Linear Technology LTC1535 Datasheet

Final Electrical Specifications

FEATURES

LTC1535

Isolated RS485 Transceiver

August 1999

U

DESCRIPTIO

■

UL Rated Isolated RS485: 2500V

■

Half- or Full-Duplex

■

Eliminates Ground Loops

■

350kBd Maximum Data Rate

■

Self-Powered with 400kHz Converter

■

Fail-Safe Output High for Open or

RMS

Shorted Receiver Inputs

■

Short-Circuit Current Limit

■

Slow Slew Rate Control

■

68kΩ Input Impedance Allows Up to 128 Nodes

■

Thermal Shutdown

■

8kV ESD Protection On Driver Outputs and Receiver
Inputs

U

APPLICATIO S

■

Isolated RS485 Receiver/Driver

■

RS485 with Large Common Mode Voltage

■

Breaking RS485 Ground Loops

■

Multiple Unterminated Line Taps

The LTC®1535 is an isolated RS485 full-duplex differential
line transceiver. Isolated RS485 is ideal for systems where
the ground loop is broken to allow for much larger com­mon mode voltage ranges. An internal capacitive isolation
barrier provides 2500V

of isolation between the line

RMS

transceiver and the logic level interface. The powered side
contains a 400kHz push-pull converter to power the iso­lated RS485 transceiver. Internal full-duplex communica­tion occurs through the capacitive isolation barrier. The
transceiver meets RS485 and RS422 requirements.

The driver and receiver feature three-state outputs, with
the driver maintaining high impedance over the entire
common mode range. The drivers have short-circuit cur­rent limits in both directions and a slow slew rate select to
minimize EMI or reflections. The 68kΩ receiver input
allows up to 128 node connections. A fail-safe feature
defaults to a high output state when the receiver inputs are
open or shorted.

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

TYPICAL APPLICATIO

1

1

28

27

26

25

4

1

V

RO

RE

DE

DI

GND

LOGIC COMMON
1

V

CC

10µF

+

RO

RE

DE

DI

U

ST1 ST2

CC

**

CTX02-14659

32

400kHz

FLOATING RS485 COMMON ** TRANSFORMER
2

1/2 BAT54C

2

1/2 BAT54C

2

COILTRONICS [phone]

+

GND2

10µF

1411

V

CC2

A

R

D

B

RO2

Y

Z

SLO

1535 TA01

16

15

17

13

12

18

TWISTED-PAIR
CABLE

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.

1

LTC1535

WW

W

U

ABSOLUTE AXI U RATI GS

(Note 1)

VCC to GND ................................................................ 6V

V

to GND2 ............................................................ 8V

CC2

Control Input Voltage to GND ...... –0.3V to (VCC + 0.3V)

Driver Input Voltage to GND ........ –0.3V to (VCC + 0.3V)

Driver Output Voltage

(Driver Disabled) to GND2 ..............(V

Driver Output Voltage

(Driver Enabled) to GND2 ............... (V

Receiver Input Voltage to GND2 ............................ ±14V

Receiver Output Voltage .............. –0.3V to (VCC + 0.3V)

Operating Temperature Range ..............0°C ≤ TA ≤ 70°C

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

– 13V) to 13V

CC2

– 13V) to 10V

CC2

UUW

PACKAGE/ORDER I FOR ATIO

TOP VIEW

1

V

CC

2

ST1

3

ST2

4

GND

11

GND2

12

Z

13

Y

14

V

CC2

SW PACKAGE

28-LEAD PLASTIC SO WIDE

T

= 125°C, θJA = 125°C/W

JMAX

Consult factory for Industrial and Military grade parts.

