LME49810 issues

[StuartR]

I've been doing quite a lot of testing lately on LME49810...

Anyone else found that it does not like when the power rails are not turned on simultaneously? Particularly if the -VE rail is connected before the +VE. The output can "lock" at the -VE rail voltage, even after the +VE rail is connected.

When the +VE rail is turned on before the -VE rail the output rises to about 7.5V.

There is obviously a horrible thump from the speaker when this happens. Hardly click or pop free.

Circuit under test is a standard app note implementation but using thermal-track output devices. Power rails for testing are from a benchtop lab supply, +/- 35V DC.

After multiple connections and disconnections of the power rails (in no particular order), either the LME49810 blows up (exploded with sparks even once), or the GND PCB trace from pin 3 to star GND burns out, or the traces between sink/source and output devices can burn out.

Circuit and implementation are fine. Perfect operation if powered up both rails simultaneously, or with toroidal based AC supply (where obviously both power rails rise simultaneously by default).

Hoping someone else has found similar issues?

[StuartR]

Just tested LM4702. It does not suffer the same issues mentioned above. There is no turn on transient, no pop, no click. No matter which power rail is turned on first.

I'll now test out LME49811...

[StuartR]

Same issues with LME49811...

Anyone have any ideas?

[hags]

Originally Posted by StuartR

Same issues with LME49811...

Anyone have any ideas?

Yeah, turn them on and off simultaneously.

[StuartR]

Originally Posted by hags

Yeah, turn them on and off simultaneously.

Thanks for the suggestion, I didn't think of that one

In this particular application I cannot gaurantee that they turn on and off at the same time. And I would like to avoid an extra relay and control circuitry.

[hags]

Originally Posted by StuartR

Thanks for the suggestion, I didn't think of that one

In this particular application I cannot gaurantee that they turn on and off at the same time. And I would like to avoid an extra relay and control circuitry.

Sure, no problem. In what application would they not be turning on and off simultaneously?

[StuartR]

External power supply with DC output. The connector joining the power supply to the amplifer doesn't join all connections at exactly the same time.

[JPV]

Originally Posted by StuartR

External power supply with DC output. The connector joining the power supply to the amplifer doesn't join all connections at exactly the same time.

May I suggest you to make some crude tests with resistors in the mute, clip ground pins. Perhaps the logic part of the chip ( baker clamp, mute ) is sensitive to the power supply. Because ground pin is mainly for these functions, I would put a resistor to see what happens. The mute command is also sensitive. Could you try to drive it with a proper low voltage source and redo your experiment.

Anyway good findings

JPV