AD7663

Hi Anita,

This part is recommended with a 2.5V Vref. Please see specification table on the datasheet. I believe you are referring to the  TPC6 FFT plot? The 4096 in the fft refers to the number of points or number of samples.

regards,

LLoben

Hi LLoben,

Can you give us direction on why?  Customer also has additional questions:

Can I use my own differential amp to drive the inputs?  Do I have to use the amp that is within the chip?

If I use my own differential amp, what do I connect to the differential amp’s Vocm pin?

How do I choose between a 2.5V reference and a 4.096V amp?

Hi,

AD7663 uses an external Vref and is specified to a minimum of  2.3V and max up to (AVDD - 1.85.), so we can't use the 4.096V reference voltage. Please note AD7663 has a dynamic input impedance therefore should be  driven by low impedance source with efficient  decoupling between REF and REFGND inputs.

It's recommended to use the amplifier as this conditions the input signal—as well as acting as a low-impedance buffer between the signal source and the ADC input. Please see page14 of the datasheet for different driver amplifier choice and page13 for the typical connection diagram.

regards,

LLoben

Hi,

In a fully differential ADC driver. the VOCM pin should be connected to your Vref/2. Please see attached example schematic using the ADA4940-1 a newer part which I also recommend  that can drive the AD7663. and then you can also use two single ended ADC driver like ADA4805 where the VCM(Vref/2) is connected to the non-inverting input of the ADC driver.

regards,

LLoben

Hi Lloben,  Thanks for the clarification. Can you advise on how to drive a differential signal into the AD7663, we need to make sure it has a Vocm of Vref/2. Typically op amp has two differential inputs and an output. ... This is the purpose of the VOCM pin, are we to assume that Vocm is not shown but is connected to Vref/2? Can you advise on how to do this?