I am building a uC board which uses an 3.3V microSD card as a storage medium. To design the switching power supply for the 3.3V, I have to know what my total current draw from the supply will be. I have average and peak current values from datasheets for all my other parts on the board, for example, SDRAM, LCD, etc., but can't find general info online about the microSD card.
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1\$\begingroup\$ Extremely vague. Add the part/model number, at the very least... \$\endgroup\$– ShamtamJun 8, 2012 at 4:46
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\$\begingroup\$ Look in it's datasheet for typical specs, or use a multimeter on amps range whilst operating under different conditions (idle, enumerating, data transferring, etc) \$\endgroup\$– Oli GlaserJun 8, 2012 at 5:07
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\$\begingroup\$ @Oli - Hey, guys, Oli is back! :-) \$\endgroup\$– stevenvhJun 8, 2012 at 5:13
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\$\begingroup\$ Hi there @steven - been extra busy lately, but couldn't stay away for too long... :-) \$\endgroup\$– Oli GlaserJun 8, 2012 at 5:29
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2 Answers
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1\$\begingroup\$ @BSEE ... but don't stop there. Go to an electronics parts distributor (like Mouser or DigiKey), look up datasheets for 3 or so different microSD cards, find more data points for current consumption. \$\endgroup\$ Jun 9, 2012 at 2:50
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1\$\begingroup\$ That's just Toshiba claiming their cards draw no more than 80mA. The SD spec allows cards to draw MUCH more than that. \$\endgroup\$ Sep 1, 2021 at 1:46
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In early versions of the SD spec (e.g., version 2.00, from 2006), cards were allowed to draw up to 200mA. In newer standards, cards are allowed to draw more current than that, but only after they've notified the host that they want more current, and the host has assented to it.. According to the Physical Layer Simplified Specification Version 8.00, if you're using the SD card in its default power-on configuration (3.3V supply, maximum clock speed 25 MHz), the power consumption shouldn't exceed 0.36W for SDSC or SDHC, or 0.54W for SDXC or SDUC.
Assuming that you're providing the nominal supply voltage, 3.3V, that means that the card can draw a maximum of 163mA. Slightly more or less as the voltage varies within the allowable range.
The Physical Layer Simplified Specification Version 8.00 is a free download (though you have to agree to terms). In that document, the relevant information is table 3-6 on page 23 (page 43 of the PDF file).
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\$\begingroup\$ Nice Job! High quality answer to an old question which adds significant value , Kudos! \$\endgroup\$– crasicSep 1, 2021 at 2:40