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LM2674MX-5.0 output voltage drops over time (radiation)

Kevin DeFever51
Prodigy 20 points

We are using the LM2674MX-5.0 in a circuit that has a max load current of about 100-150mA. 

This circuit part of a product that is used in conjunction with a medical linear accelerator that produces high energy (6MV) X-ray radiation.

The product/part never exposed to a direct radiation beam, it is subject to scatter component of the beam only.

We have found that the output of this fixed 5.0 volt regulator drops to about 4.6 volts over a period of about 1.5-2.0 years and needs to be replaced.

The part continues to regulate at the reduced voltage even under load... but is obviously well out of tolerance.

We are suspecting radiation exposure as the root cause... and are weighing our options for designing the component out of the circuit.

Have any other engineers experienced this type of "slow-n-soft" radiation induced component failure with the LM2674MX-5.0?  (or other switching regulator)

In addition, do any engineers have knowledge of a fixed 5.0 Volt regulator that has good radiation tolerance?

It is my assumption that an internally adjusted (laser trimmed) reference voltage/current source within the part is getting altered (re-trimmed) by radiation exposure... however, the surrounding regulation/feedback circuitry just keeps regulating accordingly.

Kevin D.

  • 0
    TI__Genius 11085 points
    I am not aware any other customer has experience the same situation. I will forward your question to the engineer support this part to get more information. Thank you. -Yang
  • 0 in reply to YangZhang
    TI__Prodigy 220 points

    Hi Kevin,

    The 5V output drifting to 4.6V is extremely unusual and not something we've come across before. It is a mature device on a mature process flow. We perform reliability testing as part of our normal checks and may see a few mV change - nothing like the 400mV you see. It is possible a single unit may have a defect which could cause this effect but you would not see it repeated over other units or even continue to drift further over 1.5-2 years as you mention. The device is trimmed at the factory to tune the internal bandgap but it is done by zener zap & not laser. It is more likely that the internal references are being affected by the radiation as you suggest.

    TI does offer some rad-hard devices. We don't have any in this family but I'll check to see if there are other alternatives.

    Regards,   Paul

  • 0 in reply to Paul Dolan
    TI__Genius 17035 points

    Hello Kevin,

    This sounds like typical degradation due to total ionizing dose (TID) radiation.   The dielectrics in the drive transistors charge up, causing leakage and a reduction in gain.

    We have not tested this part.  But, we have tested another product that uses the same process and it failed under 300 gray (30 krad). 

    We do not test many commercial grade products for radiation and do not have a huge database.   Most of the commercial switching regulators and linear regulators we gave tested have had similar results.

    We do offer radiation qualified space products.   Test reports can be found on ti.com/radiation and a part selection list can be found at ti.com/space

    Many of these products would likely last 5 times longer or more.

  • 0 in reply to Kirby Kruckmeyer96848
    Prodigy 20 points

    Kirby,

    Indeed accumulated dose is the suspected failure. 

    The link you provided to the qualified space products page may prove to be very useful!

    Thanks much for the reply!

    Kevin D.