low power RS-485/RS-422 transceiver
Features
■ Low supply current: 5 mA max
■ High data rate > 30 Mbps
■ Designed for RS 485 interface applications
■ -7 to 12 common mode input voltage range
■ Driver maintains high impedance in 3-state or
with the power off
■ 70mV typical input hysteresis
■ Operate from single 5 supply
■ ±4 kV ESD protection
■ Current limiting and thermal shutdown for
driver overload protection
■ Latch-up free up to 500 mA
ST485AB
Very high speed
DIP-8 SO-8
The ST485A is designed for bi-directional data
communications or multipoint bus transmission
lines.
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 3 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
ST485ABN -40 to 85 °C DIP-8 50parts per tube / 40tube per box
ST485ABDR -40 to 85 °C SO-8 (Tape & reel) 2500 parts per reel
August 2007 Rev. 3 1/19
www.st.com
19
Contents ST485AB
Contents
1 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Truth tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Test circuit and typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2/19
ST485AB Pin configuration
1 Pin configuration
Figure 1. Pin configuration
Table 2. Pin description
Pin n° Symbol Name and function
1 RO Receiver output. If A>B by 200 mV, RO will be high; if A<B by 200 mV, RO will be low
2RE
3DE
4DI
5 GND Ground
6 A Non-inverting receiver input and non-inverting driver output
7 B Inverting receiver input and inverting driver output
8V
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.
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.
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
Supply voltage: VCC= 4.75 V to 5.25 V
CC
3/19
Truth tables ST485AB
2 Truth tables
Table 3. Truth table (driver)
Inputs Outputs Mode
RE
XHHLHNormal
XHLHLNormal
LLXZZNormal
DE DI B A A
Note: X = Don’t care; Z = High impedance
Table 4. Truth table (receiver)
Inputs Outputs
RE
LL
LL
L L Inputs open H Normal
DE A-B RO
≥ -0.2 V H Normal
≤ -0.2 V L Normal
Note: X = Don’t care; Z = High impedance
Mode
4/19
ST485AB Maximum ratings
3 Maximum ratings
Table 5. Absolute maximum ratings
Symbol Parameter Value Unit
V
V
V
V
V
V
CC
DI
DO
RI
RO
Supply voltage 7 V
Control input voltage (RE, DE) -0.3 to 7 V
I
Driver input voltage (DI) -0.3 to 7 V
Driver output voltage (A, B) -7.5 to 12.5 V
Receiver input voltage (A, B) -7.5 to 12.5 V
Receiver output voltage (RO) -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.
5/19
Electrical characteristics ST485AB
4 Electrical characteristics
Table 6. DC electrical characteristics (V
specified. Typical values are referred to T
= 4.5 V to 5.5 V, TA = -40 to 85°C, unless otherwise
CC
= 25°C, VCC = 5 V) (Note: 1)
A
Symbol Parameter Test conditions Min. Typ. Max. Unit
I
SUPPLYVCC
C
C
Input/output capacitance 10 pF
I/O
Driver output capacity 10 pF
AB
Power supply current No load, VRE=0 V or V
CC
= V
DE
CC
= 0 V 2.6 5 mA
V
DE
2.3 5 mA
V
Table 7. Logic input electrical characteristics (VCC = 4.5 V to 5.5 V, TA = -40 to 85°C, unless
otherwise specified. Typical values are referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
Input logic threshold low DE, DI, RE 0.8 V
IL
V
I
I
Input logic threshold high DE, DI, RE 2 V
IH
Logic input current DE, DI, RE ± 2.0 µA
IN1
=0 V,
V
Input current (A, B)
IN2
DE
VCC= 0 or 5.25 V
= 25°C, VCC = 5 V) (Note: 1)
A
=12 V 1 mA
V
IN
=-7 V -0.8 mA
V
IN
Table 8. Transmitter electrical characteristics (VCC = 4.5 V to 5.5 V, TA = -40 to 85°C, unless
otherwise specified. Typical values are referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
= 25°C, VCC = 5 V) (Note: 1)
A
V
V
Differential driver output (No load) 5 V
OD1
= 54 Ω (RS-422)
R
Differential driver output (with load)
OD2
L
VCM= -7 V to 12 V
Change in magnitude of driver
ΔV
differential output voltage for
OD
complementary output states
= 27 Ω or 50 Ω 00.2V
R
L
(Note: 1)
V
Driver common mode output
OC
voltage
= 27 Ω or 50 Ω 13V
R
L
Change in magnitude of driver
ΔV
common mode output voltage
OC
RL= 54 Ω or 100 Ω 00.2V
(Note: 1)
I
OSD
Driver short circuit output current VO= -7 V to 12 V ± 250 mA
6/19
1.5 2.7 5 V
ST485AB Electrical characteristics
