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DS36C278
Low Power Multipoint EIA-RS-485 Transceiver
General Description
The DS36C278 is a low power differential bus/line transceiver designed to meet the requirements of RS-485 standard formultipoint data transmission. In addition it is compatible with TIA/EIA-422-B.
The CMOS design offers significant power savings over its
bipolar andALS counterparts without sacrificing ruggedness
against ESD damage. The device is ideal for use in battery
powered or power conscious applications. I
CC
is specified at
500 µA maximum.
The driver and receiver outputs feature TRI-STATE
®
capability.The driver outputs operate over the entire common mode
range of −7V to +12V. Bus contention or fault situations that
cause excessive power dissipation within the device are
handled by a thermal shutdown circuit, which forces the
driver outputs into the high impedance state.
The receiver incorporates a fail safe circuit which guarantees
a high output state when the inputs are left open. (Note 1)
The DS36C278T is fully specified over the industrial temperature range (−40˚C to +85˚C).
Features
n 100%RS-485 compliant
— Guaranteed RS-485 device interoperation
n Low power CMOS design: I
CC
500 µA max
n Built-in power up/down glitch-free circuitry
— Permits live transceiver insertion/displacement
n DIP and SOIC packages available
n Industrial temperature range: −40˚C to +85˚C
n On-board thermal shutdown circuitry
— Prevents damage to the device in the event of
excessive power dissipation
n Wide common mode range: −7V to +12V
n Receiver open input fail-safe (Note 1)
n
1
⁄4unit load (DS36C278): ≥128 nodes
n
1
⁄2unit load (DS36C278T): ≥64 nodes
n ESD (human body model): ≥2kV
n Drop in replacement for:
— LTC485, MAX485, DS75176, DS3695
Connection and Logic Diagram Truth Table
DRIVER SECTION
RE* DE DI DO/RI DO*/RI*
XHH H L
XHL L H
XLX Z Z
RECEIVER SECTION
RE* DE RI-RI* RO
LL ≥+0.2V H
LL ≤−0.2V L
HL X Z
L L OPEN (Note 1) H
Note 1: Non-terminated, open input only
TRI-STATE®is a registered trademark of National Semiconductor Corporation.
DS012040-1
Order Number DS36C278TM, DS36C278TN,
DS36C278M, DS36C278N
See NS Package Number M08A or N08E
July 1998
DS36C278 Low Power Multipoint EIA-RS-485 Transceiver
© 1999 National Semiconductor Corporation DS012040 www.national.com
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Absolute Maximum Ratings (Note 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
CC
) +12V
Input Voltage (DE, RE*, & DI) −0.5V to (V
CC
+0.5V)
Common Mode (V
CM
)
Driver Output/Receiver Input
±
15V
Input Voltage (DO/RI, DO*/RI*)
±
14V
Receiver Output Voltage −0.5V to (V
CC
+0.5V)
Maximum Package Power Dissipation
@
+25˚C
M Package 1190 mW, derate 9.5 mW/˚C above +25˚C
N Package 744 mW, derate 6.0 mW/˚C above +25˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature
(Soldering 4 sec) +260˚C
Recommended Operating
Conditions
Min Typ Max Units
Supply Voltage (V
CC
) +4.75 +5.0 +5.25 V
Bus Voltage −7 +12 V
Operating Free Air Temperature (Ta)
DS36C278T −40 25 +85 ˚C
