RClamp0504N
PROTECTION PRODUCTS
Applications Information
Device Connection Options for Protection of Four
High-Speed Data Lines
This device is designed to protect four data lines from
transient over-voltages by clamping them to a fixed
reference. When the voltage on the protected line
exceeds the reference voltage (plus diode V
F
) the
steering diodes are forward biased, conducting the
transient current away from the sensitive circuitry.
Data lines are connected at pins 1, 3, 4 and 6. The
negative reference is connected at pin 2. This pin
should be connected directly to a ground plane on the
board for best results. The path length is kept as short
as possible to minimize parasitic inductance.
The positive reference is connected at pin 5. The
options for connecting the positive reference are as
follows:
1. To protect data lines and the power line, connect
pin 5 directly to the positive supply rail (V
CC
). In this
configuration the data lines are referenced to the
supply voltage. The internal TVS diode prevents
over-voltage on the supply rail.
ESD Protection With RailClamps
RailClamps are optimized for ESD protection using the
rail-to-rail topology. Along with good board layout,
these devices virtually eliminate the disadvantages of
using discrete components to implement this topology.
Consider the situation shown in Figure 1 where dis-
crete diodes or diode arrays are configured for rail-to-
rail protection on a high speed line. During positive
duration ESD events, the top diode will be forward
biased when the voltage on the protected line exceeds
the reference voltage plus the V
F
drop of the diode.
For negative events, the bottom diode will be biased
when the voltage exceeds the V
F
of the diode. At first
approximation, the clamping voltage due to the charac-
teristics of the protection diodes is given by:
V
C
= V
CC
+ V
F
V
C
= -V
F
(for positive duration pulses)
(for negative duration pulses)
In 1
In 2
1
In 4
Vcc
In 3
“Rail-T
Pro
Topology
Figure 1 - “Rail-To-Rail” Pr o t ection Topology
(First Approximation)
2. In applications where the supply rail does not exit
the system, the internal TVS may be used as the
reference. In this case, pin 5 is not connected.
The steering diodes will begin to conduct when the
voltage on the protected line exceeds the working
voltage of the TVS (plus one diode drop).3.
However, for fast rise time transient events, the
effects of parasitic inductance must also be consid-
ered as shown in Figure 2. Therefore, the actual
clamping voltage seen by the protected circuit will be:
V
C
= V
CC
+ V
F
+ L
P
di
ESD
/dt (for positive duration pulses)
V
C
= -V
F
- L
G
di
ESD
/dt
(for negative duration pulses)
ESD current reaches a peak amplitude of 30A in 1ns
for a level 4 ESD contact discharge per IEC 61000-4-2.
In 1
In 2
1
In 4
NC
In 3
4
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