Error in reference circuit for nRF52840 CKAA WLCSP

[lrb]

On the Nordic Semiconductor infocenter, 12 reference designs for the nRF52840 are given, 6 for the big QIAA chip and 6 for the small CKAA chip. However the reference designs for the CKAA lead to some confusion for me. The configuration tables given are the same for all 6 reference circuits, which makes no sense. The pinouts used for the CKAA reference circuits are also equal to the QIAA case, while in reality this is not true. CKAA has 93 pins and QIAA 73 pins. I think there must be some error here.

If using these reference circuits for design, would I be fine when using the QIAA reference circuits directly when designing a circuit for the CKAA chip?

[Andreas]

Hi,

 

The configuration table just summarizes what supply configuration is supported, and whether or not external supply, DCDC mode, USB or NFC is supported for the configurations. QIAA and CKAA are the same device, just different package alternative, meaning the exact same configuration and features are supported with the same external circuitry, you just need to keep in mind that the pin locations on the packages are different.

The pinouts are similar if you look at the pin names, but the pin numbers are different (eg.g top left VDD pin on pin B8 CKAA vs on pin B1 on QIAA).

 

You are right though that there are a number of pins missing from the schematic symbol of CKAA, there are a handful of VSS pins in the center of the device that does not have a pin. These should be included in the layout model we provide through our reference layout download. If you just look at the schematic and replicate your design you should probably keep this in mind to avoid an unfortunate surprise somewhere down the road.

 

Best regards,

Andreas

[lrb]

Thank you for the quick and helpful reply.

However I still believe the configuration tables and reference circuits do not match for the CKAA examples. Take for example reference circuit number 5, the table says NFC is not provided, while the circuit clearly shows an NFC antenna. The tables are identical for all 6 examples, which makes no sense.

[Andreas]

Hi,

 

I see I misunderstood what you meant, I was looking at the two tables at the top (table 1 and 2). Tables 15, 17, 19, 23 and 25 are most definitely incorrect, table 21 seems to be the root of the issue. Thanks for reporting this, I will forward it to our documentation team.

The circuit configurations are examples only though, as explained at the top of the section you can mix and match to support the features you want.

 

Best regards,

Andreas