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AMC1303E2510: Spurious SDFM output with Manchester Encoded AMC13032510 chip

Part Number: AMC1303E2510
Other Parts Discussed in Thread: AMC1303

Hi,

I'm using Filters1, 2 and 3 of the TMS320F28075 SDFM1 to read the Manchester Encoded output from 3 separate AMC1303E2510 chips. You can get all the setup details in the original question link above.

The problem I have is that the output from the SDFM module is wrong sometimes. In the oscilloscope shot below:

- CH1 (yellow) is a +/-10V input (via resistor divider) to the AMC1303E2510 chip for Filter 1. +/-10V produces +/-250mV at the AMC1303E2510 input.

- CH2 (pink) is the DAC output for Filter 1 (note that it is passed through an external op-amp buffer to increase it's amplitude).

At first I thought it was a problem with the MCU SDFM, however now I'm wondering if I am exceeding the valid input range of the AMC1303E2510 chip. In the oscilloscope shot below the input is +/-10V which produces +/-250mV at the AMC1303E2510 input. From the datasheet the AMC1303E2510 the full input range is +/-320mV, however linear operation is only guaranteed for +/-250mV. So perhaps the input is just exceeding +/-250mV when one of these incorrect readings occurs.

When I reduced the input to +/-9V (+/-225mV at the AMC1303E2510 input) the behaviour is good (i.e. no spurious/incorrect results).

Can you provide more info on the expected behaviour when the AMC1303E2510 input is between 250mV and 320mV? Can the data be completely corrupted as in the shot below? 

Many thanks,

Fearghal

  • Hi Fearghal,

    Thanks for your post!

    Can you post a schematic?
    Any way we can see the bitstream output from the AMC1303 at the time of the spurious output?
    If it's an issue with the AMC1303 input range I would expect to see this behavior at every peak of the input signal.

    If you have not reviewed the fail-safe output modes of the AMC1303 please take a look at section 8.4 Device Functional Modes in the datasheet. To verify that these modes are not causing the issue, try probing AVDD and the input signal (at the pin) at the time of the spurious output. Due to resistor tolerances, it could be that your resistor divider is producing an unexpected voltage and causing a common mode issue.