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PGA280 , No output signal, Please help

TYB
Prodigy 165 points
Other Parts Discussed in Thread: PGA280

Dear all,

We are a set of undergraduates doing one of our projects. We need to use a programmable gain controller to control the gain coming out from a multiplexer. We are going to input the output of the Programmable gain controller to an ADC. We have selected PGA280, since it can attenuate as well as amplify the incoming signal. We found that it is extremely hard to find any design materials on PGA280. We gave the signal input but we are not getting any output. We are communicating with the chip using PIC 18f4550 microcontroller and we have verified that SPI signal from the PIC is ok. Diagram shows the way we connected the connections to the PGA. We have input a signal and changed the gain, but we were unable to get any signal output.. Please help... 

Thank you.

Thilina

PS: Is there any other way,  we can check weather the chip is working?

 

 

 

  • 0
    TI__Guru* 94295 points

    Thilina,

    I think you'll need to redo some of the supplies to get this to work. First, I would note that VSON should be tied to GND and I would use a -12V supply on VSN. The problem is that the lower bound for the input range for the PGA is 2.5V above VSN.  With INN1 grounded you would need VSN to be at -2.5V just to work.

    Once you get that fixed, a basic thing to try is to short the inputs together and put about 2.5V on VOCM and make sure the VON and VOP both servo back to the same 2.5V. The VOCM sets the output common-mode voltage and with the inputs shorted the differential voltage from VOP to VON should be 0V but at an output common mode of 2.5V.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 165 points

    Dear Mr. Joseph Wu,

    Thank you very much for your quick reply. We are indeed overwhelmed that we are getting the preferred outpu from the PGA because of your perfect guidance. Thank you again and we would be seeking for more help if we get any..

    Best regards.

    Thilina Yapa Bandara