problem with Negative supply for ADC

Thread Starter

omarcillo

Joined Mar 2, 2009
3
Hi:
I have a problem using the output of a TC7660 as floating ground fro a voltage reference, so the output of the TC7660 (-2.5V) is the ground for the LT1021 (5 V) reference, I think I need a resistor between this 2 elements but I do no know how to connect that..

Any suggestion is appreciated..
 

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bertus

Joined Apr 5, 2008
22,270
Hello,

What is the voltage of V+ in your drawing ?
What is the reference voltage you expect on the output of the LT1021 ?
(When the ground pin is at - 2.5 Volts, the reference output pin will be + 2.5 Volt).

Greetings,
Bertus
 

Thread Starter

omarcillo

Joined Mar 2, 2009
3
Hi,
V+ is 2.5V that comes from a regulator, and the idea is that output of the LT1021 is +2.5 measured from GND or 5V measured form -2.5V
The output of the LT1021 is very stable 5V, that is why I am using that......
regards
 

bertus

Joined Apr 5, 2008
22,270
Hello,

If the - 2.5 Volts is not stable the + 2.5 volts from the LT1021 is also not stable as it is references to the - 2.5 Volts of the ICL7660.

Greetings,
Bertus
 

Thread Starter

omarcillo

Joined Mar 2, 2009
3
Hello,
Yeah the 2.5 will no be stable measured from GND but it will be the difference between -2.5 and 2.5, but the reference for my ADC is the difference between the -2.5V and 2.5V....
Regards
 

bertus

Joined Apr 5, 2008
22,270
Hello,

What is your problem then ?
I see you have used 1 μF caps at the ICL7660.
In the datasheet they always use 10 μF caps.
Perhaps this makes it a little bit more stable.

Greetings,
Bertus
 

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