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ST491A
LOW POWER HIGH SPEED RS-485/RS-422 TRANSCEIVER
■ LOW SUPPLY CURRENT: 5mA MAX
■ DESIGNED FOR RS485 INTERFACE
APPLICATIONS
■ -7 TO 12 COMMON MODE INPUT VOLTAGE
RANGE
■ 70mV TYPICAL INPUT HYSTERESIS
■ DESIGNED FOR 25Mbps OPERATION
■ OPERATE FROM SINGLE 5 SUPPLY
■ ±4kV ESD PROTECTION
■ CURRENT LIMITING AND T HER MAL
SHUTDOWN FOR DRIVER OVERLOAD
PROTECTION
DESCRIPTION
The ST491A is a low power transceiver for
RS-485 and RS-422 communications. The device
contains one driver and one receiver in full duplex
configuration. The ST491A draws 5mA (typ.) of
supply current when unloaded a nd operates from
a single 5V supply.
Driver is short-circuit current limited and is
protected against ex cessive 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 out put if both inputs are open circuit.
DIP SOP
ORDERING CODES
Type
ST491ACN 0 to 70 °C DIP-14 25parts per tube /40tube per box
ST491ABN -40 to 85 °C DIP-14 25parts per tube / 40tube per box
ST491ACD 0 to 70 °C SO-14 (Tube) 50parts per tube / 20tube per box
ST491ABD -40 to 85 °C SO-14 (Tube) 50parts per tube / 20tube per box
ST491ACDR 0 to 70 °C SO-14 (Tape & Reel) 2500 parts per reel
ST491ABDR -40 to 85 °C SO-14 (Tape & Reel) 2500 parts per reel
Temperature
Range
Package Comments
1/12July 2003
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ST491A
PIN CONFIGURA TION
PIN DESCRIPTION
PlN N° SYMBOL NAME AND FUNCTION
1 NC Not Connected
2 RO Receiver Output.
3 RE Receiver Output Enable
4 DE Driver Output Enable
5 DI Inverting Driver Input.
6 GND Ground
7 GND Ground
8 NC Not Connected
9 Y Non-inverting Driver Output
10 Z Inverting Driver Output
11 B Inverting Receiver Input
12 A Non-inverting Receiver Input
13 NC Not Connected
14
V
CC
Supply Voltage
TRUTH TABLE (DRIVER)
INPUT OUTPUTS
DI DE Y Z
LHLH
HHHL
XLZZ
X= Don’t Care; Z=High Impedance
2/12
TRUTH TABLE (RECEIVER)
INPUT OUTPUT
A-B RE RO
≥ -0.2V L H
between -0.2V to 0.2V L ?
≤ -0.2V L L
OPEN L H
XHZ
?= Irrelevant; X= Don’t Care; Z=High Impedance
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ST491A
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
V
V
V
Y,VZ
V
A,VB
V
RO
ESD Human Body Model 3.5 KV
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
=4.5Vto5.5V,TA=-40to85°C, unless otherwise specified.TypicalvaluesarereferredtoTA=25°C)
CC
Symbol Parameter Test Conditions Min. Typ. Max. Unit
I
SUPPLY
C
IN
C
YZ
C
OUT
Supply Voltage
CC
Driver Input Voltage
DI
Driver Output Voltage
Receiver Input Voltage
7V
-0.5 to 7 V
-7.5 to 12.5 V
-7.5 to 12.5 V
Receiver Output Voltage -0.3 to (VCC+ 0.3)
No Load Supply Current 2 5 mA
Input Capacitance 1.8 pF
Driver Output Capacitance 1.2 pF
Output Capacitance 2.3 pF
V
TRANSMITTER ELECTRICAL CHARACTERISTICS
V
