Can I lower flash power consumption by pre-flashing all values to high?












1












$begingroup$


I am designing an embedded system that will use either embedded flash memory or an SD card.
The system must survive without much power and the estimated 30mA draw of an SD card sounds too high for me.
My idea is to prepare the SD card before it is deployed by writing 1's to every single flash cell then formatting the card.
When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply.
Is this reasonable, or will I not notice any power savings?






flash sd nand flash-memories nand-flash







share|improve this question









$endgroup$












  • $begingroup$
    Keep in mind that the capacitances of those cells are measured in femtofarads.
    $endgroup$
    – Hearth
    3 hours ago










  • $begingroup$
    Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
    $endgroup$
    – Chris Stratton
    2 hours ago










  • $begingroup$
    IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
    $endgroup$
    – The Photon
    2 hours ago
















1












$begingroup$


I am designing an embedded system that will use either embedded flash memory or an SD card.
The system must survive without much power and the estimated 30mA draw of an SD card sounds too high for me.
My idea is to prepare the SD card before it is deployed by writing 1's to every single flash cell then formatting the card.
When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply.
Is this reasonable, or will I not notice any power savings?






flash sd nand flash-memories nand-flash







share|improve this question









$endgroup$












  • $begingroup$
    Keep in mind that the capacitances of those cells are measured in femtofarads.
    $endgroup$
    – Hearth
    3 hours ago










  • $begingroup$
    Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
    $endgroup$
    – Chris Stratton
    2 hours ago










  • $begingroup$
    IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
    $endgroup$
    – The Photon
    2 hours ago














1












1








1





$begingroup$


I am designing an embedded system that will use either embedded flash memory or an SD card.
The system must survive without much power and the estimated 30mA draw of an SD card sounds too high for me.
My idea is to prepare the SD card before it is deployed by writing 1's to every single flash cell then formatting the card.
When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply.
Is this reasonable, or will I not notice any power savings?






flash sd nand flash-memories nand-flash







share|improve this question









$endgroup$




I am designing an embedded system that will use either embedded flash memory or an SD card.
The system must survive without much power and the estimated 30mA draw of an SD card sounds too high for me.
My idea is to prepare the SD card before it is deployed by writing 1's to every single flash cell then formatting the card.
When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply.
Is this reasonable, or will I not notice any power savings?






flash sd nand flash-memories nand-flash




flash sd nand flash-memories nand-flash






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 3 hours ago









Sina RSina R

133




133












  • $begingroup$
    Keep in mind that the capacitances of those cells are measured in femtofarads.
    $endgroup$
    – Hearth
    3 hours ago










  • $begingroup$
    Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
    $endgroup$
    – Chris Stratton
    2 hours ago










  • $begingroup$
    IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
    $endgroup$
    – The Photon
    2 hours ago


















  • $begingroup$
    Keep in mind that the capacitances of those cells are measured in femtofarads.
    $endgroup$
    – Hearth
    3 hours ago










  • $begingroup$
    Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
    $endgroup$
    – Chris Stratton
    2 hours ago










  • $begingroup$
    IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
    $endgroup$
    – The Photon
    2 hours ago
















$begingroup$
Keep in mind that the capacitances of those cells are measured in femtofarads.
$endgroup$
– Hearth
3 hours ago




$begingroup$
Keep in mind that the capacitances of those cells are measured in femtofarads.
$endgroup$
– Hearth
3 hours ago












$begingroup$
Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
$endgroup$
– Chris Stratton
2 hours ago




$begingroup$
Flash can only be written in one direction, changing it in the other is erasure, which is only possible for an entire block. So you do not get to choose the ready-to-write state, it is whatever the technology requires, as represented by the interface circuitry.
$endgroup$
– Chris Stratton
2 hours ago












$begingroup$
IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
$endgroup$
– The Photon
2 hours ago




$begingroup$
IIRC, "all-high" is how flash are generally shipped from the factory. (I don't recall if this is specific to some particular type of flash)
$endgroup$
– The Photon
2 hours ago










2 Answers
2






active

oldest

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3












$begingroup$

The way to save battery when having a SD card in the system is to use a transisor or FET to switch off the DC power supply to the card connector when you are not needing to access the card for data reading or writing.



You want to keep the SD card GND intact with the MCU GND. So make sure to have the power switch turn the SD card VDD on and off.



Also to prevent excess leakage into the powered down SD card make sure to set all of the I/O pins that connect to the SD card interface to a low output level before turning off the card via the transistor or FET.



Skip any ideas that you dreamed up regarding to save power by changing the content of the flash memory to a certain default data.






share|improve this answer









$endgroup$





















    1












    $begingroup$


    When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply. Is this reasonable, or will I not notice any power savings?




    No, this is not reasonable. Flash memory is not DRAM. Its cells do not need to be recharged from a battery, nor can they be used as a power source.



