Datasheet LTC489, LTC488 Datasheet (Linear Technology)

LTC488/LTC489

Quad RS485 Line Receiver

EATU

F

■

Low Power: ICC = 7mA Typ

■

Designed for RS485 or RS422 Applications

■

Single 5V Supply

■

–7V to 12V Bus Common Mode Range Permits ±7V

RE

S

Ground Difference Between Devices on the Bus

■

60mV Typical Input Hysteresis

■

Receiver Maintains High Impedance in Three-State or
with the Power Off

■

28ns Typical Receiver Propagation Delay

■

Pin Compatible with the SN75173 (LTC488)

■

Pin Compatible with the SN75175 (LTC489)

U

O

PPLICATI

A

■

Low Power RS485/RS422 Receivers

■

Level Translator

S

DUESCRIPTIO

The LTC®488 and LTC489 are low power differential bus/
line receivers designed for multipoint data transmission
standard RS485 applications with extended common mode
range (12V to –7V). They also meet the requirements of
RS422.

The CMOS design offers significant power savings over its
bipolar counterpart without sacrificing ruggedness against
overload or ESD damage.

The receiver features three-state outputs, with the receiver
output maintaining high impedance over the entire com­mon mode range.

The receiver has a fail-safe feature which guarantees a
high output state when the inputs are left open.

Both AC and DC specifications are guaranteed 4.75V to

5.25V supply voltage range.

, LTC and LT are registered trademarks of Linear Technology Corporation.

A

U

O

PPLICATITYPICAL

EN

EN

2

DI

DI

DRIVER
1/4 LTC486

EN12

DRIVER
1/4 LTC487

120Ω

4000 FT 24 GAUGE TWISTED PAIR

120Ω

4000 FT 24 GAUGE TWISTED PAIR

120Ω

120Ω

1

2

1

EN

4

RECEIVER
1/4 LTC488

EN12

4

RECEIVER
1/4 LTC489

EN

12

3

RO

3

RO

LTC488/9 TA01

1

LTC488/LTC489

A

W

O

LUTEXI T

S

A

WUW

ARB

U
G

I

(Note 1)

S

Supply Voltage (VCC) .............................................. 12V

Control Input Currents ........................ – 25mA to 25mA

Control Input Voltages ................ –0.5V to (VCC + 0.5V)

Receiver Input Voltages ........................................ ±14V

Receiver Output Voltages ........... – 0.5V to (VCC + 0.5V)

WU

/

PACKAGE

1

B1

2

A1

3

RO1

4

EN

5

RO2

6

A2

7

B2

8

GND

N PACKAGE

16-LEAD PLASTIC DIP

T

= 150°C, θJA = 70°C/W (N PKG)

JMAX

= 150°C, θJA = 90°C/W (S PKG)

T

JMAX

O

TOP VIEW

R

R

16-LEAD PLASTIC SOL

RDER I FOR ATIO

ORDER PART

V

16
15

R

14
13
12
11
10

R

9

S PACKAGE

CC

B4
A4
RO4
EN
RO3
A3
B3

NUMBER

LTC488CN
LTC488CS
LTC488IN
LTC488IS

Operating Temperature Range

LTC488C/LTC489C ................................. 0°C to 70°C

LTC488I/LTC489I .............................. –40°C to 85°C

Storage Temperature Range ................ – 65°C to 150°C

Lead Temperature (Soldering, 10 sec)................. 300°C

U

TOP VIEW

1

B1
A1

RO1

EN12

RO2

A2
B2

GND

N PACKAGE

16-LEAD PLASTIC DIP

R

2
3
4
5
6

R

7
8

T

= 150°C, θJA = 70°C/W (N PKG)

JMAX

= 150°C, θJA = 90°C/W (S PKG)

T

JMAX

V

16

CC

B4

15

R

R

16-LEAD PLASTIC SOL

14
13
12
11
10

9

S PACKAGE

A4
RO4
EN34
RO3
A3
B3

ORDER PART

NUMBER

LTC489CN
LTC489CS
LTC489IN
LTC489IS

Consult factory for Military grade parts.

