DS1487_11 [TI]
Low Power RS-485 Unit Load Multipoint Transceiver;
| 型号： | DS1487_11 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | Low Power RS-485 Unit Load Multipoint Transceiver |
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DS1487
DS1487 Low Power RS-485 ¼ Unit Load Multipoint Transceiver
Literature Number: SNLS132
July 1998
DS1487
1
Low Power RS-485 ⁄ Unit Load Multipoint Transceiver
4
General Description
Features
n Meets TIA/EIA RS-485 multipoint standard
n Allows up to 128 transceivers on the bus (1⁄
The DS1487 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
2.0 Mbps (see Applications Information section). The trans-
4
U.L.)
n Guaranteed full load output voltage (VOD3
n Low quiescent current: 200 µA typ
n −7V to +12V common-mode input voltage range
n TRI-STATE outputs on driver and receiver
n AC performance:
— Driver transition time: 25 ns typ
— Driver propagation delay: 40 ns typ
— Driver skew: 1 ns typ
)
ceiver presents 1⁄
unit loading to the RS-485 bus allowing up
4
to 128 nodes to be connected together without the use of re-
peaters.
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
(VOD3).
— Receiver propagation delay: 200 ns typ
— Receiver skew: 20 ns typ
n Half-duplex flow through pinout
n Operates from a single 5V supply
n Current-limiting and thermal shutdown for driver
overload protection
n Pin and functional compatible with MAX1487
The receiver has a failsafe feature that guarantees a
logic-high output if the input is open circuit.
The DS1487 is available in surface mount and DIP pack-
ages.
Connection and Logic Diagram
Truth Table
DRIVER SECTION
DIP and SOIC
RE
DE
DI
A
B
(Note 1)
X
X
X
H
H
L
H
L
H
L
L
H
Z
X
Z
RECEIVER SECTION
RE
DE
A-B
RO
DS012920-1
(Note 1)
*Note: Non Terminated, Open Input only
L
L
L
L
X
L
≥+0.2V
≤−0.2V
X
H
L
###
Order Number
DS1487N
Temp. Range
0˚C to +70˚C
0˚C to +70˚C
Package/
DIP/N08E
SOP/M08A
H
L
Z
H
OPEN (Note 1)
DS1487M
X = indeterminate
Z = TRI-STATE
Note 1: Non Terminated, Open Input only
TRI-STATE® is a registered trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation
DS012920
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.
M Package
0.76W
0.47W
N Package
Storage Temperature Range
Lead Temperature Range
(Soldering, 4 sec.)
ESD (HBM)
−65˚C to +150˚C
+260˚C
Supply Voltage (VCC
)
+12V
≥2 kV
Enable Input Voltage
(RE (Note 1), DE)
−0.5V to (VCC + 0.5V)
−0.5V to (VCC + 0.5V)
−14V to +14V
Recommended Operating
Conditions
Driver Input Voltage (DI)
Driver Output Voltage (A, B)
Receiver Input Voltage (A, B)
Receiver Output Voltage (RO)
−14V to +14V
Min
Typ
Max Units
−0.5V to (VCC + 0.5V)
Supply Voltage (VCC
Operating Free Air
Temperature (TA)
DS1487
)
+4.75
+5.0 +5.25
V
@
Maximum Package Power Dissipation +25˚C
M Package
1.19W
0.74W
N Package
0
+25
+70
+12
˚C
V
Derate M Package 9.5 mW/˚C above +25˚C
Derate N Package 6.0 mW/˚C above +25˚C
Bus Common Mode Voltage
−7
@
Maximum Package Power Dissipation +70˚C
Electrical Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 4)
Symbol
VOD1
Parameter
Differential Driver Output Voltage
Differential Driver Output Voltage
with Load
Conditions
Pin
Min Typ Max Units
(No Load)
A, B
1.5
2
5
V
V
VOD2
RL = 50Ω, (RS422), Figure 1
RL = 27Ω, (RS485), Figure 1
RL = 27Ω or 50Ω (Note 5)
2.8
1.5 2.3
5
V
∆VOD
Change in Magnitude of Output
Differential Voltage
0.2
|V|
VOD3
Differential Driver Output Voltage—
Full Load with Max VCM
R1 = 54Ω, R2 = 375Ω
1.5 2.0
0
5
V
VTEST = −7V to +12V, Figure 2
VOC
Driver Common-Mode Output Voltage RL = 27Ω or 50Ω, Figure 1
3
V
∆VOC
Change in Magnitude of
Common-Mode Output Voltage
RL = 27Ω or 50Ω, Figure 1 (Note 5)
0.2
|V|
VIH
VIL
IIN1
IIN2
Input High Voltage
Input Low Voltage
DI, DE,
2.0
V
V
RE (Note 1)
0.8
±
Input Current
VIN = 0V or VCC
VIN = +12V
2
µA
µA
µA
V
Input Current (Note 6)
DE = 0V, VCC = 0V or 5.25V
A, B
0
0
190 250
−100 −200
0.2
VIN = −7V
VTH
Receiver Differential Threshold
Voltage
−7V ≤ VCM ≤ +12V
−0.2
∆VTH
VOH
VOL
Receiver Input Hysteresis
VCM = 0V
70
mV
V
Receiver Output High Voltage
Receiver Output Low Voltage
IO = −4 mA, VID = 0.2V
IO = 4 mA, VID = −0.2V
0.4V ≤ VO ≤ 2.4V
RO
3.5
48
0.5
V
±
IOZR
TRI-STATE Output Current at
Receiver
1
µA
RIN
ICC
Receiver Input Resistance
−7V ≤ VIN ≤ +12V
A, B
VCC
68
kΩ
µA
µA
No-Load Supply Current (Note 7)
DE = VCC, RE (Note 1) = 0V or VCC
DE = 0V, RE (Note 1) = 0V or VCC
−7V ≤ VO ≤ +12V
200 500
200 500
IOSD1
IOSD2
IOSR
Driver Short Circuit Current, VO
HIGH
=
A, B
250 mA
Driver Short Circuit Current, VO
LOW
=
−7V ≤ VO ≤ +12V
−250 mA
Receiver Short Circuit Current
VO = GND
