Problem with LMP90100 in single scan mode.

Hello,

After the single scan the LMP90100 enters stand-by mode.  You can put it back into active mode by using the PWRCN register.  You may need to also issue a restart command to get a new conversion.

Mike

Hi Mike,

Thanks for your advice - it worked well.  The conversion started immediately after entering active mode, and I didn't have to issue the RESTART command.  However, this does present a new problem for me.  In stand-by mode IB1&2 are off.  When it enters active mode it turns IB1&2 on, but the rise time is relatively slow.  Meanwhile, the conversion completes and IB1&2 is turned off again.

Is there a way of using IB1&2 in single scan mode?

Cheers,

David

Hi David,

Because of the relatively slow rise time of IB1 and IB2, you are correct, it may not be possible to use in the single scan mode.  How about putting it in the ScanMode2 (Multiple channel continuous scan), set FIRST_CH and LAST_CH to the same value so that it only scans the one channel, and then put in stand by mode.  When you want to make a measurement put the device in Active mode, wait enough time so that IB1 and IB2 are stable, read the conversion data, then put back in stand by mode.

Mike

Hi Mike,

Thanks - My aim is to synchronize each conversion to an external source.  I've taken your advice and run the ADC in ScanMode2.  I'm also keeping it in Active mode so IB1&2 are always energized.

The external source is running at 22 Hz and the ODR is set to 26.83125 Hz.  This means I'm sending the RESTART command for every conversion.

The sequence seems to work, since I get ADC_DOUT at the expected rate.  However, after 2 or 3 conversions the OFLO_FLAGS is set to 1 and remains there for subsequent conversions (ADC_DOUT got clamped).  The short circuit and rails flags are clear.

When running the ADC without sending the RESTART command (i.e just free running) I consistently get valid ADC_DOUT.

Is there a problem sending the RESTART command for every conversion?

Thanks for your help.

David.

Hi David,

There is one problem with using the RESTART command but it is not related to your problem.  After a RESTART conversion, the first sample is not valid.  The first sample should be discarded and any of the following samples can be used.  We are in the process of going through the paper work to put this statement into the datasheet. 

I am not sure why OFLO_FLAGS is being set to 1.  One thing to check with an oscilloscope is to make sure that nothing is happening to the input and it is being over driven during the time the command is issued and several cycles afterwards.  You could also lower the gain and see if it still happens.  Another thing to try is a faster ODR.  Maybe the 26.8 SPS is too close the 22Hz rate you are restarting it with.  Try 53 or 107 SPS to see it that helps.

Mike