LECTRICAL C CHARA TERIST

E

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

INH

V

INL

I

IN1

I

IN2

V

TH

∆V

TH

V

OH

V

OL

I

OZR

I

CC

RINReceiver Input Resistance –7V ≤ VCM ≤ 12V, VCC = 0V ● 12 kΩ
I

OSR

t

PLH

t

PHL

t

SKD

Input High Voltage EN, EN, EN12, EN34 ● 2.0 V
Input Low Voltage EN, EN, EN12, EN34 ● 0.8 V
Input Current EN, EN, EN12, EN34 ● ±2 µA
Input Current (A, B) VCC = 0V or 5.25V, VIN = 12V ● 1.0 mA

Differential Input Threshold Voltage for Receiver –7V ≤ VCM ≤ 12V ● – 0.2 0.2 V
Receiver Input Hysteresis VCM = 0V 60 mV
Receiver Output High Voltage IO = – 4mA, VID = 0.2V ● 3.5 V
Receiver Output Low Voltage IO = 4mA, VID = – 0.2V ● 0.4 V
Three-State Output Current at Receiver VCC = Max 0.4V ≤ VO ≤ 2.4V ● ±1 µA
Supply Current No Load, Digital Pins = GND or V

Receiver Short-Circuit Current 0V ≤ VO ≤ V
Receiver Input to Output CL = 15pF (Figures 1, 3) ● 12 28 55 ns
Receiver Input to Output CL = 15pF (Figures 1, 3) ● 12 28 55 ns
| t

– t

PLH

Differential Receiver Skew

|C

PHL

VCC = 5V (Notes 2, 3), unless otherwise noted.

ICSCD

= 0V or 5.25V, VIN = – 7V ● – 0.8 mA

V

CC

● 710 mA

CC

CC

= 15pF (Figures 1, 3) 4 ns

L

● 785mA

2

LTC488/LTC489

OUTPUT VOLTAGE (V)

0

0

OUTPUT CURRENT (mA)

16

1.0

488 G04

8

0.5 1.5

24

32

2.0

4

12

20

28

36

LECTRICAL C CHARA TERIST

E

VCC = 5V ± 5% (Notes 2, 3), unless otherwise noted.

ICSCD

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

t

ZL

t

ZH

t

LZ

t

HZ

The ● denotes specifications that apply over the operating temperature
range.

Note 1: Absolute Maximum Ratings are those beyond which the safety of
the device may be impaired.

Receiver Enable to Output Low CL = 15pF (Figures 2, 4) S1 Closed ● 30 60 ns
Receiver Enable to Output High CL = 15pF (Figures 2, 4) S2 Closed ● 30 60 ns
Receiver Disable from Low CL = 15pF (Figures 2, 4) S1 Closed ● 30 60 ns
Receiver Disable from High CL = 15pF (Figures 2, 4) S2 Closed ● 30 60 ns

Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.

Note 3: All typicals are given for V

= 5V and TA = 25°C.

CC

UW

LPER

F

O

R

ATYPICA

Receiver Output Low Voltage vs
Temperature at I = 8mA

0.9

0.8

0.7

0.6

0.5

0.4

0.3

OUTPUT VOLTAGE (V)

0.2

0.1

0

–25 125

–50

0
TEMPERATURE (°C)

50

25

CCHARA TERIST

E

C

75 100

488 G01

ICS

4.8

4.6

4.4

4.2

4.0

3.8

3.6

OUTPUT VOLTAGE (V)

3.4

3.2

3.0

Receiver Output High Voltage vs
Temperature at I = 8mA

–25 125

–50

0

25

TEMPERATURE (°C)

50

75 100

488 G02

Receiver Output High Voltage vs
Output Current at TA = 25°C

–18

–16

–14

–12

–10

–8

–6

OUTPUT CURRENT (mA)

–4

–2

0

5

43

OUTPUT VOLTAGE (V)

Receiver Output Low Voltage vs
Output Current at TA = 25°C

2

488 G03

3

LTC488/LTC489

TEMPERATURE (°C)

–50

5.4

SUPPLY CURRENT (mA)

6.2

50

488 G07

5.8

–25 125

6.6

7.0

0

25

75 100

LPER

F

O

R

ATYPICA

UW

CCHARA TERIST

E

C

ICS

TTL Input Threshold vs
Temperature

1.63

1.61

1.59

1.57

INPUT THRESHOLD VOLTAGE (V)

1.55
–50

0

–25 125

25

TEMPERATURE (°C)

U

75 100

50

488 G05

UU

Receiver |t
Temperature

5

4

3

TIME (ns)

2

1

–50

PLH

0

–25 125

TEMPERATURE (°C)

PI FU CTIO S

B 1 (Pin 1) Receiver 1 Input.
A1 (Pin 2) Receiver 1 Input.
RO1 (Pin 3) Receiver 1 Output. If the receiver output is

enabled, then if A > B by 200mV, RO1 will be high. If
A < B by 200mV, then RO1 will be low.

