DocID7041 Rev 8 7/13
USBUF Technical information
13
Figure 8. Remaining voltage at both stages S1 (Vinput) and S2 (Voutput) during ESD
surge
Please note that the USBUF is not only acting for positive ESD surges but also for negative
ones. For these kinds of disturbances it clamps close to ground voltage as shown in Figure
8. (negative surge.
2.4 Latch-up phenomenon
The early aging and destruction of IC’s is often due to latch-up phenomenon which is mainly
induced by dV/dt. Thanks to its structure, the USBUF provides a high immunity to latch-up
phenomenon by smoothing very fast edges.
2.5 Crosstalk behavior
Figure 9. Crosstalk phenomenon
The crosstalk phenomenon is due to the coupling between 2 lines. The coupling factor (β
12
or β
21
) increases when the gap across lines decreases, particularly in silicon dice. In the
example above the expected signal on load R
L2
is α
2
V
G2
, in fact the real voltage at this
point has got an extra value β
21
V
G1
. This part of the V
G1
signal represents the effect of the
crosstalk phenomenon of the line 1 on the line 2. This phenomenon has to be taken into
account when the drivers impose fast digital data or high frequency analog signals in the
disturbing line. The perturbed line will be more affected if it works with low voltage signal or
high load impedance (few kΩ).
Vin
Vout
Vin
Vout
Positive surge Negative surge
Line 1
Line 2
V
G1
V
G2
R
G1
R
G2
DRIVERS
R
L1
R
L2
RECEIVERS
αβ
1 G1 1 2 G2
V+ V
αβ
2 G2 2 1 G1
V+ V
