I am looking to work with the following DC979A (eval board for LTC2442)
I have a question regarding powering the 5V, LT1236 reference of the DC979A from the DC590 USB serial controller.
Page 3 of the DC979A demo manual mentions the following
"VCC: This is the supply for the ADC. Do not draw any power from this point. External power may be applied to this point after disabling the switching supply on the DC590. If the DC590 serial controller is being used, the voltage must be regulated 5V only, as the isolation circuitry will also be powered from this supply. See the DC590 Quick Start guide for details."
1. I looked at the DC590B schematic. There is no switching supply on the DC590. Its seems like they are all linear regulators. If I use the DC590, the are only options are 2.7V, 3.3V and 5V for the VCCA which powers the VCC rail of the DC979A. Here in lies my confusion. If the max supply when powered from DC590B is 5V and this rail powers the LT1236, how can the LT1236 provide 5V for the reference. This means the LT1236 should have zero dropout. Am I missing something in my understanding here?
2. Also since the LTC2442 can only have a VCC range between 4.5V to 5.5V, I am confused as to how I use the DC979A being powered from the DC590B? Is the DC590B only for communication and the supplies all have to be external?