UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

cancel
Showing results for 
Search instead for 
Did you mean: 
Adventurer
Adventurer
5,758 Views
Registered: ‎04-20-2009

XADC temperature alarms, hysteresis?

Jump to solution

Hi all!

We are starting to use the XADC in our Zynq (XC7Z020) and the SW guys want to know if there is some hysteresis in the temperature alarm interrupts? There are two bits in particular that seems useful, bit 0 (OT) of cource and bit 8 (OT Deactive). If the temperature fluctuates around the limit (125 °C) these could easily generate bursts of interrups, so I assume there must be some sort of hysteresis, but I have not been able to find any such information in either the data sheet (DS187), the XADC User guide (UG480) or the LogiCORE IP AXI XADC product guide (PG019).

 

This question would apply to the supply sensor alarms as well.

 

Anyone with a clue?

/Lars

0 Kudos
1 Solution

Accepted Solutions
Highlighted
Adventurer
Adventurer
7,616 Views
Registered: ‎04-20-2009

Re: XADC temperature alarms, hysteresis?

Jump to solution

Thank you all for the input!

 

I gather that there is no hysteresis, but that if I enable averaging the low-pass effect of that will take care of any flipping around the threshold. That should be fine, considering that thermal effect should be quite slow in comparison.

 

/Lars

0 Kudos
7 Replies
Scholar austin
Scholar
5,741 Views
Registered: ‎02-27-2008

Re: XADC temperature alarms, hysteresis?

Jump to solution

l,

 

http://www.xilinx.com/products/intellectual-property/System_Monitor_Wizard.htm

 

Yes, the system monitor has various settings.  In the past (V5, V6) the users guides detailed the settings.  Now there is the above wizard to assist you.

 

and

 

http://www.xilinx.com/products/technology/analog-mixed-signal/index.htm

 

Austin Lesea
Principal Engineer
Xilinx San Jose
0 Kudos
Xilinx Employee
Xilinx Employee
5,735 Views
Registered: ‎10-11-2007

Re: XADC temperature alarms, hysteresis?

Jump to solution

Use the average function. Take perhaps 256 samples (or some other average) before ringing the alarm.

0 Kudos
Scholar markcurry
Scholar
5,727 Views
Registered: ‎09-16-2009

Re: XADC temperature alarms, hysteresis?

Jump to solution

 

Be careful, and analyze your application.  A generic "average 256 samples" may sound like an appropriate filter, but this adds 128 samples of latency to your measurements.  Is this ok?

 

This kind of falls under a similar quote from Knuth:

"Random numbers should not be generated with a method chosen at random"'.

 

A similar quote should be crafted for digital filters.

 

Regards,

 

Mark

 

 

0 Kudos
Xilinx Employee
Xilinx Employee
5,723 Views
Registered: ‎10-11-2007

Re: XADC temperature alarms, hysteresis?

Jump to solution

Averaging is perfectly fine for this. That's why it's there. The key is that the part will not instantly "heat up" if current goes up. For sake of argument, if you take the current from 0 to 50A in an instant then that does not mean Tj will instantly go to 125C (or whatever). Depending on environment (air, heat sink, etc.) and package you may experience an increase in Tj of about 8 - 10C per sec. So the sampling is plenty fast for that. The idea is to filter out the noise factor. Even if latency was an issue, which it isn't, you could set your alarm right below the threshold.

0 Kudos
Highlighted
Adventurer
Adventurer
7,617 Views
Registered: ‎04-20-2009

Re: XADC temperature alarms, hysteresis?

Jump to solution

Thank you all for the input!

 

I gather that there is no hysteresis, but that if I enable averaging the low-pass effect of that will take care of any flipping around the threshold. That should be fine, considering that thermal effect should be quite slow in comparison.

 

/Lars

0 Kudos
Scholar austin
Scholar
5,693 Views
Registered: ‎02-27-2008

Re: XADC temperature alarms, hysteresis?

Jump to solution

l,

 

You can place your own hysterisis in software.  If the threshold is reached in 256 samples (or 2048, etc.), set a flag to overtemp=true.  If overtemp=true is set, then subsequent interrupts check the value.  If the value falls below a windowed value, reset the flag, else do nothing (return).

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
0 Kudos
Xilinx Employee
Xilinx Employee
5,669 Views
Registered: ‎03-21-2008

Re: XADC temperature alarms, hysteresis?

Jump to solution

Hi Lars,

 

There actually is 'hysteresis' on the OT - the defaul OT  power-down temp is 125C, and the default OT power-up temp is 70C - so OT is set when temperature is > 125C, and it stays set until the temperature falls back below 70C.

 

Both thresholds are programmable.

 

Hope this helps,

John

 

0 Kudos