USB interface circuit analysis and fault maintenance.

Last Update Time: 2019-06-04 16:06:11

1. USB interface introduction.

USB interface is the mainstream mobile device interface in the current board, which is often used to connect U disk, mobile hard disk, mobile phone, printer, USB keyboard and mouse, etc. It is also an indispensable interface in the use of computer. The USB interface is shown in figure 1. It can be divided into 2. 0 and 3. 0 species.

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Fig. 1 physical diagram of USB interface.

 

2. The working principle of USB interface.

The USB interface is an input / output interface of the USB bus managed by the South Bridge chip, which is usually 4 pins, respectively, power supply, data positive, data negative, ground wire. Among them, power supply is provided by 5VSB standby power supply or VCC5 power supply, and most motherboards are re-powered by dual switching circuits. Data lines and clock lines are connected to the South Bridge chip control, as shown in figure 2. The USB controller is integrated inside the South Bridge chip. When the South Bridge chip receives the (USBPLL), powered by the USB controller and the clock chip sends the clock signal of the USB controller of the 48MHz, the USB controller is self-tested when the main board is powered on the self-test. South bridge chip and USB interface through DATA- and DATA data line for data exchange.

 

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Fig.2 USB interface circuit working principle diagram.

 

3. Maintenance method of USB interface fault.

 

1) Check interface 5V power supply, ground.

 

2)To measure whether the USB interface data line to the ground value is normal, the normal value is about 500. The value is not normal, may be broken line or South Bridge bad.

 

3) Check if the South Bridge chip 48MHz clock signal is normal.

 

4) Check the South Bridge chip V5REF, VccUSBPLL power supply is normal.

 

5)Check if the precision resistance around the South Bridge chip is lost.

 

6) If the above conditions are normal, or do not recognize the USB, finally replace the South Bridge chip.


 This article is from Allicdata Electronics Limited.