EN (Pin 4) (LTC488) Receiver Output Enabled. See
Function Table for details.

EN12 (Pin 4) (LTC489) Receiver 1, Receiver 2 Output
Enabled. See Function Table for details.

RO2 (Pin 5) Receiver 2 Output. Refer to RO1.
A2 (Pin 6) Receiver 2 Input.
B2 (Pin 7) Receiver 2 Input.
GND (Pin 8) Ground Connection.

– t

| vs

PHL

25

75 100

50

488 G06

Supply Current vs Temperature

B3 (Pin 9) Receiver 3 Input.
A3 (Pin 10) Receiver 3 Input.
RO3 (Pin 11) Receiver 3 Output. Refer to RO1.
EN (Pin 12)(LTC488) Receiver Output Disabled. See

Function Table for details.
EN34 (Pin 12)(LTC489) Receiver 3, Receiver 4 output

enabled. See Function Table for details.

RO4 (Pin 13) Receiver 4 Output. Refer to RO1.
A4 (Pin 14) Receiver 4 Input.
B4 (Pin 15) Receiver 4 Input.
V

(Pin 16) Positive Supply; 4.75V ≤ VCC ≤ 5.25V.

CC

4

LTC488/LTC489

U

U

FU CTIO TABLES

LTC488

DIFFERENTIAL ENABLES OUTPUT

A – B EN EN RO
V

≥ 0.2V H X H

ID

–0.2V < V

V

ID

XLHZ

< 0.2V H X ?

ID

≤ 0.2V H X L

XLH

XL?

XLL

LTC489

DIFFERENTIAL ENABLES OUTPUT

A – B EN12 or EN34 RO
VID ≥ 0.2V H H
–0.2V < VID < 0.2V H ?
VID ≤ 0.2V H L
XLZ

H: High Level
L: Low Level
X: Irrelevant

TEST CIRCUITS

100pF

A

?: Indeterminate
Z: High Impedance (Off)

D

DRIVER RECEIVER

54Ω

100pF

B

RO

C

L

488/9 F01

Figure 1. Receiver Timing Test Circuit

Note: The input pulse is supplied by a generator having the following characteristics:

f = 1MHz, Duty Cycle = 50%, t

RECEIVER

OUTPUT

C

L

< 10ns, tf ≤ 10ns, Z

r

S1

1k

1k

S2

OUT

= 50Ω

V

CC

488/9 F02

Figure 2. Receiver Enable and Disable Timing Test Circuit

5

LTC488/LTC489

WITCHI

U

G

TI

W

E

WAVEFORS

INPUT

A, B

EN OR

EN12

RO

W

S

V

OD2

–V

OD2

V

OH

RO

V

OL

3V

0V



5V

RO

V

OL

V

OH

0V

0V

t

PHL

Figure 3. Receiver Propagation Delays

f = 1MHz; tr ≤ 10ns; tf ≤ 10ns

1.5V

t

ZL

t

ZH

1.5V

INPUT

f = 1MHz; tr ≤ 10ns; tf ≤ 10ns

1.5V

1.5V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

1.5V

t

t

0V

t

PLH

1.5V

488/9 F03

LZ

0.5V

HZ

0.5V

488/9 F04

Figure 4. Receiver Enable and Disable Times

PPLICATI

A

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O

S

I FOR ATIO

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Typical Application

A typical connection of the LTC488/LTC489 is shown in
Figure 5. Two twisted-pair wires connect up to 32 driver/
receiver pairs for half-duplex data transmission. There are
no restrictions on where the chips are connected to the
wires, and it isn’t necessary to have the chips connected
at the ends. However, the wires must be terminated only
at the ends with a resistor equal to their characteristic
impedance, typically 120Ω. The input impedance of a
receiver is typically 20k to GND, or 0.5 unit RS485 load, so
in practice 50 to 60 transceivers can be connected to the
same wires. The optional shields around the twisted-pair
help reduce unwanted noise, and are connected to GND at
one end.

Cables and Data Rate

The transmission line of choice for RS485 applications is
a twisted-pair. There are coaxial cables (twinaxial) made
for this purpose that contain straight-pairs, but these are
less flexible, more bulky, and more costly than twisted­pairs. Many cable manufacturers offer a broad range of
120Ω cables designed for RS485 applications.

Losses in a transmission line are a complex combination
of DC conductor loss, AC losses (skin effect), leakage, and
AC losses in the dielectric. In good polyethylene cable
such as the Belden 9841, the conductor losses and dielec­tric losses are of the same order of magnitude, leading to
relatively low overall loss (Figure 6).