DS36C278 0 25 +70 ˚C
Electrical Characteristics (Notes 3, 4)
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified
Symbol Parameter Conditions Reference Min Typ Max Units
DIFFERENTIAL DRIVER CHARACTERISTICS
V
OD1
Differential Output Voltage IO= 0 mA (No Load)
(422)
(485)
1.5 5.0 V
V
OD0
Output Voltage IO= 0 mA 0 5.0 V
V
OD0*
Output Voltage (Output to GND) 0 5.0 V
V
OD2
Differential Output Voltage RL=50Ω (422)
Figure 1
2.0 2.8 V
(Termination Load) R
L
=27Ω (485) 1.5 2.3 5.0 V
∆V
OD2
Balance of V
OD2
RL=27Ωor 50Ω (Note 5) −0.2 0.1 +0.2 V
|V
OD2−V0D2*
| (422, 485)
V
OD3
Differential Output Voltage
(Full Load)
R1=54Ω,R2=375Ω
V
TEST
= −7V to +12V
Figure 2
1.5 2.0 5.0 V
V
OC
Driver Common Mode
Output Voltage
RL=27Ω (485)
Figure 1
0 3.0 V
R
L
=50Ω (422) 0 3.0 V
∆V
OC
Balance of V
OC
|VOC−V
OC*
|
R
L
=27Ωor
R
L
=50Ω
(Note 5)
(422, 485)
−0.2 +0.2 V
I
OSD
Driver Output Short-Circuit
Current
VO= +12V (485)
Figure 4
200 +250 mA
V
O
= −7V (485) −190 −250 mA
RECEIVER CHARACTERISTICS
V
TH
Differential Input High
Threshold Voltage
VO=VOH,IO= −0.4V
−7V ≤ V
CM
≤ +12V
(Note 6)
(422, 485)
+0.035 +0.2 V
V
TL
Differential Input Low
Threshold Voltage
VO=VOL,IO= 0.4 mA
−7V ≤ V
CM
≤ +12V
−0.2 −0.035 V
V
HST
Hysteresis VCM= 0V (Note 7) 70 mV
R
IN
Input Resistance −7V ≤ VCM≤ +12V DS36C278T 24 68 kΩ
R
IN
Input Resistance −7V ≤ VCM≤ +12V DS36C278 48 68 kΩ
I
IN
Line Input Current Other Input = 0V, DS36C278 VIN= +12V 0 0.19 0.25 mA
(Note 8) DE = V
IL
,RE*=VIL,V
IN
= −7V 0 −0.1 −0.2 mA
V
CC
= 4.75 to 5.25 DS36C278T VIN= +12V 0 0.19 0.5 mA
or 0V V
IN
= −7V 0 −0.1 −0.4 mA
I
ING
Line Input Current Glitch Other Input = 0V, DS36C278 VIN= +12V 0 0.19 0.25 mA
(Note 8) DE = V
IL
,RE*=VIL,V
IN
= −7V 0 −0.1 −0.2 mA
V
CC
= +3.0V or 0V, DS36C278T VIN= +12V 0 0.19 0.5 mA
T
A
= 25˚C VIN= −7V 0 −0.1 −0.4 mA
I
B
Input Balance Test RS = 500Ω (422) (Note 10)
±
400 mV
V
OH
High Level Output Voltage IOH= −4 mA, VID= +0.2V
RO
Figure 11
3.5 4.6 V
V
OL
Low Level Output Voltage IOL= +4 mA, VID= −0.2V 0.3 0.5 V
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Electrical Characteristics (Notes 3, 4) (Continued)
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified
Symbol Parameter Conditions Reference Min Typ Max Units
RECEIVER CHARACTERISTICS
I
OSR
Short Circuit Current VO= GND
RO
73585mA
I
OZR
TRI-STATE Leakage
Current
VO= 0.4V to 2.4V
±
1µA
DEVICE CHARACTERISTICS
V
IH
High Level Input Voltage
DE,
RE*,
DI
2.0 V
CC
V
V
IL
Low Level Input Voltage GND 0.8 V
I
IH
High Level Input Current VIH=V
CC
2µA
I
IL
Low Level Input Current VCC=5V
V
IL
=0V
−2 µA
V
CC
= +3.0V −2 µA
I
CC
Power Supply Current Driver and Receiver ON
V
CC
200 500 µA
I
CCR
(No Load) Driver OFF, Receiver ON 200 500 µA
I
CCD
Driver ON, Receiver OFF 200 500 µA
I
CCZ
Driver and Receiver OFF 200 500 µA
Switching Characteristics (Notes 4, 9)
Over Supply Voltage and Operating Temperature ranges, unless otherwise specified
Symbol Parameter Conditions Reference Min Typ Max Units
DRIVER CHARACTERISTICS
t
PHLD
Differential Propagation
Delay High to Low
RL=54Ω,CL= 100 pF
Figures 5, 6
