ANALOG DEVICES LTC 1480 CS8 Datasheet

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Page 1

FEATURES

■

True RS485 from a Single 3.3V Supply

■

Low Power: ICC = 500µA Max with Driver Disabled

■

ICC = 600µA Max with Driver Enabled, No Load

■

1µA Quiescent in Shutdown Mode

■

–7V to 12V Common Mode Range Permits ±7V Ground Difference Between Devices on the Data Line

■

Thermal Shutdown Protection

■

Power Up/Down Glitch-Free Driver Outputs Permit Live Insertion or Removal of Transceiver

■

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

■

Up to 32 Transceivers on the Bus

■

50ns Typical Driver Propagation Delays with 10ns Skew

■

Pin Compatible with the LTC485

■

Available in 8-Lead DIP and SO Packages

APPLICATIO S

LTC1480

3.3V Ultralow Power RS485 Transceiver

DESCRIPTIO

The LTC®1480 is an ultralow power differential line transceiver which provides full RS485 compatibility while operating from a single 3.3V supply. It is designed for data transmission standard RS485 applications with extended common mode range (12V to –7V). It also meets the requirements of RS422 and features high speed operation up to 2.5Mb/s. The CMOS design offers significant power savings without sacrificing ruggedness against overload or ESD damage. Typical quiescent current is only 300µA while operating and 1µA in shutdown.

The driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common mode range. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open.

■

Battery-Powered RS485/RS422 Applications

■

Low Power RS485/RS422 Transceiver

■

Level Translator

TYPICAL APPLICATIO

3.3V RS485 Network

LTC1480

3.3V

SHIELD SHIELD

3.3V

ABB

RO RE DE DI

The LTC1480 is fully specified over the commercial and extended industrial temperature range. The LTC1480 is available in 8-pin SO and DIP packages.

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

All other trademarks are the property of their respective owners.

Driver Differential

Output Voltage vs Output Current

3.3V LTC1480

120Ω120Ω

LTC1480

1480 TA01

DE DI

3.5

3.0

2.5

2.0

1.5

1.0

OUTPUT VOLTAGE (V)

0.5

10 20 30 40 50 90

OUTPUT CURRENT (mA)

VCC = 3.3V

= 25°C

60 70 80

1480 TA02

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LTC1480

TOP VIEW

GND

N8 PACKAGE 8-LEAD PDIP

S8 PACKAGE

8-LEAD PLASTIC SO

ABSOLUTE AXI U RATI GS

(Note 1)

Supply Voltage (VCC) ................................................ 7V

Control Input Voltage..................... – 0.3V to V

Driver Input Voltage....................... – 0.3V to V

Driver Output Voltage ........................................... ±14V

Receiver Input Voltage.......................................... ±14V

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

Operating Temperature Range

LTC1480C ....................................... 0°C ≤ T

LTC1480I.................................... – 40°C ≤ T

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

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

+ 0.3V

≤ 70°C

≤ 85°C

UUW

PACKAGE/ORDER I FOR ATIO

= 125°C, θ

JMAX

= 125°C, θ

JMAX

ORDER PART NUMBER

LTC1480CN8 LTC1480IN8 LTC1480CS8 LTC1480IS8

Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts specified with wider operating temperature ranges.

= 130°C/ W (N8)

= 150°C/ W (S8)

S8 PART MARKING

1480

1480I

ELECTRICAL CHARACTERISTICS

temperature range. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OD1

OD2

∆V

∆⏐V

IN1

IN2

∆V

OZR

SHDN

Differential Driver Output Voltage (Unloaded) IO = 0V Differential Driver Output Voltage (with Load) R = 27Ω (RS485) (Figure 1)

Change in Magnitude of Driver Differential Output R = 27Ω or R = 50Ω (Figure 1) Voltage for Complementary Output States

Driver Common Mode Output Voltage R = 27Ω or R = 50Ω (Figure 1)

⏐

Change in Magnitude of Driver Common Mode R = 27Ω or R = 50Ω (Figure 1)

