TVS devices used with LPT-11 transceivers must meet the following requirements:
• bi-directional protection;
• rated at 400W minimum peak power (10/1000µs waveform) rating;
• working peak reverse voltage rating Vrwm
≥
42.4V (-40°C to +85°C); Vrwm
should be as low as possible over the temperature range but not less than 42.4V.
Typical reverse breakdown voltage ratings, Vbr, for such devices will be
approximately 53V;
• bi-directional capacitance C
≤
2
75pF @Vr = 26V; bi-directional capacitance in this
application is typically 80% of data book unidirectional rating. Capacitance
increases as voltage across the device decreases.
Table 6.1 lists recommended TVS devices for use with LPT-11 transceivers. Note
that bi-directional devices must be used.
Table 6.1
Recommended TVS Devices
Manufacturer
Part Number
Peak Power
Package
Fairchild SA45(c)A
500W
Axial
Vishay SA45A
500W
Axial
Building Entrance Protection
Echelon recommends using shielded twisted pair wire for all networks, or portions of
networks, that are run outside of buildings. The shield should be connected to earth
at each building entry point via a data lightning/surge arrester, to conduct excessive
surges or lightning strike energy to ground and prevent their entry inside the
building via the network. Data line lightning/surge arresters should also be used at
each building entrance and connected to the network data lines. Therefore, two
arresters, one for each conductor of the twisted pair, are required, and Echelon
recommends the use of the gas discharge type. The gas discharge type of arrester
presents extremely low capacitance to the transmission line, minimizing possible
corruption of the network data traffic. MOV and TVS protection devices should not
be used in this way because their intrinsically high capacitance as well as low
matching tolerance will likely create imbalance in the transmission line, preventing
network data traffic. However, TVS devices from Table 6.1 may be connected
differentially
across the network for surge protection.
Gas discharge devices are typically used for data line lightning/surge arresters due
to their very low capacitance (typically < 5pF) and rapid response. Use of this type of
device will not reduce the number of possible nodes used on a network segment.
Since there is minimal amount of “leakage capacitance” or unbalance to ground
allowed in a link power network, the two arresters used should match (be balanced)
within 10pF.
L
ON
W
ORKS
LPT-11 Transceiver User’s Guide
6-7