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Digital control board documentation (view source)
Revision as of 20:41, 15 June 2009
, 20:41, 15 June 2009→Channel Mapping: added ADC
| DACHEALTH... anything else??
| DACHEALTH... anything else??
|}
|}
==ADC==
The board includes an Analog Devices AD7928 analog to digital converter. The ADC is located just to the right and slightly below the FPGA. It is labelled U4.
===Power Details===
The ADC is powered by the +5V power island, regulated by an off-board power supply, and decoupled near the ADC. It also requires a precise (±1%) 2.5V reference to which it compares voltages when converting from analog to digital. Since the +5V power source is not used for comparison, it is flexible and may vary by ±0.25V without affecting ADC precision.
===Setting the Measuring Range===
The measuring range is set programmatically by the FPGA over the SPI bus. The way the ADC is connected on the digital board requires that its measuring range be set to 5V, so the RANGE bit should be set to 1 by the FPGA (see Analog Devices documentation).
===Channel Descriptions===
This table shows what signals are monitored by the ADC.
{| cellpadding=3 border=1 |
| '''ADC Channel #'''
| '''ADC Pin #'''
| '''Net Name'''
| '''Description'''
|-
| VIN0
| 16
| AD7928/VHEALTH
| This net helps to monitor to overall health of power on the board, but is specifically intended to monitor -5V. It's voltage is the output of a resistor divider between the +5 and -5V power supplies, with resistor values of 33.2K, and 100K. Assuming +5V and -5V are both correct, the output of the divider will be +2.51V. A reading of other than 2.51V indicates a problem with one of the power supplies. Problems with the +5V power supply can be ruled out by reading VIN3. Based on the reading from VIN3, the voltage of the -5V supply can be calculated.
|-
| VIN1
| AD5535/CATHODE
| This is the thermal diode output from the DAC. Should read 4.35V (typical) at 25°C. Drops 2.20mV/°C.
|-
| VIN2
| +3.3V
| This is the +3.3V power plane. A reading of other than +3.3V indicates a problem with VR1.
|-
| VIN3
| +5V
| This is the +5V power island. A reading of other than +5V indicates a problem with the +5V power supply.
|-
| VIN4
| ADC_EXT1
| The trace routes to the backplane via Eurocard pin A7. It is intended to measure the output of thermistor on the amplifier board.
|-
| VIN5