DocID7041 Rev 8

5/13

USBUF

Technical information

13

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

minimized.

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 USBUF ensures a filtering protection against Electromagnetic and Radio-frequency

Interferences thanks to its low-pass filter structure. This filter is characterized by the

following parameters:

•

cut-off frequency

•

Insertion loss

•

high frequency rejection.

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 USBUF is particularly optimized to perform ESD protection. ESD protection is based on

the use of device which clamps at:

This protection function is spitted 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.

Figure 4. USBUF typical attenuation

Figure 5. Measurement configuration

1

10

100

1,000

-30

-20

-10

0

Frequency (MHz)

S21 (dB)

TEST BOARD

50

Ω

Vg

50

Ω