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# Doubt regarding 1) -ve voltage input to AD7864 2) 12-bit Word generated by the AD7864

Hi,

I would be very grateful, if someone could answer my questions.

1) I am using the AD7864 adc(schematics have been attached). Though i am not giving any -ve voltage as Vcc (My Vcc is +5V only) i am able to get even -ve cycles of sinewaves or whatever -ve voltage i give as input to pins VINAx at my output( my Output is the output of DAC AD5447).

How is this possible??

According to my understanding, for Bi-polar operation of any device both +Vcc and -Vcc must be present. If possible please clear my doubt.

2) The datasheet says that For the ±5 V range, 1 LSB = 10 V/4096 = 2.44 mV.

What word does this (2.44mV) correspond to??

What word will be generated if +5V is given as input to the ADC??

Any help or any link to a document will be greatly appreciated ;-)

best wishes

janmay

Parents
• Hi Jonathan,

Thanks a lot for your exhaustive reply. Due to your answer to the second question, i was able to check and verify whether the ADC was producing the word for the required voltage i was giving it(by using a AD5447). And the ADC is behaving as per the datasheet words given in the table.

I would be grateful to you, if you could answer my following questions:

1)How can  the AD7684-1 take as input a -ve voltage when according to my understanding, for Bi-polar operation of any device both +Vcc and -Vcc must be present.

2) How can this device take as input(+/- 10V) when its supply range (AVdd and DVdd) can take a maximum  input of +7V (Page 6).

best wishes

janmay

• Hi Jonathan,

Thanks a lot for your exhaustive reply. Due to your answer to the second question, i was able to check and verify whether the ADC was producing the word for the required voltage i was giving it(by using a AD5447). And the ADC is behaving as per the datasheet words given in the table.

I would be grateful to you, if you could answer my following questions:

1)How can  the AD7684-1 take as input a -ve voltage when according to my understanding, for Bi-polar operation of any device both +Vcc and -Vcc must be present.

2) How can this device take as input(+/- 10V) when its supply range (AVdd and DVdd) can take a maximum  input of +7V (Page 6).