, which is software and hardware compatible, if your project is just beginning now. We will not be investing in new software for the K32W148 in the future, just making maintenance updates. We also have better pricing on the MCX W71. The main reason is that MCX W is our platform moving forward. K32W148 is not going EOL, but we are focusing our investments on MCX W.

Let me know if there are any questions and wish you have a nice weekend!

Best regards,

Christine.

[Christine_Li]

Hi, @Dannii 

For the connection between PTD2 and #Wakup, I want to double confirm with you because in the shared schematics, it shows there is a red cross.

Besides, we want to know what kind of sleep mode are you using? And what is your wakeup source?

And please let me know whether our suggestions and findings are helpful for you.

If it helps and you do not have any other concerns, please do not hesitate to mark my answer as a solution so that we can close this case.

Best regards,

Christine.

[Dannii]

korr. K32W148