Datasheet

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LTC1484

Low Power

RS485 Transceiver

with Receiver Fail-Safe

■

No Damage or Latchup to

15kV ESD (Human

Body Model), IEC-1000-4-2 Level 4 Contact (

8kV)

and Level 3 (

8kV) Air Gap Specifications

■

Guaranteed High Receiver Output State for Floating,

Shorted or Terminated Inputs with No Signal

Present

■

Drives Low Cost Residential Telephone Wires

■

Low Power: I

= 700µA Max with Driver Disabled

■

= 900µA Max for Driver Enable with No Load

■

20µA Max Quiescent Current in Shutdown Mode

■

Single 5V Supply

■

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

Ground Difference Between Devices on the Data Line

■

Power Up/Down Glitch-Free Driver Outputs

■

Up to 32 Transceivers on the Bus

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Pin Compatible with the LTC485

■

Available in 8-Lead MSOP, PDIP and SO Packages

The LTC

1484 is a low power RS485 compatible trans-

ceiver. In receiver mode, it offers a fail-safe feature which

guarantees a high receiver output state when the inputs

are left open, shorted together or terminated with no

signal present. No external components are required to

ensure the high receiver output state.

Both driver and receiver feature three-state outputs with

separate receiver and driver control pins. The driver

outputs maintain high impedance over the entire com-

mon mode range when three-stated. Excessive power

dissipation caused by bus contention or faults is pre-

vented by a thermal shutdown circuit that forces the

driver outputs into a high impedance state.

Enhanced ESD protection allows the LTC1484 to with-

stand ±15kV (human body model), IEC-1000-4-2 level 4

(±8kV) contact and level 3 (±8kV) air discharge ESD

without latchup or damage.

The LTC1484 is fully specified over the commercial and

industrial temperature ranges and is available in 8-lead

MSOP, PDIP and SO packages.

■

Battery-Powered RS485/RS422 Applications

■

Low Power RS485/RS422 Transceiver

■

Level Translator

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

RO1

RE1

DE1

DI1

CC1

LTC1484

GND1

120Ω 120Ω

CC2

GND2

1484 TA01

RO2

RE2

DE2

DI2

LTC1484

RS485 Interface

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

Driving a 2000 Foot STP Cable

Dl1 ↑↓ DE1 = V

1484 TA01a

Dl2 = 0 DE2 = 0

RE1 = RE2 = 0

Dl1

RO2

Summary of content (16 pages)

