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Custom PCB - nRF52840 VDDH and USB

Matthew K

Hi, guys. I'm trying to create a custom 4-layered 1.6mm thick FR-4 PCB which uses the NRF52840-QIAA-R.

It's my first time using the nRF52840 so I have some questions, please.

This uses external 5V USB and there is a buck converter connected to the USB to create 3.3V.

Q0. About the VDDH (High voltage mode operating voltage, max 5.5V), I noticed that both VDD_HV and VDD_nRF (on the PCA10056) were showing the same voltage to 2.981V when SW9 is positioned to the middle.

For my USB application, can I connect the buck converter's output (3.3V) to both VDDH(Y2) and VDD(W1) for using the

Normal voltage mode (pin VDD shorted to pin VDDH)?

Also, if I connect both VDDH and VDD to 3.3V, I can only use DC/DC converter which can be enabled by REG1, right?

Q1. Although this application uses USB, I have to create a Li-ion powered version later. The High Voltage mode - DC/DC converter part is interesting

If I add the external LC filters, configure the registers for the internal DC/DC regulators, and connect the Li-ion's 3.7V or USB 5V to VDDH, does this mean that

I can remove an external buck converter? This looks like if I connect the 3.7V Li-ion to the VDDH, I don't need to provide an external 3.3V, right?

Q2. The schematic symbol,

what does the red pulse, next to D* N and D* P, mean?

Q3. The USB D+, D- trace

I noticed the thin line and removed copper. Are there any guidelines for drawing USB connection (D+, D- trace width/length, keep out area, etc)?

  • +1

    Hi,

    • For my USB application, can I connect the buck converter's output (3.3V) to both VDDH(Y2) and VDD(W1) for using the Normal voltage mode (pin VDD shorted to pin VDDH)? Also, if I connect both VDDH and VDD to 3.3V, I can only use DC/DC converter which can be enabled by REG1, right? If I add the external LC filters, configure the registers for the internal DC/DC regulators, and connect the Li-ion's 3.7V or USB 5V to VDDH, does this mean that I can remove an external buck converter? This looks like if I connect the 3.7V Li-ion to the VDDH, I don't need to provide an external 3.3V, right?
      • VDD and VDDH should be connected together in normal mode. 3.3 V is within the operating range of normal mode. Yes, only REG1 is available in normal mode. Yes, the buck converter is not necessary for the IC to function. See the reference design on what parts that are necessary. 
    • What does the red pulse, next to D* N and D* P, mean?
      • It means that the data lines D negative and D positive will change values ( 0, 1) and not be a steady value.
    • The USB D+, D- trace I noticed the thin line and removed copper. Are there any guidelines for drawing USB connection (D+, D- trace width/length, keep out area, etc)?
      • We don't have any guidelines except our advice on following the reference design as close as possible. 

    Regards

    Jared

  • 0 in reply to Jared
    Jared said:
    We don't have any guidelines except our advice on following the reference design as close as possible. 

    Thanks, Jared. Meaning keep a large keep out area for D+, D-?

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