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LM48580: LM48580 bootup

Michele Lucchi
Prodigy 80 points
Part Number: LM48580
Other Parts Discussed in Thread: TPS62133

Hello,

we are experiencing some problems with booting up a set of LM48580 amplifiers, which we are using as speaker drivers.

On the PCB we have seven LM48580, they are all powered by the same 5V supply.

The supply and shutdown pins are connected directly to eachother and the 5V supply.

As a supply we are using a Lab Supply with its current limit set to max (3A).

We observe, that sometimes the amplifiers do not start. It is possible to start the amplifiers quite consistently by powering off and on quickly.

Question: Can there be a bootup failure, when supply and shutdown! are supplied at the same time?

In addition we have the problem, that a few amplifiers are distorting heavily. Could this issue be related?

We have used this amplifier in different applications before, and never observed this problem. The difference in this case, to previous projects is, that we have more LM48580's starting at the same time.

BR

Michele

  • 0
    TI__Genius 10512 points
    Hi Michele,

    Can you provide us with your schematic and images of the signals being delivered to VDD and the shutdown pins? We have not seen any boot up issues with this device.
  • 0 in reply to Kelly Griffin
    Prodigy 80 points

    Hello Kelly,

    unfortunately I cannot share the schematics here. I could deliver them in a provate conversation...

    I can however show you the supply voltage progression.

    See the two attached figures.

    LM48580_OFF: shows the progression when the amplifiers do not start

    - Yellow: 15V supply from which the 5V supply is generated with a TPS62133 step down converter

    - Blue: 5V supply that supplies the LM48580 amplifiers, there are 7 amplifiers starting at the same time

    - Pink: 3,3V supply for other components

    LM48580_ON: shows the progression when the amplifiers start properly

    - Yellow: 15V supply from which the 5V supply is generated with a TPS62133 step down converter

    - Blue: 5V supply that supplies the LM48580 amplifiers, there are 7 amplifiers starting at the same time

    - Pink: 3,3V supply for other components

    The problem usually occurs when booting the system from a longer off phase. If you quickly turn the 15V supply off and then back on again the startup is usually successful.

    BR

    Michele

  • 0 in reply to Michele Lucchi
    TI__Intellectual 1910 points

    Hey Michele,

    Do the amplifiers have any capacitors on the power supply lines? Try adding at least a 10uF capacitor. VBST should also have at least a 1uF cap. Thanks for your interest in our products, if this doesn't resolve the issue I'll reach out via email if that is okay with you.

  • 0 in reply to Micah B Brouwer
    Prodigy 80 points
    Hi Micah,

    yes the amps are buffered with 10µF and 1µF in parallel on the supply side. The boost output side has a 10µF cap.

    Yes an e-mail conversation would be most welcome!

    BR
    Michele
  • 0 in reply to Michele Lucchi
    TI__Intellectual 1910 points
    Hey Michele,

    I sent you an email so I will close this thread.