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Digital control board debugging notes (view source)
Revision as of 15:38, 30 September 2010
, 15:38, 30 September 2010no edit summary
This page contains a list of all currently known problems with the digital control board.
This page contains a list of all currently known problems with the digital control board.
== Resistor on DAC temperature measurement diode too high ==
=== Description ===
When the readout is programmed using the DAC manual's coefficients and offset, the temperature value ends up tens of degrees off.
=== Cause/Solution ===
The board was designed with R1=270kΩ to sink the current from the DAC's internal temperature-measuring diode to ground. The manual specifies the expected diode drop at 25degC will be 0.65V at a current of 100uA. Given the sensitivity of this device (with a coefficient of 2.2mV/degC) it is seems best to match their measurement conditions and adjust the resistor so that 0.65V drop from the biasing 5V results in 100uA through the resistor. So, ''R1 should be set to 43.5kΩ''.
Three parallel resistors have been soldered into place on the prototype board providing a nominal R1 of 43.6kΩ. The readout values are now reasonable.
== No Power on +1.2V Power Island ==
== No Power on +1.2V Power Island ==