MKW21D design questions

[thebhef]

I'm working on a PCB layout using an MK21D part, and I have a few questions about the design.

First, is there a more stripped down reference design available than the FRDM board schematic? Something with just the minimum for chip support and wireless comms?

Second, what do I need to do with the TAMPER pin if I don't want to use it? I didn't see this in the reference manual.

Lastly, I'm pretty new to RF design, so I have some more general questions about it.

• How critical is controlled impedance on a transmission line (with a chip antenna)? Does anyone know roughly how bad an uncontrolled PCB could be if I had the trace and board stackup correct? Is it just the fact that it's not controlled? Any idea what difference there might be in cost?
• What changes would I need to make in the design if I wanted to use a surface mount chip antenna
• Is there a more integrated balun available? What do I need to know to search for one?

Any guidance I can get would be appreciated.

Thanks,

Ben

[Antonio_Quiroz]

Hello Ben,

NXP also has the USB-KW24D512, this design includes almost the minimum components to start working with the KW24D in a 4-layers stack-up.

If you don't want to use the TAMPER, KW2xD pin should be connected to a pull-up, 1M is recommend. If you are not using the NMI pin I also recommend 10k pull-up.

For the RF section:

-   For an optimal performance, the controlled impedance are strongly recommended, NXP references include an optimal design, an uncontrolled impedance performance will affect the RF performance, sensitivity and/or output power, please remember that 3dB losses is the half of the power - reduced than the expected power

-   Any changes on the Antenna selection is just minimal, just change the Printed F-Antenna with the surface mount, but keep same trace width (controlled impedance trace) and follow the recommendations from the antenna supplier that normally requires a keep out area from any other component, GND patter (including vias), all this need to be follow almost exactly from the supplier.

-   For MKW24D NXP doesn't have any integrated balun to reduce the amount of components on the RF section. In case you are interested in one component for the MKW40Z device, Johanson developed a single component for matching MPN:2450BM15B0026E link: http://www.mouser.com/ds/2/611/Johanson_06032016_2450BM15B0026-948309.pdf . This component is matched and recommended for MKW40Z/20Z/30Z devices however some customers includes on their MKW24D designs but need to consider the DC feed capacitor is required -- NXP DOES NOT have any test data for this, so I can not fully recommend --

If you have any other layout recommendations NXP has a guideline for the KW2xD devices on the following link  http://cache.nxp.com/files/microcontrollers/doc/app_note/AN4957.pdf?fsrch=1&sr=1&pageNum=1 

Regards,

Antonio