ST ST485B, ST485C User Manual

ST485B

ST485C

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

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

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

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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
	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
	8		VCC	Supply voltage

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Truth tables							ST485B - ST485C
2	Truth tables
Table 3.	Truth table (driver)
		Inputs				Outputs
RE		DE	DI		B		A
X		H	H		L		H
X		H	L		H		L
X		L	X		Z		Z
Note:	X = Don’t care; Z = High impedance
Table 4.	Truth table (receiver)
		Inputs				Outputs
RE		DE	A-B			RO
L		L	≥ +0.2V			H
L		L	≤ -0.2V			L
L		L	Inputs open			H
H		L	X			Z
Note:	X = Don’t care; Z = High impedance

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ST485B - ST485C					Maximum ratings
3	Maximum ratings
Table 5.	Absolute maximum ratings
Symbol			Parameter		Value	Unit
VCC	Supply voltage				7	V
VI	Control input voltage		DE)		-0.5 to (VCC + 0.5)	V
		(RE,
VDI	Driver input voltage (DI)				-0.5 to (VCC + 0.5)	V
VDO	Driver output voltage (A, B)				± 14	V
VRI	Receiver input voltage (A, B)				± 14	V
VRO	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.

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Electrical characteristics	ST485B - ST485C

4 Electrical characteristics

VCC = 5 V ± 5 %, TA = TMIN to TMAX, unless otherwise specified. Typical values are referred to TA = 25 °C

Table 6.

DC electrical characteristics

Value

Test conditions (1)

Symbol

Parameter

-40 to 85 °C

-55 to 125 °C

Unit

Min.

Typ.

Max.

Min.

Max.

VOD1

Differential driver output

5

5

V

(no load)

VOD2

Differential driver output

RL = 27Ω (RS-485) Figure 2

1.5

5

1.4

5

V

(with load)

RL = 50Ω (RS-422) Figure 2

5

5

V

Change in magnitude of

VOD

driver differential output

RL = 27Ω or 50Ω Figure 2

0.2

0.2

V

voltage for complementary

output states

VOC

Driver common-mode

RL = 27Ω or 50Ω Figure 2

3

3

V

output voltage

Change in magnitude of

driver common-mode

RL = 27Ω or 50Ω Figure 2

VOC

output voltage for

0.2

0.2

V

complementary output

states

VIH

Input high voltage

DE, DI

2.0

2.0

V

RE,

VIL

Input low voltage

DE, DI

0.8

0.8

V

RE,

IIN1

Input current

DE, DI

± 2

± 2

µA

RE,

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

1

1

mA

IIN2

Input current (A, B)

VIN = 12V

VIN = -7V

-0.8

-0.8

mA

VTH

Receiver differential

VCM = -7 to 12V

-0.2

0.2

-0.2

0.2

V

threshold voltage

VTH

Receiver input hysteresis

VCM = 0V

70

mV

VOH

Receiver output high

IO = -4mA, VID = 200mV

3.5

3.4

V

voltage

VOL

Receiver output low

IO = 4mA, VID = -200mV

0.4

0.55

V

voltage

IOZR

3-state (high impedance)

VO = 0.4 to 2.4V

± 1

± 1

µA

output current at receiver

RIN

Receiver input resistance

VCM = -7 to 12V

24

24

kΩ

I

No load supply current (2)

VRE = 0V or VCC

V

DE

= V

400

900

900

µA

CC

CC

VDE = 0V

300

500

500

µA

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