MC75174BDW ON Semiconductor, MC75174BDW Datasheet - Page 9

• Manufacturer Part Number: MC75174BDW
• Description: Bus Transmitters Quad EIA-485 Line
• Manufacturer: ON Semiconductor

Specifications of MC75174BDW

• Data Rate: 10 Mbps
• Interface: EIA/TIA-422-A, EIA/TIA-485, V.11, V.27
• Supply Voltage (max): 5.25 V
• Supply Voltage (min): 4.75 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-20 Wide
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: No

(applicable to both EIA−485 and EIA−422−A) is listed as
85°C. However, a lower ambient may be required
depending on system use (i.e. specifically how many
drivers within a package are used) and at what current
levels they are operating. The maximum power which may
be dissipated within the package is determined by:
where:
150°C, ±20°C, T
dissipated within the package is calculated from:
PD
where:
must be calculated and summed for each of the four drivers,
while the last term is common to the entire package.
driver, V
package can be used?
300 mW, that leaves 1.2 W (1.5 W − 0.3 W) for the drivers.
From Figures 7 and 9, V
The power dissipated in each driver is:
Since each driver dissipates 160 mW, the four drivers per
package could be used in this application.
each driver, V
per package can be used?
300 mW, that leaves 230 mW (530 mW − 300 mW) for the
The
Since the thermal shutdown feature has a trip point of
As indicated in the equation, the first term (in brackets)
Example 1: T
Maximum allowable power dissipation is:
Since the power supply current of 60 mA dissipates
{(5.0 − 3.85) • 0.055} + (1.75 • 0.055) = 160 mW.
Example 2: T
Maximum allowable power dissipation is:
Since the power supply current of 60 mA dissipates
CC
maximum
PD max + 130
= {[(V
driver
V
V
Figures 7 to 10;
I
(typical 60 mA).
CC
PD max +
CC
OH
R
70°C/W for the DIP package, 85°C/W for
SOIC package);
T
temperature, and
T
= 5.0 V, DIP package. How many drivers per
A
Jmax
qJA
= the quiescent power supply current
CC
, V
= the supply voltage;
= ambient temperature.
A
A
CC
=
= 5.0 V, SOIC package. How many drivers
Jmax
OL
PD max +
= package thermal resistance (typical
= 85°C, I
= max. operating junction
+ (V
= 25°C, I
− V
are measured or estimated from
ambient
is selected to be 130°C. The power
130°C * 25°C
OH
CC
85
°C
OL
70°C W
) • I
• I
OL
°
C W
* 85
[1.75 V, and V
OL
T
CC
= 27.8 mA, I
OH
Jmax
R
)
= I
] + V
°
qJA
operating
C
OH
–T
+ 0.53 W
+ 1.5 W
A
OL
= 55 mA for each
• I
OH
OL
OH
= 20 mA for
MC75172B, MC75174B
temperature
)} each
[3.85 V.
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9
drivers. From Figures 8 and 10 (adjusted for V
V
in each driver is:
drivers in a package would be marginal. Options include
reducing the load current, reducing the ambient
temperature, and/or providing a heat sink.
System Requirements
transmitting data differentially to at least 32 unit loads, plus
an equivalent DC termination resistance of 60W, over a
common mode voltage of −7.0 to 12 V. A unit load (U.L.),
as defined by EIA−485, is shown in Figure 17.
impedance of less than one U.L., while a load current of a
magnitude outside the shaded area is greater than one U.L.
A system’s total load is the sum of the unit load equivalents
of each receiver’s input current, and each disabled driver’s
output leakage current. The 60W termination resistance
mentioned above allows for two 120W terminating
resistors.
the graphs of Figures 7 and 9, it can be determined that the
maximum current an MC75172B or MC75174B driver will
source or sink is [65 mA.
System Example
Figure 18. In this example, it is assumed each receiver’s
input characteristics correspond to 1.0 U.L. as defined in
Figure 17. Each “off” driver, with a maximum leakage of
±50 mA over the common mode range, presents a load of
[0.06 U.L. The total load for the active driver is therefore
8.3 unit loads, plus the parallel combination of the two
terminating resistors (60W). It is up to the system software
to control the driver Enable pins to ensure that only one
driver is active at any time.
Reprinted from EIA−485, Electronic Industries Association,
Washington,DC.
OL
{(5.0 − 4.27) • 0.020} + (1.38 • 0.0278) = 53 mW
Since each driver dissipates 53 mW, the use of all four
EIA−485 requires each driver to be capable of
A load current within the shaded regions represents an
Using the EIA−485 requirements (worst case limits), and
An example of a typical EIA−485 system is shown in
−7.0 V
[1.38 V, and V
Figure 17. Unit Load Definition
−3.0 V
1.0 mA
OH
−0.8 mA
I
[4.27 V. The power dissipated
5.0 V
CC
12 V
= 5.0 V),
V