Input signal protection on ADAU1761/1781
What kind of protections are built in to the analog inputs of the Sigma dsps? Put another way, what kind of precautions should I take to condition incoming signals that may be too hot for the ADCs?
Do you recommend clamping the inputs? Or are they internally clamped? And other than excessive distortion, are there any dangers to the chip in overdriving the inputs with signals from, say, +/-12V analog rails?
Lastly, Does the sigma dsp have some kind of built-in thermal protection?
Any help you can offer is appreciated.
Audio Signal Processors
input
clamping
adau1781
SigmaDSP Audio Processors
adau1761
protection
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Hi chuckwin,
It looks like this is an old thread, but I'll try to answer if it's helpful for you.
I personally have fried a few ADAU1701s in my day. I believe there are internal overvoltage protection diodes in all of the IO pins, but there are only designed to protect against short spikes and were not designed to protect long-term abuse. If you overdrive them regularly, they will fail.
The solution is to put TVS diodes on any pins that might see an overvoltage event. I would suggest doing this especially on the ADCs (if you're unsure of what somebody might plug in to your product!) and definitely on the main 3.3 V supply line.
I have had very good results with the NSR0320 from On Semi.
Layout it key. It's quite important to place the device as close as possible to the SigmaDSP for solid local transient suppression.
Yagami
I forgot to answer your question about thermal protection.
Based on the datasheets, there is no evidence of thermal protection built-in to SigmaDSPs.
However, the new ADAU1452 has an integrated thermal diode. You can read the temperature using an external IC and then have a microcontroller trigger some kind of an event if the temperature exceeds a threshold. Pretty cool!
The class D amplifier products from ADI tend to have thermal sensing and diagnostics built-in, but that's pretty understandable, since they can dissipate quite a lot of power. SigmaDSPs are low power in comparison, so I guess that's why thermal monitoring isn't included.
Yagami,
Yes it was an old thread, but I'm glad someone replied finally!
My questions stemmed from some behaviors I observed using the 1761 & 1781. I've noticed that when the inputs are overdriven, the part shuts down but seems to recover OK when the signal is backed off.
I just wondered if the shutdown mode was designed in and, if so, what the criteria were . If not designed in, I wanted to understand the mechanism so I could address it.
Thanks for your suggestion on the TVS diodes.
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