AMC6821 THERM and OVR Control

Howdy Joseph,

The structure of the THERM pin with associated temperature alarms are displayed in Figure 14 and 22 of the DS. As an open-drain output, the THERM pin is the indicator of temperature over the THERM limit.  When the remote temperature exceeds the Remote-THERM-Limit, or when the local temperature is greater than the Local-THERM-Limit, the THERM pin goes low and remains low until the measured temperature falls 5C below the exceeded THERM limit.  There is no way to separate these two alarm conditions as both are essentially used as inputs to an internal OR gating structure in asserting the THERM pin. 

The same goes for OVR (remote and local functionality is not separated when reporting).  If OVR is enabled, it takes into account multiple over-critical temperature limits, such as the remote and local critical temperature.  When these temperatures are over the critical limit, the corresponding over-critical limit flag of the Status Register (RTC for the remote channel and LTC for the local channel) is set to '1' and OVR is asserted low. Additionally, the OVR pin remains low until the measured temperature falls 5C below the exceeded critical limit. This information is explained in page 30 of the DS.

Have you read the status of the 'RTF' bit, this bit would also assert OVR if the external temp sensor failure condition is detected ( either short-circuit or open-circuit)?

 One thing that may work, if the external sensor still continues not to work correctly, is to replace the sensor with a resistor of 1k or less between the IN+/IN- inputs.  The resistor value will get translated into a fixed temp, and as long as the fixed temp is within the temperature limits, then only the LT limit should be reported to OVR and THERM.

Is it possible to share the section of the schematic that connects to the external temp sensor?  I can send you my email if you wish to send the item over email rather than e2e.

Best Regards,

Matt

Howdy Joseph,

Has this issue been resolved?  If you have any more questions about the device please let me know.

Best Regards,

Matt

Matt,

Thanks for checking in. No. the Issue is still outstanding. Though I am onto a solution that may work. Testing it now. If this does not work. I may need to have a direction conversation. That might be the easiest way to resolve it quickly. I will post another reply and let you know.

Thanks!!