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The image below shows a Micro USB connector in a smartphone. I understand what the first 5 pins of the USB are i.e. USB_DM, USB_DP, USB_ID , VBUS and GND.

enter image description here

The pin S1 is connected to VBAT (battery voltage pin) through a load switch.

Can anyone explain to me the function of the S1 pin?

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  • \$\begingroup\$ It might have something to do with detecting charging via USB cable vs wireless inductive charging (ex: qi) \$\endgroup\$ – user2813274 Jun 17 '15 at 2:55
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S1 is the "USB cable connected" status pin. It wakes up the CPU so a PC is able to detect the phone or so it can display the "charging" status with the USb wall wart.

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  • \$\begingroup\$ Does the USB jack have a switch in it, like phono jacks? \$\endgroup\$ – Austin Apr 8 '15 at 16:56
  • \$\begingroup\$ Usually not, but the one in the schematic seems to have that switch. \$\endgroup\$ – Turbo J Apr 8 '15 at 18:49
  • \$\begingroup\$ I can confirm that when we connect usb cable, VBUS_5V_IF pin goes up, which is connected to MUIC(micro usb interface controller) and MUIC is sending interrupt to core(CPU) for wakeup and then core sends interrupt to charging IC to enable charging if supported. So we can check "USB cable presence" from VBUS_5V_IF pin. Why s1 is needed when USB cable presence can be checked by VBUS? @TurboJ ... I think S1 is used in case of JIG or some other testing environment, when battery is not inserted, but not sure. Can any one confirm. \$\endgroup\$ – Roy Miller Apr 10 '15 at 11:45
  • \$\begingroup\$ An USB OTG cable (micro-B->USB A) would not provide 5 volts. \$\endgroup\$ – Turbo J Apr 10 '15 at 13:23
  • \$\begingroup\$ we don't charge a phone in case of An USB OTG cable (micro-B->USB A). @TurboJ \$\endgroup\$ – Roy Miller Apr 24 '15 at 4:05

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