DS1487
Low Power RS-485
1
/
4
Unit Load Multipoint Transceiver
General Description
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-
ceiver presents
1
/
4
unit loading to the RS-485 bus allowing up
to 128 nodes to be connected together without the use of re-
peaters.
The transceiver draws 200 A 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 DS1487 is available in surface mount and DIP pack-
ages.
Features
n
Meets TIA/EIA RS-485 multipoint standard
n
Allows up to 128 transceivers on the bus (
1
/
4
U.L.)
n
Guaranteed full load output voltage (V
OD3
)
n
Low quiescent current:
200 A 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
-- 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
Connection and Logic Diagram
Order Number
Temp. Range
Package/###
DS1487N
0C to +70C
DIP/N08E
DS1487M
0C to +70C
SOP/M08A
Truth Table
DRIVER SECTION
RE
(Note 1)
DE
DI
A
B
X
H
H
H
L
X
H
L
L
H
X
L
X
Z
Z
RECEIVER SECTION
RE
(Note 1)
DE
A-B
RO
L
L
+0.2V
H
L
L
-0.2V
L
H
X
X
Z
L
L
OPEN (Note 1)
H
X = indeterminate
Z = TRI-STATE
Note 1: Non Terminated, Open Input only
TRI-STATE
is a registered trademark of National Semiconductor Corporation.
DIP and SOIC
DS012920-1
*Note: Non Terminated, Open Input only
July 1998
DS1487
Low
Power
RS-485
1
/
4
Unit
Load
Multipoint
T
ransceiver
1999 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.
Supply Voltage (V
CC
)
+12V
Enable Input Voltage
(RE (Note 1), DE)
-0.5V to (V
CC
+ 0.5V)
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
@
+25C
M Package
1.19W
N Package
0.74W
Derate M Package 9.5 mW/C above +25C
Derate N Package 6.0 mW/C above +25C
Maximum Package Power Dissipation
@
+70C
M Package
0.76W
N Package
0.47W
Storage Temperature Range
-65C to +150C
Lead Temperature Range
(Soldering, 4 sec.)
+260C
ESD (HBM)
2 kV
Recommended Operating
Conditions
Min
Typ
Max
Units
Supply Voltage (V
CC
)
+4.75
+5.0
+5.25
V
Operating Free Air
Temperature (T
A
)
DS1487
0
+25
+70
C
Bus Common Mode Voltage
-7
+12
V
Electrical Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 4)
Symbol
Parameter
Conditions
Pin
Min
Typ
Max Units
V
OD1
Differential Driver Output Voltage
(No Load)
A, B
1.5
5
V
V
OD2
Differential Driver Output Voltage
R
L
= 50
, (RS422),
Figure 1
2
2.8
V
with Load
R
L
= 27
, (RS485),
Figure 1
1.5
2.3
5
V
V
OD
Change in Magnitude of Output
R
L
= 27
or 50
(Note 5)
0.2
|V|
Differential Voltage
V
OD3
Differential Driver Output Voltage --
R1 = 54
, R2 = 375
1.5
2.0
5
V
Full Load with Max V
CM
V
TEST
= -7V to +12V, Figure 2
V
OC
Driver Common-Mode Output Voltage
R
L
= 27
or 50
,
Figure 1
0
3
V
V
OC
Change in Magnitude of
Common-Mode Output Voltage
R
L
= 27
or 50
,
Figure 1 (Note 5)
0.2
|V|
V
IH
Input High Voltage
DI, DE,
2.0
V
V
IL
Input Low Voltage
RE (Note 1)
0.8
V
I
IN1
Input Current
V
IN
= 0V or V
CC
2
A
I
IN2
Input Current (Note 6)
V
IN
= +12V
A, B
0
190
250
A
DE = 0V, V
CC
= 0V or 5.25V
V
IN
= -7V
0
-100 -200
A
V
TH
Receiver Differential Threshold
Voltage
-7V
V
CM
+12V
-0.2
0.2
V
V
TH
Receiver Input Hysteresis
V
CM
= 0V
70
mV
V
OH
Receiver Output High Voltage
I
O
= -4 mA, V
ID
= 0.2V
RO
3.5
V
V
OL
Receiver Output Low Voltage
I
O
= 4 mA, V
ID
= -0.2V
0.5
V
I
OZR
TRI-STATE Output Current at
Receiver
0.4V
V
O
2.4V
1
A
R
IN
Receiver Input Resistance
-7V
V
IN
+12V
A, B
48
68
k
I
CC
No-Load Supply Current (Note 7)
DE = V
CC
, RE (Note 1) = 0V or V
CC
V
CC
200
500
