Technical information

USBUFxxW6

8/11

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. 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.

Note:

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

Figure 14.

Typical rise and fall times:

measurement configuration

Figure 15.

Typical rise times with and

without protection device

D+

D-

+5V

+5V

74HC04

+5V

Square

Pulse

Generator

74HC04

USBDF

01W6

without

with