USB62(2006) Ver la hoja de datos (PDF) - STMicroelectronics
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USB62 Datasheet PDF : 9 Pages
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Technical information
2
Technical information
USB6B1
2.1
Note:
Surge protection
The USB6B1 is optimized to perform surge protection based on the rail to rail topology.
The clamping voltage VCL can be estimated as follow:
VCL+ = VCC + VF for positive surges
VCL - = - VF for negative surges
with: VF =Vt + rd.Ip
VF = forward drop voltage, Vt = forward drop threshold voltage
The estimations do not take into account phenomena due to parasitic inductances.
Figure 4. Surge behavior
ESD
SURGE
Lw
Lw di
Vf
dt
I/O
+Vcc
VI/O
Lw di
dt
Vcl+
=
Vcc+Vf+Lw
di
dt
Vcl- =
-Vf-
Lw
di
dt
surge >0
surge <0
GND
Vcl+
Lw di
dt
POSITIVE
SURGE
Vcc+Vf
t
tr=1ns
tr=1ns
t
-Vf
-Lw di
dt
NEGATIVE
SURGE
Vcl-
Figure 5.
ESD
SURGE
ESD behavior: optimized
layout and addition of a
100 nF capacitor
Lw
C=100nF
REF2=+Vcc
I/O
VI/O
Vcl+ = Vcc+Vf surge >0
Vcl- = -Vf surge <0
REF1=GND
Vcl+
POSITIVE
SURGE
t
t
NEGATIVE
SURGE
Vcl-
2.2
How to ensure good ESD protection
While the USB6B1 provides a high immunity to ESD surge, an efficient protection depends
on the layout of the board. In the same way, with the rail to rail topology, the track from the
VCC pin to the power supply and from the GND pin to GND voltage must be as short as
possible to avoid overvoltages due to parasitic phenomena (see Figure 4.)
It’s often harder to connect the power supply near to the USB6B1 unlike the ground thanks
to the ground plane that allows a short connection. To ensure the same efficiency for
positive surges when the connections can’t be short enough, we recommend to putting a
100 nF c apacitor close to the USB6B1 between VCC and ground to prevvent these kinds of
overvoltage disturbances (see Figure 5.) The addition of this capacitor offers better
protection by providing a constant voltage during the surge.
Figure 6. shows the improvement of the ESD protection according to the recommendations
described above.
Important: An imortant precaution to take is to put the protection device closer to the disturbance
source (generally the connection).
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