A
DE = 0V, RE (Note 1) = 0V or V
CC
200
500
A
I
OSD1
Driver Short Circuit Current, V
O
=
HIGH
-7V
V
O
+12V
A, B
250
mA
I
OSD2
Driver Short Circuit Current, V
O
=
LOW
-7V
V
O
+12V
-250
mA
I
OSR
Receiver Short Circuit Current
V
O
= GND
RO
7
85
mA
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2
Switching Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 4, 8, 9)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
t
PLHD
Driver Differential Propagation Delay -- Low to High
R
L
= 54
, C
L
= 100 pF
10
40
80
ns
t
PHLD
Driver Differential Propagation Delay -- High to Low
10
39
80
ns
t
SKEW
Differential Skew |t
PHLD
- t
PLHD
|
0
1
10
ns
t
r
Driver Rise Time
3
25
50
ns
t
f
Driver Fall Time
3
25
50
ns
t
ZH
Driver Enable to Output High
C
L
= 100 pF
50
200
ns
t
ZL
Driver Enable to Output Low
C
L
= 100 pF
65
200
ns
t
LZ
Driver Disable from Output Low
C
L
= 15 pF
80
200
ns
t
HZ
Driver Disable from Output High
C
L
= 15 pF
80
200
ns
t
PLHD
Receiver Differential Propagation Delay -- Low to High
C
L
= 15 pF (RO)
30
190
400
ns
t
PHLD
Receiver Differential Propagation Delay -- High to Low
30
210
400
ns
t
SKEW
Differential Skew |t
PHLD
- t
PLHD
|
0
20
50
ns
t
ZH
Receiver Enable to Output High
C
L
= 15 pF
45
150
ns
t
ZL
Receiver Enable to Output Low
40
150
ns
t
LZ
Receiver Disable from Output Low
50
150
ns
t
HZ
Receiver Disable from Output High
55
150
ns
f
max
Maximum Data Rate
(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
OD1/2/3
and
V
ID
.
Note 4: All typicals are given for: V
CC
= +5.0V, T
A
= +25C.
Note 5:
|V
OD
| and
|V
OC
| are changes in magnitude of V
OD
and V
OC
respectively, that occur when the input changes state.
Note 6: I
IN2
includes the receiver input current and driver TRI-STATE leakage current.
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
r
and t
f
6 ns, Z
O
= 50
.
Note 9: C
L
includes jig and probe capacitance.
Note 10: 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)/50 ns = 2.0 Mb/s. Higher data rates may be supported by allowing larger ratios.
Parameter Measurement Information
DS012920-2
FIGURE 1. V
OD
DS012920-3
FIGURE 2. V
OD3
DS012920-4
FIGURE 3.
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3
Parameter Measurement
Information
(Continued)
DS012920-5
FIGURE 4.
DS012920-6
FIGURE 5.
DS012920-7
FIGURE 6.
DS012920-8
FIGURE 7.
DS012920-9
FIGURE 8.
DS012920-10
*Note: Non Terminated, Open Input only
FIGURE 9.
DS012920-11
FIGURE 10.
DS012920-12
*Note: Non Terminated, Open Input only
FIGURE 11.
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4
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 (Note 1)
Receiver Output Enable: RO is enabled when RE (Note 1) is low; RO is in TRI-STATE when RE
(Note 1) 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
Ground
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
V
CC
Power Supply: 4.75V
V
CC
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 provides a
1
/
4
unit load to the RS-485 bus across the
common mode range of -7V to +12V. This allows up to 128
transceivers (
1
/
4
unit load) to be connected to the bus. 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.
DS012920-13
*Note: Non Terminated, Open Input only
FIGURE 12.
DS012920-14
*Note: Non Terminated, Open Input only
FIGURE 13.
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5
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