SLLS187B − NOVEMBER 1994 − REVISED JUNE 2007
D Four Independent Drivers and Receivers
D Driver Slew Rate Controlled by a Single
D Fast Driver Transition Times Down to
1.5 µs and Receiver Transition Times of
20 ns Typ
D Internal Thermal-Overload Protection
D RS-423-B Inputs and Outputs Designed to
Withstand ± 25 V
D ESD Protection Exceeds 2000 V Per
MIL-STD-833C Method 3015
D LinBICMOS Process Technology
The SN75LBC784 performs as four independent
RS-423-B driver/receiver pairs designed to interface data
terminal equipment (DTE) with data circuit-terminating
equipment (DCE) at rates up to 120 kbps and distances to
1.2 km. The SN75LBC784 provides an upgrade to the
RS-232 serial interface and can be backwards-compatible
with existing serial ports while offering the higher
performance required by new faster peripherals, such as
v.34 (v.fast) modems. The RS-232 standard, and
subsequent revisions, only supports data rates up to 20
kbps over about 15 meters of cable. For RS-423-B the data
rate is increased to 120 kbps and transmission distance to
1.2 km by reducing the maximum output signal swing,
increasing the driver output current, and reducing the
receiver input voltage thresholds.
H = high level, L = low level,
X = irrelevant, Z = high impedance (off)
? = indeterminate
The receivers consist of differential comparators with hysteresis and resistive attenuation on the inputs. The resistive attenuation
improves the input common-mode range and also provides additional protection from ESD and over-voltage stress. The differential
and common-mode input impedances are sufficiently high to meet RS-423-B. When a differential voltage input of 500 mV is applied
across the entire common-mode range (see Figure 5), the receiver characteristics and bias voltage allow the receiver to remain
in its intended binary state.
The drivers meet all RS-423-B specifications with built-in current limits and thermal overload protection. Slew-rate controlling
circuitry is included in the design, which is adjusted to suit the application by means of an external resistor (Rws). The slew rate
controlling circuitry also has a default mode—if the Rws pin is shorted to 5 V externally, the transistion time defaults to approximately
1.5 ms. The BIAS input, when shorted to 5 V externally, provides the internal node voltages. The receiver is compatible to RS-232
with the use of external input resistors to meet the RS-232 input resistance specification of 3 kΩ to 7 kΩ.
The SN75LBC784 is characterized for operation over the temperature range of 0°C to +70°C.
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PRODUCTION DATA information is current as of publication date. Products
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.
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