RO
7
85
mA
www.national.com
2
Switching Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 4, 8, 9)
Symbol
tPLHD
tPHLD
tSKEW
tr
Parameter
Conditions
Min
10
10
0
Typ
40
39
1
Max
80
Units
ns
Driver Differential Propagation Delay—Low to High
Driver Differential Propagation Delay—High to Low
RL = 54Ω, CL = 100 pF
80
ns
Differential Skew |tPHLD − tPLHD
Driver Rise Time
|
10
ns
3
25
25
50
65
80
80
190
210
20
45
40
50
55
50
ns
tf
Driver Fall Time
3
50
ns
tZH
Driver Enable to Output High
Driver Enable to Output Low
CL = 100 pF
CL = 100 pF
CL = 15 pF
200
200
200
200
400
400
50
ns
tZL
ns
tLZ
Driver Disable from Output Low
ns
tHZ
Driver Disable from Output High
CL = 15 pF
ns
tPLHD
tPHLD
tSKEW
tZH
Receiver Differential Propagation Delay—Low to High
Receiver Differential Propagation Delay—High to Low
CL = 15 pF (RO)
30
30
0
ns
ns
Differential Skew |tPHLD − tPLHD
|
ns
Receiver Enable to Output High
Receiver Enable to Output Low
Receiver Disable from Output Low
Receiver Disable from Output High
Maximum Data Rate
CL = 15 pF
150
150
150
150
ns
tZL
ns
tLZ
ns
tHZ
ns
fmax
(Note 10)
2.0
Mbps
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
and
OD1/2/3
V
ID
.
Note 4: All typicals are given for: V
= +5.0V, T = +25˚C.
A
CC
Note 5: ∆|V | and ∆|V | are changes in magnitude of V
and V
respectively, that occur when the input changes state.
OC
OD
OC
OD
Note 6: I
includes the receiver input current and driver TRI-STATE leakage current.
IN2
Note 7: Supply current specification is valid for loaded transmitters when DE = 0V or enabled (DE = H) with no load.
Note 8: f = 1 MHz, t and t ≤ 6 ns, Z = 50Ω.
r
f
O
Note 9: C includes jig and probe capacitance.
L
Note 10: f
is the guaranteed data rate for 50 ft of twisted pair cable. f
may be conservatively determined from the ratio of driver transition time (t ) to the data
max
m
a
x
r
rate unit interval (1/f
). Using a 10% ratio yields f
= (0.1)/50 ns = 2.0 Mb/s. Higher data rates may be supported by allowing larger ratios.
max
max
Parameter Measurement Information
DS012920-2
FIGURE 1. VOD
DS012920-4
FIGURE 3.
DS012920-3
FIGURE 2. VOD3
3
www.national.com
Parameter Measurement
Information (Continued)
DS012920-8
FIGURE 7.
DS012920-5
DS012920-9
FIGURE 4.
FIGURE 8.
DS012920-10
*Note: Non Terminated, Open Input only
FIGURE 9.
DS012920-6
FIGURE 5.
DS012920-7
DS012920-11
FIGURE 6.
FIGURE 10.
DS012920-12
*Note: Non Terminated, Open Input only
FIGURE 11.
www.national.com
4
Parameter Measurement Information (Continued)
DS012920-13
*Note: Non Terminated, Open Input only
FIGURE 12.
DS012920-14
*Note: Non Terminated, Open Input only
FIGURE 13.
Pin Descriptions
Pin I/O
Name
Function
#
>
<
1
O
I
RO
RE (Note 1)
DE
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
3
4
Receiver Output Enable: RO is enabled when RE (Note 1) is low; RO is in TRI-STATE when RE
(Note 1) is high.
I
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).
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
6
NA
I/O
GND
A
Ground
Non-inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
7
8
I/O
NA
B
Inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling
levels.
VCC
Power Supply: 4.75V ≤ VCC ≤ 5.25V
Applications Information
The DS1487 is a low power transceiver designed for use in
RS-485 multipoint applications. The DS1487 can transmit
data up to 2.0 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
DS1487 also guarantees the driver’s output differential volt-
age into a worst case load that models standard termination
loads and 32 unit loads (=128 DS1487’s) 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 rejec-
tion range of the receivers.
DS1487 provides a 1⁄
common mode range of −7V to +12V. This allows up to 128
transceivers (1⁄
unit load) to be connected to the bus. The
4
unit load to the RS-485 bus across the
4
5
www.national.com
A typical multipoint application is shown in the following fig-
ure. Note that termination is typically required but is only lo-
cated at the two ends of the cable (not on every node). Com-
monly pull up and pull down resistors may be required at one
end of the bus to provide a failsafe bias. These resistors pro-
vide 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.
Applications Information (Continued)
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 tem-
perature 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.
DS012920-16
www.national.com
6
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number DS1487N
NS Package Number N08E
7
www.national.com
Notes
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