®
USB6Bx
DATA LINES PROTECTION
Application Specific Discretes
A.S.D.
APPLICATIONS
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
FEATURES
n
Full diode bridge with integrated clamping protection
n
Breakdown voltage : VBR = 6V min.
n
Peak pulse power dissipation : P
PP
= 500W (8/20µs)
n
Very low capacitance, compatible with high debit
data or signal rates.
DESCRIPTION
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.
BENEFITS
n
SO8
DIL8
n
n
n
Provides protection for each line and between
the supply voltage and GND : 25A , 8/20µs.
High ESD protection level : up to level 3 per
MIL STD 883C-Method 3015-6
Separated inputs and outputs (so-called 4-point
structure) to improve ESD susceptibility.
Comprehensive package pin-out for immediate
implementation.
FUNCTIONAL DIAGRAM
COMPLIES WITH THE FOLLOWING STANDARDS:
MIL STD 883C - Method 3015-6
class 3
C = 100 pF
R = 1500
Ω
3 positive strikes and 3 negative strikes (F = 1 Hz)
IEC-1000-4-2 level 4
15 kV (air discharge)
8 kV (contact discharge)
TM: ASD and TRANSIL are trademarks of ST Microelectronics.
Vcc
I/01
I/02
GND
Vcc
I/01
I/02
GND
August 1999 Ed : 5A
1/9
USB6Bx
TECHNICAL INFORMATION
SURGE PROTECTION
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
for negative surges
V
CL
- = - V
F
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.
Fig. A1 :
ESD
SURGE
Vf
I/O
Lw
+Vcc
Lw di
dt
di
Vcl+ = Vcc+Vf+ Lw dt surge >0
VI/O
Lw di
dt
Vcl- =
-Vf- Lw
di
dt
surge <0
GND
tr=1ns
Vcl+
t
-Vf
Lw di
dt
Vcc+Vf
t
POSITIVE
SURGE
-Lw
di
dt
NEGATIVE
SURGE
Vcl-
tr=1ns
2/9
USB6Bx
HOW TO ENSURE A GOOD ESD PROTECTION
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.
Fig. A2:
ESD behavior: optimized layout and add
of a capacitance of 100nF.
Lw
REF2=+Vcc
C=100nF
ESD
SURGE
I/O
Vcl+ = Vcc+Vf
VI/O
Vcl- =
-Vf
surge >0
surge <0
REF1=GND
Vcl+
t
POSITIVE
SURGE
NEGATIVE
SURGE
t
Vcl-
IMPORTANT:
A main precaution to take is to put the protection
device closer to the disturbance source (generally
the connection).
3/9
USB6Bx
TECHNICAL INFORMATION
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.
Fig. A3:
recommended configuration for USB port protection.
Vbus
D+
D-
GND
USB output
connector
1
USB
IC
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.
4/9
USB6Bx
TELECOM AND DATACOM APPLICATIONS
ISDN U interface protection.
USB6Bx
3* SMP100
+Vcc
LT
DC Power
Source
T1 / E1 Line Card Protection.
USB6B1
SMP75-8 or SMP100-8
RTIP
+Vcc
RRING
TTIP
+Vcc
TRING
USB6B1
SMP75-8 or SMP100-8
High Speed Line Driver / Receiver Protection.
+5V
SM6T6V8A
+5V
SM6T6V8A
+Vcc
+Vcc
INPUT
DRIVER
RECEIVER
OUTPUT
USB6B1
USB6B1
5/9
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
