NSC DS485N Low power rs-485/rs-422 multipoint transceiver Datasheet

DS485
Low Power RS-485/RS-422 Multipoint Transceiver
General Description
Features
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 unloaded or fully loaded with the driver disabled and operates
from a single +5V supply.
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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
(VOD3).
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 temperature range operation.
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Connection and Logic Diagram
Truth Table
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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
DRIVER SECTION
DIP and SOIC
RE*
DE
DI
A
X
H
H
H
L
X
H
L
L
H
X
L
X
Z
Z
B
RECEIVER SECTION
DS012880-1
Order Number
DS485N
Temp. Range
0˚C to +70˚C
Package/###
DIP/N08E
DS485M
0˚C to +70˚C
SOP/M08A
DS485TN
−40˚C to +85˚C
DIP/N08E
DS485TM
−40˚C to +85˚C
SOP/M08A
RE*
DE
A-B
RO
L
L
≥+0.2V
H
L
L
≤−0.2V
L
H
X
X
Z
L
L
OPEN*
H
*Note: Non Terminated, Open Input only
X = indeterminate
Z = TRI-STATE
TRI-STATE ® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS012880
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DS485 Low Power RS-485/RS-422 Multipoint Transceiver
July 1998
Absolute Maximum Ratings (Note 1)
N Package
Storage Temperature Range
Lead Temperature Range
(Soldering, 4 sec.)
ESD (HBM)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (VCC)
+12V
−0.5V to (VCC + 0.5V)
Enable Input Voltage (RE*, DE)
Driver Input Voltage (DI)
−0.5V to (VCC + 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 (VCC + 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
0.47W
−65˚C to +150˚C
+260˚C
≥2 kV
Recommended Operating
Conditions
Supply Voltage (VCC)
Operating Free Air
Temperature (TA)
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
Max
Units
Electrical Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 2, 3)
Symbol
Parameter
VOD1
Differential Driver Output Voltage
VOD2
Differential Driver Output Voltage
with Load
∆VOD
Change in Magnitude of Output
Conditions
(No Load)
RL = 50Ω, (RS422), Figure 1
RL = 27Ω, (RS485), Figure 1
RL = 27Ω or 50Ω (Note 4)
Pin
Min Typ
A, B
5
2
2.8
1.5
2.3
V
V
5
V
0.2
|V|
5
V
Differential Voltage
VOD3
Differential Driver Output Voltage —
Full Load with Max VCM
VOC
Driver Common-Mode Output Voltage
∆VOC
Change in Magnitude of Common-Mode
R1 = 54Ω, R2 = 375Ω
VTEST = −7V to +12V, Figure 5
RL = 27Ω or 50Ω, Figure 1
RL = 27Ω or 50Ω, Figure 1 (Note 4)
1.5
2.0
3
V
0.2
|V|
Output Voltage
VIH
Input High Voltage
VIL
Input Low Voltage
IIN1
Input Current
IIN2
Input Current (Note 5)
DE = 0V, VCC = 0V or 5.25V
VIN = 0V or VCC
VIN = +12V
VIN = −7V
DI,
DE,
RE*
−7V ≤ VCM ≤ +12V
VCM = 0V
Receiver Differential Threshold Voltage
∆VTH
Receiver Input Hysteresis
VOH
Receiver Output High Voltage
VOL
Receiver Output Low Voltage
IO = −4 mA, VID = 0.2V
IO = 4 mA, VID = −0.2V
IOZR
TRI-STATE Output Current at Receiver
0.4V ≤ VO ≤ 2.4V
RIN
Receiver Input Resistance
No-Load Supply Current (Note 6)
−7V ≤ VIN ≤ +12V
DE = VCC, RE* = 0V or VCC
DE = 0V, RE* = 0V or VCC
A, B
ICC
−7V ≤ VO ≤ +12V
A, B
IOSD2
Driver Short Circuit Current, VO = HIGH
Driver Short Circuit Current, VO = LOW
IOSR
Receiver Short Circuit Current
0V ≤ VO ≤ VCC
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−0.2
0.8
V
±2
µA
1.0
mA
−0.8
mA
0.2
70
RO
RO
V
mV
3.5
V
0.4
V
±1
µA
12
VCC
−7V ≤ VO ≤ +12V
2
V
A, B
VTH
IOSD1
2.0
kΩ
200
900
200
500
µA
µA
35
250
mA
35
250
mA
7
85
mA
Switching Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 7, 8)
Symbol
Parameter
Conditions
RL = 54Ω, CL = 100 pF
Min
Typ
Max
Units
10
40
65
ns
10
39
65
ns
1
10
ns
3
25
40
ns
3
25
40
ns
CL = 100 pF
CL = 100 pF
CL = 15 pF
170
ns
170
ns
170
ns
CL = 15 pF
CL = 15 pF (RO)
170
ns
tPLHD
Driver Differential Propagation Delay — Low to High
tPHLD
Driver Differential Propagation Delay — High to Low
tSKEW
Differential Skew |tPHLD − tPLHD|
tr
Driver Rise Time
tf
Driver Fall Time
tZH
Driver Enable to Output High
tZL
Driver Enable to Output Low
tLZ
Driver Disable from Output Low
tHZ
Driver Disable from Output High
tPLHD
Receiver Differential Propagation Delay — Low to High
tPHLD
Receiver Differential Propagation Delay — High to Low
tSKEW
Differential Skew |tPHLD − tPLHD|
tZH
Receiver Enable to Output High
tZL
Receiver Enable to Output Low
110
ns
tLZ
Receiver Disable from Output Low
110
ns
tHZ
Receiver Disable from Output High
fmax
Maximum Data Rate
70
190
320
ns
70
210
320
ns
20
50
ns
110
ns
CL = 15 pF
110
(Note 9)
2.5
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 VOD1/2/3 and
VID.
