ST ST490AB User Manual
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
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