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Precision Data Converters
Precision Data Converters Forum
ADS1271EVM-PDK: Can't detect the input signal
I am a customer of ADS1271EVM-PDK,I connect the MMB0 board with 1271EVM and power the system with DC 6V .
when I connected this system with PC(OS:windows XP) ,It was shown that "Firmware loaded and ready" on status item of ADS 1271 user interface .
But when inputed signals from J4 on 1271EVM, I couldn't get the signal from user interface .
For this input connector, I connected "A1+","A1-"and"GND" wires with the signal source and kept the "AR1+","AR1-" open.
What should I do next? Thanks.
The ADS1271EVM requires bipolar supplies to be connected for the OPA1632 input op amps. Do you have these supplies connected? Where do you have switch settings for S1, S3 and S4?
Best regards,Bob B
Referring to the schematic of the ADS1271EVM-PDK Users Guide (page 14), can you tell us exactly which input(s) you are referring to when you reference AR1+ and AR1-?
The switch settings for S1, S3 and S4 are as follows:
S1:MIDDLE(Input from J4/J5 auxiliary inputs)
S3:MIDDLE(External Reference from J1.20 (REFP) referenced to J1.18 (REFN))
S4:LEFT(Input from Buffer Amplifier)
Am I right?
Thanks for your reply.
I applid +/-12V(I know I'd better supply +/-15V,but now I can only get +/-12V power suply ) to the +/-VA terminals on the MMB0 to drive the OPA1632 buffers on the ADS1271EVM.
S3 provides the reference, so it must be driven. The center position requires that you provide an external reference. I would suggest changing the position to the 2.5V position which would mean the setting would be to the left.
My input signal range is -10V~10V, so I need an external reference,right? Now I provide -/+12V DC power as reference from J14 Pin1,2 and 6(-VA,+VA and GND).
So could you tell me which should I set on S3? "Left "(Onboard 2.5V reference) or "Middle"(External Reference from J1.20 (REFP) referenced to J1.18 (REFN))?
I'm sorry for the delay in responding. You may have a misunderstanding about how the device is operating. The nominal reference voltage is 2.5V. The analog input range is +/- 2.5V. This means you cannot have a +/- 10V as your input. This will exceed the absolute maximum input voltage for the ADS1271 and can damage the device. Even though the OPA1632 may allow for this input range, the ADS1271 does not.
As far as the S3 position, you would want to place it in the left position.
I can understand that I cannot have a +/- 10V as your input to ADS1271 directly.Now my scheme is that I can realize the A/D conversion for -/+10V by OPA1632+ADS1271+MMB0(TMS320),can't I?
Happy New Year!
Happy New Year to you too! It is possible to input a higher voltage at the input of the OPA1632 if the resistors are sized properly on the ADS1271EVM. You will see a typical circuit for reducing the input voltage by 4 in Figure 70 of the datasheet for the ADS1271. Figure 70 is a single ended input, so if you are driving differentially you will need to remove the one input from ground and connect your input appropriately so that the configuration is similar to Figure 69, but with the values of Figure 70.
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