LM4862 Audio Amplifier

Hi Jedidiah,

I will take a look at this issue and get back to you soon.

Andy

Hi Jedidiah,

Is it possible for you to post the schematic you are talking about? So we can help you more with your issue.

Andy

How do i post a schematic in here?

The easiest way is to upload a screenshot file.

Andy

Where and how to i upload any file in this website for you to see? I dont see an apparent way of doing that. Can i just reply to the email notifications that i get with a screenshot attached?

Hi Jedidiah,

When you reply, click "Use rich formatting" below. 

Then, you will go to another window like this.  Click the button in red box below to upload your screenshot.

Andy

The GIA 63H contains the LM4862s and is isolated through a transformer.  As you can see, they introduced a feedback circuit into 247 amplifier when they are attempting to bypass it in case of failures. Only one of those GIAs are initiating alerts at a time. So when one GIA plays an alert, it is amplified and also fed back to the GIA not issuing the alert. Because of the transformer i dont see that the 4862 getting damaged but i dont know for 100% and would hate for them to ruin a peice of equipment.

 

 

Hi Jedidiah,

I discussed with my colleague about you question. Actually, we don't quite catch the meaning of “reverse breakdown voltage”. We think you would like to know how much voltage can be applied to LM4862 output when LM4862 is in shutdown mode but Vdd is applied. Is that correct?

Could you explain more on your question?

Andy

Andy,
I would definitely like to know how much voltage can be applied to the LM4862 ouput when it is in shutdown mode. Not exceed VDD? Transistors, diodes, etc have reverse breakdown voltages which the output stage of the LM4862 may have. VDD may not always be applied when a voltage would be present at those outputs in this application. It is possible that someone may pull a circuit breaker disabling power to one of those units while the other is operating. I just want to ensure they wont damage the LM 4862 with what they are proposing though.
Thanks,
Ryan

Hi Jedidiah,

OK. I have got some comment from my colleague for you:
"If the device is in shutdown mode with Vdd supplied, the device output is high impedance but feedback network is connected. In this condition, if the device output has a voltage injection from outside via some impedance (resistance), the applied voltage from outside to LM4862 will be clamped by ESD Di and current flows into device output. If this current is more than +/-50mA, the device may get into latch up and be damaged. But prior to this number, please look at abs max rating portion: “Input Voltage −0.3V to VDD + 0.3V”. This applies to all pins to avoid ESD or parasitic Di or Tr turn ON. So within abs max ratings, the device would not be damaged, but exceeding this spec, we cannot guarantee whether the device will remain OK or not."

Andy

Andy,
Thank you very much for the information. That is what i was looking for. Just for clarification though, the applied voltage specs apply even when Vdd is not supplied? They are not reduced by any means and the device output is still in a high impedance state? Thank you for all your support. You have been very helpful.
Thanks,
Ryan

Hi Ryan,

Yes. I think you are right!

Andy