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HS08QG8, ADC and Vhref drop

Question asked by Giacomo Petrini on Jun 17, 2009
Latest reply on Jun 18, 2009 by Giacomo Petrini

Hi,

I've a problem, caused by a bad design (not mine). Now I'm looking for a solution that does not involve HW redesign.

 

I'm using one channel of the QG8 ADC module to read the voltage from a temperature sensor (a LM20 from National). The problem is that the QG8 Vdd is connected directly to a 3V battery. So when the battery voltage drops, it drops the Vdd, the Vddad and of course the Vhref. So the range of the AD shrinks and I read different values even if the temperature does not change.

 

The question is: there is a (sw) way to solve this? I think that the internal bandgap reference can have a major role in this, but I don't see how...

 

Thanks for any hint.

 

Bye Jack 

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