28

RO

27

RE

26

DE

25

DI

18

SLO

17

RO2

16

A

15

B

ORDER PART

NUMBER

LTC1535CSW

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC

V

CC2

I

CC

I

CC2

V

OD1

V

OD2

I

OSD1

V

IH

V

IL

I

IN

V

TH

∆V
R

IN

V

OH

V

OL

TH

VCC Supply Range ● 4.5 5.5 V
V

Supply Range ● 4.5 7.5 V

CC2

VCC Supply Current No Load ● 13 18 mA
V

Supply Current R = 27Ω, Figure 1 ● 63 73 mA

CC2

Differential Driver Output No Load ● 5V
Differential Driver Output R = 50Ω (RS422) Note 2 ● 2V

Driver Short-Circuit Current

= HIGH –7V ≤ VCM ≤ 10V ● 75 100 135 mA

V

OUT

V

= LOW –7V ≤ VCM ≤ 10V ● 75 100 135 mA

OUT

Logic Input High Voltage DE, DI, RE VCC = 4.5V ● 2V
Logic Input Low Voltage DE, DI, RE VCC = 4.5V ● 0.8 V
Input Current (A, B) Note 3 VIN = 12V ● 0.25 mA

Receiver Input Threshold –7V ≤ VCM ≤ 12V, Note 4 ● –200 –90 –10 mV
Receiver Input Hysteresis –7V ≤ VCM ≤ 12V ● 10 30 70 mV
Receiver Input Impedance ● 50 68 85 kΩ
RO Output High Voltage IRO = –4mA, VCC = 4.5V ● 3.7 4.0 V

RO Output Low Voltage IRO = 4mA, VCC = 4.5V ● 0.4 0.8 V

No Load

R = 27Ω(RS485), Figure 1

I

I

The ● denotes the specifications which apply over the full operating

= 25°C. 0°C ≤ TA ≤ 70°C, V

A

= –10mA, VCC = 4.5V 3.4 V

RO

= 10mA, VCC = 4.5V 0.9 V

RO

= 5V, V

CC

VIN = –7V ● –0.20 mA

= 5V unless otherwise noted.

CC2

● 712 mA

● 1.5 2 V

2

LTC1535

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes the specifications which apply over the full operating

= 25°C. 0°C ≤ TA ≤ 70°C, V

A

= 5V, V

CC

= 5V unless otherwise noted.

CC2

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I
V

V

f
R
R
I
I
V
V
V

OZ

OH2

OL2

SW

SWH

SWL

REL

REH

UVL

UVH

ISO

Driver Output Leakage 1 µA
RO2 Output High Voltage I

RO2 Output Low Voltage I

= –4mA, VCC = 4.5V ● 3.7 3.9 V

RO2

I

= –10mA, VCC = 4.5V 3.4 V

RO2

= 4mA, VCC = 4.5V ● 0.4 0.8 V

RO2

I

= 10mA, VCC = 4.5V 0.9 V

RO2

DC Converter Frequency ● 290 420 520 kHz
DC Converter R High VCC = 4.5V ● 46 Ω
DC Converter R Low VCC = 4.5V ● 2.5 5 Ω
RE Output Low Current RE Sink Current, Fault = 0 ● –40 –50 –80 µA
RE Output High Current RE Source Current, Fault = 1 ● 80 100 130 µA
Undervoltage Low Threshold RE Fault = 1, Note 5 ● 3.90 4.00 4.25 V
Undervoltage High Threshold RE Fault = 0, Note 5 ● 4.05 4.20 4.40 V
Isolation Voltage 1 Minute, Note 6 2500 V

1 Second 3000 V

RMS
RMS

U

SWITCHI G CHARACTERISTICS

temperature range, otherwise specifications are at T
otherwise noted.

The ● denotes the specifications which apply over the full operating

= 25°C. 0°C ≤ TA ≤ 70°C, V

A

= 5V, V

CC

= 5V, R = 27Ω (RS485) unless

CC2

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

t

SJ

f

MAX

t

PLH

t

PHL

tr, t

t

ZH

t

ZL

t

LZ

t

HZ

t

PLH

t

PHL

t

PLH

t

PHL

tr, t
t

LZ

t

HZ

t

START

t

TOF

f

f

Data Sample Jitter Figure 8, Note 7 ● 250 285 ns
Max Baud Rate Jitter = 10% Max, SLO = 1, Note 8 ● 350 kBd
Driver Input to Output DE = 1, SLO = 1, Figure 3, Figure 5 ● 600 855 ns

