Upgrading a device female micro-USB connector to USB-C

Question

I have a battery manager PCB, which has a microUSB female connector for power-input (5V from smartphone charger for instance). The power input is fed to a PMU which charges a lipo battery and power a system (an old toy-train that was running on LR14). It does not need data transmission. Only power to charge the battery.

I want to replace the power input connector by a female USB-C. Should I just connect the microUSB VBUS to the USBC VBUS and GND to GND? Or should I also add pull up/down resistors?

I got that female USB-C breakout board from aliexpress (the blue one from the pictures) : https://fr.aliexpress.com/item/1005001337982060.html?spm=a2g0s.9042311.0.0.87526c37416MK1 But it has only 1 footprint for a resistor.

I was expecting 2 resistors footprint, one for A5 and one for B5, on which I thought I needed to put 5.2k pull down resistors.

Also this connector has only 7 pins on each side instead of 12. From the PCB pictures it looks like the R1 resistor is connected to both A5 and B5 on one side, and to GND to the other side. Is it OK to solder only one pull down resistor like this?

It feels dirty and makes me think about the issues the raspberry pi 4 had where they applied only one resistor. Though I could not find the exact schematic error that RaspberryPi did.

Answer 1

Yes, on a female USB C connector for a device (hosts, dual-role devices etc are another matter) CC1 and CC2 should be pulled down separately.

If the pull-downs are omitted completely then a power supply with a USB C socket should not turn on it's output.

As Raspberry pi found out if you tie them together and use a single pull-down then it will work with passive cables, but at least some (not clear if it's all) electronically marked cables will fail to operate correctly.