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I want to use a power regulator PCB I designed to switch down 60V to 12V and 12V to 5V in order to power a USB plug and use it as a phone charger. My only worry is that the switching regulators I am using (TI TPS54560) can provide up to 5A of current whereas the plug is rated for 1A. Do phones cap their charging current at 1 or 2A on their own or is this something I need to implement in my system in order to avoid damaging them? Thank you for your help!


marked as duplicate by Ignacio Vazquez-Abrams, mkeith, Voltage Spike, Wesley Lee, ThreePhaseEel Mar 11 '17 at 5:59

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  • \$\begingroup\$ This is a variation of a question that has been asked multiple times \$\endgroup\$ – Voltage Spike Mar 10 '17 at 16:24
  • \$\begingroup\$ One of those "Huh? How can you design a switch mode regulator and not understand how voltage and current interact?" \$\endgroup\$ – pipe Mar 10 '17 at 17:15
  • 1
    \$\begingroup\$ electronics.stackexchange.com/questions/177788/… \$\endgroup\$ – Bruce Abbott Mar 10 '17 at 18:16
  • \$\begingroup\$ @pipe, unfortunately, it is not generally possible to "understand" how phones interact with DC voltage supply, because phones involve intelligent electronics to determine how much load they can/want take, depending on their perception of source capabilities and SOC (State Of Charge) of their internal battery, which is known only to the particular phone at the very particular moment. \$\endgroup\$ – Ale..chenski Mar 10 '17 at 23:35
  • \$\begingroup\$ General selection of PSU for voltage and current ratings are not applicable to this question, because mobile devices are not simple Ohmic loads, and they determine the amount of current draw, not the power supply design. I vote to re-install the question. If to mark it as duplicate, the reference by Bruce Abbott would be a much better choice. \$\endgroup\$ – Ale..chenski Mar 11 '17 at 18:07

Yes, phones do cap their charging current. The cap depends on "charger signature" provided through D+/D- USB lines from the charger side, and on the state of charge (SOC) of their internal battery, plus consumption of internal CPU/display and current state of their operations (sleep/active etc.).

If you don't provide any signature (leave D+/D- floating), phones will cap their consumption at about 500 mA.

And yes, you do need to "cap" your power delivery in accord with certain I-V curves that are detailed in BC (battery charging) and PD (power delivery) USB specifications, which can be found on usb.org website, in "developers" section.


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