ST ST485EB, ST485EC, ST485EX User Manual

Features

■ Low quiescent current: 300 µA

■ Designed for RS-485 interface application

■ - 7 V to 12 V common mode input voltage range

■ Driver maintains high impedance in 3-state or

with the power OFF

■ 70 mV typical input hysteresis

■ 30 ns propagation delay, 5 ns skew

■ Operates from a single 5 V supply

■ Current limiting and thermal shutdown for

driver overload protection

■ ESD protection:

– ± 15 kV (HBM)
– ± 8 kV (IEC-1000-4-2 contact discharge)

■ Allows up to 256 transceivers on the bus

ST485EB

ST485EC - ST485EX

±15 kV ESD protected, low power

RS-485/RS-422 transceiver

SO-8

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 ST485E is designed for bi-directional data
communications on multipoint bus transmission
lines (half-duplex applications).

Description

The ST485E is a low power transceiver for RS­485 and RS-422 communication. Each driver
output and receiver input is protected against
± 15 kV electrostatic discharge (HBM) (ESD)
shocks, without latch-up. These parts contain one
driver and one receiver in half duplex
configuration.

This transceiver draws 300 µA (typ.) of supply
current when unloaded or fully loaded with
disabled drivers.

It operates from a single 5 V supply.

Table 1. Device summary

Order codes

ST485EBD - 40 to 85 °C SO-8 (tube) 100 parts per tube / 20 tube per box

ST485ECDR 0 to 70 °C SO-8 (tape and reel) 2500 parts per reel

ST485EBDR - 40 to 85 °C SO-8 (tape and reel) 2500 parts per reel

ST485EXDR - 55 to 125 °C SO-8 (tape and reel) 2500 parts per reel

Temperature

range

Package Packaging

February 2009 Rev 14 1/18

www.st.com

18

Contents ST485EB - ST485EC - ST485EX

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2/18

ST485EB - ST485EC - ST485EX Pin configuration

1 Pin configuration

Figure 1. Pin connections (top view)

Table 2. Pin description

Pin n° Symbol Name and function

1 RO Receiver output

2REReceiver output enable

3 DE Driver output enable

4 DI Driver input

5 GND Ground

6 A Non-inverting receiver input and non-inverting driver output

7 B Inverting receiver input and inverting driver output

8V

CC

Supply voltage

3/18

Truth tables ST485EB - ST485EC - ST485EX

2 Truth tables

Table 3. Truth table (driver)

Inputs Outputs

RE DE DI B A

XHHLH

XHLHL

XLXZZ

Note: X = Don’t care; Z = High impedance

Table 4. Truth table (receiver)

Inputs Outputs

RE DE A-B RO

LL

LL

L L Inputs open H

HLX Z

Note: X = Don’t care; Z = High impedance

≥ +0.2V H

≤ -0.2V L

4/18

ST485EB - ST485EC - ST485EX 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) -0.5 to (VCC + 0.5) V

I

Driver input voltage (DI) -0.5 to (VCC + 0.5) V

Driver output voltage (A, B) ± 14 V

Receiver input voltage (A, B) ± 14 V

Receiver output voltage (RO) -0.5 to (VCC + 0.5) V

Note: Absolute maximum ratings are those values beyond which damage to the device may occur.

Functional operation under these is not implied.

5/18

Electrical characteristics ST485EB - ST485EC - ST485EX

4 Electrical characteristics

Table 6. ESD performance: transmitter outputs, receiver inputs

Symbol Parameter Test conditions Min. Typ. Max. Unit

ESD ESD protection voltage Human body model ±15 kV

ESD ESD protection voltage IEC-1000-4-2 ±8kV

VCC = 5 V ± 5 %, TA = T
to T

= 25 °C

A

Table 7. DC electrical characteristics

MIN

to T

, unless otherwise specified. Typical values are referred

MAX

Symbol Parameter Test conditions

V

V

OD1

OD2

Differential driver output (no
load)

Differential driver output
(with load)

RL = 27 Ω (RS-485) (Figure 2)
RL = 50 Ω (RS-422) (Figure 2.)

Change in magnitude of

ΔV

driver differential output

OD

voltage for complementary

= 27 Ω or 50 Ω (Figure 2)0.2V

R

L

output states

V

Driver common-mode output

OC

voltage

R

= 27 Ω or 50 Ω (Figure 2)3V

L

Change in magnitude of

ΔV

driver common-mode output

OC

voltage for complementary

= 27 Ω or 50 Ω (Figure 2)0.2V

R

L

output states

V

ΔV

V

I

V

V

I

IN1

I

IN2

V

OZR

Input high voltage RE, DE, DI 2.0 V

IH

Input low voltage RE, DE, DI 0.8 V

IL

Input current RE, DE, DI ± 2µA

V

= 0 V or 5.25 V, VDE = 0 V

Input current (A, B)

Receiver differential

TH

threshold voltage

Receiver input hysteresis VCM = 0 V 70 mV

TH

Receiver output high voltage IO = -4 mA, VID = 200 mV 3.5 V

OH

Receiver output low voltage IO = 4 mA, VID = -200 mV 0.4 V

OL

3-State (high impedance)
output current at receiver

CM

= 12 V

V

IN

= -7 V

V

IN

= -7 to 12 V -0.2 0.2 V

V

CM

V

= 0.4 to 2.4 V ± 1µA

O

(1)

Min. Typ. Max. Unit

5V

1.5

5
5

V
V

1

-0.8mAmA

R

I

CC

Receiver input resistance VCM = -7 to 12 V 96 kΩ

IN

VRE = 0V or V

No load supply current

(2)

VDE = V

CC

VDE = 0 V

6/18

CC

400
300

900
500

µA
µA