10 39 80 ns
t
PLHD
Differential Propagation
Delay Low to High
10 40 80 ns
t
SKD
Differential Skew
|t
PHLD−tPLHD
|
0 1 10 ns
t
r
Rise Time 32550 ns
t
f
Fall Time 32550 ns
t
PHZ
Disable Time High to Z CL=15pF
Figures 7, 8
— 80 200 ns
t
PLZ
Disable Time Low to Z RE*=L
Figures 9, 10
— 80 200 ns
t
PZH
Enable Time Z to High CL= 100 pF
Figures 7, 8
— 50 200 ns
t
PZL
Enable Time Z to Low RE*=L
Figures 9, 10
— 65 200 ns
RECEIVER CHARACTERISTICS
t
PHL
Propagation Delay
High to Low
CL=15pF
Figures 12, 13
30 210 400 ns
t
PLH
Propagation Delay
Low to High
30 190 400 ns
t
SK
Skew, |t
PHL−tPLH
| 0 20 50 ns
t
PLZ
Output Disable Time CL=15pF
Figures 14, 15, 16
— 50 150 ns
t
PHZ
— 55 150 ns
t
PZL
Output Enable Time — 40 150 ns
t
PZH
— 45 150 ns
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Switching Characteristics (Notes 4, 9) (Continued)
Note 2: “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the devices
should be operated at these limits. The table of “Electrical Characteristics” specifies conditions of device operation.
Note 3: Current into devicepins is defined as positive. Current out of devicepins is defined as negative. All voltages are referenced to ground exceptV
OD1
and V
OD2
.
Note 4: All typicals are given for: V
CC
= +5.0V, TA= + 25˚C.
Note 5: Delta |V
OD2
| and Delta |VOC| are changes in magnitude of V
OD2
and VOC, respectively, that occur when input changes state.
Note 6: Threshold parameter limits specified as an algebraic value rather than by magnitude.
Note 7: Hysteresis defined as V
HST=VTH−VTL
.
Note 8: I
IN
includes the receiver input current and driver TRI-STATE leakage current.
Note 9: C
L
includes probe and jig capacitance.
Note 10: For complete details of test, see RS-485.
Parameter Measurement Information
DS012040-2
FIGURE 1. Driver V
OD2
and V
OC
DS012040-18
FIGURE 2. Driver V
OD3
DS012040-3
FIGURE 3. Driver VOHand V
OL
DS012040-4
Vtest = −7V to +12V
FIGURE 4. Driver I
OSD
DS012040-5
FIGURE 5. Driver Differential Propagation Delay Test Circuit
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Parameter Measurement Information (Continued)
DS012040-6
FIGURE 6. Driver Differential Propagation Delays and Differential Rise and Fall Times
DS012040-7
FIGURE 7. TRI-STATE Test Circuit (t
PZH,tPHZ
)
DS012040-8
FIGURE 8. TRI-STATE Waveforms (t
PZH,tPHZ
)
DS012040-9
FIGURE 9. TRI-STATE Test Circuit (t
PZL,tPLZ
)
DS012040-10
FIGURE 10. TRI-STATE Waveforms (t
PZL,tPLZ
)
DS012040-11
FIGURE 11. Receiver VOHand V
OL
DS012040-12
FIGURE 12. Receiver Differential Propagation Delay
Test Circuit
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Parameter Measurement Information (Continued)
DS012040-13
FIGURE 13. Receiver Differential Propagation Delay Waveforms
DS012040-14
FIGURE 14. Receiver TRI-STATE Test Circuit
DS012040-15
FIGURE 15. Receiver Enable and Disable Waveforms (t
PLZ,tPZL
)
DS012040-16
FIGURE 16. Receiver Enable and Disable Waveforms (t
PHZ,tPZH
)
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Typical Application Information
TABLE 1. Device Pin Descriptions
Pin
No.
