1/13
November 2002
s
LOW SUPPLY CURRENT: 5mA MAX
s
HIGH DATA RATE > 30Mbps
s
DESIGNED FOR RS 485 INTERFACE
APPLICATIONS
s
-7 TO 12 COMMON MODE INPUT VOLTAGE
RANGE
s
DRIVER MANTAINS HIGH IMPEDANCE IN
3-STATE OR WITH THE POWER OFF
s
70mV TYPICAL INPUT HYSTERESIS
s
OPERATE FROM SINGLE 5 SUPPLY
s
4kV ESD PROTECTION
s
CURRENT LIMITING AND THERMAL
SHUTDOWN FOR DRIVER OVERLOAD
PROTECTION
s
LATCH-UP FREE UP TO 500mA
DESCRIPTION
The
ST485A
is a
low
power, high speed
transceiver
for
RS-485
and
RS-422
communications. The device contains one driver
and one receiver in half duplex configuration. The
ST485A draws 3mA (typ.) of supply current when
unloaded or fully loaded with disabled drivers. It
operates from a single 5V supply.
Driver is short-circuit current limited and is
protected against excessive power dissipation by
thermal shutdown circuitry that place the driver
outputs into a high-impedance state. The receiver
input has a fail-safe feature that guarantees a
logic high output if both inputs are open circuit.
The ST485A is designed for bi-directional data
communications or multipoint bus transmission
lines.
ORDERING CODES
Type
Temperature
Range
Package
Comments
ST485ACN
0 to 70 C
DIP-8
50parts per tube / 40tube per box
ST485ABN
-40 to 85 C
DIP-8
50parts per tube / 40tube per box
ST485ACD
0 to 70 C
SO-8 (Tube)
100parts per tube / 20tube per box
ST485ABD
-40 to 85 C
SO-8 (Tube)
100parts per tube / 20tube per box
ST485ACDR
0 to 70 C
SO-8 (Tape & Reel)
2500 parts per reel
ST485ABDR
-40 to 85 C
SO-8 (Tape & Reel)
2500 parts per reel
ST485A
VERY HIGH SPEED
LOW POWER RS-485/RS-422 TRANSCEIVER
DIP
SOP
ST485A
2/13
PIN CONFIGURATION
PIN DESCRIPTION
TRUTH TABLE (DRIVER)
X= Don't Care; Z=High Impedance
TRUTH TABLE (RECEIVER)
X= Don't Care; Z=High Impedance
PlN N
SYMBOL
NAME AND FUNCTION
1
RO
Receiver Output. If A>B by 200mV, RO will be high; if A<B by 200mV, RO will be
low
2
RE
Receiver Output Enable. RO is enabled when RE is low; RO is high impedance
when RE is high. If RE is high and DE is low, the device will enter a low power
shutdown mode.
3
DE
Driver Output Enable. The driver outputs are enabled by bringing DE high. They
are high impedance when DE is low. If RE is high DE is low, the device will enter a
low-power shutdown mode. If the driver outputs are enabled, the part functions as
line driver, while they are high impedance, it functions as line receivers if RE is
low.
4
DI
Driver Input. A low on DI forces output A low and output B high. Similarly, a high
on DI forces output A high and output B low
5
GND
Ground
6
A
Non-inverting Receiver Input and Non-inverting Driver Output
7
B
Inverting Receiver Input and Inverting Driver Output
8
V
CC
Supply Voltage: V
CC
= 4.75V to 5.25V
INPUTS
OUTPUTS
MODE
RE
DE
DI
B
A
X
H
H
L
H
Normal
X
H
L
H
L
Normal
L
L
X
Z
Z
Normal
INPUTS
OUTPUT
MODE
RE DE
A-B
RO
L
L
-0.2V
H
Normal
L
L
-0.2V
L
Normal
L
L
Inputs Open
H
Normal
ST485A
3/13
ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is
not implied.
