Features
■ Low supply current: 5 mA max
■ -7 V to 12 V common mode input voltage range
■ 70 mV typical input hysteresis
■ Designed for 25 Mbps operation
■ Operate from a single 5 V supply
■ ±4 kV ESD protection
■ Current limiting and thermal shutdown for
driver overload protection
ST490AB
Low power high speed
RS-485/RS-422 transceiver
DIP-8 SO-8
Description
The ST490A is a low power transceiver for RS485 and RS-422 communications. The device
contains one driver and one receiver in full duplex
configuration. The ST490A draws 5 mA (typ.) of
supply current when unloaded or fully loaded with
disabled drivers. It operates from a single 5 V
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.
Table 1. Device summary
Order code Temperature range Package Packaging
ST490ABN -40 to 85 °C DIP-8 50 parts per tube / 40 tube per box
ST490ABDR -40 to 85 °C SO-8 (tape and reel) 2500 parts per reel
February 2008 Rev 5 1/17
www.st.com
17
Contents ST490AB
Contents
1 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Truth tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Test circuit and typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2/17
ST490AB Pin configuration
1 Pin configuration
Figure 1. Pin connections
Table 2. Pin description
Pin n° Symbol Name and function
1V
2 RO Receiver output
3 DI Driver input
4 GND Ground
5 Y Non-inverting driver output
6 Z Inverting driver output
7 B Inverting receiver input
8 A Non-inverting receiver input
CC
Supply voltage
3/17
Truth tables ST490AB
2 Truth tables
Table 3. Truth table (driver)
Inputs Outputs
DI Y Z
LLH
HHL
Note: X = Don’t care; Z = High impedance
Table 4. Truth table (receiver)
Differential inputs Outputs
A-B RO
≥ -0.2V H
between -0.2V to 0.2V ?
≤ -0.2V L
OPEN H
Note: X = Don’t care; Z = High impedance
4/17
ST490AB Maximum ratings
3 Maximum ratings
Table 5. Absolute maximum ratings
Symbol Parameter Value Unit
V
V
, VZDriver output voltage -7.5 to 12.5 V
V
Y
V
, VBReceiver input voltage -7.5 to 12.5 V
A
V
RO
ESD Human body model 3.5 kV
CC
DI
Supply voltage 7 V
Driver input voltage -0.5 to 7 V
Receiver output voltage -0.3 to (VCC + 0.3) V
Note: Absolute maximum ratings are those values beyond which damage to the device may occur.
Functional operation under these condition is not implied.
5/17
Electrical characteristics ST490AB
4 Electrical characteristics
Table 6. Electrical characteristics
(V
= 4.5 V to 5.5 V, TA = -40 to 85 °C, unless otherwise specified. Typical values are
CC
referred to T
Symbol Parameter Min. Typ. Max. Unit
= 25 °C)
A
I
SUPPLY
C
IN
C
YZ
C
OUT
No load supply current 2 5 mA
Input capacitance 1.8 pF
Driver output capacitance 1.2 pF
Output capacitance 2.3 pF
Table 7. Transmitter electrical characteristics
(V
= 4.5 V to 5.5 V, TA = -40 to 85 °C, unless otherwise specified. Typical values are
CC
referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
V
V
ΔV
V
ΔV
I
I
OSD
V
V
OD1
OD2
OD3
OC
OFF
Differential drive output (no load) V
Differential drive output (with
load)
Differential drive output (with
load)
Change in magnitude of driver
differential output voltage for
OD
complementary output states
Driver common mode output
voltage
Change in magnitude of driver
OC
common mode output voltage
Power off output current VCC = 0V, VO=-7V to 12V ± 100 µA
Driver short circuit output current VO=-7V to 12V ± 35 ± 250 mA
Input logic threshold low 0.8 V
IL
Input logic threshold high 2 V
IH
= 25 °C)
A
CC
= 54Ω (RS-422) (Figure 1)1.52.65 V
R
L
R
= 100Ω (RS-422) (Figure 1)2 3 V
L
RL= 54Ω or 100Ω (Figure 1)00.2V
= 54Ω (Figure 1)13V
R
L
= 54Ω (Figure 1)00.2V
R
L
V
6/17
ST490AB Electrical characteristics
Table 8. Receiver electrical characteristics
(V
= 4.5 V to 5.5 V, TA = -40 to 85 °C, unless otherwise specified. Typical values are
CC
referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
= 25 °C)
A
I
I
V
ΔV
V
V
R
I
IN1
IN2
OSR
Logic input current ± 2.0 μA
=12V 0.5 1 mA
V