Output Voltage for Complementary Output States

Input HIGH Voltage DE, DI, RE

Input LOW Voltage DE, DI, RE

Input Current DE, DI, RE

Input Current (A, B) DE = 0, VCC = 0V or 3.6V, VIN = 12V

Differential Input Threshold Voltage for Receiver –7V ≤ VCM ≤ 12V

Receiver Input Hysteresis VCM = 0V 70 mV

Receiver Output HIGH Voltage IO = – 4mA, VID = 200mV

Receiver Output LOW Voltage IO = 4mA, VID = – 200mV

Three-State (High Impedance) Output VCC = Max, 0.4V ≤ VO ≤ 2.4V Current at Receiver

Receiver Input Resistance –7V ≤ VCM ≤ 12V

Supply Current No Load, Output Enabled

Supply Current in Shutdown Mode DE = 0, RE = V

= 3.3V (Notes 2, 3).

The ● denotes the specifications which apply over the full operating

R = 50Ω (RS422)

DE = 0, V

No Load, Output Disabled

= 0V or 3.6V, VIN = – 7V

●

1.5 3.3 V

●

2.0 V

●

–0.2 0.2 V

●

12 kΩ

●

400 600 µA 300 500 µA

110µA

3.3 V

0.2 V

0.8 V

±2 µA

1.0 mA

–0.8 mA

0.4 V

±1 µA

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LTC1480

TEMPERATURE (°C)

–40

1.9

2.0

2.2

20 60

1480 G03

1.8

1.7

–20 0

40 80 100

1.6

1.5

2.1

DIFFERENTIAL VOLTAGE (V)

RL = 100Ω

RL = 54Ω

VCC = 3.3V

SWITCHI G CHARACTERISTICS

temperature range. V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OSD1

OSD2

OSR

PLH

PHL

SKEW

tR, t

PLH

PHL

SKD

MAX

SHDN

ZH(SHDN)

ZL(SHDN)

ZH(SHDN)

ZL(SHDN)

Note 1: Absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed.

Driver Short-Circuit Current, V

Driver Short-Circuit Current, V Receiver Short-Circuit Current 0V ≤ VO ≤ V

Driver Input to Output R

Driver Input to Output

Driver Output to Output

Driver Rise or Fall Time

Driver Enable to Output HIGH CL = 100pF (Figures 4, 6), S2 Closed

Driver Enable to Output LOW CL = 100pF (Figures 4, 6), S1 Closed

Driver Disable Time from LOW CL = 15pF (Figures 4, 6), S1 Closed

Driver Disable Time from HIGH CL = 15pF (Figures 4, 6), S2 Closed

Receiver Input to Output R

Receiver Input to Output

⏐

PLH

Receiver Enable to Output LOW CRL = 15pF (Figures 2, 8), S1 Closed

Receiver Enable to Output HIGH CRL = 15pF (Figures 2, 8), S2 Closed

Receiver Disable from LOW CRL = 15pF (Figures 2, 8), S1 Closed

Receiver Disable from HIGH CRL = 15pF (Figures 2, 8), S2 Closed

Maximum Data Rate

Time to Shutdown DE = 0, RE =

Driver Enable from Shutdown to Output HIGH CL = 100pF (Figures 4, 6), S2 Closed

Driver Enable from Shutdown to Output LOW CL = 100pF (Figures 4, 6), S1 Closed

Receiver Enable from Shutdown to Output HIGH CL = 15pF (Figures 2, 8), S2 Closed

Receiver Enable from Shutdown to Output LOW CL = 15pF (Figures 2, 8), S1 Closed

= 3.3V (Notes 2, 3).

= HIGH –7V ≤ VO ≤ 12V

OUT

= LOW – 7V ≤ VO ≤ 12V

OUT

– t

⏐

Differential Receiver Skew 13 ns

PHL

The ● denotes the specifications which apply over the full operating

●

35 250 mA

●

35 250 mA

●

= 54Ω, CL1 = CL2 = 100pF,

DIFF

(Figures 3, 5)

= 54Ω, CL1 = CL2 = 100pF,

DIFF

(Figures 3, 7)

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

Note 3: All typicals are given for VCC = 3.3V and TA = 25°C.

