DS36C278
Low Power Multipoint EIA-RS-485 Transceiver
General Description
The DS36C278 is a low power differential bus/line trans-
ceiver designed to meet the requirements of RS-485 stan-
dard for multipoint data transmission. In addition it is compat-
ible with TIA/EIA-422-B.
The CMOS design offers significant power savings over its
bipolar and ALS 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 A maximum.
The driver and receiver outputs feature TRI-STATE
capabil-
ity. 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 tem-
perature range (-40C to +85C).
Features
n
100% RS-485 compliant
-- Guaranteed RS-485 device interoperation
n
Low power CMOS design:
I
CC
500 A 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:
-40C to +85C
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
/
4
unit load (DS36C278):
128 nodes
n
1
/
2
unit load (DS36C278T):
64 nodes
n
ESD (human body model):
2 kV
n
Drop in replacement for:
-- LTC485, MAX485, DS75176, DS3695
Connection and Logic Diagram
Truth Table
DRIVER SECTION
RE*
DE
DI
DO/RI
DO*/RI*
X
H
H
H
L
X
H
L
L
H
X
L
X
Z
Z
RECEIVER SECTION
RE*
DE
RI-RI*
RO
L
L
+0.2V
H
L
L
-0.2V
L
H
L
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
T
ransceiver
1999 National Semiconductor Corporation
DS012040
www.national.com
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
@
+25C
M Package 1190 mW, derate
9.5 mW/C above +25C
N Package 744 mW, derate
6.0 mW/C above +25C
Storage Temperature Range
-65C to +150C
Lead Temperature
(Soldering 4 sec)
+260C
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
I
O
= 0 mA (No Load)
(422)
(485)
1.5
5.0
V
V
OD0
Output Voltage
I
O
= 0 mA
0
5.0
V
V
OD0*
Output Voltage
(Output to GND)
0
5.0
V
V
OD2
Differential Output Voltage
R
L
= 50
(422)
Figure 1
2.0
2.8
V
(Termination Load)
R
L
= 27
(485)
1.5
2.3
5.0
V
V
OD2
Balance of V
OD2
R
L
= 27
or 50
(Note 5)
-0.2
0.1
+0.2
V
|V
OD2
- V
0D2*
|
(422, 485)
V
OD3
Differential Output Voltage
(Full Load)
R1 = 54
, R2 = 375
V
TEST
= -7V to +12V
Figure 2
1.5
2.0
5.0
V
V
OC
Driver Common Mode
Output Voltage
R
L
= 27
(485)
Figure 1
0
3.0
V
R
L
= 50
(422)
0
3.0
V
V
OC
Balance of V
OC
|V
OC
- V
OC*
|
R
L
= 27
or
R
L
= 50
(Note 5)
(422, 485)
-0.2
+0.2
V
I
OSD
Driver Output Short-Circuit
Current
V
O
= +12V
(485)
Figure 4
200
+250
mA
V
O
= -7V
(485)
-190
-250
mA
RECEIVER CHARACTERISTICS
V
TH
Differential Input High
Threshold Voltage
V
O
= V
OH
, I
O
= -0.4V
-7V
V
CM
+12V
(Note 6)
(422, 485)
+0.035
+0.2
V
V
TL
Differential Input Low
Threshold Voltage
V
O
= V
OL
, I
O
= 0.4 mA
-7V
V
CM
+12V
-0.2
-0.035
V
V
HST
Hysteresis
V
CM
= 0V
(Note 7)
70
mV
R
IN
Input Resistance
-7V
V
CM
+12V
DS36C278T
24
68
k
R
IN
Input Resistance
-7V
V
CM
+12V
DS36C278
48
68
k
I
IN
Line Input Current
Other Input = 0V,
DS36C278
V
IN
= +12V
0
0.19
0.25
mA
(Note 8)
DE = V
IL
, RE* = V
IL
,
V
IN
= -7V
0
-0.1
-0.2
mA
V
CC
= 4.75 to 5.25
DS36C278T
V
IN
= +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
V
IN
= +12V
0
0.19
0.25
mA
(Note 8)
DE = V
IL
, RE* = V
IL
,
V
IN
= -7V
0
-0.1
-0.2
mA
V
CC
= +3.0V or 0V,
DS36C278T
V
IN
= +12V
0
0.19
0.5
mA
T
A
= 25C
V
IN
= -7V
0
-0.1
-0.4
mA
I
B
Input Balance Test
RS = 500
(422) (Note 10)
400
mV
V
OH
High Level Output Voltage
I
OH
= -4 mA, V
ID
= +0.2V
RO
Figure 11
3.5
4.6
V
V
OL
Low Level Output Voltage
I
OL
= +4 mA, V
ID
= -0.2V
0.3
0.5
V
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2
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
V
O
= GND
RO
7
35
85
mA
I
OZR
TRI-STATE Leakage
Current
V
O
= 0.4V to 2.4V
1
A
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
V
IH
= V
CC
2
A
I
IL
Low Level Input Current
V
CC
= 5V
V
IL
= 0V
-2
A
V
CC
= +3.0V
-2
A
I
CC
Power Supply Current
Driver and Receiver ON
V
CC
200
500
A
I
CCR
(No Load)
Driver OFF, Receiver ON
200
500
A
I
CCD
Driver ON, Receiver OFF
200
500
A
I
CCZ
Driver and Receiver OFF
200
500
A
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
R
L
= 54
, C
L
= 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
- t
PLHD
|
0
1
10
ns
t
r
Rise Time
3
25
50
ns
t
f
Fall Time
3
25
50
ns
t
PHZ
Disable Time High to Z
C
L
= 15 pF
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
C
L
= 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
C
L
= 15 pF
Figures 12, 13
30
210
400
ns
t
PLH
Propagation Delay
Low to High
30
190
400
ns
t
SK
Skew, |t
PHL
- t
PLH
|
0
20
50
ns
t
PLZ
Output Disable Time
C
L
= 15 pF
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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3
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 device pins is defined as positive. Current out of device pins is defined as negative. All voltages are referenced to ground except V
OD1
and V
OD2
.
Note 4: All typicals are given for: V
CC
= +5.0V, T
A
= + 25C.
Note 5: Delta |V
OD2
| and Delta |V
OC
| are changes in magnitude of V
OD2
and V
OC
, 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
= V
TH
- V
TL
.
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 V
OH
and 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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4
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
, t
PHZ
)
DS012040-8
FIGURE 8. TRI-STATE Waveforms (t
PZH
, t
PHZ
)
DS012040-9
FIGURE 9. TRI-STATE Test Circuit (t
PZL
, t
PLZ
)
DS012040-10
FIGURE 10. TRI-STATE Waveforms (t
PZL
, t
PLZ
)
DS012040-11
FIGURE 11. Receiver V
OH
and V
OL
DS012040-12
FIGURE 12. Receiver Differential Propagation Delay
Test Circuit
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5
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