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We have a typical USB 2.0 wall charger that has a USB A receptacle. Our charger has D+/D- connected together through a small resisor (<200Ω) to let devices know the maximum power is 1.5A/5V following the USB BC1.2 spec for a "Dedicated Charging Port" (DCP). Our charger is "dumb", it does not communicate with the devices.

Now we would like to modify the charger to use a USB C connector. We don't want to upgrade to the Power Delivery spec, we just want to use a different connector. We want to keep using the USB BC1.2 spec. I have done a bit of research and I have found that USB A to USB C cables add a 56 kΩ Rp pull-up resistor between VBUS and CC.

My idea is then to keep the rest of the connector circuitry basically the same and simply add Rp to the CC pin pulling up to 5V. Here is the schematic:

Would this work?

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Your line of thinking is correct. But... if your charger can supply 1.5A, you need to use 22k pull-up, and use it on BOTH CC1 and CC2 lines separately. Shorting D+ and D- to mimic DCP is a good idea too.

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  • \$\begingroup\$ Shorting D+/D− is required in section 4.8.1.1 USB-based Chargers with USB Type-C Receptacles. "USB-based charger with a USB Type-C receptacle ... which is not capable of data communication shall advertise USB Type-C Current of at least 1.5 A ... and shall short D+ and D− together ... will ensure backwards compatibility with legacy sinks which may use USB BC 1.2 for charger detection." \$\endgroup\$
    – endolith
    Oct 23 '20 at 5:22

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