6

LTC488/LTC489

DATA RATE (bps)

10k

10

CABLE LENGTH (FT)

100

1k

10k

100k 1M 10M

488/9 F07

2.5M

PPLICATI

A

DX

O

DX

1

1/4 LTC486

U

S

I FOR ATIO

EN

4

3

120Ω

12

EN

WU

12

EN

SHIELD

2

DX

1/4 LTC486

U

1

DX

SHIELD

2

RX

120Ω

1

2

EN

1/4 LTC488 OR

1/4 LTC489

RX

3

RX

3

4


1/4 LTC488 OR 
1/4 LTC489

1

3

488/9 F05

RX

Figure 5. Typical Connection

10

When using low loss cables, Figure 7 can be used as a
guideline for choosing the maximum line length for a given
data rate. With lower quality PVC cables, the dielectric loss
factor can be 1000 times worse. PVC twisted-pairs have
terrible losses at high data rates (> 100kbps), and greatly
reduce the maximum cable length. At low data rates
however, they are acceptable and much more economical.

1

LOSS PER 100 FT (dB)

0.1

0.1

1 10 100

FREQUENCY (MHz)

488/9 F06

Figure 6. Attenuation vs Frequency for Belden 9841

Figure 7. Cable Length vs Data Rate

Cable Termination

The proper termination of the cable is very important. If the
cable is not terminated with its characteristic impedance,
distorted waveforms will result. In severe cases, distorted
(false) data and nulls will occur. A quick look at the output
of the driver will tell how well the cable is terminated. It is

7

LTC488/LTC489

PPLICATI

A

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O

S

I FOR ATIO

WU

U

best to look at a driver connected to the end of the cable,
since this eliminates the possibility of getting reflections
from two directions. Simply look at the driver output while
transmitting square wave data. If the cable is terminated
properly, the waveform will look like a square wave
(Figure 8).

If the cable is loaded excessively (47Ω), the signal initially
sees the surge impedance of the cable and jumps to an
initial amplitude. The signal travels down the cable and is
reflected back out of phase because of the mistermination.
When the reflected signal returns to the driver, the ampli­tude will be lowered. The width of the pedestal is equal to
twice the electrical length of the cable (about 1.5ns/foot).
If the cable is lightly loaded (470Ω), the signal reflects in
phase and increases the amplitude at the drive output. An
input frequency of 30kHz is adequate for tests out to 4000
ft. of cable.

PROBE HERE

DX

DRIVER

Rt

RECEIVER

RX

AC Cable Termination

Cable termination resistors are necessary to prevent un­wanted reflections, but they consume power. The typical
differential output voltage of the driver is 2V when the
cable is terminated with two 120Ω resistors, causing
33mA of DC current to flow in the cable when no data is
being sent. This DC current is about 60 times greater than
the supply current of the LTC488/LTC489. One way to
eliminate the unwanted current is by AC coupling the
termination resistors as shown in Figure 9.

The coupling capacitor must allow high frequency energy
to flow to the termination, but block DC and low frequen­cies. The dividing line between high and low frequency
depends on the length of the cable. The coupling capacitor
must pass frequencies above the point where the line
represents an electrical one-tenth wavelength. The value
of the coupling capacitor should therefore be set at 16.3pF
per foot of cable length for 120Ω cables. With the coupling
capacitors in place, power is consumed only on the signal
edges, and not when the driver output is idling at a 1 or 0
state. A 100nF capacitor is adequate for lines up to 4000
feet in length. Be aware that the power savings start to
decrease once the data rate surpasses 1/(120Ω )(C).

Rt = 120Ω

Rt = 47Ω

Rt = 470Ω

Figure 8. Termination Effects

488/9 F08

120Ω

C

C = LINE LENGTH (FT)(16.3pF)

Figure 9. AC Coupled Termination

RECEIVER

RX

488/9 F09

8

LTC488/LTC489

PPLICATI

A

U

O

S

I FOR ATIO

WU

U

Receiver Open-Circuit Fail-Safe

Some data encoding schemes require that the output of
the receiver maintains a known state (usually a logic 1)
when the data is finished transmitting and all drivers on the
line are forced in three-state. The receiver of the LTC488/
LTC489 has a fail-safe feature which guarantees the out­put to be in a logic 1 state when the receiver inputs are left
floating (open-circuit). When the input is terminated with
120Ω and the receiver output must be forced to a known
state, the circuits of Figure 10 can be used.

