Behind the Kelvin alarm of AD5560

Dear Sir or Madam

A  phenomenon  is quite tricky about AD5560.

A   10V  voltage had been applied to  pin F7 (SENSE) . while  the force output was only  3.6V ( setting 5V ). Generally ,the FORCE should be the same with SENSE . isn't it?

So , what happened after the Kelvin alarm asserted ?  and  what  actions  usually be done behind the  Kelvin Alarm , other than setting up the flag ? Protective actions?

  • 0
    •  Analog Employees 
    on Feb 9, 2021 2:43 AM

    Hi ,

    Yes, you are correct. In a normal operation of the AD5560, the FORCE and SENSE pin are tied together to create a feedback loop going to the force driver. This means that the voltage at FORCE pin should be equal to the SENSE pin. Otherwise, OSD will be flagged with the condition that FORCE and SENSE pin voltage difference reaches the OSD DAC value. With regards to your query on seeing only 3.6V instead of 5V on the FORCE pin, this occurrence could be caused by the Open Sense Detect circuitry being triggered. If this happens, the OSD block will perform the three functions stated at the datasheet below (Rev. E page 29 of 66).

    From what I understand, you are forcing 5V while applying a 10V to the SENSE pin. With this setting, the voltage difference between your FORCE and SENSE pin is already at 5V. This could have triggered the OSD circuitry. May I know your OSD DAC setting? Additionally, one of the functions is that the OSD will limit the FORCE pin to a certain value stated above so that it won’t go to your supply rail. This could be the reason why you are seeing a 3.6V drop on the FORCE pin. The OSD block should also clamp the SENSE line but since you have a constant 10V on the SENSE pin, even if you clear the alarm, the OSD will be flagged continuously.

    Lastly, may I know your application on the AD5560? This would help us give you a better support. Also, if you want to continue this conversation offline, you may email me @ danilojames.marciano@analog.com. Thanks!

     

    Best Regards,

    DJ