Datasheet
R
C
R
D
C
S
High-Voltage
Pulse
Generator
Device
Under
Test
Current - A
40
35
30
25
20
15
10
5
0
Time - ns
0 50 100 150 200 250 300
10kV IEC
10kV HBM
330Ω
(1.5k)
150pF
(100pF)
50M
(1M)
V
ID
- mV
R
-20-70 0
V
HYS-min
70
V
noise-max
= 140mVpp
50mV
SN65HVD72
SN65HVD75
SN65HVD78
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SLLSE11C –MARCH 2012–REVISED SEPTEMBER 2013
The maximum bus length is typically given as 4000 ft or 1200 m, and represents the length of an AWG 24 cable
whose cable resistance approaches the value of the termination resistance, thus reducing the bus signal by half
or 6 dB. Actual maximum usable cable length depends on the signaling rate, cable characteristics, and
environmental conditions.
Noise Immunity
The input sensitivity of a standard RS-485 transceiver is ± 200 mV. When the differential input voltage, V
ID
, is
greater than + 200 mV, the receiver output turns high, for V
ID
< –200 mV the receiver outputs low.
Figure 20. SN65HVD7x Noise Immunity
The SN65HVD7x transceiver family implements high receiver noise-immunity by providing a maximum positive-
going input threshold of - 20 mV and a minimum hysteresis of 50 mV. In the case of a noisy input condition
therefore, a differential noise voltage of up to 140 mVPP can be present without causing the receiver output to
change states from high to low. This increased noise immunity eliminates the need for idle-bus failsafe bias
resistors and allows for long haul data transmissions in noisy environments.
Transient Protection
The bus terminals of the SN65HVD7x transceiver family possess on-chip ESD protection against ±15 kV human
body model (HBM) and ± 12 kV IEC61000-4-2 contact discharge. The IEC-ESD test is far more severe than the
HBM-ESD test. The 50 % higher charge capacitance, CS, 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 test method; although IEC air-gap
testing is less repeatable than contact testing, air discharge protection levels are inferred from the contact
discharge test results.
Figure 21. HBM and IEC-ESD Models and Currents in Comparison (HBM Values in Parenthesis)
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