ST ST485B, ST485C User Manual

Low power RS-485/RS-422 transceiver

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

■ Allows up to 64 transceivers on the bus

ST485B
ST485C

DIP-8 SO-8

The ST485 is available in three temperature
range: commercial (0 °C to 70 °C), industrial (- 40
°C to 85 °C) and automotive (- 55 °C to 125 °C).

Description

The ST485 is al low power transceiver for RS-485
and RS-422 communication. Each part contains
one driver and one receiver.

This transceiver draw 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 placed the driver
outputs into a high-impedance state.

The ST485 is designed for bi-directional data
communications on multipoint bus transmission
line (half-duplex applications).

Table 1. Device summary

Order code Temperature range Package Packaging

ST485CN 0 to 70 °C DIP-8 50 parts per tube / 40 tube per box

ST485BN - 40 to 85 °C DIP-8 50 parts per tube / 40 tube per box

ST485CDR 0 to 70 °C SO-8 (tape and reel) 2500 parts per reel

ST485BDR - 40 to 85 °C SO-8 (tape and reel) 2500 parts per reel

February 2009 Rev 16 1/19

www.st.com

19

Contents ST485B - ST485C

Contents

1 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Truth tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.1 Driver switching characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.2 Receiver switching characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 Test circuit and typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2/19

ST485B - ST485C Pin configuration

1 Pin configuration

Figure 1. Pin connections

Table 2. Pin description

Pin n° Symbol Name and function

1 RO Receiver output

2 RE Receiver output enable

3 DE Driver output enable

4DIDriver 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 ST485B - ST485C

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

4/19

ST485B - ST485C 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 condition is not implied.

5/19

Electrical characteristics ST485B - ST485C

4 Electrical characteristics

VCC = 5 V ± 5 %, TA = T

= 25 °C

to T

A

Table 6. DC electrical characteristics

MIN

to T

, unless otherwise specified. Typical values are referred

MAX

Symbol Parameter Test conditions

V

V

Differential driver output

OD1

(no load)

Differential driver output

OD2

(with load)

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

Change in magnitude of

ΔV

driver differential output

OD

voltage for complementary

= 27Ω or 50Ω Figure 2 0.2 0.2 V

R

L

output states

V

Driver common-mode

OC

output voltage

= 27Ω or 50Ω Figure 2 33V

R

L

Change in magnitude of
driver common-mode

ΔV

output voltage for

OC

= 27Ω or 50Ω Figure 2 0.2 0.2 V

R

L

complementary output
states

V

Input high voltage RE, DE, DI 2.0 2.0 V

IH

Input low voltage RE, DE, DI 0.8 0.8 V

V

IL

I

Input current RE, DE, DI ± 2 ± 2µA

IN1

VCM = 0V or 5.25V, VDE = 0V

Input current (A, B)

I

IN2

V

Receiver differential

TH

threshold voltage

VIN = 12V

= -7V

V

IN

V

= -7 to 12V -0.2 0.2 -0.2 0.2 V

CM

(1)

Val ue

Min. Typ. Max. Min. Max.

55V

1.5

5
5

1

-0.8

1.4

5
5

1

-0.8mAmA

Unit-40 to 85 °C -55 to 125 °C

V
V

ΔV

V

V

I

Receiver input hysteresis VCM = 0V 70 mV

TH

Receiver output high

OH

voltage

Receiver output low

OL

voltage

3-state (high impedance)

OZR

output current at receiver

R

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

IN

I

No load supply current

CC

= -4mA, VID = 200mV 3.5 3.4 V

I

O

I

= 4mA, VID = -200mV 0.4 0.55 V

O

= 0.4 to 2.4V ± 1 ± 1µA

V

O

VRE = 0V or V

(2)

VDE = V

CC

CC

VDE = 0V

6/19

400
300

900
500

900
500µAµA