DS485 Low Power RS-485/RS-422 Multipoint Transceiver
July 1998
DS485
Low Power RS-485/RS-422 Multipoint Transceiver
General Description
The DS485 is a low-power transceiver for RS-485 and
RS-422 communication. The device contains one driver and
one receiver. The drivers slew rate allows for operation up to
2.5 Mbps (see Applications Information section).
The transceiver draws 200 µA of supply current when un-
loaded or fully loaded with the driver disabled and operates
from a single +5V supply.
The driver is short-circuit current limited and is protected
against excessive power dissipation by thermal shutdown
circuitry that places the driver outputs into TRI-STATE
®
(High Impedance state) under fault conditions. The driver
guarantees a minimum of 1.5V differential output voltage
with maximum loading across the common mode range
(V
OD3
).
The receiver has a failsafe feature that guarantees a
logic-high output if the input is open circuit.
The DS485 is available in surface mount and DIP packages
and is characterized for Industrial and Commercial tempera-
ture range operation.
Features
n
n
n
n
n
n
Meets TIA/EIA RS-485 multipoint standard
Guaranteed full load output voltage (V
OD3
)
Low quiescent current: 200 µA typ
−7V to +12V common-mode input voltage range
TRI-STATE outputs on driver and receiver
AC performance:
— Driver transition time: 25 ns typ
— Driver propagation delay: 40 ns typ
— Driver skew: 1 ns typ
— Receiver propagation delay: 200 ns typ
— Receiver skew: 20 ns typ
Half-duplex flow through pinout
Operates from a single 5V supply
Allows up to 32 transceivers on the bus
Current-limiting and thermal shutdown for driver
overload protection
Industrial temperature range operation
Pin and functional compatible with MAX485 and LTC485
n
n
n
n
n
n
Connection and Logic Diagram
DIP and SOIC
Truth Table
DRIVER SECTION
RE
*
X
X
X
RE
*
L
DE
H
H
L
DE
L
L
X
L
DI
H
L
X
A-B
≥+0.2V
≤−0.2V
X
OPEN
*
A
H
L
Z
B
L
H
Z
RO
H
L
Z
H
RECEIVER SECTION
DS012880-1
L
H
L
X = indeterminate
Z = TRI-STATE
Order Number
DS485N
DS485M
DS485TN
DS485TM
Temp. Range
0˚C to +70˚C
0˚C to +70˚C
−40˚C to +85˚C
−40˚C to +85˚C
Package/###
DIP/N08E
SOP/M08A
DIP/N08E
SOP/M08A
*
Note: Non Terminated, Open Input only
TRI-STATE
®
is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS012880
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Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
CC
)
+12V
*
, DE)
−0.5V to (V
CC
+ 0.5V)
Enable Input Voltage (RE
Driver Input Voltage (DI)
−0.5V to (V
CC
+ 0.5V)
Driver Output Voltage (A, B)
−14V to +14V
Receiver Input Voltage (A, B)
−14V to +14V
Receiver Output Voltage (RO)
−0.5V to (V
CC
+ 0.5V)
Maximum Package Power Dissipation
@
+25˚C
M Package
1.19W
N Package
0.74W
Derate M Package 9.5 mW/˚C above +25˚C
Derate N Package 6.0 mW/˚C above +25˚C
Maximum Package Power Dissipation
@
+70˚C
M Package
0.76W
N Package
Storage Temperature Range
Lead Temperature Range
(Soldering, 4 sec.)
