Thanks for confirming my original observation! I think John raises some important points regarding power handling...some of which go well beyond the context of my original post. As he suggests a software solution is not an option ...unless you have some other platform to run the software on! For the application about which I originally posted, we are less concerned with power fail warnings, writing system state to nv memory, etc so the only real issue for us is that when power is available we want the Bone to run! Unfortunately, if there is a power disturbance that is enough to trigger the TPS65217C into shutdown you can have perfectly good power for a month and the system will never come back on. I worked around this by doing something like the following....
1. Find a watchdog chip that will run off the raw 5V supply available and connect the watchdog ICs input/tickler to some digital signal which tends to be available an an early stage in the boot process. The horizontal/vertical sync lines for an external LCD are available on the P8/P9 headers and usually start toggling pretty soon. You also need to make sure that the watchdog IC can be configured for a fairly long timeout period and that its reset output is also longish (seconds). 2. Wire the RESET output of the watchdog IC to a power switch so that if the watchdog times out it will cut power to the BBB. There are some fairly inexpensive USB host power switch ICs that can handle 2A so these are sometimes appropriate. Another option, if you are stepping down a raw input voltage to 5V for the bone and the dc/dc converter IC has a shutdown input, you can use the watchdog IC to turn off the dc/dc converter. In this case you have to generate an independent 5V supply just for the watchdog IC ...but a simple linear regulator can do that for low cost given the small current required. With this configuration if your TPS65217 gets stuck in the shutdown state the watchdog will eventually time out, cut 5V power, and (hopefully) kick the TPS back into normal operation. One thing to watch for however, is that with the TPS in shutdown mode, there is very little current drawn from the 5V supply so it will take some time for the 5V supply to decay to 0V even with the power source removed. This is why you need a watchdog IC with a long reset output pulse width. Maybe the TPS65217D will have some additional internal logic which makes all this unnecessary! Jim- On Fri, Apr 4, 2014 at 3:58 PM, John Syn <[email protected]> wrote: > > From: <[email protected]> > Reply-To: <[email protected]> > Date: Friday, April 4, 2014 at 2:17 AM > To: <[email protected]> > Subject: [beagleboard] Re: Possible TPS65217C/Beaglebone Black Issue > > Just to confirm this. > > From the TPS datasheet: > > OFF In OFF mode the PMIC is completely shut down with the exception of a > few circuits to monitor the AC, > USB, and push-button input. All power rails are turned off and the > registers are reset to their default > values. The I2C communication interface is turned off. This is the > lowest-power > mode of operation. To exit > OFF mode one of the following wake-up events has to occur: > * The push button input is pulled low. > * The USB supply is connected (positive edge). > * The AC adapter is connected (positive edge). > To enter OFF state, set the OFF bit in the STATUS register to '1' and > thenpull the PWR_EN > pin low. Please note that in normal operation OFF state can only be > entered from ACTIVE > state. Whenever a fault occurs during operation such as thermal shutdown,power > -good fail, > under voltage lockout, or PWR_EN pin timeout, all power rails are shut-down > and the device > goes to OFF state. The device will remain in OFF state until the fault > has been removed and > a new power-up event has occurred. > > When the brownout occurs, the unit goes in the "off" state and happily > stays there. Apperently, the voltages subject to brownout recovering does > not define as a "positive edge". > > If anyone has a pretty solution for this, I'd be interested. Obviously, I > can implement some kind of a watchdog that cuts the 5V altogether at some > point but is there a SW or other 'easy' solution? > > Unfortunately no, there is no software solution since the processor has no > power. You have to use a power supply monitor/controller with a state > machine to deal with this issue. This type of circuit is normally included > a small energy reserve (battery or supercaps) so that the OS has time to > close open files and prevent file system corruption during power fail > issues. Normally, any power supply interruptions initiates an orderly > shutdown of the OS. When the processor finally halts, power is removed from > the PMIC. When power is available, power is applied to the PMIC and > everything powers up normally. There are several corner cases that must be > considered, such as power interruption during power up phase or power > available during power down phase. A simple state machine takes care of > these corner cases. Overall, the circuitry includes several voltage > regulators (input buck convertor, output boost convertor), energy balance > (supercaps), battery charger (battery), and a state machine (8 bit micro or > my preference - GreenPAK). > > Regards, > John > > > > On Tuesday, December 17, 2013 1:35:13 PM UTC+1, James Littlefield wrote: >> >> As I said in the original post, the bench supply is capable of more than >> 3A...far more than the BBB takes. I've duplicated the problem on 2 >> difference bench supplies and with multiple BBBs (ie the problem is not >> specific to one particular BBB board). >> >> J- >> >> >> On Friday, December 13, 2013 10:49:07 AM UTC-5, Kees k wrote: >>> >>> Hey, did you try another power supply? Probably the PS has problem >>> supplying the current and drops voltage? Or there is a current limitation. >>> >>> I tried to reproduce by only connecting P9.5, P9.6 and P9.1 (GND) , but >>> could not. >>> >>> On Tuesday, November 19, 2013 2:00:55 AM UTC+1, James Littlefield wrote: >>>> >>>> New to BBB but experienced with embedded systems. >>>> >>>> I'm working on a project using the BBB. Supplying +5V (up to 3A) >>>> directly to the pins on P9 from a quality bench supply. I've found that >>>> briefly switching the +5V supply OFF and then back on can pretty reliably >>>> leave the BBB in an odd state characterized by... >>>> a) No LEDs on >>>> b) Very little current drawn from supply (10mA or less) >>>> c) +5 present on P9.5 and P9.6 >>>> d) 0.687V on P9.7 and P9.8 ( should be SYS_5V ). >>>> e) P9.9 = 3.57V >>>> f) P9.10 = 0V >>>> >>>> I've found that once the system is in this mode no amount of >>>> pressing/holding the momentary BBB pushbuttons will get the system working >>>> again. Removing input power, waiting 10 sec or so, then restoring power >>>> will get things working again. >>>> >>>> Has anyone else seen this? It seems sort of like an issue with >>>> the TPS65217C chip but I've not found any reported errata on that part. >>>> >>>> Thanks >>>> Jim >>>> >>>> >>>> -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > For more options, visit https://groups.google.com/d/optout. > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/p0CwsGzNYNw/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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