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LMX2571: Unexpected calibration at high temperature

Alex Strelbytskyy
Expert 1980 points

Part Number: LMX2571

Hello,

During temperature tests in the temperature chamber we discovered that the synthesizer LMX2571 goes into some faulty state for short time at +70C (the temperature is rising very slowly and calibration is executed every time when we write into the register R0 with FCAL=1 during transition interval - expected calibration). It looks like synthesizer performs unexpected auto-calibration during transmission when it reaches a temperature threshold. There is no information about this in Manual. Could you confirm this? How we can disable this feature?

Thank you,

Alex

  • 0
    TI__Guru** 122380 points

    Hi Alex,

    Did you mean, you calibrated the chip regularly while the temperature is gradually rising, when the temperature reach 70C, the chip "went into some faulty state for a short time"?

    Could you describe what is faulty state?

    It sounds like that the faulty state will self recover?

    Did you see the faulty state happen again after 70C?

  • 0 in reply to Noel Fung
    Expert 1980 points

    Hello,

    It is not clear if it is an auto-calibration, but "Lock Detection" signal goes low. Yes, the faulty state is present when temperature is higher +75C.

    Thanks,

    Alex 

  • 0 in reply to Alex Strelbytskyy
    TI__Guru** 122380 points

    Hi Alex,

    The device will not do calibration unless we write R0 (with FCAL_EN=1). Since temperature will affect VCO characteristic, Vtune will change accordingly. This is the only parameter that I expect will change "automatically" against temperature.

    Did it actually lock (determines by the RF output, not Lock Detect) in the faulty state?