MC34059 查看數據表（PDF） - Motorola => Freescale
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MC34059 Datasheet PDF : 12 Pages
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MC34058 MC34059
Table 1. Driver Truth Table
Enables
Outputs
Driver Data Inputs
H
L
X
X
DEX
H
H
L
H
REX
H
H
H
L
OAX
H
L
Z
Not Defined
OBX
L
H
Z
Not Defined
The outputs will be in a high impedance state when:
a) The Enable inputs are set according to Table 1;
b) The junction temperature exceeds the trip point of the thermal shutdown circuit. When in this condition, the output’s source and sink capability are shut off, and a
leakage current of less than 20 µA will flow. Disabled outputs may be taken to any voltage between –7.0 V and 12 V without damage to internal circuitry.
The drivers are protected from short circuits by two methods:
a) Current limiting is provided at each output, in both the source and sink direction, for shorts to any voltage within the 12 V to –7.0 V range, with respect to circuit
ground. The short circuit current will flow until the fault is removed, or until the thermal shutdown activates. The current limiting circuit has a negative temperature
coefficient and requires no resetting upon removal of the fault condition.
b) A thermal shutdown circuit disables the outputs when the junction temperature reaches +150°C, ± 20°C. The thermal shutdown circuit has a hysteresis of ∼ 12°C
to prevent oscillations. When this circuit activates, the output stage of each driver is put into the high impedance mode, thereby shutting off the output currents.
However, the remainder of the internal circuitry remains biased and the outputs will become active once again as the IC cools down.
Receiver Inputs
The receiver inputs and enable logic determine the state of
the receiver outputs in accordance with Table 2. Each
receiver input pair has a nominal differential threshold of at
most 200 mV (Pin OAX with respect to OBX) and a common
mode voltage range of –7.0 V and 12 V must be maintained
for proper operation. A nominal hysteresis of 100 mV is
typical. The receiver input characteristics are shown in
Figure 8. When the inputs are in the high impedance state,
they remain capable of the common mode voltage range of
–7.0 V to 12 V.
Receiver Outputs
The receiver outputs are TTL type outputs and act in
accordance with Table 2.
Enable Logic
Each driver output is active when the Driver Enable input
is true according to Table 1. Each receiver output is active
when the Receiver Enable input is true according to Table 2.
The Enable inputs have a nominal threshold of 1.2 V and
their voltage must be kept within the range of 0 V and VCC for
proper operation. If the voltage is taken more than 0.5 V
below ground or above VCC, excessive currents will flow and
proper operation of the drivers will be affected. An open pin is
equivalent to a logic high, but good design practices dictate
that inputs should never be left open. The enable inputs are
TTL compatible. Since the same pins are used for driver input
and receiver output, care must be taken to make sure that
DEX and REX are not both enabled. This may result in
corruption of both the transmitted and received data.
Receiver Data Inputs
OAX–OBX
≥ + 200 mV
≤ – 200 mV
X
X
Table 2. Receiver Truth Table
Enables
DEX
L
REX
L
L
L
L
H
H
L
Outputs
DRX
H
L
Z
Not Defined
APPLICATIONS
The MC34058/9 was designed to meet EIA/TIA–422 and
EIA/TIA–485 standards. EIA/TIA–422 specifies balanced
point–to–point transmission with the provision for multiple
receivers on the line. EIA/TIA–485 specifies balanced
point–to–point transmission and allows for multiple drivers
and receivers on the line. Refer to EIA/TIA documents for
more details. Figure 9 shows a typical EIA/TIA–422 example.
Figure 10 shows a typical EIA/TIA–485 example.
Figure 9. Typical EIA/TIA–422 Application
RT
100 Ω
MOTOROLA ANALOG IC DEVICE DATA
7
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