DE = 1, SLO = 0, Figure 3, Figure 5

● 1300 1560 ns

Driver Input to Output DE = 1, SLO = 1, Figure 3, Figure 5 ● 600 855 ns

DE = 1, SLO = 0, Figure 3, Figure 5

● 1300 1560 ns

Driver Rise or Fall Time DE = 1, SLO = 1, Figure 3, Figure 5 ● 20 50 ns

DE = 1, SLO = 0

● 150 500 1000 ns

Driver Enable to Output DI = 1, SLO = 1, Figure 4, Figure 6 ● 1000 1400 ns
Driver Enable to Output DI = 0, SLO = 1, Figure 4, Figure 6 ● 1000 1400 ns
Driver Disable to Output DI = 0, SLO = 1, Figure 4, Figure 6 ● 700 1000 ns
Driver Disable to Output DI = 1, SLO = 1, Figure 4, Figure 6 ● 700 1000 ns
Receiver Input to RO RE = 0, Figure 2, Figure 7 ● 600 855 ns
Receiver Input to RO RE = 0, Figure 2, Figure 7 ● 600 855 ns
Receiver Input to RO2 RE = 0, Figure 2, Figure 7 30 ns
Receiver Input to RO2 RE = 0, Figure 2, Figure 7 30 ns
Receiver Rise or Fall Time RE = 0, Figure 2, Figure 7 20 ns
Receiver Disable to Output Figure 2, Figure 8 30 ns
Receiver Disable to Output Figure 2, Figure 8 30 ns
Initial Start-Up Time Note 9 1200 ns
Data Time-Out Fault Note 9 1200 ns

3

LTC1535

ELECTRICAL CHARACTERISTICS

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

Note 2: RS422 50Ω specification based on RS485 27Ω test.
Note 3: IIN is tested at V

V

= GND2 ≤ 5.25V.

CC2

Note 4: Input fault conditions on the RS485 receiver are detected with a
fixed receiver offset. The offset is such that an input short or open will
result in a high data output.

Note 5: The low voltage detect faults when V
and reenables when greater than 4.4V. The fault can be monitored
through the weak driver output on RE.

Note 6: Value derived from 1 second test.

= 5V, guaranteed by design from

CC2

or VCC drops below 4.2V

CC2

UUU

PI FU CTIO S

POWER SIDE

V

(Pin 1): 5V Supply. Bypass to GND with 10µF capaci-

CC

tor.

ST1 (Pin 2): DC Converter Output 1 to DC Transformer.
ST2 (Pin 3): DC Converter Output 2 to DC Transformer.
GND (Pin 4): Ground.

Note 7: The input signals are internally sampled and encoded. The internal

sample rate determines the data output jitter since the internal sampling is
asynchronous with respect to the external data. Nominally, a 4MHz
internal sample rate gives 250ns of sampling uncertainty in the input
signals.

Note 8: The maximum baud rate is 350kBd with 10% sampling jitter.
Lower baud rates have lower jitter.

Note 9: Start-up time is the time for communication to recover after a fault
condition. Data time-out is the time a fault is indicated on RE after data
communication has stopped.

ISOLATED SIDE
GND2 (Pin 11): Isolated Side Power Ground.
Z (Pin 12): Differential Driver Inverting Output.
Y (Pin 13): Differential Driver Noninverting Output.

V

(Pin 14): 5V to 7.5V Supply from DC Transformer.

CC2

Bypass to GND with 10µF capacitor.

DI (Pin 25): Transmit Data TTL Input to the Isolated Side
RS485 Driver. Do not float.

DE (Pin 26): Transmit Enable TTL Input to the Isolated
Side RS485 Driver. A high level enables the driver. Do not
float.

RE (Pin 27): Receive Data Output Enable TTL Input. A low
level enables the receiver. This pin also provides a fault
output signal. (See Applications Information.)

RO (Pin 28): Receive Data TTL Output.

B (Pin 15): Differential Receiver Inverting Input.
A (Pin 16): Differential Receiver Noninverting Input.
RO2 (Pin 17): Isolated Side Receiver TTL Output.
SLO (Pin 18): Slow Slew Rate Control of RS485 Driver. A

low level forces the driver outputs into slow slew rate
mode.

4