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William Murray

Power-On Reset: The Analog, the Digital & Some of What Can Go Wrong

William Murray
RituGupta
RituGupta
9/18/2018 2:03:33 AM
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Newbie
Re: Voltage supervisor ICs provide a level of sophistication needed to prevent uncertainty.
Don't you wish that there's a power reset button in every day life too? I mean, I would  be very happy if every night it would be as easy as powering down and rebooting to get some of that stress off my shoulders. Sadly, I think that this analogy is only hypothetical - there's way too many things to handle to allow a power down to get in the way...

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BillWM
BillWM
7/25/2013 4:03:25 PM
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Blogger
Re: Voltage supervisor ICs provide a level of sophistication needed to prevent uncertainty.
Sureena, Your post is most appreaciated.   Over Voltage Reset, Crowbar, or Clamping is one area I see many embedded designs go astray in the area of.  Most do not realize that timing on occaision can speed up to much when the CPU, FPGA, Memory or other digital component has a Over Volts Condition.   This can result in logic race conditions, that end in improper operation.

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Sureena Gupta
Sureena Gupta
7/25/2013 12:50:43 PM
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Blogger
Voltage supervisor ICs provide a level of sophistication needed to prevent uncertainty.
William, I would agree with your thoughts.  System requirements for today's processors, MCUs and FPGA are very complex. Voltage supervisor ICs provide a level of sophistication needed to prevent uncertainty.

Some supply voltage supervisor ICs offer features like overvoltage (OV) on top of traditional under voltage (UV) monitoring with tight accuracy to protect the design from spikes and transients; watchdog timer / window watchdog timer for system handshake between the processor (or FPGA) and power solution; adjustable reset delay to ensure proper system power-up; and power fail input to help with proper system power-down. 

I wanted to share a link to an application note from Texas Instrumetns that help explain Window Watchdog Timer functionality and how they can be implemented to add a level of sophistication to your design beyond traditional Watchdog Timer.  In short is helps catch a system error if the processor is stuck n an infinite loop.  http://www.ti.com/lit/an/slva365/slva365.pdf

Also an application note on How to add additional hysteresis to Voltage supervisor.  http://www.ti.com/lit/an/slva360/slva360.pdf

I hope it is helpful.

 

Sureena Gupta

Engineer at Texas Instruments

 

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JeffL_2
JeffL_2
7/25/2013 10:14:02 AM
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Newbie
Write data flash on BOR
I'm having trouble getting a write of user parameters back to data flash on brownout reset on a Microchip part (16F series) but I don't know whether it's an analog or digital problem, I just know that if I put a breakpoint in the brownout portion of the ISR I can never see it execute regardless of brownout voltage setting (and I can access all my other ISR routines without difficulty so it doesn't appear to be a configuration issue). I don't see a lot of help on the data sheet in figuring the size of the holdup cap (and in application there isn't a separate pin for this so you have to calculate total system current drain and your main supply output cap to figure it out) versus the number of bytes to be written (flash write current and worst case timing). It would seem like writing back to flash on the power down cycle to minimize total flash write cycles would be an obvious application situation but they don't appear to give the necessary data or an application note to figure it out so I'm stuck.

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Vishal Prajapati
Vishal Prajapati
7/25/2013 6:56:39 AM
User Rank
Master
Re: Unusual POR apps
My company is running a Training Institute in which students learns embedded systems. We have covered the basic microcontroller circuits in the practical session. Students make ATmega8 demo boards in their practial. In this circuit we still suggest them to use the old RC Power On Reset circuit along with IC. For the perticular application, this is sufficient for reset as there is only one IC to be sync. There is no external flash or external RAM and it works fine.

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Netcrawl
Netcrawl
7/24/2013 9:11:49 PM
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Master
Re: Unusual POR apps
I believe WDT in all new devices has now the ability to generate interrupst instead of resetting the system and since WDT runs from or have its own clock it can used to wake up the devices from sleep modes-this makes WDT an ideal wake up timer. WDT also can easily combined with operation as a system reset source, its main job is automatic handling and recovery. 

 

 

 

 

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DaeJ
DaeJ
7/24/2013 8:30:47 PM
User Rank
Master
Re: Unusual POR apps
When implementing S/W for safe critical system, system goes to limp-hone mode or safe mode to avoid catastrophic case. Also, Limp-hone mode is thoroughly tested in the bench. Power on Reset or Watch Dog timer is used commonly in SW, even though there is lack of information related to POR/WDT application.  

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BillWM
BillWM
7/24/2013 5:39:09 PM
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Blogger
Re: Unusual POR apps
One of the more unusual applications I have seen is to used the POR/WDT to enable a pneumatic back up for an electromechanical / chemical process.  (If the software in anyway hung and failed to toggle lo-hi-lo at the right duty cycle and rate the WDT or the voltage browned out the pneumatic back-up came into play.)

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Dirceu
Dirceu
7/24/2013 5:25:23 PM
User Rank
Artist
Unusual POR apps
   There are several non standard applications for integrated POR devices. For example, on a boost converter, connecting the POR output to the gate of a series mosfet its possible shutdown the converter and removing  the undesirable path for dc current flow (input-to-load).

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