ST ST485ERB 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

■ Operate 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

ST485ERB

±15 kV ESD protected, low power

RS-485/RS-422 transceiver

DIP-8 SO-8

The ST485ERB is designed for bi-directional data
communications on multipoint bus transmission
line (half-duplex applications).

Description

The ST485ERB is al low power transceiver for
RS-485 and RS-422 communication. Each driver
output and receiver input is protected against ±15
kV electrostatic discharge (HBM) ± 8 kV (IEC­1000-4-2 contact discharge) shocks, without
latch-up. These parts contain one driver and one
receiver.

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.

Driver is short-circuit current limited and is
protected against excessive power dissipation by
thermal shutdown circuitry that places the driver
outputs into a high-impedance state.

Table 1. Device summary

Order code Temperature range Package Packaging

ST485ERBN - 40 to 85 °C DIP-8 50 parts per tube / 40 tube per box

ST485ERBDR - 40 to 85 °C SO-8 (tape and reel) 2500 parts per reel

February 2009 Rev 7 1/19

www.st.com

19

Contents ST485ERB

Contents

1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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

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ST485ERB Pin settings

1 Pin settings

Figure 1. Pin configuration

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

3/19

Truth tables ST485ERB

2 Truth tables

Table 3. Truth table (driver)

Inputs Outputs

RE

XHHLH

XHLHL

XLXZZ

DE DI B A

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

Table 4. Truth table (receiver)

Inputs Outputs

RE

LL

LL

L L Inputs open H

HLX Z

DE A-B RO

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

≥ +0.2V H

≤ -0.2V L

4/19

ST485ERB Maximum ratings

3 Maximum ratings

Table 5. Absolute maximum ratings

Symbol Parameter Value Unit

V

V

V

V

V

Supply voltage 7 V

CC

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

DI

Driver output voltage (A, B) ± 14 V

DO

Receiver input voltage (A, B) ± 14 V

RI

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

RO

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 ST485ERB

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

Differential driver output (no

OD1

load)

Differential driver output

OD2

(with load)

RL = 27Ω (RS-485) (Figure 2)

= 50Ω (RS-422) (Figure 2)

R

L

Change in magnitude of

ΔV

driver differential output

OD

voltage for complementary

= 27Ω or 50Ω (Figure 2)0.2V

R

L

output states

V

Driver common-mode

OC

output voltage

= 27Ω or 50Ω (Figure 2)3V

R

L

Change in magnitude of

ΔV

driver common-mode output

OC

voltage for complementary

= 27Ω or 50Ω (Figure 2)0.2V

R

L

output states

V

Input high voltage RE, DE, DI 2.0 V

IH

V

Input low voltage RE, DE, DI 0.8 V

IL

I

I

V

ΔV

V

V

I

R

Input current RE, DE, DI ± 2µA

IN1

V

= 0V or 5.25V, VDE = 0V

Input current (A, B)

IN2

Receiver differential

TH

threshold voltage

Receiver input hysteresis VCM = 0V 70 mV

TH

Receiver output high

OH

voltage

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

OL

3-State (high impedance)

OZR

output current at receiver

Receiver input resistance VCM = -7 to 12V 24 kΩ

IN

CM

= 12V

V

IN

V

= -7V

IN

= -7 to 12V -0.2 0.2 V

V

CM

= -4mA, VID = 200mV 3.5 V

I

O

= 0.4 to 2.4V ± 1µA

V

O

(1)

Min. Typ. Max. Unit

5V

5

1.5

V

5

V

1

-0.8mAmA

6/19