ELECTRICAL CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
A
= 25C,
V
CC
= 5V) (See Note 1)
LOGIC INPUT ELECTRICAL CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
A
= 25C,
V
CC
= 5V) (See Note 1
Symbol
Parameter
Value
Unit
V
CC
Supply Voltage
7
V
V
I
Control Input Voltage (RE, DE)
-0.3 to 7
V
V
DI
Driver Input Voltage (DI)
-0.3 to 7
V
V
DO
Driver Output Voltage (A, B)
-7.5 to 12.5
V
V
RI
Receiver Input Voltage (A, B)
-7.5 to 12.5
V
V
RO
Receiver Output Voltage (RO)
-0.3 to (V
CC
+ 0.3)
V
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
I
SUPPLY
V
CC
Power Supply Current
No Load, V
RE
=0V or V
CC
V
DE
=V
CC
2.3
5
mA
V
DE
=0V
2.6
5
mA
C
I/O
Input/Output Capacitance
10
pF
C
AB
Driver Output Capacity
10
pF
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
IL
Input Logic Threshold Low
DE, DI, RE
0.8
V
V
IH
Input Logic Threshold High
DE, DI, RE
2
V
I
IN1
Logic Input Current
DE, DI, RE
2.0
A
I
IN2
Input Current (A, B)
V
DE
=0V, V
CC
= 0 or 5.25V
V
IN
=12V
1
mA
V
IN
=-7V
-0.8
mA
ST485A
4/13
TRANSMITTER ELECTRICAL CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
a
= 25C,
V
CC
= 5V) (See Note 1)
RECEIVER ELECTRICAL CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
a
= 25C,
V
CC
= 5V) (See Note 1)
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
OD1
Differential Driver Output
(No load)
5
V
V
OD2
Differential Driver Output
(With Load)
R
L
= 54
(RS-422) V
CM
=-7V to 12V
1.5
2.7
5
V
V
OD
Change in magnitude of
Driver Differential Output
Voltage for Complementary
Output States (Note1)
R
L
= 27
or 50
0
0.2
V
V
OC
Driver Common Mode
Output Voltage
R
L
= 27
or 50
1
3
V
V
OC
Change in magnitude of
Driver Common Mode
Output Voltage (Note1)
R
L
= 54
or 100
0
0.2
V
I
OSD
Driver Short Circuit Output
Current
V
O
=-7V to 12V
250
mA
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
TH
Receiver Differential
Threshold Voltage
V
CM
= -7V to 12V
-0.2
0.2
V
V
TH
Receiver Input Hysteresis
V
CM
= 0V
70
mV
V
OH
Receiver Output High
Voltage
I
OUT
= -4mA, V
ID
= 200mV
3.5
4.7
V
V
OL
Receiver Output Low
Voltage
I
OUT
= 4mA, V
ID
= -200mV
0.2
0.4
V
I
OZR
3-State (High Impedance)
Output Current at Receiver
V
O
= 0.4V to 2.4V
1
A
R
RIN
Receiver Input Resistance
V
CM
= -7V to 12V
12
24
K
I
OSR
Receiver Short-Circuit
Current
V
O
= 0V to V
CC
7
95
mA
ST485A
5/13
DRIVER SWITCHING CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
a
= 25C,
V
CC
= 5V) (See Note 1, 3)
RECEIVER SWITCHING CHARACTERISTICS
V
CC
= 4.5V to 5.5V, T
A
= -40 to 85C, unless otherwise specified. Typical values are referred to T
a
= 25C,
V
CC
= 5V) (See Note 1, 3)
Note 1: All currents into device pins are positive; all cuttents out of device pins are negative; all voltages are referenced to device ground
unless specified.
Note 2: Applies to peak current. See typical Operating Characteristics.
Note 3: t
r
=t
f
6ms
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
D
R
Maximum Data Rate
Jitter <5%
30
50
Mbps
t
PLH
t
PHL
Propagation Delay Input to
Output
R
L
= 54
C
L1
=C
L2
=50pF, (Figure 1)
18
30
ns
t
SKEW
Differential Output Delay
Skew
R
L
= 54
C
L1
=C
L2
=50pF, (Figure 1)
0.5
2
ns
t
TLH
t
THL
Rise or Fall Differential
Time
R
L
= 54
C
L1
=C
L2
=50pF, (Figure 1)
8
12
ns
t
PZL
Output Enable Time
C
L
= 50pF
S1 Closed
30
ns
t
PZH
Output Enable Time
C
L
= 50pF
S2 Closed
30
ns
t
PHZ
Output Disable Time
C
L
= 15pF
S2 Closed
30
ns
t
PLZ
Output Disable Time
C
L
= 15pF
S1 Closed
30
ns
t
SK(EN)
Synchronous Driver
Operation A-B at Enable
2
ns
t
SK(DS)
Synchronous Driver
Operation A-B at Disable
4
6
ns
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
t
PLH
t
PHL
Propagation Delay
C
L
= 15pF
18
30
ns
t
RPDS
|t
PLH -
t
PHL
| Propagation
Delay Skew
C
L
= 15pF
0.5
2
ns
t
PZL
Output Enable Time
C
RL
= 15pF
S1 Closed
7
12
ns
t
PZH
Output Enable Time
C
RL
= 15pF
S2 Closed
7
12
ns
t
PHZ
Output Disable Time
C
RL
= 15pF
S2 Closed
7
12
ns
t
PLZ
Output Disable Time
C
RL
= 15pF
S1 Closed
7
12
ns
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