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alex_at_thimble
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DA14531 single ground under chip?

Dear Dialog - I'm reading your AN-B-075 DA14531 Hardware Guidelines and looking at the layouts of the dev kit, and I have a question about ground connections.

The app note says

"Separate RF ground pins of DA14531 CFGQFN24 from the rest ground pins
Connect pin 19 to GND with vias as shown in Figure 26
Short 20, 21, 23 GND pins together and use two GND vias, as shown in Figure 26"

The examples show GNDRF1 and GNDRF2 separated from each other, as well as RFIOm separated from GNDRF1.  Basically, there are four independent ground connections: 2, 18, 19, 20+21+23. 

Is it necessary to separate all four?  Can 19 and 2 be tied directly to each other?  How about 18, 19 and 2? 

I'd like to attempt a simplified design with all grounds tied directly to a ground island under the chip with multiple vias; I'd give up the ability to use P0_5 and P0_6 and tie them to ground as well, so that pcb tolerances can be reduced.  Would this work?  If it doesn't, what would be the negative effect?

If not everything tied together, is it possible to at least tie all RF pins 18+19+2 and all non-RF pins 20+21+22+23 in two groups?  (multiple vias each)

Thanks,

Alex

 

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PM_Dialog
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Hi Alex,

Hi Alex,

My suggestion would be to separate all four grounds as described in AN-B-075. If every ground is tied together there might be a performance reduction because of added noise. Pin 21 (GND_DCDC) is quite noisy and should be separated from the RF grounds. In our daughter card we combined GND_DCDC, GND and VSS. While GNDRF1 GNDRF2 and RFIOm are separated.

Thanks, PM_Dialog

alex_at_thimble
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Understood, thank you for the

Understood, thank you for the additional info.

1. Is GND_DCDC also noisy if operating in LDO mode?

2. Could you explain in more detail why keep GNDRF1 GNDRF2 and RFIOm separated from each other?

3. " performance reduction because of added noise " -  Is that RF performance, and is it RX or TX?  How would I be able to measure this?

Thanks!

Alex

PM_Dialog
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Last seen: 9 hours 13 min ago
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Hi Alex,

Hi Alex,

Apologies for the delay. Please find below answer for your queries:

1. If mean with the “LDO mode” the “bypass mode” the GND_DCDC is not noisy.

2. The reason is because different RF blocks are connected to that grounds and it would be beneficial to have the grounds isolated.

3.Yes, I meant RF performance. On RX you might see a reduction in RX sensitivity and on TX the modulation might be worse. This can be measured with a Bluetooth tester.

Thanks, PM_Dialog