AnsweredAssumed Answered

AD8280 - Hysteresis on OV, UV and OT Trip Points

Question asked by LorenzoB on Aug 26, 2014
Latest reply on Aug 28, 2014 by prb

Hello,

 

I'm using the AD8280 in a Lithium Polymer Battery Pack Monitoring System as safety device (together with the AD7280A device used as main monitoring device).

While testing the system functionality I found that the trip points of Overvoltage, Undervoltage and Overtemperature have no Hysteresys, in spite of what stated by the datasheet (in the TRIP POINT ERRORS section of Table 1).

Or maybe my understanding of the Hysteresis concept applied to trip points is not correct.

 

To give an example,  the behavior I expected was the following:

 

1) One (or more) of the monitored cell voltage inputs reaches the Overvoltage trip point (that is the voltage at the OV input);

2) The AVOUTOV output became active;

3) The  AVOUTOV stays active until all the monitored voltage inputs drop below the trip point MINUS the stated Hysteresis (at least 40 mV)

 

The behavior I get is instead:

 

1) One (or more) of the monitored cell voltage inputs reaches the Overvoltage trip point (that is the voltage at the OV input);

2) The AVOUTOV output is activated and deactivated continuously, following the slight variations of input voltages;

3) Further increasing of input voltages leads to a more and more stable activation of the AVOUTOV output;

4) When one (or more) of the monitored cell voltage is more than 60mV greater than the Trip Point the AVOUTOV becomes steady active;

5) Decreasing of cell voltages leads again to AVOUTOV blinking;

6) Dropping all the monitored cell voltages back below the overvoltage trip point leads to a stable deactivation of the AVOUTOV output;


Undervoltage and overtemperature alarms show the same behavior.

I've checked out the OV, UV and OT voltage levels and they are totally stable as they are generated by means of resistive voltage dividers starting from the REF voltage.


Am I missing something or is it a misbehavior?


Thank You and regards,


Lorenzo.



Outcomes