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PGA308: Power-up requirements especially when NOW register is '1'

Frank Rothoff
Expert 6130 points
Part Number: PGA308

Related to thread: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1091351/pga308-power-on-response-time-for-pga308?tisearch=e2e-sitesearch&keymatch=pga308 

We initially struggled with the the goal of less than 2.5 ms from power-on to output stable but which NOW register set to ‘1’ this works quite well.

 

But in the mean time we faced some other difficulty. In our application we build in a range check to identify sensor faults. This is observing the output of the PGA308 to be in in the valid range of 10 – 90%. Since this is implemented we occasionally observe sensor faults. The sensor is activated once per second. When having test runs over a day it can occur that the output signal is not activated at all for 10 to 20 times and we are not quite sure what is happening.

 

When looking at the datasheet it seems on power-up the PGA308 is generating a POR followed by loading offset an gain information from the calibration data stored in the OTP memory bank. In case the checksum of this is not correct the output will not be enabled. We are assuming that we face this behavior occasionally in our system.

 

So the question would be if this is a known issue and if there are any suggestions to avoid this. For instance are there any requirements for a valid POR in the voltage slope during power-up?

 

Your help would be highly appreciated.

  • 0
    TI__Expert 8565 points

    Hi Frank,

    Is your device configured in 3-wire mode or 4-wire? Can you provide a schematic?

    Can you also provide your register configuration for CFG2?

    It is recommended to disable the one-wire interface when operating in standalone mode to prevent noise from being interpreted as valid communication on the one-wire. If you are operating in 3-wire mode with the NOW bit high, your CFG2 register (D15:D12) should be set up in configuration 2 from table 5-1. If your CFG2 configuration is different, your device may be sensitive to noise coupling into the one-wire which could be putting your device into an unknown state.

    The power-on threshold for the PGA308 is between 1.5V and 2.5V. It may be possible that voltage spikes/dips in the supply voltage ramp within this threshold range could interrupt the POR, but I am not aware of this being an issue in the past. Can you provide a scope capture of your voltage ramp?

    Thanks,

    Zach