Hi I have never fully traced out the DAC on the TBolt. I have gone far enough to see that it's a "sum of several" sort of circuit. My guess is that they sum and then measure the result with a good ADC. If so, the DAC would likely function fine as long as the ADC was not impacted by the loss of power.
Bob On May 12, 2012, at 9:37 AM, Mark Sims wrote: > > It sounds like the -12V supply is used to generate the DAC low voltage > reference. If it is floating, the DAC output will be unstable. If it is at > a solid voltage, the DAC output will be stable. The standard EFC range for > a tbolt is -5V to +5V, but since almost all Tbolts are running the osc with > a positive EFC voltage, it will work with the -12V line grounded. > > I suspect that although it may appear to be working, the DAC output may not > be as stable as with a negative rail available since whatever is generating > the negative DAC reference voltage will be well below its dropout voltage. > > One thing to try is to do an oscillator autotune with the -12V line grounded > and at -12V. Your DAC gain will probably double (or half) since the DAC > output range is now 0V..5V instead of -5V to 5V. The tbolt firmware knows > what the expected dac voltages rails are (readable via an undocumented TSIP > message) are and also has settings for what range to allow the EFC to swing. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
