Nithin, There shouldn't be any other configuration to set to detect the open circuit condition. I ran the test for this using the DAC8775EVM, and I only had a few configuration settings: Enable the buck-boost (both pos and neg) Enable the reference Set the power-off condition to remove the 30kΩ resistor Set the output mode to 0-20mA Enable the DAC output The DAC data starts at 0x0000, and I increment it one bit at a time. With an open circuit, after a couple of increments, the DAC output voltage increases as does the VPOS_IN_x. I see that both the supply and the output rail at a code of roughly 0x000C, which is about 3.6uA. Both end up near 21V In your case, the output gets to about 13mA and stops giving more current to the 1kΩ load. That means there is excess current being shunted away by some other path. In your setup at full scale output, the VPOS_IN_x is set to 15V, and the output voltage is still 3V belov the supply. That means the DAC buffer output is still able to drive the full output current. My guess is that you have some sort of 12V to 13V TVS somewhere on the output that's not shown on the schematic and that is what is shunting away extra current. Can you give the full schematic? Can you show a picture of the board? Joseph Wu
↧