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using external voltage reference for DC , what's the problem

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Member level 5
Aug 30, 2005
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dc voltage reference

Dear all,

I have a CC2430 chip "i think it's based on the 8051 MCU" , which i use to measure some analog sensor readings, the AVDD of the chip is 3.3 volts, and in the manual it's said that the chip can measure up to AVDD only.

I have a sensor that outputs a range of 5 volts, and I need to measure this voltage too, I rescaled it to 3 volts somehow , to measure it means i need to compare against EXTERNAL VOLTAGE REFERENCE, which the manual says should be applied to input pin 7 (the MCU has AIN0 to AIN7 , ADC pins)

when I connect the voltage reference to it. it shorts out, I measured the resistance and it turns out to be approximately ZERO !
how could I get this to work ?

anyone ?

5 volts thru a 2:1 divider would present 2.5 volts to the input. Your reference should also be 2.5 volts. By exceeding the 3.3 volts input on pin 7 you have damaged the pin 7 input, shorting the input protection diodes. You'll need to start over with another chip.

The software needs only to recognize that 5-volts is = to 2.5 on it's input and do the math for you in giving an output, or to read out the input value as a percentage of the reference on pin 7.

I measured the internal resistance of a new CC2430 chip and it measured to zero also, does this mean that it also has a defect or it may mean something new ?

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