785mA

●

25 50 80 ns

●

25 50 80 ns

●

51540ns

●

30 140 200 ns

●

30 140 200 ns

●

2.5 Mbits/s

●

50 200 600 ns

●

10 20 ns

70 120 ns

50 80 ns

70 120 ns

4500 ns

TYPICAL PERFOR A CE CHARACTERISTICS

Supply Current vs Temperature

425

400

375

350

325

300

275

SUPPLY CURRENT (µA)

250

225

200

VCC = 3.3V

–50

–25

THERMAL SHUTDOWN

WITH DRIVER ENABLED

DRIVER DISABLED

25 175125

0 150100

TEMPERATURE (°C)

Driver Output Low/High Voltage vs Output Current

150

VCC = 3.3V

= 25°C

100

–50

OUTPUT CURRENT (mA)

–100

–150

1480 G01

0.5 1.0 OUTPUT VOLTAGE (V)

2.0 3.0 3.5

1.5 2.5

1480 G02

Driver Differential Output Voltage vs Temperature

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LTC1480

TEMPERATURE (°C)

–40

2.0

OUTPUT VOLTAGE (V)

2.4

3.0

1480 G09

2.2

2.8

2.6

–20

100

VCC = 3.3V I

= 8mA

TYPICAL PERFORMANCE CHARACTERISTICS

Driver Skew vs Temperature

7.0 VCC = 3.3V

6.5

6.0

5.5

5.0

TIME (ns)

4.5

4.0

3.5

3.0 –20 0 40

–40

Receiver

TEMPERATURE (°C)

⏐⏐

– t

⏐t

⏐⏐

PLH

PHL

vs Temperature

VCC = 3.3V

60 80 100

⏐⏐

⏐

⏐⏐

1480 G04

Receiver Output Low Voltage vs Output Current

VCC = 3.3V

= 25°C

OUTPUT CURRENT (mA)

0.2 0.4 0.6 1.0 1.4 1.8

0.8

OUTPUT VOLTAGE (V)

Receiver Output Low Voltage vs Temperature

0.6 VCC = 3.3V

= 8mA

0.5

0.4

1.2

1.6

1480 G05

2.0

Receiver Output High Voltage vs Output Current

–16

VCC = 3.3V

= 25°C

–14

–12

–10

–8

–6

OUTPUT CURRENT (mA)

–4

–2

3.30

3.05

2.80

2.30

2.55

OUTPUT VOLTAGE (V)

Receiver Output High Voltage vs Temperature

2.05

1.80

1.55

1.30

1480 G06

TIME (ns)

UU U

PI FU CTIO S

RO (Pin 1): Receiver Output. If the receiver output is enabled (RE LOW) and A > B by 200mV, then RO will be HIGH. If A < B by 200mV, then RO will be LOW.

RE (Pin 2): Receiver Output Enable. A LOW enables the receiver output, RO. A HIGH input forces the receiver output into a high impedance state.

DE (Pin 3): Driver Outputs Enable. A HIGH on DE enables the driver output. A, B and the chip will function as a line driver. A low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. If RE is high and DE is LOW, the part will enter a low power (1µA) shutdown state. If RE is low and DE is

–40

–20 0

40 80 100

20 60

TEMPERATURE (°C)

1480 G07

0.3

0.2

OUTPUT VOLTAGE (V)

0.1

–40

–20 0

40 80 100

20 60

TEMPERATURE (°C)

1480 G08

high, the driver outputs will be fed back to the receiver and the receive output will correspond to the driver input.

DI (Pin 4): Driver Input. If the driver outputs are enabled (DE HIGH) then a low on DI forces the outputs A LOW and B HIGH. A HIGH on DI with the driver outputs enabled will force A HIGH and B LOW.

GND (Pin 5): Ground.

A (Pin 6): Driver Output/Receiver Input.

B (Pin 7): Driver Output/Receiver Input.

VCC (Pin 8): Positive Supply. 3.0V < VCC < 3.6V.

