USBUF(2006) データシートの表示（PDF） - STMicroelectronics

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USBUF
(Rev.:2006)

EMI filter and line termination for USB upstream ports

STMicroelectronics 

Technical information

USBUFxxW6

2.6

Transition times

This low pass filter has been designed in order to meet the USB 1.1 standard requirements

that implies the signal edges are maintained within the 4 -20 ns stipulated USB specification

limits. To verify this point, we have measured the rise time of VD+ voltage with and without

the USBUFxxW6 device.

Figure 14. Typical rise and fall times: Figure 15. Typical rise times with and

measurement configuration

without protection device

Square

Pulse

Generator

+5V

74HC04

D+

+5V

D-

+5V

74HC04

USBDF

01W6

without

with

Note:

Figure 14. shows the circuit used to perform measurements of the transition times. In Figure

15., we see the results of such measurements:

trise = 3.8 ns driver alone

trise = 7.8 ns with protection device

The adding of the protection device causes the rise time increase of roughly 4ns.

Rise time has been measured between 10% and 90% of the signal (resp. 90% and 10%)

8/11

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