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DAC8760: Behaviour of current output at SPI error

Gerhard Klein
Prodigy 10 points
Part Number: DAC8760
Other Parts Discussed in Thread: DAC8771

Hi,

on a PCB with current outputs 4....20mA we use the Ti device DAC8760.
Within the scope of an FMEDA, the question arose how the current output of the device behaves if
the SPI communication to the master is interrupted or disturbed.

The SPI bus can be monitored via the 8.3.10 watchdog timer and 8.3.11 frame error checking.
But does a detected SPI bus fault also have access to the output current?

If the current output of the DAC8760 is then permanently at the last value or if it goes to 0mA or into the high-Z state?

0mA would be the safe state, which would be important for us.

Thank all

  • 0
    TI__Expert 5820 points
    Hi Gerhard,

    Welcome to the E2E forums!

    DAC8760 does not have the functionality internally to set the DAC output to zero-scale in the case of watchdog or frame error faults. So when a fault occurs the alarm pin will go low and the output current will remain at the last value. The alternative would be to use external circuitry and alarm pin to toggle the CLR pin which could set the output to zero-scale in case of fault.

    You can also look at DAC8771 which is single channel Vout/Iout DAC with the option for integrated DC/DC. This device has internal 'safe actions on alarm conditions' which function as you describe above.

    Thanks,
    Garrett