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MAX45711

I'm trying to use the MAX4571 essentially to mute some audio channels,

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I got the controller to work and it seems fine. My test was to put V+ on the input and scope the output(with a pull down to ground for when the switch is off). It seems to work fine. My code simply toggles the state the switches every 1s or so.

But when I put an audio signal on the input instead I get the negative half clipped and it is extremely attentuated(About 1/10 or more). What I did was actually pass a sin wave generated by my computer which goes into a mixer(for easy volume control and other things that I tend to do) then from the mixer's headphone out into the input of the MAX4571.

Audio+ --- MAX4571 NO1

MAX4571 COM1 ---+--- Audio- R | GND

(R anywhere from 500 to 3k but didn't help any and made it worse for lower and high values)

With the scope connected to +.

Any ideas why the signal would be clipped and severly attenuated?

Its possible I ruined the device. For some reason my first PIC's I2C channels stopped working so I might have shorted something out when I was probing around. I replaced the pic and everything seemed to work but maybe I screwed up the MAX4571 although it will passes the constant voltage just fine.

First thing I need to know is if it passes AC completely(the scope says no and the datasheet doesn't mention it except that its "audio").

Any potential ideas to try out? I guess the next step is to try another IC but maybe there is something else going on here that I'm not seeing?

My concept how how it works is that I should just be able to put an audio signal on the input and it will mute it when I tell it too. Maybe I have to worry about input and output impedence too to get it to work properly?

Thanks, Jon

Reply to
Jon Slaughter
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Your output is exactly what I would expect to see from a device which only uses a single supply and has an AC signal applied that is centred about GND. You need to bias the input to VCC/2 and AC couple the signal through a capacitor. Just as you would for a single supply op-amp circuit.

VCC | .-. | | 10k | | '-' | |] | Audio In -|]-----o----- MAX4571 |]+ | | .-. | | 10k | | '-' | GND

(created by AACircuit v1.28.6 beta 04/19/05

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--
The Force is dark on one side, light on the other and holds the world
together.

Hmmm, just like Gaffer Tape then.
Reply to
Hot Jock

Seems that the IC then is not truely "audio" if you gotta bias it so it will take audio inputs. Not sure why they didn't do like many of there other chips and use a charge pump to generate -V. Unfortunately this seems to be the only chip I can find for audio that has a lot of switches on it. I need about 80 of them and I need to keep the size down as small as possible.

I expected the clipping to occur without attenuation though. I can see why it would clip but not why it would attenuate the signal.

I'll try the biasing and see. This chip doesn't seem all that great (35ohms RON when some of there newer ones have < 1ohm RON) and only -90dB but its the only one that comes close to a large number of switches per package and is for audio(I've seen some video crosspoint switches that have a large number but not exactly what I need).

Thanks, Jon

Reply to
Jon Slaughter

Those devices don't need level shifting. It's suppose to work directly:

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Either I screwed up the chip or theres something wrong with the external components. Theres really not many extra components though so not sure what it could be.

Reply to
Jon Slaughter

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