MAX14938 Datasheet, PDF (18/22 Pages) Maxim Integrated Products – 2.75kVRMS Isolated 20Mbps Half-Duplex PROFIBUS

MAX14938/MAX14939
2.75kV_RMS Isolated 20Mbps Half-Duplex PROFIBUS/
RS-485 Transceivers with ±35kV ESD Protection
Profibus Termination
These devices are designed for driving PROFIBUS-DP
terminated networks. The driver maintains 2.1V (min)
when driving a worst-case loading condition of two
standard 220Ω termination resistors with 390Ω pullups/
pulldowns.
Layout Considerations
It is recommended to design an isolation, or “keep-out,”
channel underneath the isolator that is free from ground and
signal planes. Any galvanic or metallic connection between
the cable-side and UART-side will defeat the isolation.
Ensure that the decoupling capacitors between VDDA and
GNDA and between VLDO, VDDB, and GNDB are located
as close as possible to the IC to minimize inductance.
Route important signal lines close to the ground plane to
minimize possible external influences. On the cable-side
of the MAX14938/MAX14939, it is good practice to have
the bus connectors and termination resistor as close as
possible to the A and B pins.
Extended ESD Protection
ESD protection structures are incorporated on all pins
to protect against electrostatic discharge encountered
during handling and assembly. The driver outputs and
receiver inputs of the MAX14938/MAX14939 have extra
protection against static electricity to both the UART-side
and cable-side ground references. The ESD structures
withstand high-ESD events during normal operation and
when powered down. After an ESD event, the devices
keep working without latch-up or damage.
Bypass VDDA to GNDA and bypass VDDB and VLDO
to GNDB with 0.1μF and 1μF capacitors to ensure maxi-
mum ESD protection.
ESD protection can be tested in various ways. The
transmitter outputs and receiver inputs of the MAX14938/
MAX14939 are characterized for protection to the cable-
side ground (GNDB) to the following limits:
●● ±35kV HBM
●● ±12kV using the Air-Gap Discharge method specified
in IEC 61000-4-2
●● ±10kV using the Contact Discharge method speci-
fied in IEC 61000-4-2
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents test
setup, test methodology, and test results.
Human Body Model (HBM)
Figure 12 shows the HBM test model, while Figure
13 shows the current waveform it generates when
discharged in a low-impedance state. This model
consists of a 100pF capacitor charged to the ESD voltage of
interest, which is then discharged into the test device
through a 1.5kΩ resistor.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD testing and
performance of finished equipment. However, it does not
specifically refer to integrated circuits. The MAX14938/
MAX14939 help in designing equipment to meet IEC
61000-4-2 without the need for additional ESD protection
components.
The major difference between tests done using the HBM
and IEC 61000-4-2 is higher peak current in IEC 61000-
4-2 because series resistance is lower in the IEC 61000-
4-2 model. Hence, the ESD withstand voltage measured
to IEC 61000-4-2 is generally lower than that measured
using the HBM.
Figure 14 shows the IEC 61000-4-2 model and
Figure 15 shows the current waveform for IEC 61000-4-2
ESD Contact Discharge Test.
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