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USB6Bx
DATA LINES PROTECTION
August 1999 Ed : 5A
Application Specific Discretes
A.S.D.
SO8
DIL8
FUNCTIONAL DIAGRAM
Vcc
Vcc
I/01
I/01
I/02
I/02
GND
GND
MIL STD 883C - Method 3015-6
class 3
C = 100 pF
R = 1500
3 positive strikes and 3 negative strikes (F = 1 Hz)
IEC-1000-4-2 level 4
15 kV
(air discharge)
8 kV
(contact discharge)
COMPLIES WITH THE FOLLOWING STANDARDS:
TM: ASD and TRANSIL are trademarks of ST Microelectronics.
Where transient overvoltage protection in sensi-
tive equipment is required, such as:
- Universal Serial Bus ports
- RS-423 interfaces
- RS-485 interfaces
- ISDN equipment
- T1/E1 line cards
- HDSL / ASDL interfaces
APPLICATIONS
n
Full diode bridge with integrated clamping protection
n
Breakdown voltage : VBR = 6V min.
n
Peak pulse power dissipation : P
PP
= 500W (8/20
s)
n
Very low capacitance, compatible with high debit
data or signal rates.
FEATURES
In order to prevent fast transients from leading
to severe damages in a high speed data sys-
tem, a specific protection has been developed
by STMicroelectronics.
The USB6Bx protects the two input lines
against overvoltage. Besides, this device also
keeps the power rails in a safe limit thanks to
the integrated Transil diode.
DESCRIPTION
n
Provides protection for each line and between
the supply voltage and GND : 25A , 8/20
s.
n
High ESD protection level : up to level 3 per
MIL STD 883C-Method 3015-6
n
Separated inputs and outputs (so-called 4-point
structure) to improve ESD susceptibility.
n
Comprehensive package pin-out for immediate
implementation.
BENEFITS
USB6Bx
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Fig. A1 :
Lw
VI/O
ESD
SURGE
GND
I/O
+Vcc
Vf
Lw di
dt
Lw di
dt
Vcl+ = Vcc+Vf+ Lw
di
dt
surge >0
-Vf- Lw
di
dt
surge <0
Vcl- =
t
tr=1ns
Vcc+Vf
Lw di
dt
Vcl+
POSITIVE
SURGE
-Lw
di
dt
t
tr=1ns
-Vf
Vcl-
NEGATIVE
SURGE
The USB6Bx is particularly optimized to perform
surge protection based on the rail to rail topology.
The clamping voltage V
CL
can be estimated as follow:
V
CL
+ =Vcc + V
F
for positive surges
V
CL
- = - V
F
for negative surges
with: V
F
= V
t
+ rd.Ip
(V
F
forward drop voltage) / (V
t
forward drop
threshold voltage)
Note: the estimations do not take into account
phenomena due to parasitic inductances.
SURGE PROTECTION
TECHNICAL INFORMATION
USB6Bx
3/9
While the USB6Bx 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 V
CC
pin to the
power supply and from the GND pin to GND volt-
age must be as short as possible to avoid
overvoltages due to parasitic phenomena (see Fig
A1).
It's often harder to connect the power supply near
to the USB6Bx 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 put close to the USB6Bx between
V
CC
and ground, a capacitance of 100nF to pre-
vent from these kinds of overvoltage disturbances
(see Fig. A2 ).
The add of this capacitance will allow a better pro-
tection by providing during surge a constant volt-
age.
Fig. A3 shows the improvement of the ESD pro-
tection according to the recommendations de-
scribed above.
HOW TO ENSURE A GOOD ESD PROTECTION
Fig. A2: ESD behavior: optimized layout and add
of a capacitance of 100nF.
REF1=GND
VI/O
ESD
SURGE
I/O
REF2=+Vcc
C=100nF
Lw
Vcl+ = Vcc+Vf
-Vf
surge >0
surge <0
Vcl- =
t
Vcl+
POSITIVE
SURGE
t
Vcl-
NEGATIVE
SURGE
IMPORTANT:
A main precaution to take is to put the protection
device closer to the disturbance source (generally
the connection).
USB6Bx
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Fig. A3: recommended configuration for USB port protection.
1
Vbus
D+
D-
GND
USB output
connector
USB
IC
Universal Serial Bus.
The new data transmission standard, Universal
Serial Bus (USB) is being driven by market leaders
in the world of Computer and Telecommunica-
tions,
including
Compaq,
DEC,
IBM,
Intel,
Microsoft, NEC and Nortel, and will become the
leading transmission protocol within the next few
years.
This
standard
mainly
provides
simplified
interconnectivity. Specialized ports on the back of
the present PC will largely be replaced by USB
ports. Many peripherals such as printers, key-
boards, monitors and joysticks will also host USB
ports.
The USB offers high speed communication rates
up to 12 Mbit/s. Only two wires (D+, D-) are re-
quired for data transfer. Additionally, limited
amount of power for USB devices located on the
downstream can also be transmitted on two sepa-
rate conductors within the same cable.
Protection to support USB.
Designers dealing with the USB chips are con-
cerned about electrostatic discharge sensitivity
(ESD) of their USB controller ICs.
The USB controller is more than just a driver /
receiver; it acts as a microcontroller which
manages power and direct signal traffic. This
complexity increases its cost over conven-
tional devices. Therefore, a failure of a USB
port could result in costly computer failure.
In order to prevent these fast transients from
leading to severe damages in a system, a
specific protection has been developed by
STMicroelectronics. The USB6Bx protects
not only the two wires of data transmission,
but also keep the power rails in a safe limit.
The capacitance between the I/O transmission
wires provides no significant signal distortion at the
12 Mbit/s data rate, thus allowing full compatibility
with USB standard.
Available either in a compact SO8 or in a
through-hole DIL8 package, this protective ele-
ment requires minimal board space and eases the
PCB layout thanks to its direct compatibility with
the USB connector pin-out.
TECHNICAL INFORMATION
USB6Bx
5/9
T1 / E1 Line Card Protection.
High Speed Line Driver / Receiver Protection.
ISDN U interface protection.
USB6Bx
3* SMP100
DC Power
Source
LT
+Vcc
RTIP
USB6B1
USB6B1
RRING
TTIP
TRING
SMP75-8 or SMP100-8
SMP75-8 or SMP100-8
+Vcc
+Vcc
DRIVER
SM6T6V8A
USB6B1
INPUT
+5V
RECEIVER
SM6T6V8A
USB6B1
OUTPUT
+5V
+Vcc
+Vcc
TELECOM AND DATACOM APPLICATIONS
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