MAX3080 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX3080 Datasheet PDF : 20 Pages
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Fail-Safe, High-Speed (10Mbps),
Slew-Rate-Limited RS-485/RS-422 Transceivers
B
ATE
VID
RR
RECEIVER
OUTPUT
20dB/div
A
Figure 13. Receiver Propagation Delay Test Circuit
A
20dB/div
B
0Hz
100kHz/div
1MHz
Figure 14. Driver Output Waveform and FFT Plot of
MAX3086/MAX3087/MAX3088, and MAX3089 with
SRL = GND, Transmitting a 20kHz Signal
A
20dB/div
B
0Hz
100kHz/div
1MHz
0Hz
100kHz/div
1MHz
Figure 15. Driver Output Waveform and FFT Plot of
MAX3083/MAX3084/MAX3085, and MAX3089
with SRL = VCC, Transmitting a 20kHz Signal
Figure 16. Driver Output Waveform and FFT Plot of
MAX3080/MAX3081/MAX3082, and MAX3089
with SRL = Unconnected, Transmitting a 20kHz Signal
components with large amplitudes are evident. Figure
15 shows the same signal displayed for a MAX3083/
MAX3084/MAX3085, and MAX3089 with SRL = VCC),
transmitting under the same conditions. Figure 15’s
high-frequency harmonic components are much lower
in amplitude, compared with Figure 14’s, and the poten-
tial for EMI is significantly reduced. Figure 16
shows the same signal displayed for a MAX3080/
MAX3081/MAX3082, and MAX3089 with SRL = uncon-
nected, transmitting under the same conditions. Figure
16’s high-frequency harmonic components are even
lower.
In general, a transmitter’s rise time relates directly to the
length of an unterminated stub, which can be driven with
only minor waveform reflections. The following equation
expresses this relationship conservatively:
Length = tRISE / (10 x 1.5ns/ft)
where tRISE is the transmitter’s rise time.
For example, the MAX3080’s rise time is typically
1320ns, which results in excellent waveforms with a stub
length up to 90 feet. A system can work well with longer
unterminated stubs, even with severe reflections, if the
waveform settles out before the UART samples them.
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