TDA7294 Mute/Stdby

[child1]

Hi!

Can anyone explain to me how the mute and stdby works on the TDA7294. Are they controlled by the current flowing into the pins? If so how much current enables/disables the mute/stdby?

Thanks so much

Mads

 

[Sangram]

TDA 7294 mute and standby are voltage driven, not current. >3.5V on the relevant pin will turn the amplifier into active state.

The ST datasheet also has a recommendation for specific turn-on of the two pins (stby turn on before mute, switch off after). It is not recommended to stray for those recommendations.

 

[child1]

okay... that's what i thought. But the mute and standby doesn't work on my sub, which i have build with this chip. when turned on the sub is muted. but when i have had it unmuted it will not return to mute condition. Really strange...

 

[Sangram]

Hi

Can you post a hand-drawn schematic of what you have done?

A voltage pin will draw very little current so if the mute cap is too big you have to create mute condition by driving the pin low (short to ground) instead of opening the drive voltage.

 

[child1]

Basically I have made the same circuit as in the datasheet. But with the exception of the mute and standby voltage being Vss (33V). Could this be the problem? To much voltage?

 

[Sangram]

It depends on the capacitor value.

At 33V, a 10uF capacitor will have a pretty long hold-up time and will continue to feed the pin.

You can sort this out by adding a 2K resistor across the mute cap. This will act as a voltage divider in conjunction with the 10k Rmute. A 5.1V zener or three LEDs in series will also perform a similar function.

 

[child1]

SOLVED!

put a 2k resistor in parallel with the cap and it worked like a charm.. ! thanks for yout help!