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FU CTIO TABLES

LTC1480

LTC1480 Transmitting

INPUTS OUTPUTS

RE DE DI B A

X1101

X1010

00XZZ

1 0 X Z* Z*

*Shutdown mode

TEST CIRCUITS

LTC1480 DRIVER

Figure 1. Driver DC Test Load

DIFF

1480 F01

LTC1480 RECEIVER

LTC1480 Receiving

INPUTS OUTPUTS

RE DE A – B RO

00≥0.2V 1 00≤–0.2V 0

0 0 Inputs Open 1

10 X Z*

*Shutdown mode

RECEIVER

OUTPUT

TEST POINT

1480 F02

Figure 2. Receiver Timing Test Load

1480 F04

15pF

1480 F03

OUTPUT

UNDER TEST

500Ω

Figure 3. Driver/Receiver Timing Test Circuit

UW W

SWITCHI G TI E WAVEFOR S

–V

1/2 V

1.5V

10%

f = 1MHz, tr ≤ 10ns, tf ≤ 10ns

PLH

SKEW

90%

Figure 5. Driver Propagation Delays

= V(A) – V(B)

DIFF

Figure 4. Driver Timing Test Load

1.5V

1/2 V

PHL

SKEW

90%

10%

1480 F05

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LTC1480

LOGIC

OUTPUT

1480 F09

UW W

SWITCHI G TI E WAVEFOR S

A, B

A – B

–V

3.3V

OD2

3.3V

1.5V

f = 1MHz, tr ≤ 10ns, tf ≤ 10ns

ZL(SHDN), tZL

2.3V

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

ZH(SHDN), tZH

1.5V

0.5V

1480 F06

Figure 6. Driver Enable and Disable Times

PHL

1.5V

f = 1MHz, tr ≤ 10ns, tf ≤ 10ns

0V 0V

OUTPUT

INPUT

PLH

1.5V

1480 F07

Figure 7. Receiver Propagation Delays

1.5V

f = 1MHz, tr ≤ 10ns, tf ≤ 10ns

, t

1.5V

ZL(SHDN)

ZH(SHDN)

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

, t

1.5V

0.5V

1480 F08

Figure 8. Receiver Enable and Disable Times

WUU

APPLICATIO S I FOR ATIO

CMOS Output Driver

The LTC1480 transceiver provides full RS485 compatibility while operating from a single 3.3V supply. The RS485 specification requires that a transceiver withstand common mode voltages of up to 12V or –7V at the RS485 line connections. Additionally, the transceiver must be immune to both ESD and latch-up. This rules out traditional CMOS drivers, which include parasitic diodes from their driver outputs to each supply rail (Figure 9). The LTC1480 uses a proprietary process enhancement which adds a pair of Schottky diodes to the output stage (Figure 10), preventing

Figure 9. Conventional CMOS Output Stage

LOGIC

Figure 10. LTC1480 Output Stage

SD3

OUTPUT

SD4

1480 F10

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LTC1480

WUU

APPLICATIO S I FOR ATIO

current from flowing when the common mode voltage exceeds the supply rails. Latch-up at the output drivers is virtually eliminated and the driver is prevented from loading the line under RS485 specified fault conditions.

When two or more drivers are connected to the same transmission line, a potential condition exists whereby more than two drivers are simultaneously active. If one or more drivers is sourcing current while another driver is sinking current, excessive power dissipation may occur within either the sourcing or sinking element. This condition is defined as driver contention, since multiple drivers are competing for one transmission line. The LTC1480 provides a current limiting scheme to prevent driver contention failure. When driver contention occurs, the current drawn is limited to about 70mA preventing excessive power dissipation within the drivers.

The LTC1480 has a thermal shutdown feature which protects the part from excessive power dissipation. Under extreme fault conditions, up to 250mA can flow through the part causing rapid internal temperature rise. The thermal shutdown circuit will disable the driver outputs when the internal temperature reaches 150°C and turns them back on when the temperature cools to 130°C. This cycle will repeat as necessary until the fault condition is removed.

Receiver Inputs

The LTC1480 features an input common mode range covering the entire RS485 specified range of –7V to 12V. Differential signals of greater than ± 200mV within the specified input common mode range will be converted to a TTL compatible signal at the receiver output. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the receiver inputs are floating (unterminated) an internal pull-up of 10µA at the A input will force the receiver output to a known high state.

driver outputs enabled but unterminated, quiescent current will rise as one of the two outputs sources current into the internal receiver input resistance. With the minimum receiver input resistance of 12k and the maximum output swing of 3.3V, the quiescent current will rise by a maximum of 275µA. Typical quiescent current rise with the driver enabled is about 100µA.