Note 3: All typicals are given for: VCC = +5.0V, TA = +25˚C.
Note 4: ∆|VOD| and ∆|VOC| are changes in magnitude of V OD and VOCrespectively, that occur when the input changes state.
Note 5: IIN2 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, tr and tf ≤ 6 ns, ZO = 50Ω.
Note 8: CL includes jig and probe capacitance.
Note 9: fmax 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 (tr) to the data
rate unit interval (1/fmax). Using a 10% ratio yields fmax = (0.1)/40 ns = 2.5 Mb/s. Higher data rates may be supported by allowing larger ratios.
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Parameter Measurement Information
DS012880-3
DS012880-2
FIGURE 5. VOD3
FIGURE 1. VOD
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.
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Parameter Measurement Information
(Continued)
Pin Descriptions
Pin #
I/O
Name
Function
1
O
RO
Receiver Output: If A > B by 200 mV, RO will be high; If A < B by 200 mV, RO will be low. RO will
be high also if the inputs (A and B) are open (non-terminated).
2
I
RE*
Receiver Output Enable: RO is enabled when RE* is low; RO is in TRI-STATE when RE* is high.
3
I
DE
Driver Output Enable: The driver outputs (A and B) are enabled when DE is high; they are in
TRI-STATE when DE is low. Pins A and B also function as the receiver input pins (see below).
4
I
DI
Driver Input: A low on DI forces A low and B high while a high on DI forces A high and B low when
the driver is enabled.
5
NA
GND
6
I/O
A
Non-inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
7
I/O
B
Inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
8
NA
VCC
Ground
Power Supply: 4.75V ≤ VCC ≤ 5.25V
Related National Low Power RS-485 Transceivers
Part Number
DS36C278
DS36C278T
DS36C279
DS36C279T
DS36C280
DS36C280T
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Temperature
Number of
Range
XCVRs on Bus
Comments
0˚C to +70˚C
128
Ultra Low Power Transceiver
−40˚C to +85˚C
64
Ultra Low Power Transceiver
0˚C to +70˚C
128
Auto-Sleep Mode
−40˚C to +85˚C
64
Auto-Sleep Mode
0˚C to +70˚C
128
Adjustable Slew Rate Control
−40˚C to +85˚C
64
Adjustable Slew Rate Control
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Applications Information
Due to the multipoint nature of the bus, contention between
drivers may occur. This will not cause damage to the drivers
since they feature short-circuit protection and also thermal
shutdown protection. Thermal shutdown senses die temperature and puts the driver outputs into TRI-STATE if a fault
condition occurs that causes excessive power dissipation
which can elevate the junction temperature to +150˚C.
A typical multipoint application is shown in the following figure. Note that termination is typically required but is only located at the two ends of the cable (not on every node). Commonly pull up and pull down resistors may be required at one
end of the bus to provide a failsafe bias. These resistors provide a bias to the line when all drivers are in TRI-STATE. See
National Application Note 847 for a complete discussion of
failsafe biasing of differention buses.
The DS485 is a low power transceiver designed for use in
RS-485 multipoint applications. The DS485 can transmit
data up to 2.5 Mbps based on a ratio of driver transition time
to the unit interval (bit time) of 10%. This maximum data rate
may be further limited by the interconnecting media. The
DS485 provides a standard unit load to the RS-485 bus
across the common mode range of −7V to +12V. This allows
up to 32 transceivers (standard unit load) to be connected to
the bus. More transceivers may be connected to the bus if
they support a reduced unit load (see DS36C278). The
DS485 also guarantees the driver’s output differential voltage into a worst case load that models standard termination
loads and 32 unit loads referenced to the maximum common
mode voltage extremes. With a minimum of 1.5V swing into
this load, a 1.3V differential noise margin is supported along
with the standard common mode rejection range of the receivers.
Multipoint RS-485 Application
DS012880-16
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Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number DS485M or DS485TM
NS Package Number M08A
Order Number DS485N or DS485TN
NS Package Number N08E
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DS485 Low Power RS-485/RS-422 Multipoint Transceiver
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