CC8520 RF Issues

Marcie Dobyns2

Other Parts Discussed in Thread: CC8520

Hello!

We have a design that uses the CC8520. This design started from the CC5831 Development kit and has been laid out with the CC8520.

We are seeing two issues:

1.) When the transmitter and receiver are hardwired together with a step attenuator between them, we have at most 55dB of range before the link disappears entirely. According to the datasheet this should be more like 85dB, which is what we see when we use the development kit.

2.) There appears to be an issue with the acceptable accuracy of the 48MHz crystals. According to the datasheet we should be able to have +/- 50ppm accuracy, which is approximately 2.5kHz. The transmitter is running at 48.0022MHz and we have a signal generator hooked up providing the oscillation for the receiver. If the sig gen is set up to provide the 48.0022MHz we are fine, however, if we adjust off of this even a little, we run into significant dropouts (1+ dropouts/second). If I set the sig gen low to 48.0007MHz, we experience the significant dropouts even though this is well withing our 50ppm accuracy. If I set the sig gen high to 48.0030MHz we also see significant dropouts.

My question is, what could be causing these issues?

Thanks!

Marcie

over 13 years ago

0 Per H over 13 years ago

TI__Expert 6825 points

Hi Marci

1. Sounds like something is very wrong. Have you measured the output power? Can you post your schematic and layouts so we can have a look at it?

3. Can you measure the frequency on the RF signal rather than the crystal frequency?

0 Marcie Dobyns2 over 13 years ago in reply to Per H

Prodigy 55 points

Hi!

1.) We did measure the output power, we measured 4.5dB and it was set to 5dB out. If you provide me with your email address I can email the schematic and layout to you, however, I cannot post them on a public forum.

2.) We also measured the RF signal frequency and it was on frequency.

Thanks,

Marcie

0 Per H over 13 years ago in reply to Marcie Dobyns2

TI__Expert 6825 points

Hi Marice,

Sounds very odd. Have you tried more than one board/chip?

I added you as a friend.

-Per

0 Marcie Dobyns2 over 13 years ago in reply to Per H

Prodigy 55 points

Hi Per,

I've responded to your message with the schematics and the gerbers. Have you had a chance to review them? We need to get this figured out.

Thanks,

Marcie

0 Per H over 13 years ago in reply to Marcie Dobyns2

TI__Expert 6825 points

I have replyed, you have a message in the inbox. Sorry for the delay.

-Per

0 Marcie Dobyns2 over 13 years ago in reply to Per H

Prodigy 55 points

Hi Per,

We are using this balun: Johanson Tech 2450BM15B0002E

It does not have a DC block to GND, which I verified with a scope. Did you see anything else suspect?

Thanks,

Marcie

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CC8520 RF Issues