USBUF(2006) 데이터 시트보기 (PDF) - STMicroelectronics

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USBUF
(Rev.:2006)

EMI filter and line termination for USB upstream ports

STMicroelectronics 

Technical information

USBUFxxW6

USB connectors. Distance between the USB controller and the USB connector must be

minimized.

The 47 pF (Ct) capacitors are used to bypass high frequency energy to ground and for edge

control, and are placed between the driver chip and the series termination resistors (Rt).

Both Ct and Rt should be placed as close to the driver chip as is practicable.

The USBUFxxW6 ensures a filtering protection against ElectroMagnetic and

RadioFrequency Interferences thanks to its low-pass filter structure. This filter is

characterized by the following parameters:

● cut-off frequency

● Insertion loss

● high frequency rejection.

Figure 4.

S21 (dB)

0

USBUFxxW6 typical

attenuation

Figure 5. Measurement configuration

TEST BOARD

-10

50Ω

Vg

50Ω

-20

-30

1

10

100

Frequency (MHz)

1,000

2.3

ESD PROTECTION

In addition to the requirements of termination and EMC compatibility, computing devices are

required to be tested for ESD susceptibility. This test is described in the IEC 61000-4-2 and

is already in place in Europe. This test requires that a device tolerates ESD events and

remains operational without user intervention.

The USBUFxxW6 is particularly optimized to perform ESD protection. ESD protection is

based on the use of device which clamps at:

Vcl = VBR + Rd . IPP

This protection function is splitted in 2 stages. As shown in figure 6, the ESD strikes are

clamped by the first stage S1 and then its remaining overvoltage is applied to the second

stage through the resistor Rt. Such a configuration makes the output voltage very low at the

output.

4/11

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