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ESD Sensitivity of the CC2500

Helgard Van Rensburg
Intellectual 475 points
Other Parts Discussed in Thread: CC2500

We have a few products in the prototype/early production phase which contain a CC2500 paired with a MSP. Some boards have chip antennas others have PCB etch antennas.

For prototyping the components are hand placed and baked.

Almost every time we receive prototype boards (usually between 5 and 10) there is at least one board on which the CC2500 is dead (no reply on comms from the MSP and  higher than normal current consumption).  After some detailed investigation we are thinking that ESD might be the cause. So far all of the boards with damaged CC2500 were using PCB antennas (the terminals of these antennas are exposed).

We work in a low lying coastal area, so normally we don't have to much static problem, nevertheless we employ basic electrostatic protection in the form of wrist straps and mats. I can not however guarantee that everybody along the line adhired to the electrostatic protection methods.

I suspect that the RF I/O's are particular sensitive since we had a dodgy batch of crystals and when two boards' crystal outputs were measured with an oscilloscope the CC2500 (which worked a few minutes before) died.

We also only used the reference design for the CC2500 and matching circuit and didn't employ extra protection circuits.

I can't find any reference to ESD protection within the CC2500 in the documentation (only a reference to ESD_voltage < 500V max limit).  Does this mean that we should include extra protection circuits?

Is the CC2500 more sensitive to ESD than say the MSP?

When the user/technician the coin cell battery on some of the products the user can touch the chip antenna, is this a problem?  Any suggestions?

 

  • 0
    TI__Expert 4435 points

    Van Rensburg,

    If you are sure the parts are ESD damaged then the most likely pin is the RF connection to the antenna.   The chip ESD is low and most designers especially for differential antennas do include an external ESD diode for protection.  This will increase the voltage to 1000 to 3000 volts which is more typical of the charge injected into this node. Generally we haven't seen single input antennas require extra ESD becasue of the matching components.    If you are use microstrip matching then extra ESD probably is necessary. 

    One othe thing to check which is a common problem is the radio chip does not get solder properly due to the solder pad.  This can also cause symptons like you mention.  This is especially trun if units are hand soldered.   The RF ground return is primarily through the power pad for the chip.    One way to check this is take a known bad chip and re-solder to a different board.   Then re-check the current. 

    We have no app notes written about adding ESD diodes.    There are several manufactures who have ESD diodes for these freuquencies.  It must have extremely low capacitance.  Once you insert it you will need to change your matching network to the antenna. 

    Regards,