Design Inquiry

Hi,

JEstayo will look into this and get back to you soon.

Thanks and regards,

Coco

Hi AbhishekManoj ,

The ADC can accept +-4V based on the supplies you have sent. Please refer to the FAQ below on the analog input range of AD7768.

AD7768: What is the analog input range? - Documents - Precision ADCs - EngineerZone

The amplifiers ADA4940 and ADAD4945 can work using single ended to differential output to drive the ADC. Please refer to the link below for suggested ADC drivers using different ADCs.

Precision ADC Driver Tool | Analog Devices

Thanks,
Janine

Hi Janine.

From the table you had shared, sorry that I didn't get it completely. I'm providing unipolar supply for ADC AVDD-5V and AVSS-Ground. 

From the above table, for 5V AVDD and 0V AVSS, the range is only +4.096. I had asked for +/-4V range which includes from -4V to +4V, 8Vpp.

Does it support the above voltage range.

For the above requirements can i give +5V and -5V supply for the amplifier ADA4945-1.

Also, please address some more queries regarding AD7768.

1.ESD Protection diodes part number AINx inputs as mentioned in datasheet. Or is those mentioned ESD diodes are internal to the IC.

2.In AD7768 evaluation board AIN pin connected directly to ground?

3. In evaluation board separate amplifier is used for AIN+ and AIN-. I'm using a single amplifier to convert single ended input to differential pair to the ADC input. Do I need to provide the below mentioned circuit between AINx+ and AINx-

4.I'm using ADA4945-1 as input amplifier to ADC, IN- pin i will connect the incoming input signal. IN+ pin how should I terminate or does i want to VCM_OUT to this pin.

5.Where should I connect VCM pin of the ADC.

6.What does the VCOM pin features and use in evaluation board, the VCM_out and AVDD1 is connected to an opamp OP2177 and the output is VCOM which is fed to IN+ of the ADC input amplifier. Can you please explain this circuit working.

7.For AVSS i need to provide analog ground or normal ground.

8.For pull up and pull down for FILTER and MODE pins, which resistor value should I use to pull to AVDD and GND. Can I use 10K resistor for that purpose.

9.For REFx pin ground, should i give analog ground or digital ground.

10.I'm not using XTAL1 pin as I'm using CMOS Clock. How should I terminate XTAL1 pin.

11.Which values should be given to XTAL1 and XTAL2 optional termination resistor and capacitor

Regards,

Abhishek

Hi JEstayo 

Please provide an update on above queries.

Regards,

Abhishek

Hi AbhishekManoj ,

The output of the ADA4940 or ADA4945 is differential. The differential limit in this case is +-4.096. Please open the excel file to verify the limits for every pin - AIN+ and AIN-, and the limit differentially (AIN+ - AIN-)

Please refer to the answers below.

1. These are internal to the IC. The AIN pins are the analog input pins of the ADC.
2. The symbol shows that the ground pin of the SMB is connected to the EVB ground.
3. The components should be provided. Please refer to the Precision ADC Driver tool to confirm the correct RC filter for the kickback.
4. You can connect to VCM_OUT. Please try to explore the excel file for the input range of the ADC using different supplies, and input configurations.
5. The VCM of the ADC is by default set to half of Vref. Please connect this to the VCM pin of the amplifier before the ADC to set the common-mode to VREF/2.
6. The VCM_OUT of the ADC is buffered using OP2177 and connected to the amplifiers to level shift the signal and set the common mode output to VREF/2.
7. AVSS can be connected normally to ground.
8. In pin mode, pull the pins up to IOVDD, or pull down to ground.
9. You can connect to analog ground.
10. For CMOS, connect CLK_SEL to ground, apply the clock to pin 32 and tie pin 31 to DGND. Please refer to the CLOCK SELECTION in page 58 of the datasheet for more details.
11. You can use this to ground XTAL1 pin.

Thanks,
Janine

Hi JEstayo 

Thanks for the detailed explaination.

In the point no:8 i  whether i can use 10k resistor for pull up and pull down.

In point no:10 what are the required resistor and capacitor values for clock termination.

Also, for AD7768-4, in one configuration i want only 2 inputs, how should i terminate the unused inputs of the ADC (AIN pins).

Regards,

Abhishek

Hi JEstayo 

Please provide an update on above.

Regards,

Abhishek

HI JEstayo 

For the ADCs AD7768-4BSTZ and AD7768BSTZ, i have unused input and output pins. Is any termination is required for the unused pins or directly can i make it as NC.

Please confirm.

Regards,

Abhishek

Hi AbhishekManoj ,

For point no. 8, 0 or 10kohm can be used. When 0 ohm, be careful not to connect the pin to both IOVDD and DGND,

For point no 10, You can connect the clock signal to XTAL2 directly.

For unused analog input pins, you can short those to VCM. For other pins, you can refer to PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS section on where to connect if unused. 

Thanks,
Janine

Hi JEstayo 

For my unused DOUT signals DOUT6 and DOUT7, how to terminate, should i make it as NC. As these pins termination details is not mentioned in datasheet.

I'm attaching the schematics of AD7768 and schematics of AD7768-4 of my board.

Please review and provide your feedbacks.

1.AD7768 with 6 channels used

PDF

2.For AD7768-4 with input amplifier

PDF

Regards,

Abhishek