Table 9. Receiver electrical characteristics (V
otherwise specified. Typical values are referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
= 4.5 V to 5.5 V, TA = -40 to 85°C, unless
CC
= 25°C, VCC = 5 V) (Note: 1)
A
V
ΔV
V
V
I
R
I
OSR
Receiver Differential Threshold
TH
Voltage
Receiver Input Hysteresis VCM = 0 V 70 mV
TH
Receiver Output High Voltage I
OH
Receiver Output Low Voltage I
OL
3-State (High Impedance) Output
OZR
Current at Receiver
Receiver Input Resistance VCM = -7 V to 12 V 12 24 KΩ
RIN
Receiver Short-Circuit Current VO = 0 V to V
V
= -7 V to 12 V -0.2 0.2 V
CM
= -4 mA, VID = 200 mV 3.5 4.7 V
OUT
= 4 mA, VID = -200 mV 0.2 0.4 V
OUT
= 0.4 V to 2.4 V ± 1 μA
V
O
CC
795mA
Table 10. Driver switching characteristics (VCC = 4.5 V to 5.5 V, TA = -40 to 85°C, unless otherwise
specified. Typical values are referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
D
Maximum data rate Jitter < 5% 30 50 Mbps
R
t
PLH
t
PHL
t
SKEW
t
TLH
t
THL
t
PZL
t
PZH
t
PHZ
t
PLZ
t
SK(EN)
Propagation delay input to output
Differential output delay skew
Rise or fall differential time
Output enable time CL= 50 pF, S1 Closed 30 ns
Output enable time CL= 50 pF, S2 Closed 30 ns
Output disable time CL= 15 pF, S2 Closed 30 ns
Output disable time CL= 15 pF, S1 Closed 30 ns
Synchronous driver operation a-b at
enable
= 54 Ω, CL1=CL2=50 pF,
R
L
(Figure 8.)
= 54Ω, CL1=CL2=50 pF,
R
L
(Figure 6.)
R
= 54Ω, CL1=CL2=50 pF,
L
(Figure 6.)
= 25°C, VCC = 5 V) (See Note: 1, Note 3)
A
18 30 ns
0.5 2 ns
812ns
2ns
t
SK(DS)
Synchronous driver operation A-B
at disable
46ns
7/19
Electrical characteristics ST485AB
Table 11. Driver switching characteristics (V
specified. Typical values are referred to T
Symbol Parameter Test conditions Min. Typ. Max. Unit
t
PLH
t
t
RPDS|tPLH - tPHL
t
t
t
t
Propagation Delay CL = 15 pF 18 30 ns
PHL
| Propagation delay skew CL = 15 pF 0.5 2 ns
Output enable time CRL = 15 pF, S1 Closed 7 12 ns
PZL
Output enable time CRL = 15 pF, S2 Closed 7 12 ns
PZH
Output disable time CRL = 15 pF, S2 Closed 7 12 ns
PHZ
Output disable time CRL = 15 pF, S1 Closed 7 12 ns
PLZ
= 4.5V to 5.5V, TA = -40 to 85°C, unless otherwise
CC
= 25°C, VCC = 5V) (See Note: 1, Note 3)
A
Note: 1 All currents into device pins are positive; all currents out of device pins are negative; all
voltages are referenced to device ground unless specified.
2 Applies to peak current. See typical Operating Characteristics.
3t
r=tf
≤ 6 ms.
8/19
ST485AB Test circuit and typical characteristics
5 Test circuit and typical characteristics
Figure 2. Driver DC test load
Figure 3. Receiver timing test load
Figure 4. Driver/receiver timing test circuit
9/19
Test circuit and typical characteristics ST485AB
Figure 5. Driver timing test load
Figure 6. Driver timing test load
10/19
ST485AB Test circuit and typical characteristics
Figure 7. Driver enable and disable time
Figure 8. Receiver propagation delay
11/19
Test circuit and typical characteristics ST485AB
Figure 9. Receiver enable and disable time
Figure 10. Receiver output current vs. output
voltage (output low)
Figure 11. Receiver output current vs. output
voltage (output high)
12/19
ST485AB Test circuit and typical characteristics
Figure 12. Driver diff. output voltage vs
common mode voltage (diff. output
low)
Figure 14. Driver short circuit current vs line
voltage (output high)
Figure 13. Driver diff. output voltage vs
common mode voltage (diff. output
low)
Figure 15. Driver short circuit current vs. line
voltage (output low)
Figure 16. Receiver input current vs input
voltage
13/19
Package mechanical data ST485AB
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
14/19
ST485AB 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
15/19
Package mechanical data ST485AB
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.
16/19
0016023/C
ST485AB 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
17/19
Revision history ST485AB
7 Revision history
Table 12. Revision history
Date Revision Changes
28-Mar-2006 2 Order codes updated and new template.
24-Aug-2007 3 Added Table 1. in cover page.
18/19
ST485AB
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