How to disconnect OPEN SDA from MCU in FRDM-KL46Z

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How to disconnect OPEN SDA from MCU in FRDM-KL46Z

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beezee
Contributor III

Hi,

In FRDM-KL46Z pin 21 of PK20DX128VFM5 is connected to pin 52 of KL46 MCU. I have been following  Tutorial: Using the FRDM-KL25Z as Low Power Board | MCU on Eclipse  and I realised that J14 should be disconnected but this is working for FRDM-KL25 and for FRDM-KL46 there is no jumper to make them disconnected. 

I looked at the schematic and I found this two:

For FRDM-KL25

pastedImage_2.png

and for FRDM-KL46

pastedImage_3.png

How can I disconnect pin 21 of PK20DX128VFM5 to pin 52 of KL46 MCU?

Thanks,

Bee Zee

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kerryzhou
NXP TechSupport
NXP TechSupport

Hi Bee Zee,

    Yes, you are correct, the FRDM-KL46 don't have the isolated circuit between the K20 and KL46 chip.

   But, could you tell me why you need to isolate it? If you just want to disconnect the on board opensda, and want to use the external,you just need to connect the external SWD pin to J11, then use J10 to power on the board.

  If you want to use FRDM-KL46 on board debugger for external chip, you just need to remove the on board J18, disconnect SWD_CLK is enough, then you can connect J11 to your external target board.

 You can try it.

Wish it helps you!

If you still have question about it, please kindly let me know!


Have a great day,
Kerry

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beezee
Contributor III

Hi,

Thanks, I need to disconnect OPEN SDA from MCU because I want only to measure the power consumption of MCU without considering other stuff on the board. At the moment this is not possible, I have removed R1, R2, R4, cut trace for J18, J6, J9, J7, J17. 

Then when I connect power 3v3 to the board (pin 2 J17) nothing is running. MCU is not doing anything.

But as soon as I put hats for the J17 and J6, J9 then the code run and I see a LED is blinking (as I set up my code).

This shows why I remove the resistors and cut the traces.

pastedImage_1.png

Current consumption with a hat on J17 is around 18mA (No LED is blinking) at 3V. Even though I put it to sleep following  Tutorial: Using the FRDM-KL25Z as Low Power Board | MCU on Eclips . I want to check how much MCU is consuming. 

Thanks,

Bee

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kerryzhou
NXP TechSupport
NXP TechSupport

Hi Bee,

   Ok, thank you for the detail information.

  If you want to get the detail MCU consumption, it is really better to cut the wire.

  Yes, I also think this part, the FRDM-KL46 is not so good, it should like the FRDM-KL25 have the isolated circuit.

  But now, maybe cut the wire in the PCB is the only choice for you.


Have a great day,
Kerry

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beezee
Contributor III

Hi,

Sorry, your answer was not clear. Which wire should I cut? Can you show me on the schematic? I do not think we have the full schematic so I could not find where to disconnect pin 21 of PK20DX128VFM5  to pin 52 of KL46 MCU.

I have removed R1, R2, R4, and cut trace for J18, J6, J9, J7, J17.

Thanks,

Bee Zee

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kerryzhou
NXP TechSupport
NXP TechSupport

Hi Bee,

   If you want to test the KL46 consumption, J17 is the KL46 power consumption test point.

1. Remove R1, R2 in the board.

2. Cut the wire between J17, then you can add the current meter between J17.

3. Disconnect J18, cut the wire between the J18.

4. Remove R47 and R48, this is the UART pin which is connected to the K20 virtual com port.

 Then, test the current consumption, as I know, this test should already meet the KL46 datasheet's power consumption demand.

If you still want to cut the RST_K20D50_B, you just need to following the PCB wire from the K20 pin 21, you can find K20 pin 21, then follow that pin wire, and cut it, but after that, the connection again will be difficult.

But as I know, you don't need to cut the reset pin any more.

Because Reset pin is high after you download the code, both K20 and KL46 reset pin is high, it won't caused more current consumption to KL46.

Wish it helps you!


Have a great day,
Kerry

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OilCastle
Contributor II

Simply, If you find PCB pattern and cut it off, your MCU will disconnect from SDA.

I also see the schematics. I think this could be helpful.

pastedImage_1.png

See, cut-off the bottom layer of J18 

Good day :smileyhappy:

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