7.3.3 Error Flags

The XTR305 is designed for testability of its proper function and allows observation of the conditions at the load connection without disrupting service.

If the output signal is not in accordance to the transfer function, an error flag is activated (limited by the dynamic response capabilities). These error flags are in addition to the monitor outputs, I_MON and IA_OUT, which allow the momentary output current (in voltage mode) or output voltage (in current mode) to be read back.

This combination of error flag and monitor signal allows easy observation of the XTR305 for function and working condition, providing the basis for not only remote control, but also for remote diagnosis.

All error flags of the XTR305 have open collector outputs with a weak pullup of approximately 1 μA to an internal 5 V. External pullup resistors to the logic voltage are required when driving 3-V or 5-V logic.

The output sink current should not exceed 5 mA. This is just enough to directly drive optical-couplers, but a current-limiting resistor is required.

There are three error flags:

1. IA Common-Mode Over Range (EF_CM): goes low as soon as the inputs of the IA reach the limits of the linear operation for the input voltage. This flag shows noise from the saturated current mirrors which can be filtered with a capacitor to GND.
2. Load Error (EF_LD): indicates fault conditions driving voltage or current into the load. In voltage output mode it monitors the voltage limits of the output swing and the current limit condition caused from short or low load resistance. In current output mode it indicates a saturation into the supply rails from a high load resistance or open load.
3. Overtemperature Flag (EF_OT): a digital output that goes low if the chip temperature reaches a temperature of 140°C and resets as soon as it cools down to 125°C. It does not automatically shut down the output; it allows the user system to take action on the situation. If desired, this output can be connected to output disable (OD) which disables the output and therefore removes the source of power. This connection acts like an automatic shut down, but requires a 2.2-kΩ external pullup resistor to safely override the internal current sources. The IA channel is not affected, which allows continuous observation of the voltage at the output.