The quiescent current rises significantly if the driver is enabled when it is externally terminated. With 1/2 termination load (120Ω between the driver outputs) the quiescent current will jump to at least 13mA as the drivers force a minimum of 1.5V across the termination resistance. With a fully terminated 60Ω line attached, the current will rise to greater than 25mA with the driver enabled, completely overshadowing the extra 100µA drawn by internal receiver inputs.

Shutdown Mode

Both the receiver output (RO) and the driver outputs (A, B) can be placed in three-state mode by bringing RE HIGH and DE LOW respectively. In addition, the LTC1480 will enter shutdown mode when RE is HIGH and DE is LOW.

In shutdown the LTC1480 typically draws only 1µA of supply current. In order to guarantee that the part goes into shutdown, RE must be high and DE must be LOW for at least 600ns simultaneously. If this time duration is less than 50ns the part will not enter shutdown mode.

Propagation Delay

Many digital encoding schemes are dependent upon the difference in the propagation delay times of the driver and receiver. Figure 11 shows the test circuit for the LTC1480 propagation delay.

The receiver delay times are:

⏐t

– t

PLH

⏐ = 13ns Typ, V

PHL

= 3.3V

Low Power Operation

The LTC1480 draws very little supply current whenever the driver outputs are disabled. In shutdown mode the quiescent current is typically less than 1µA. With the receiver active and the driver outputs disabled, the LTC1480 will typically draw 300µA quiescent current. With the

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.

The driver’s skew times are:

= 10ns Typ, VCC = 3.3V

SKEW

20ns Max, VCC = 3.3V, TA = –40°C to 85°C

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Page 8

LTC1480

WUU

APPLICATIO S I FOR ATIO

TTL IN

, tf < 6ns

Figure 11. Receiver Propagation Delay Test Circuit

PACKAGE DESCRIPTIO

.300 – .325

(7.620 – 8.255)

.065

(1.651)

.008 – .015

(0.203 – 0.381)

+.035

.325

–.015 +0.889

8.255

()

NOTE:

1. DIMENSIONS ARE

–0.381

MILLIMETERS

.050 BSC

TYP

INCHES

.045 ±.005

.045 – .065

(1.143 – 1.651)

.100

(2.54)

BSC

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)

8-Lead Plastic Small Outline (Narrow .150 Inch)

100pF

R 100Ω

100pF

1480 F11

N8 Package

8-Lead PDIP (Narrow .300 Inch)

(Reference LTC DWG # 05-08-1510)

.130 ± .005

(3.302 ± 0.127)

.020

MIN

.255 ± .015*

(6.477 ± 0.381)

.120

(3.048)

MIN

.018 ± .003

(0.457 ± 0.076)

(0.508)

S8 Package

(Reference LTC DWG # 05-08-1610)

.189 – .197

(4.801 – 5.004)

NOTE 3

.053 – .069

(1.346 – 1.752)

RECEIVER OUT

87 6

1234

.400*

(10.160)

MAX

N8 1002

.004 – .010

(0.101 – 0.254)

.245

MIN

.030 ±.005

TYP

RECOMMENDED SOLDER PAD LAYOUT

NOTE:

1. DIMENSIONS IN

2. DRAWING NOT TO SCALE

INCHES

(MILLIMETERS)

.160

±.005

.228 – .244

(5.791 – 6.197)

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

.150 – .157

(3.810 – 3.988)

NOTE 3

.014 – .019

(0.355 – 0.483)

TYP

.008 – .010

(0.203 – 0.254)

.010 – .020

(0.254 – 0.508)

.016 – .050

(0.406 – 1.270)

× 45°

.050

(1.270)

BSC

0°– 8° TYP

SO8 0303

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC485 5V Low Power RS485 Interface Transceiver Low Power LTC1481 5V Ultralow Power RS485 Transceiver with Shutdown Lowest Power LTC1483 5V Ultralow Power RS485 Low EMI Transceiver with Shutdown Low EMI/Lowest Power LTC1485 5V Differential Bus Transceiver High Speed, 10Mbps LTC1487 5V Ultralow Power RS485 with Low EMI, Shutdown High Input Impedance/Low EMI/Lowest Power

and High Input Impedance

LT/LT 0605 REV A • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear.com

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