USB power supply and DC power supply issues

平漂流

USB power supply and DC power supply issues [Copy link]

 

The 12V switching power supply is input, and the circuit board has 12V to 5V and 5V to 3.3V. Now we need to add a function to the circuit board, USB to serial port, as shown in the circuit diagram. The VBUS of the USB interface is also 5V. What should I do in the circuit? Directly connect VBUS and 5V? PS: The USB port is not used for power supply.

qwqwqw2088

Just connect VBUS and 5V

chunyang

If the USB power supply is not used for power supply, do not connect it directly to your 5V power supply. Just keep it floating. Otherwise, if there is a sufficient voltage difference between the 5V of the USB interface and your 5V, it may cause problems. At this time, the 5V power supply of the USB serial bridge chip is connected to your 5V. Use your 5V power supply instead of USB power supply, and be sure to power on your system before connecting the USB cable.

平漂流

chunyang posted on 2019-9-3 23:37 If the USB power supply terminal is not used for power supply, do not connect it directly to your 5V power supply. Just keep it floating. Otherwise, once there is enough voltage between the 5V of the USB interface and your 5V...

If I connect the USB cable first and then power on the system, will the USB-to-serial chip be burned out?

chunyang

Pingpiaoliu published on 2019-9-6 15:00 If I connect the USB cable first and then power on the system, will the USB-to-serial port chip be burned out?

If there is a power supply potential difference, it has nothing to do with your power-on sequence. The risk of damage is the power supply rather than the serial port bridge.

蓝天007

It is best to connect a 0 ohm resistor between vbus and +5v.

平漂流

chunyang posted on 2019-9-6 15:42 If there is a power supply potential difference, it has nothing to do with your power-on sequence. The risk of damage is the power supply rather than the serial port bridge.

Signals connecting the USB cable to the circuit board: D+, D-, GND.

If I connect the USB system first and then the power system, will there be any problems?

chunyang

Pingpiaoliu published on 2019-9-6 16:29 The signals connected between the USB cable and the circuit board are: D+, D-, GND. If I connect the USB system first and then the power system, will there be any problems?

As I said, it has nothing to do with the power-on sequence. Can the voltage difference between short-circuited power supplies be solved by the power-on sequence? First, think about what a sufficient voltage difference will cause.

乘风云上

蓝天007 发表于 2019-9-6 16:15 It is best to connect a 0 ohm resistor between vbus and +5v.

What is the function of connecting a 0 ohm jumper resistor in series?

平漂流

chunyang posted on 2019-9-6 18:06 As I said, it has nothing to do with the power-on sequence. Can the voltage difference between short-circuited power supplies be solved by the power-on sequence? First figure out what a sufficient voltage difference will lead to. ...

OK, got it.

summer2019

Pingpiaoliu published on 2019-9-6 16:29 The signals connected between the USB cable and the circuit board are: D+, D-, GND. If I connect the USB system first and then the power system, will there be any problems?

I often use this, no problem

平漂流

summer2019 posted on 2019-9-10 09:15 I often use this, no problem

OK, thanks

曾半仙

Most USB bridge chips have a self-powered configuration. The CP2102 is no exception.

The picture you posted is the first page of the datasheet, the configuration of buspowred.

There are two configurations on page 20. You can use the one without the voltage divider resistor.

That is, the chip vbus is disconnected from regin, the 5v power supply is connected to regin, the filter capacitor is also connected to this network, and the vbus is connected to vbus alone.

Regin is used by the internal LDO to generate 3V3, and the vbus pin input is only used to detect the voltage. The current drawn can be ignored.

The voltage division is suitable for situations where VDD and resin may lose power, to ensure that the electrical characteristics of Vbus do not exceed the standard.

generalcircuits

蓝天007 发表于 2019-9-6 16:15 It is best to connect a 0 ohm resistor between vbus and +5v.

Same question, what is the role of the 0 ohm jumper resistor in series?

平漂流

generalcircuits posted on 2019-9-19 15:12 Same question, what is the function of the 0 ohm jumper resistor in series

Balanced voltage

generalcircuits

Ping Drift published on 2019-9-23 13:36 Balanced voltage

Thanks

未来电子巨头

generalcircuits posted on 2019-9-19 15:12 Same question, what is the function of the 0 ohm jumper resistor in series

Buffering effect