Applications Information
Propagation-Delay Matching
The MAX3093E/MAX3094E exhibit propagation delays
that are closely matched from one device to another,
even between devices from different production lots. This
feature allows multiple data lines to receive data and
clock signals with minimal skewing with respect to each
other. The MAX3093E receiver propagation delays are
trimmed to a predetermined value ±8ns, while the
MAX3094E delays are trimmed to a predetermined value
±10ns.
128 Receivers on the Bus
The standard RS-485 input impedance is 12kΩ (one-
unit load). The standard RS-485 transmitter can drive
32 unit loads. The MAX3093E/MAX3094E present a 1/4-
unit-load input impedance (48kΩ), which allows up to
128 receivers on a bus. Any combination of these RS-
485 receivers with a total of 32-unit loads can be con-
nected to the same bus.
Fail-Safe Implementation
The MAX3093E/MAX3094E receiver inputs guarantee a
logic high output when the inputs are open circuit (no
termination resistor used). This occurs when the trans-
mitter is removed from the bus or when all transmitter
outputs are high impedance. However, when the line is
terminated and the transmitters are disabled, the differ-
ential voltage between the _+ and _- inputs falls below
the ±200mV RS-485 sensitivity threshold. Consequent-
ly, the outputs become undefined. To maintain a fail-
safe receiver output while using a terminating resistor,
input _+ must be biased at least 200mV above input B.
The resistor-divider network shown in Figure 6 is rec-
ommended.
MAX3093E/MAX3094E
±15kV ESD-Protected, 10Mbps, 3V/5V,
Low-Power Quad RS-422/RS-485 Receivers
10 ______________________________________________________________________________________