Name Description
1 RO Receiver Output: When RE (Receiver Enable) is LOW, the receiver is enabled (ON), if DO/RI ≥
DO*/RI* by 200 mV, RO will be HIGH. If DO/RI ≤ DO*/RI* by 200 mV, RO will be LOW. Additionally
RO will be HIGH for OPEN (Non-terminated) Inputs.
2 RE* Receiver Output Enable: When RE* is LOW the receiver output is enabled. When RE* is HIGH, the
receiver output is in TRI-STATE (OFF).
3 DE Driver Output Enable: When DE is HIGH, the driver outputs are enabled. When DE is LOW, the driver
outputs are in TRI-STATE (OFF).
4 DI Driver Input: When DE (Driver Enable) is HIGH, the driver is enabled, if DI is LOW, then DO/RI will be
LOW and DO*/RI* will be HIGH. If DI is HIGH, then DO/RI is HIGH and DO*/RI* is LOW.
5 GND Ground Connection.
6 DO/RI Driver Output/Receiver Input, 485 Bus Pin.
7 DO*/RI* Driver Output/Receiver Input, 485 Bus Pin.
8V
CC
Positive Power Supply Connection: Recommended operating range for VCCis +4.75V to +5.25V.
Unit Load
Aunit load for anRS-485 receiver is defined by the input current versus the input voltage curve. The gray shaded region
is the defined operating range from −7V to +12V. The top
border extending from −3V at 0 mA to +12V at +1 mA is defined as one unit load. Likewise, the bottom border extending
from +5V at 0 mA to −7V at −0.8 mA is also defined as one
unit load (see
Figure 18
). An RS-485 driver is capable of
driving up to 32 unit loads. This allows up to 32 nodes on a
single bus. Although sufficient for many applications, it is
sometimes desirable to have even more nodes. For example, an aircraft that has 32 rows with 4 seats per row
would benefit from having 128 nodes on one bus. This would
allow signals to be transferred to and from each individual
seat to 1 main station. Usually there is one or two less seats
in the last row of the aircraft near the restrooms and food
storage area. This frees the node for the main station.
The DS36C278, the DS36C279, and the DS36C280 all have
1
⁄2unit load and1⁄4unit load (UL) options available. These
devices will allow up to 64 nodes or 128 nodes guaranteed
over temperature depending upon which option is selected.
The
1
⁄2UL option is available in industrial temperature and
the
1
⁄4UL is available in commercial temperature.
First, for a
1
⁄2UL device the top and bottom borders shown in
Figure 18
are scaled. Both 0 mA reference points at +5V and
−3V stay the same. The other reference points are +12V at
+0.5 mA for the top border and −7V at −0.4 mA for the bottom border (see
Figure 18
). Second, for a1⁄4UL device the
top and bottom borders shown in
Figure 18
are scaled also.
Again, both 0 mA reference points at +5V and −3V stay the
same. The other reference points are +12V at +0.25 mA for
the top border and −7V at −0.2 mA for the bottom border
(see
Figure 18
).
The advantage of the
1
⁄2UL and1⁄4UL devices is the increased number of nodes on one bus. In a single master
multi-slave type of application where the number of slaves
exceeds 32, the DS36C278/279/280 may save in the cost of
extra devices like repeaters, extra media like cable, and/or
extra components like resistors.
The DS36C279 and DS36C280 have an additional feature
which offers more advantages. The DS36C279 has an automatic sleep mode function for power conscious applications.
The DS36C280 has a slew rate control for EMI conscious
applications. Refer to the sleep mode and slew rate control
portion of the application information section in the corresponding datasheet for more information on these features.
DS012040-17
FIGURE 17. Typical RS-485 Bus Interface
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Unit Load (Continued)
DS012040-19
FIGURE 18. Input Current vs Input Voltage Operating Range
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Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC
Order Number DS36C278TM, DS36C278M
NS Package Number M08A
8-Lead (0.300" Wide) Molded Dual-In-Line Package
Order Number DS36C278TN, DS36C278N
NS Package Number N08E
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LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into
the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
DS36C278 Low Power Multipoint EIA-RS-485 Transceiver
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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