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CC1121: Confirm the PA pin.

Guru 24520 points
Other Parts Discussed in Thread: CC1121, CC1200

Hi TI experts,

Now customer has using the CC1121 for their application and some of CC1121 has been broken by something on field test. The resistance value between PA pin and GND is from 10 ohm to 30 ohm. So it seems that this pin is shorting. So we got some questions from my customer about PA pin. Would you please provide your answer for them?

Question.1:
Can customer think those CC1121 is broken by this checking?

Question.2 :
Would you please show us the surge resistance specification of PA pin?

Question.3:
Do you have any solution for protection circuit on PA pin?
Note: The supplied power source for their system is battery. So they did not add the varistor. If you have some good solution of protection circuit for battery operating application, please provide it.

Question.4:
Would you please show us the expected/possible failure mode on PA pin? And would you please point out the possible internal block on CC1121?

Question.5 :
Can CC1121 receive the data correctly even though the PA pin is this condition? According to my customer, those CC1121 could transmit the data but the power consumption is very high.

If you have any questions, please let me know.
Best regards.
Kaka

  • From the description it sounds like the chip has been damaged by an ESD event.
    - Do they have extra ESD protection on the antenna connection point?
    - What sort of antenna do they use?
    - In the field test, have they used a casing for their PCB and if yes, is the antenna sticking out from the casing?

    The PA pin is connected to the output of the PA (Power Amplifier). When the PA pin is close to shorted the chip will most probably still work in Rx since the PA is off. In Tx most of the energy will go to ground.
  • Hi TER,

    Thank you for your quick response. I answered you questions as below.

    - Do they have extra ESD protection on the antenna connection point?
    [Kaka]
    No. They almost copied the reference design of "Using the CC1200 Under ARIB STD T108".
    This design does not have Extra ESD protection. Right? If we get their schematic around CC1121 circuit, would you please check them?

    - What sort of antenna do they use?
    [Kaka]
    I do not have this information at this time. I need to confirm this question to my customer. I will ask them the kind of antenna.

    - In the field test, have they used a casing for their PCB and if yes, is the antenna sticking out from the casing?
    [Kaka]
    I also do not have this information. I will ask them to them.

    Also we need to answer for customer's questions in order to ask your questions. Would you please provide answers for them?

    Best regards.
    Kaka
  • Q1: When the impedance towards ground is very low the chip is damaged. A very likely source to the damage is ESD.
    Q2: Could you please specify what you mean by "surge resistance specification"

    Q3:
    We are a chip provider and we deliver reference designs to make it easier for customers to get up and running with our product. ESD protection is a system level design task and the ESD protection needed will be dependent on your product. Typically if you use an antenna that is exposed to the user (eq the user can touch it) ESD protection has to be used on the antenna input. If the product uses a PCB antenna that is within the product casing extra ESD protection is probably not needed since a ESD pulse will not go through the antenna.

    A typical ESD protection is a ESD diode with low capacitance connected between the antenna and ground.

    Q4/5: Covered by previous post.
  • Hi TER,

    Thank you for your answers. Please let me confirm my understanding just in case.
    For Q1, there is a potential that that device has been damaged by ESD event because the impedance between PA pin and GND is low.
    For Q3, TI does not provide the ESD solution because the ESD solution depends on the antenna type, casing for customer product.
    For Q4, the PA pin is connected to internal Power Amplifier. So regarding to failure mode, there is a potential that the PA pin is shorted to GND by damaging internal PA.
    Please let me confirm the Q4. Is there a potential that the PA pin will be shorted to VDD by damaging the device?
    For Q5, If the PA is close to be shorted to GND, the RX will most probably still work because the receive operation does not related to PA. For TX side, the most of energy/power will go to ground but some of power will output the power from antenna. So, there is a potential that customer think the CC1121 could work correctly even though the CC1121 has been damaged.

    If there is any misunderstanding, please let me know.
    For Q2, I will explain this question with other words.
    Thanks.
    Kaka
  • An ESD damage is not predictable. How a damage will look will depend on exactly which transistor that damaged and the nature of the damage. Based on how the PA is designed I would assume that it's more likely with a short to ground than a short to Vdd after an ESD event.
  • Hi TER,

    Thank you for your response.
    I informed your comments to my customer. And regarding to the "surge resistance specification", I informed the ESD specification like HBM or CMD to my customer. And I got the feedback against your questions.

    - What sort of antenna do they use?
    [Kaka]
    They have used some kinds of external antenna(Sticking antenna) for their product. For example, MEG-241XSAXX, ME-467XSAXX, MEGWX-241XSAXX-920, MEGAF-350XSA3X-920 and so on.

    - In the field test, have they used a casing for their PCB and if yes, is the antenna sticking out from the casing?
    [Kaka]
    The antenna of their application is out of casing.

    If you have any questions, please let me know.
    Best regards.
    Kaka