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LM675 below operating temperature

Volker Noack
Prodigy 10 points

Other Parts Discussed in Thread: LM1875, LM675, OPA544

Hello everybody,

 The TDA2030 is no longer availably. I was searching for a replacement typ. I found the LM1875 and the LM675. Unfortunately the LM1875 wasn’t running in my application. The input overcurrent protection was activated during the power up. However, I used the LM675 and it is working.

The problem in this case is that the datasheet is specified for an operating temperature range from 0°C to 70°C. I don’t want to use it in over 70°C but it is possible that the ambient temperature is below 0°C. I searched different information, what could happen below the operating temperature. I can accept that the offset current and the input offset voltage are dropping. I didn’t found any limitations below the operating temperature. So why isn’t the LM675 specified below 0°C? Have I missed something?

I’m looking forward for your reply.

 Volker

  • 0
    TI__Guru 66666 points

    Hello Volker,

     The LM1875 and LM675 are basically the the same device.

     They are tested and guaranteed under different conditions. The LM1875 has looser DC specs since DC is not critical for most audio applications.

    But both are “commercial” (or consumer) temp range devices, where the minimum spec is 0°C. Nobody bothered to look any lower. High temperatures are usually the concern for these devices.

    Operation below zero should no be a big problem. Devices hate heat and do not mind going cold, but certain parameters do start to degrade going cold. BW, phase margin and output drive could be affected.

    Note that the LM675 and LM1875 are NOT unity gain stable and have a minimum closed loop gain of 10. If operated as a buffer, it WILL oscillate at high frequencies, heat up & shut down. Make sure the "noise gain" is at least 10.

     Also have a look at the OPA544. It has the same pin-out, is spec'd down to -40°C and has FET inputs.

    Regards,