Input current (A, B)
Receiver differential threshold
TH
voltage
Receiver input hysteresis VCM = 0V 70 mV
TH
Receiver output high voltage I
OH
Receiver output low voltage I
OL
Receiver input resistance VCM = -7V to 12V 12 24 kΩ
RIN
Receiver short-circuit current VO = 0V to V
Other input=0V
= 0 or 5.25V
V
CC
V
= -7V to 12V -0.2 0.2 V
CM
= -8mA, VID = 200mV 3.5 4.7 V
OUT
= 8mA, VID = -200mV 0.2 0.4 V
OUT
CC
IN
V
=-7V -0.35 -0.8 mA
IN
795mA
Table 9. Driver switching characteristics
(V
= 4.5 V to 5.5 V, TA = -40 to 85 °C, unless otherwise specified. Typical values are
CC
referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
D
t
PLH
t
PHL
t
SKEW
t
TLH
t
THL
Maximum data rate Jitter <5% 25 50 Mbps
R
Propagation delay input
to output
Differential output delay
skew
Rise or fall differential
time
= 25 °C)
A
= 54Ω, CL1=CL2=50pF, (Figure 1)1016ns
R
L
= 54Ω, CL1=CL2=50pF, (Figure 1)13ns
R
L
R
= 54Ω, CL1=CL2=50pF, (Figure 1)812ns
L
Table 10. Receiver switching characteristics
(V
= 4.5 V to 5.5 V, TA = -40 to 85 °C, unless otherwise specified. Typical values are
CC
referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
t
PLH
t
PHL
t
SKD
t
TLH
t
THL
Propagation delay input
to output
|t
PLH - tPHL
output skew
Rise or fall time CL = 15pF, (Figure 2, Figure 4)8ns
= 25 °C)
A
| Receiver
C
= 15pF, (Figure 2, Figure 4)1930ns
L
= 15pF, (Figure 2, Figure 4)13ns
C
L
7/17
Test circuit and typical characteristics ST490AB
5 Test circuit and typical characteristics
Figure 2. Driver DC test load
Figure 3. Drive/receiver timing test circuit
8/17
ST490AB Test circuit and typical characteristics
Figure 4. Driver propagation delay
Figure 5. Receiver propagation delay
9/17
Test circuit and typical characteristics ST490AB
Figure 6. Receiver output current vs. output
low voltage (output low)
Figure 8. Driver diff. output voltage vs
common mode voltage (diff. output
low)
Figure 7. Receiver output current vs. output
high voltage (output high)
Figure 9. Driver diff. output voltage vs
common mode voltage (diff. output
high)
Figure 10. driver short circuit current vs line
10/17
voltage (output high)
Figure 11. Receiver high level output voltage
vs. temperature
ST490AB Test circuit and typical characteristics
Figure 12. Receiver input current vs input
voltage
11/17
Package mechanical data ST490AB
6 Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a lead-free second level interconnect. The category of
second level interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com
12/17
ST490AB Package mechanical data
Plastic DIP-8 mechanical data
Dim.
Min. Typ. Max. Min. Typ. Max.
A 3.3 0.130
a1 0.7 0.028
B1.39 1.65 0.055 0.065
B1 0.91 1.04 0.036 0.041
b 0.5 0.020
b10.38 0.5 0.015 0.020
D 9.8 0.386
E 8.8 0.346
e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300
F 7.1 0.280
I4.8 0.189
L 3.3 0.130
Z 0.44 1.6 0.017 0.063
mm. inch.
P001F
13/17
Package mechanical data ST490AB
SO-8 mechanical data
Dim.
A1.35 1.75 0.053 0.069
A1 0.10 0.25 0.04 0.010
A2 1.10 1.65 0.043 0.065
B0.33 0.51 0.013 0.020
C0.19 0.25 0.007 0.010
D4.80 5.00 0.189 0.197
E 3.80 4.00 0.150 0.157
e 1.27 0.050
H5.80 6.20 0.228 0.244
h 0.25 0.50 0.010 0.020
L 0.40 1.27 0.016 0.050
k 8° (max.)
ddd 0.1 0.04
Min. Typ. Max. Min. Typ. Max.
mm. inch.
14/17
0016023/C
ST490AB Package mechanical data
Tape & reel SO-8 mechanical data
mm. inch.
Dim.
Min. Typ. Max. Min. Typ. Max.
A 330 12.992
C 12.8 13.2 0.504 0.519
D 20.2 0.795
N60 2.362
T 22.4 0.882
Ao 8.1 8.5 0.319 0.335
Bo 5.5 5.9 0.216 0.232
Ko 2.1 2.3 0.082 0.090
Po 3.9 4.1 0.153 0.161
P7.98.1 0.311 0.319
15/17
Revision history ST490AB
7 Revision history
Table 11. Document revision history
Date Revision Changes
06-Jul-2005 2 Typing error on table 2 - pin 5 non-inverting, pin 6 inverting.
04-May-2006 3 Order codes updated.
08-Nov-2007 4 Added: Ta b le 1.
07-Feb-2008 5 Modified: Table 1 on page 1.
16/17
ST490AB
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