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Audio HP Amp TI LM4811 - am I getting crazy?

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Saimoun:
Yeps I saw as well - thanks :)

I made a few more measurements - now with a completely new chip, which I was super careful with not to touch in case I could have fried the previous ones. There are no shorts and all pins are soldered as they should. There is nothing else on the PCB, just the chip. Measuring resistance between the digital pins and ground, and between the digital pins and VDD, with my multimeter.

UP/DN and SHUTDOWN pins always give something above 1M \$\Omega\$ (to both GND and VDD pins) while the CLOCK gives around 10k \$\Omega\$ to GND (and around 100k to VDD)?!

Then I tested the following: 10k \$\Omega\$ pull-down resistors on Shutdown, CLOCK and UP/DN, and give 5V on VDD (and 0V on GND). All other pins floating.
I get the following, yellow is the Bypass pin and blue is VDD.



(at around 7s I removed the pulldown resistor on CLOCK, making it float, and again this affected the Bypass pin).

I am getting out of ideas of what to test, and out of chips... 

OM222O:
those pins are meant to be driven actively. I don't understand why you're "testing" the IC with EVERYTHING FLOATING. connect it to an MCU, drive the volume control and clock pins, add your audio source and speakers, see if it works as expected or not. many ICs may not function well under random circumstances. I remember having a seven segment driver which kept burning out under "testing" with floating pins, and I thought it was a bad chip, but when actually connected it to everything, worked as expected.

Saimoun:
Fair point OM2020 - but at the end the only floating pins were the inputs since the outputs are internally tied to GND and I pulled down the digital ones. And the inputs are meant to be analog anyways so it should not make much difference?

And tbh I would rather not drive the pins from a MCU since the amount of current the clock pin seems to sink.

But ok I will try to follow their Demo board schematics then - it has buttons and jumpers to control the digital pins.

tooki:
Let’s review some assumptions and facts:
1. It’s extraordinarily unlikely that the chips are fake since they were bought from a reputable vendor
2. It’s extraordinarily unlikely that multiple chips in a row would leave the factory faulty
3. The datasheet lists a maximum current draw of 3mA for the chip
4. Given that the IC is specified as being a low-power part, it wouldn’t make sense for its support components to draw large amounts of current.

So, what’s left?
5. Does the schematic actually make sense and work in theory?
6. Does the PCB match the schematic?
7. Are all the support components good, and of the correct values?
8. Was the PCB assembled properly?
9. Was care taken to ensure the chip isn’t damaged during soldering, due to excessive heat or ESD damage?
10. Is the device being tested under sensible conditions?


You probably have more than one PCB. Try building up another one.

Try leaving out the low pass filters on the inputs (omit C1/9 and bridge R17/21).
Make sure you have a load on the outputs.

What are you powering it from?

Remember that if it’s not the IC that’s bad, then it’s something else, i.e. the rest of the circuit.

Take the original populated PCB and remove just the IC. What happens to the voltage at the pads for the clock, up/down, shutdown, bypass, and VDD pins as you feed in high and low signals on the clock, up/down, and shutdown inputs? Somehow, I suspect that there is a short elsewhere on the board acting as a near short to ground.

OM222O:
An MCU won't "burn" or "source" amperes of current! They're internally limited by the small fets that activate them. They have a "max current rating" that is usually less than 40mA and even then, the voltage will drop to close to 0. You can literally short out an MCU pin to GND forever and nothing happens. These pins are not meant to be analog. CLOCK definetly means digital, there are timing diagrams for them in the datasheet! Floating pins cause unreliable and random operation modes. Even if they were analog (op amp inputs for example) "best practice" is to tie them to GND or VCC if they're not used. Floating pins are always bad.

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