=4.5Vto5.5V,TA= -40 to 85°C,unless oth erwise specified. Typical v alues arereferred to Ta= 25°C)
CC
Symbol Parameter Test Conditions Min. Typ. Max. Unit
V
V
V
∆V
V
∆V
I
I
OSD
V
Differential Drive Output
OD1
(No load)
Differential Drive Output
OD2
(With Load)
Differential Drive Output
OD3
(With Load)
Change in magnitude of
OD
Driver Differential Output
RL=54Ω(RS-422) (Figure 1) 1.5 2.6 5 V
RL= 100Ω (RS-422) (Figure 1) 2 3 V
=54Ωor 100Ω (Figure 1) 0 0.2 V
R
L
Voltage for Complementary
Output States (Note1)
Driver Common Mode
OC
Output Voltage
Change in magnitude of
OC
Driver Common Mode
RL=54Ω(Figure 1) 1 3 V
=54Ω(Figure 1) 0 0.2 V
R
L
Output Voltage (Note1)
Power Off Output Current VCC=0V VO=-7V to 12V ± 100 µA
OFF
Driver Short Circuit Output
VO=-7V to 12V ± 35 ± 250 mA
Current
V
Input Logic Threshold Low 0.8 V
IL
Input Logic Threshold High 2 V
IH
V
CC
V
3/12
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ST491A
RECEIVER ELECTRICAL CHARACTERISTICS
V
=4.5Vto5.5V,TA= -40 to 85°C,unless oth erwise specified. Typical v alues arereferred to Ta= 25°C)
CC
Symbol Parameter Test Conditions Min. Typ. Max. Unit
I
Input Current (A, B) other input=0V
V
∆V
V
V
R
IN
Receiver Differential
TH
Threshold Voltage
Receiver Input Hysteresis VCM=0V 70 mV
TH
Receiver Output High
OH
Voltage
Receiver Output Low
OL
Voltage
Receiver Input Resistance VCM= -7V to 12V 12 24 KΩ
RIN
= 0 or 5.25V
V
CC
VCM= -7V to 12V -0.2 0.2 V
I
= -8mA, VID= 200mV 3.5 4.7 V
OUT
I
= 8mA, VID= -200mV 0.3 0.5 V
OUT
DRIVER SWITCHING CHARACTERISTICS
=4.5Vto5.5V,TA=-40to 85°C, unlessotherwise specified. Typicalvalues are referred toTa=25°C)
V
CC
Symbol Parameter Test Conditions Min. Typ. Max. Unit
Maximum Data Rate Jitter <5% 25 50 Mbps
D
R
t
PLH
t
PHL
t
SKEW
t
TLH
t
THL
t
PZL
t
PZH
t
PHZ
t
PLZ
Propagation Delay Input to
Output
Differential Output Delay
Skew
Rise or Fall Differential
Time
Output Enable Time CL= 50pF S1 Closed 14 25 ns
Output Enable Time CL= 50pF S2 Closed 14 25 ns
Output Disable Time CL= 15pF S2 Closed 10 25 ns
Output Disable Time CL= 15pF S1 Closed 16 25 ns
RL=54Ω CL1=CL2=50pF, (Figure 1) 10 16 ns
RL=54Ω CL1=CL2=50pF, (Figure 1) 1 3 ns
RL=54Ω CL1=CL2=50pF, (Figure 1) 8 12 ns
V
=12V 0.5 1 mA
IN
=-7V -0.35 -0.8 mA
V
IN
RECEIVER SWITCHING CHARACTERISTICS
=4.5Vto5.5V,TA=-40to85°C, unless otherwisespecified.Typicalvalues are ref erred toTa=25°C)
V
CC
Symbol Parameter Test Conditions Min. Typ. Max. Unit
Propagation Delay Input to
t
PLH
Output
t
PHL
t
SKD|tPLH -tPHL
Skew
t
t
t
t
Rise or Fall Time CL= 15pF (Figures 2,4) 6 ns
TLH
THL
Output Enable Time CRL= 15pF S1 Closed 6 12 ns
t
PZL
Output Enable Time CRL= 15pF S2 Closed 7 12 ns
PZH
Output Disable Time CRL= 15pF S2 Closed 6 12 ns
PHZ
Output Disable Time CRL= 15pF S1 Closed 6 12 ns
t
PLZ
4/12
| Receiver Output
CL= 15pF (Figures 2,4) 19 30 ns
CL= 15pF (Figures 2,4) 1 3 ns