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MAX481E Datasheet(PDF) 12 Page - Maxim Integrated Products

Part No. MAX481E
Description  ±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 Transceivers
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX481E Datasheet(HTML) 12 Page - Maxim Integrated Products

 
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±15kV ESD-Protected, Slew-Rate-Limited,
Low-Power, RS-485/RS-422 Transceivers
12
______________________________________________________________________________________
The major difference between tests done using the
Human Body Model and IEC1000-4-2 is higher peak
current in IEC1000-4-2, because series resistance is
lower in the IEC1000-4-2 model. Hence, the ESD with-
stand voltage measured to IEC1000-4-2 is generally
lower than that measured using the Human Body
Model. Figure 7 shows the current waveform for the 8kV
IEC1000-4-2 ESD contact-discharge test.
The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.
Machine Model
The Machine Model for ESD tests all pins using a
200pF storage capacitor and zero discharge resis-
tance. Its objective is to emulate the stress caused by
contact that occurs with handling and assembly during
manufacturing. Of course, all pins require this protec-
tion during manufacturing—not just inputs and outputs.
Therefore, after PC board assembly, the Machine Model
is less relevant to I/O ports.
MAX487E/MAX1487E:
128 Transceivers on the Bus
The 48k
Ω, 1/4-unit-load receiver input impedance of the
MAX487E and MAX1487E allows up to 128 transceivers
on a bus, compared to the 1-unit load (12k
Ω input
impedance) of standard RS-485 drivers (32 transceivers
maximum). Any combination of MAX487E/MAX1487E
and other RS-485 transceivers with a total of 32 unit
loads or less can be put on the bus. The MAX481E,
MAX483E, MAX485E, and MAX488E–MAX491E have
standard 12k
Ω receiver input impedance.
MAX483E/MAX487E/MAX488E/MAX489E:
Reduced EMI and Reflections
The MAX483E and MAX487E–MAX489E are slew-rate
limited, minimizing EMI and reducing reflections
caused by improperly terminated cables. Figure 16
shows the driver output waveform and its Fourier analy-
sis of a 150kHz signal transmitted by a MAX481E,
MAX485E, MAX490E, MAX491E, or MAX1487E. High-
frequency harmonics with large amplitudes are evident.
Figure 17 shows the same information displayed for a
MAX483E, MAX487E, MAX488E, or MAX489E transmit-
ting under the same conditions. Figure 17’s high-fre-
quency harmonics have much lower amplitudes, and
the potential for EMI is significantly reduced.
Low-Power Shutdown Mode
(MAX481E/MAX483E/MAX487E)
A low-power shutdown mode is initiated by bringing
both RE high and DE low. The devices will not shut
down unless both the driver and receiver are disabled.
In shutdown, the devices typically draw only 0.5µA of
supply current.
RE and DE may be driven simultaneously; the parts are
guaranteed not to enter shutdown if RE is high and DE
is low for less than 50ns. If the inputs are in this state
for at least 600ns, the parts are guaranteed to enter
shutdown.
For the MAX481E, MAX483E, and MAX487E, the tZH
and tZL enable times assume the part was not in the
low-power shutdown state (the MAX485E, MAX488E–
MAX491E, and MAX1487E can not be shut down). The
tZH(SHDN) and tZL(SHDN) enable times assume the
parts were shut down (see
Electrical Characteristics).
500kHz/div
0Hz
5MHz
10dB/div
Figure 16. Driver Output Waveform and FFT Plot of
MAX485E/MAX490E/MAX491E/MAX1487E Transmitting a
150kHz Signal
500kHz/div
0Hz
5MHz
10dB/div
Figure 17. Driver Output Waveform and FFT Plot of
MAX483E/MAX487E–MAX489E Transmitting a 150kHz Signal


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