THVD1510 Datasheet, PDF (21/39 Pages) Texas Instruments – 5-V RS-485 Transceivers With 18-kV IEC ESD Protection

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THVD1510, THVD1512
THVD1550, THVD1551, THVD1552
SLLSEV1 – SEPTEMBER 2017
Typical Application (continued)
10.2.1.5 Transient Protection
The bus pins of the THVD15xx transceiver family include on-chip ESD protection against ±30-kV HBM and ±18-
kV IEC 61000-4-2 contact discharge. The International Electrotechnical Commission (IEC) ESD test is far more
severe than the HBM ESD test. The 50% higher charge capacitance, C_(S), and 78% lower discharge resistance,
R_(D), of the IEC model produce significantly higher discharge currents than the HBM model. As stated in the IEC
61000-4-2 standard, contact discharge is the preferred transient protection test method.
R_(C)
R_(D)
High-Voltage
Pulse
Generator
50 M
(1 M)
C_(S)
330 Ω
(1.5 kΩ)
150 pF
(100 pF)
Device
Under
Test
40
35
30 10-kV IEC
25
20
15
10
5
10-kV HBM
0
0 50 100 150 200 250 300
Time (ns)
Figure 25. HBM and IEC ESD Models and Currents in Comparison (HBM Values in Parenthesis)
The on-chip implementation of IEC ESD protection significantly increases the robustness of equipment. Common
discharge events occur because of human contact with connectors and cables. Designers may choose to
implement protection against longer duration transients, typically referred to as surge transients.
EFTs are generally caused by relay-contact bounce or the interruption of inductive loads. Surge transients often
result from lightning strikes (direct strike or an indirect strike which induce voltages and currents), or the
switching of power systems, including load changes and short circuit switching. These transients are often
encountered in industrial environments, such as factory automation and power-grid systems.
Figure 26 compares the pulse power of the EFT and surge transients with the power caused by an IEC ESD
transient. The left-hand diagram shows the relative pulse-power for a 0.5-kV surge transient and 4-kV EFT
transient, both of which dwarf the 10-kV ESD transient visible in the lower-left corner. 500-V surge transients are
representative of events that may occur in factory environments in industrial and process automation.
The right-hand diagram shows the pulse-power of a 6-kV surge transient, relative to the same 0.5-kV surge
transient. 6-kV surge transients are most likely to occur in power generation and power-grid systems.
22
20
18
0.5-kV Surge
16
14
12
4-kV EFT
10
8
6
4
2 _{10-kV ESD}
0
0 5 10 15 20 25 30 35 40
Time (µs)
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
6-kV Surge
0.5-kV Surge
5 10 15 20 25 30 35 40
Time (µs)
Figure 26. Power Comparison of ESD, EFT, and Surge Transients
Copyright © 2017, Texas Instruments Incorporated
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