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Power Dissipation

Paul Huter
Intellectual 390 points

Other Parts Discussed in Thread: AM3715, AM3517

Does anyone know how much heat is dissipated by the AM3715-1000? I know it's a function of power, so a range will be sufficient. I'm thinking about stacking PCBs, and wondering how much space needs to be between them. Thanks.

  • 0
    TI__Mastermind 41665 points

    Paul Huter said:
    Does anyone know how much heat is dissipated by the AM3715-1000? I know it's a function of power, so a range will be sufficient.

    Have you seen the AM/DM37x power consumption article on the wiki here? That article includes a spreadsheet you can use to estimate the power consumption of these devices under specific scenarios, which should give you an idea of what you will need to be able to dissipate, for an AM3715 at 1GHz you are looking at about 1 watt that needs to dissipate as heat. Keep in mind this is only the power for the processor itself, the surrounding circuitry (DDR, power supply, etc.) will also be dissipating power as heat, so your thermal considerations tend to be very application specific. How closely you can stack your boards would depend a lot on your chassis ventilation characteristics, and how much air flow you can get between and around the boards.

  • 0 in reply to Bernie Thompson TI
    Intellectual 390 points

    I've seen and used the spreadsheet, which was helpful. So if my processor is consuming 88mW of power, that's how much needs to be dissipated as heat. I figured more of it would go into actually doing stuff, not generating heat. My whole application needs to consume less than 2W of power, but it's going to be in a tight configuration. Thanks.

     

    Paul

  • 0 in reply to Paul Huter
    TI__Mastermind 41665 points

    Paul Huter said:
    So if my processor is consuming 88mW of power, that's how much needs to be dissipated as heat. I figured more of it would go into actually doing stuff, not generating heat.

    That is about right, the energy going into a IC like this has no where else to go but to exit as heat, some small portion may be going off in forms of radiation (such as EMI) but the vast majority will go directly into heat. The only way you would get appreciable energy coming out of your board in a form other than heat would be LEDs emitting light or antennas emitting electromagnetic waves, at least that I can think of off hand.

  • 0 in reply to Bernie Thompson TI
    Prodigy 20 points

    Will I be able to operate AM3703-1000 at extended temperature range if i operate the processor at 800MHz?

  • 0 in reply to MaheshwariDhayanandan
    TI__Mastermind 41665 points

    MaheshwariDhayanandan said:
    Will I be able to operate AM3703-1000 at extended temperature range if i operate the processor at 800MHz?

    The device is only supported for extended temperature operation if it is marked as an extended temperature part (with the A after the package suffix); operating a AM3703-1000 at 800MHz does not guarantee it will operate throughout the extended temperature range.

    In other words, devices that are not marked as extended temperature are not tested at the temperature extremes and may fail regardless of their operating frequency.

  • 0 in reply to Bernie Thompson TI
    Intellectual 390 points

    Bernie:

     

    Do you know how much heat will be generated by the AM3715A operating at 800MHz using about 1W of power? I know the heat generated will be a function of the thermal characteristics of the chip (Q=mCT). Basically I need to know if the heat generated by the chip will be enough to keep my application within the operational temperature bounds (I know the chip will operate at -40C, but I'm not sure about the rest of my application...may need 0C or higher) without any external heat source. Also, need to know if the heat generated by the chip will cause an overheating situation of my application without any external heat dissipation. My application is aerospace and there is a pretty extreme temperature extreme that it will be exposed to. Thanks.

     

    Paul

  • 0 in reply to Paul Huter
    TI__Mastermind 41665 points

    Before responding here, I would like to say that I am not an expert in thermodynamics, so I apologize if any of this is not perfectly correct or does not make sense.

    Paul Huter said:
    Do you know how much heat will be generated by the AM3715A operating at 800MHz using about 1W of power?

    I am not sure I understand your question, a Watt is a unit of heat generation/transfer, if your system is consuming 1W of electrical energy and we assume that the majority of that becomes heat than the device will be giving off 1W of heat (i.e. 1 joule per second of electrical energy becomes thermal energy). How much temperature increase over ambient that you get on the device and around the device depends on the thermal characteristics (namely thermal resistance) of both the device itself (which TI does define) as well as your board and environmental conditions (such as air flow). This being said, the thermal system outside of the well defined package of the processor can be complex to model precisely, so for exact values one would generally measure the system directly.

    The most I can really offer are the thermal characteristics of the device itself, section 6.1 of the AM3517 datasheet goes into the thermal specifications of the package. Taking those figures you can calculate approximately (not accurately) what the effective operating temperature will be immediately around the device, there is a good discussion on the thermal considerations for BGA devices like this here. Keep in mind that the thermal figures provided are very generic, and based on a JEDEC simulation, their primary purpose is not to determine how hot your system will get, but rather to compare the thermal properties of various devices and packages, it is unlikely that your system will match the JEDEC test board that these figures represent, you may have vastly different thermal characteristics.

    Paul Huter said:
    Basically I need to know if the heat generated by the chip will be enough to keep my application within the operational temperature bounds (I know the chip will operate at -40C, but I'm not sure about the rest of my application...may need 0C or higher) without any external heat source.

    Though the processor will warm the board up, it seems risky to rely on the heat from the processor to keep other devices in your system within spec. Particularly due to the edge conditions like powering up in the cold when the heat from the processor may not have the time to warm the rest of the components, which might be important for the processor's operation. Also keep in mind that different individual AM3517 devices will vary in their power consumption, and that varying loading on the processor will also cause the power consumption to vary, which would give you variance in how much heat is generated, though the device generates heat it is not meant to be a heater. This being said, it is a good idea to keep the heat from the processor in mind for your thermal situation, and accounting for it keeping your system in a good thermal state is important, so you could leverage the device as a heater as long as you are sure you have covered all the possible ramifications of doing so.

     

  • 0 in reply to Bernie Thompson TI
    Intellectual 390 points

    Thanks, Bernie. I'll begin looking into a secondary thermal control system.

     

    Paul

  • 0 in reply to Paul Huter
    Intellectual 310 points

    Logic PD released their new Wattson software for the AM3517 EVM today which will help you see actual power consumption across all power rails on the CPU and SOM design.  There is an adapter required to connect to the PC available from this website: http://createnewstuff.webs.com/breakoutboardwattson.htm

    The Logic PD software is available from here: http://www.logicpd.com/wattson

    -A