IMXRT117x PCB design: is it recommended to short the DCDC_DIG and VDD_SOC_IN by same plane?

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IMXRT117x PCB design: is it recommended to short the DCDC_DIG and VDD_SOC_IN by same plane?

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TCL_1
Contributor II

Hi,

I'm designing a custom board based on IMXRT1175DVMAA, and plan to use the internal DCDC to output supply the MCU core power 'VDD_SOC_IN'. I noticed the EVK design used some jump resistors between DCDC output 'DCDC_DIG' and core power 'VDD_SOC_IN', my question is: can I remove these resistors in my design? then the power plane of 'DCDC_DIG' and 'VDD_SOC_IN' will be connected directly, whether it will introduce noise form DCDC to MCU core power directly?

Or, is it recommended a resistor/ferrite bead to separate the power plane of  'DCDC_DIG' and 'VDD_SOC_IN', for EMC consideration?

In my design, I have to place all the decoupling/buck capacitors around MCU chip on same PCB side, due to the mechanical limitation. So the actual PCB layout will be as follows, please comment which on will be better, thanks!

Plan #1 Separate the DCDC_DIG and VDD_SOC_INPlan #1 Separate the DCDC_DIG and VDD_SOC_INPlan #2 Shorting the DCDC_DIG and VDD_SOC_INPlan #2 Shorting the DCDC_DIG and VDD_SOC_IN

BR

Tyrone Liu

 

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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Additionally, this application note might be helpful to improve the EMC performance: EMC Design Recommendation on i.MXRT Series (nxp.com)
This application note along with the Hardware Development Guide have the guidelines for a good design. 

Bes regards,
Omar

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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Hello
I Hope you are well.

They can be tied together, but we need to assure that DCDC current loop is small as possible. The #2 option is correct but from my perspective the trace is long, please correct me if I'm wrong.

To keep good EMC performance, the below items are critical for the layout of DCDC circuit.
• Keep the DC/DC current loop as small as possible to avoid EMI issues.
• Enable current first pass through filter capacitors and then go to pins.
• Avoid unnecessary via between inductor and bulk capacitors.

If you have more questions do not hesitate to ask me.
Best regards,
Omar

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TCL_1
Contributor II

Hi Omar,

Thanks for your comment, I think this general requirement is correspond to our EMC concern, thus I decide to adopt #1 option.

  •  Enable current first pass through filter capacitors and then go to pins.

 

Best Regard

Tyrone

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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Additionally, this application note might be helpful to improve the EMC performance: EMC Design Recommendation on i.MXRT Series (nxp.com)
This application note along with the Hardware Development Guide have the guidelines for a good design. 

Bes regards,
Omar