    The vast majority of power draw by an SD card comes from the SD controller, and from the charge pumps on the flash memory die (which are only active when writing or erasing flash). Its power consumption will drop significantly when the card is idle.






    share|improve this answer









    $endgroup$













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      2 Answers
      2






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      2 Answers
      2






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      3












      $begingroup$

      The way to save battery when having a SD card in the system is to use a transisor or FET to switch off the DC power supply to the card connector when you are not needing to access the card for data reading or writing.



      You want to keep the SD card GND intact with the MCU GND. So make sure to have the power switch turn the SD card VDD on and off.



      Also to prevent excess leakage into the powered down SD card make sure to set all of the I/O pins that connect to the SD card interface to a low output level before turning off the card via the transistor or FET.



      Skip any ideas that you dreamed up regarding to save power by changing the content of the flash memory to a certain default data.






      share|improve this answer









      $endgroup$


















        3












        $begingroup$

        The way to save battery when having a SD card in the system is to use a transisor or FET to switch off the DC power supply to the card connector when you are not needing to access the card for data reading or writing.



        You want to keep the SD card GND intact with the MCU GND. So make sure to have the power switch turn the SD card VDD on and off.



        Also to prevent excess leakage into the powered down SD card make sure to set all of the I/O pins that connect to the SD card interface to a low output level before turning off the card via the transistor or FET.



        Skip any ideas that you dreamed up regarding to save power by changing the content of the flash memory to a certain default data.






        share|improve this answer









        $endgroup$
















          3












          3








          3





          $begingroup$

          The way to save battery when having a SD card in the system is to use a transisor or FET to switch off the DC power supply to the card connector when you are not needing to access the card for data reading or writing.



          You want to keep the SD card GND intact with the MCU GND. So make sure to have the power switch turn the SD card VDD on and off.



          Also to prevent excess leakage into the powered down SD card make sure to set all of the I/O pins that connect to the SD card interface to a low output level before turning off the card via the transistor or FET.



          Skip any ideas that you dreamed up regarding to save power by changing the content of the flash memory to a certain default data.






          share|improve this answer









          $endgroup$



          The way to save battery when having a SD card in the system is to use a transisor or FET to switch off the DC power supply to the card connector when you are not needing to access the card for data reading or writing.



          You want to keep the SD card GND intact with the MCU GND. So make sure to have the power switch turn the SD card VDD on and off.



          Also to prevent excess leakage into the powered down SD card make sure to set all of the I/O pins that connect to the SD card interface to a low output level before turning off the card via the transistor or FET.



          Skip any ideas that you dreamed up regarding to save power by changing the content of the flash memory to a certain default data.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 3 hours ago









          Michael KarasMichael Karas

          42.8k34599




          42.8k34599

























              1












              $begingroup$


              When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply. Is this reasonable, or will I not notice any power savings?




              No, this is not reasonable. Flash memory is not DRAM. Its cells do not need to be recharged from a battery, nor can they be used as a power source.



              The vast majority of power draw by an SD card comes from the SD controller, and from the charge pumps on the flash memory die (which are only active when writing or erasing flash). Its power consumption will drop significantly when the card is idle.






              share|improve this answer









              $endgroup$


















                1












                $begingroup$


                When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply. Is this reasonable, or will I not notice any power savings?




                No, this is not reasonable. Flash memory is not DRAM. Its cells do not need to be recharged from a battery, nor can they be used as a power source.



                The vast majority of power draw by an SD card comes from the SD controller, and from the charge pumps on the flash memory die (which are only active when writing or erasing flash). Its power consumption will drop significantly when the card is idle.






                share|improve this answer









                $endgroup$
















                  1












                  1








                  1





                  $begingroup$


                  When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply. Is this reasonable, or will I not notice any power savings?




                  No, this is not reasonable. Flash memory is not DRAM. Its cells do not need to be recharged from a battery, nor can they be used as a power source.



                  The vast majority of power draw by an SD card comes from the SD controller, and from the charge pumps on the flash memory die (which are only active when writing or erasing flash). Its power consumption will drop significantly when the card is idle.






                  share|improve this answer









                  $endgroup$




                  When being used in the application, the controller will never need to charge the flash cells with the battery, and will instead discharge them, perhaps lowering power draw further by acting as a micro power supply. Is this reasonable, or will I not notice any power savings?




                  No, this is not reasonable. Flash memory is not DRAM. Its cells do not need to be recharged from a battery, nor can they be used as a power source.



                  The vast majority of power draw by an SD card comes from the SD controller, and from the charge pumps on the flash memory die (which are only active when writing or erasing flash). Its power consumption will drop significantly when the card is idle.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 1 hour ago









                  duskwuffduskwuff

                  16.8k32650




                  16.8k32650






























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