5V

110Ω

130Ω

RX

RX

130Ω

5V

110Ω

1.5k

120Ω

1.5k

RECEIVER

RECEIVER

The termination resistors are used to generate a DC bias
which forces the receiver output to a known state, in this
case a logic 0. The first method consumes about 208mW
and the second about 8mW. The lowest power solution is
to use an AC termination with a pullup resistor. Simply
swap the receiver inputs for data protocols ending in
logic 1.

Fault Protection

All of LTC’s RS485 products are protected against ESD
transients up to 2kV using the human body model (100pF,

1.5k). However, some applications need more protection.
The best protection method is to connect a bidirectional
TransZorb® from each line side pin to ground (Figure 11).

A TransZorb is a silicon transient voltage suppressor that
has exceptional surge handling capabilities, fast response
time, and low series resistance. They are available from
General instruments, GSI, and come in a variety of break­down voltages and prices. Be sure to pick a breakdown
voltage higher than the common mode voltage required
for your application (typically 12V). Also, don’t forget to
check how much the added parasitic capacitance will load
down the bus.

5V

100k

C

120Ω

Figure 10. Forcing “0” When All Drivers Are Off

RECEIVER

RX

488/9 F10

Y

DRIVER

Figure 11. ESD Protection with TransZorbs

TransZorb is a registered trademark of General Instruments, GSI

120Ω

Z

488/9 F11

®

9

LTC488/LTC489

PACKAGE DESCRIPTIO

U

Dimensions in inches (millimeters) unless otherwise noted.

N Package

16-Lead PDIP (Narrow 0.300)

(LTC DWG # 05-08-1510)

0.770*

(19.558)

MAX

12

13

4

5

0.255 ± 0.015*
(6.477 ± 0.381)

14

15

16

2

1

3

11

6

910

8

7

0.300 – 0.325

(7.620 – 8.255)

0.009 – 0.015

(0.229 – 0.381)

+0.035

0.325

–0.015

+0.889

8.255

()

–0.381

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

0.020

(0.508)

MIN

0.130 ± 0.005

(3.302 ± 0.127)

0.125

(3.175)

MIN

0.100 ± 0.010

(2.540 ± 0.254)

0.045 – 0.065

(1.143 – 1.651)

0.065

(1.651)

TYP

0.018 ± 0.003

(0.457 ± 0.076)

N16 1197

10

PACKAGE DESCRIPTIO

U

Dimensions in inches (millimeters) unless otherwise noted.

SW Package

16-Lead Plastic Small Outline (Wide 0.300)

(LTC DWG # 05-08-1620)

0.398 – 0.413*

(10.109 – 10.490)

15 14

16

12

13

LTC488/LTC489

10 9

11

NOTE 1

2345678

0.050

(1.270)

TYP

1

0.014 – 0.019

(0.356 – 0.482)

TYP

0.291 – 0.299**
(7.391 – 7.595)

0.010 – 0.029

(0.254 – 0.737)

0.009 – 0.013

(0.229 – 0.330)

NOTE:

1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

*

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE

**




NOTE 1

× 45°

0.016 – 0.050

(0.406 – 1.270)

0° – 8° TYP

0.093 – 0.104

(2.362 – 2.642)

0.394 – 0.419

(10.007 – 10.643)

0.037 – 0.045

(0.940 – 1.143)

0.004 – 0.012

(0.102 – 0.305)

S16 (WIDE) 0396

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

11

LTC488/LTC489

U

TYPICAL APPLICATION

RS232 Receiver

RS232

IN

5.6k

RECEIVER
1/4 LTC488 OR
1/4 LTC489


RX

LTC488/9 TA02

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC485 Low Power RS485 Transceiver Low Power, Half-Duplex
LTC490 Low Power RS485 Full-Duplex Transceiver Full-Duplex in SO-8
LTC1480 3V, Ultralow Power RS485 Transceiver 1µA Shutdown Mode
LTC1481 3V, Ultralow Power RS485 Transceiver Lowest Power on 5V Supply
LTC1483 Ultralow Power RS485 Low EMI Transceiver Low EMI/Low Power with Shutdown
LTC1485 Fast RS485 Transceiver 10Mbps Operation
LTC1487 Ultralow Power RS485 with Low EMI and High Input Impedance Up to 256 Nodes on a Bus
LTC1685 High Speed RS485 Transceiver 52Mbps, Pin Compatible with LTC485
LTC1686/LTC1687 High Speed RS485 Full-Duplex Transceiver 52Mbps, Pin Compatible LTC490/LTC491

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear-tech.com

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 LINEAR TECHNOLOGY CORPORATION 1992