ESD (HBM)
0.47W
−65˚C to +150˚C
+260˚C
≥2
kV
Recommended Operating
Conditions
Supply Voltage (V
CC
)
Operating Free Air
Temperature (T
A
)
DS485
DS485T
Bus Common Mode Voltage
Min
+4.75
Typ
+5.0
Max
+5.25
Units
V
0
−40
−7
+25
+25
+70
+85
+12
˚C
˚C
V
Electrical Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 2, 3)
Symbol
V
OD1
V
OD2
∆V
OD
V
OD3
V
OC
∆V
OC
V
IH
V
IL
I
IN1
I
IN2
V
TH
∆V
TH
V
OH
V
OL
I
OZR
R
IN
I
CC
I
OSD1
I
OSD2
I
OSR
Parameter
Differential Driver Output Voltage
Differential Driver Output Voltage
with Load
Change in Magnitude of Output
Differential Voltage
Differential Driver Output Voltage —
Full Load with Max V
CM
Driver Common-Mode Output Voltage
Change in Magnitude of Common-Mode
Output Voltage
Input High Voltage
Input Low Voltage
Input Current
Input Current (Note 5)
DE = 0V, V
CC
= 0V or 5.25V
Receiver Differential Threshold Voltage
Receiver Input Hysteresis
Receiver Output High Voltage
Receiver Output Low Voltage
TRI-STATE Output Current at Receiver
Receiver Input Resistance
No-Load Supply Current (Note 6)
Driver Short Circuit Current, V
O
= HIGH
Driver Short Circuit Current, V
O
= LOW
Receiver Short Circuit Current
V
IN
= 0V or V
CC
V
IN
= +12V
V
IN
= −7V
−7V
≤
V
CM
≤
+12V
V
CM
= 0V
I
O
= −4 mA, V
ID
= 0.2V
I
O
= 4 mA, V
ID
= −0.2V
0.4V
≤
V
O
≤
2.4V
−7V
≤
V
IN
≤
+12V
DE = V
CC
, RE
*
= 0V or V
CC
DE = 0V, RE
*
= 0V or V
CC
−7V
≤
V
O
≤
+12V
−7V
≤
V
O
≤
+12V
0V
≤
V
O
≤
V
CC
RO
A, B
V
CC
A, B
35
35
7
12
200
200
900
500
250
250
85
RO
DI,
DE,
RE
*
A, B
−0.2
70
3.5
0.4
2.0
0.8
V
V
µA
mA
mA
V
mV
V
V
µA
kΩ
µA
µA
mA
mA
mA
R1 = 54Ω, R2 = 375Ω
V
TEST
= −7V to +12V,
Figure 5
R
L
= 27Ω or 50Ω,
Figure 1
R
L
= 27Ω or 50Ω,
Figure 1
(Note 4)
1.5
2.0
5
3
0.2
V
V
|V|
Conditions
(No Load)
R
L
= 50Ω, (RS422),
Figure 1
R
L
= 27Ω, (RS485),
Figure 1
R
L
= 27Ω or 50Ω (Note 4)
Pin
A, B
2
1.5
2.8
2.3
5
0.2
Min Typ
Max
5
Units
V
V
V
|V|
±
2
1.0
−0.8
0.2
±
1
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2
Switching Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 7, 8)
Symbol
t
PLHD
t
PHLD
t
SKEW
t
r
t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLHD
t
PHLD
t
SKEW
t
ZH
t
ZL
t
LZ
t
HZ
f
max
Parameter
Driver Differential Propagation Delay — Low to High
Driver Differential Propagation Delay — High to Low
Differential Skew |t
PHLD
− t
PLHD
|
Driver Rise Time
Driver Fall Time
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable from Output Low
Driver Disable from Output High
Receiver Differential Propagation Delay — Low to High
Receiver Differential Propagation Delay — High to Low
Differential Skew |t
PHLD
− t
PLHD
|
Receiver Enable to Output High
Receiver Enable to Output Low
Receiver Disable from Output Low
Receiver Disable from Output High
Maximum Data Rate
(Note 9)
2.5
C
L
= 15 pF
C
L
= 100 pF
C
L
= 100 pF
C
L
= 15 pF
C
L
= 15 pF
C
L
= 15 pF (RO)
70
70
190
210
20
3
3
Conditions
= 54Ω, C
L
= 100 pF
R
L
Min
10
10
Typ
40
39
1
25
25
Max
65
65
10
40
40
170
170
170
170
320
320
50
110
110
110
110
Units
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Mbps
Note 1:
“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 2:
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
OD1/2/3
and
V
ID
.
Note 3:
All typicals are given for: V
CC
= +5.0V, T
A
= +25˚C.
Note 4:
∆|V
OD
| and
∆|V
OC
| are changes in magnitude of V
OD
and V
OC
respectively, that occur when the input changes state.
Note 5:
I
IN2
includes the receiver input current and driver TRI-STATE leakage current.
Note 6:
Supply current specification is valid for loaded transmitters when DE = 0V or enabled (DE = H) with no load.
Note 7:
f = 1 MHz, t
r
and t
f
≤
6 ns, Z
O
= 50Ω.
Note 8:
C
L
includes jig and probe capacitance.
Note 9:
f
max
is the guaranteed data rate for 50 ft of twisted pair cable. f
max
may be conservatively determined from the ratio of driver transition time (t
r
) to the data
rate unit interval (1/f
max
). Using a 10% ratio yields f
max
= (0.1)/40 ns = 2.5 Mb/s. Higher data rates may be supported by allowing larger ratios.
3
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Parameter Measurement Information
DS012880-3
DS012880-2
FIGURE 1. V
OD
FIGURE 5. V
OD3
DS012880-4
FIGURE 2.
DS012880-5
FIGURE 6.
DS012880-6
FIGURE 3.
DS012880-7
FIGURE 7.
DS012880-9
FIGURE 8.
DS012880-8
FIGURE 4.
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Parameter Measurement Information
(Continued)
DS012880-10
FIGURE 9.
DS012880-11
FIGURE 10.
DS012880-12
FIGURE 11.
DS012880-13
FIGURE 12.
DS012880-14
FIGURE 13.
5
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