PAGE 1
LTC1484 Low Power RS485 Transceiver with Receiver Fail-Safe U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ No Damage or Latchup to ±15kV ESD (Human Body Model), IEC-1000-4-2 Level 4 Contact (±8kV) and Level 3 (±8kV) Air Gap Specifications Guaranteed High Receiver Output State for Floating, Shorted or Terminated Inputs with No Signal Present Drives Low Cost Residential Telephone Wires Low Power: ICC = 700µA Max with Driver Disabled ICC = 900µA Max for Driver Enable with No Load 20µA Max Quiescent Curre
PAGE 2
LTC1484 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC)............................................... 6.5V Control Input Voltages ................. – 0.3V to (VCC + 0.3V) Driver Input Voltage ..................... – 0.3V to (VCC + 0.3V) Driver Output Voltages ................................. – 7V to 10V Receiver Input Voltages (Driver Disabled) .. –12V to 14V Receiver Output Voltage ............... – 0.3V to (VCC + 0.3V) Junction Temperature ..........................................
PAGE 3
LTC1484 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN ∆VTH Receiver Input Hysteresis VCM = 0V, DE = 0 ● VOH Receiver Output High Voltage IOUT = – 4mA, (VA – VB) = 200mV ● VOL Receiver Output Low Voltage IOUT = 4mA, (VA – VB) = – 200mV ● 0.
PAGE 4
LTC1484 U SWITCHING CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ±5% (Notes 2 and 3) unless otherwise noted.
PAGE 5
LTC1484 U W TYPICAL PERFOR A CE CHARACTERISTICS Receiver Input Offset Voltage vs Temperature Receiver Hysteresis vs Temperature –60 –80 –100 VCM = –7V –120 VCM = 0V –140 VCC = 5V 90 –40 VCM = 12V –160 –180 80 70 60 VTH(HIGH) – VTH(LOW) VCM = –7V TO 12V 50 40 30 20 10 –200 –55 –35 –15 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) –0.06 –0.10 –0.12 3.5 3.0 2.5 2.0 1.5 1.0 0.5 –20 –15 –10 –5 OUTPUT CURRENT (mA) –0.16 –0.18 4.75 5 SUPPLY VOLTAGE (V) 4.5 0.7 0.6 0.5 0.4 0.3 0.2 0.
PAGE 6
LTC1484 U W TYPICAL PERFOR A CE CHARACTERISTICS Receiver Short-Circuit Current vs Temperature Receiver Propagation Delay vs Temperature 200 80 70 OUTPUT LOW SHORT TO VCC 60 50 40 30 OUTPUT HIGH SHORT TO GROUND 20 10 0 –55 –35 –15 180 30 VCC = 5V 160 140 tPHL 100 80 60 40 5 tPLH tPHL 120 4.75 5 5.25 SUPPLY VOLTAGE (V) 0.8 0.7 1.00 0.6 0.5 0.4 0.3 0.2 0.1 0 –55 –35 –15 5.
PAGE 7
LTC1484 U W TYPICAL PERFOR A CE CHARACTERISTICS RL = 44Ω 2.5 1.5 VCC = 5V VCC = 4.75V VCC = 4.5V 1.0 0.5 ∆VOD, VCC = 4.5V TO 5.25V 0 –0.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 2.5 2.0 VCC = 5.25V VCC = 5V VCC = 4.75V 1.5 VCC = 4.5V 1.0 0.5 ∆VOD, VCC = 4.5V TO 5.25V 0 –0.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G22 Driver Common Mode Output Voltage vs Temperature 2.0 3.0 RL = 44Ω 2.5 VCC = 5.25V VCC = 5V VCC = 4.75V 1.5 VCC = 4.5V 1.0 0.5 ∆VOC, VCC = 4.
PAGE 8
LTC1484 U W TYPICAL PERFOR A CE CHARACTERISTICS Driver Output High Voltage vs Output Current Driver Output Low Voltage vs Output Current 3.0 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 –100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0 OUTPUT CURRENT (mA) 50 VCC = 4.75V DRIVER PROPAGATION DELAY (ns) VCC = 4.75V 4.5 DRIVER OUTPUT LOW VOLTAGE (V) DRIVER OUTPUT HIGH VOLTAGE (V) 5.0 2.5 2.0 1.5 1.0 0.5 0 50 15 10 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G33 40 4.5 35 3.5 3.0 2.5 2.0 1.5 0.
PAGE 9
LTC1484 U U U PIN FUNCTIONS A (Pin 6): Driver Output/Receiver Input. The input resistance is typically 22k when the driver is disabled (DE = 0). When the driver is enabled, the A output follows the logic level at the DI pin. B (Pin 7): Driver Output/Receiver Input. The input resistance is typically 22k when the driver is disabled (DE = 0). When the driver is enabled, the B output is inverted from the logic level at the DI pin. VCC (Pin 8): Positive Supply. 4.75V ≤ VCC ≤ 5.25V. A 0.
PAGE 10
LTC1484 U W W SWITCHI G TI E WAVEFOR S 3V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DI 1.5V 0V t PLH VO 10% –VO t PHL 90% 50% VO = V(A) – V(B) 50% tr 90% 10% tf B VO A tSKEW 1/2 VO t SKEW 1484 F06 NOTE: DE = 1 Figure 6. Driver Propagation Delays 3V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DE 1.5V 0V t ZL(SHDN), t ZL 5V A, B 2.3V OUTPUT NORMALLY LOW VOL VOH A, B t LZ 0.5V 0.5V OUTPUT NORMALLY HIGH 2.
PAGE 11
LTC1484 U W W SWITCHI G TI E WAVEFOR S 3V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DE 0V t DZR V(A) – V(B) OUTPUT NORMALLY LOW RO 1.5V OUTPUT NORMALLY HIGH 1484 F10 NOTE: DI = 0, RE = 0, A AND B ARE THREE-STATED WHEN DE = 0 Figure 10. Driver Enable to Receiver Valid Timing U W U U APPLICATIONS INFORMATION Low Power Operation The LTC1484 has a quiescent current of 900µA max when the driver is enabled. With the driver in three-state, the supply current drops to 700µA max.
PAGE 12
LTC1484 U W U U APPLICATIONS INFORMATION Shutdown Mode The receiver output (RO) and the driver outputs (A, B) can be three-stated by taking the RE and DE pins high and low respectively. Taking RE high and DE low at the same time puts the LTC1484 into shutdown mode and ICC drops to 20µA max. In some applications (see CDMA), the A and B lines are pulled to VCC or GND through external resistors to force the line to a high or low state when all connected drivers are disabled.
PAGE 13
LTC1484 U U W U APPLICATIONS INFORMATION 1k 1 2 3 8 5V 4 D 5 1k 3 2 1 4 D R 5V 1.2k DE2 RO2 RO4 DE4 R 5V 5 8 6 7 120Ω 1.2k 5V 1.2k 7 6 120Ω 5V 6 7 8 R 1 5 D 2 3 4 7 6 5 8 5V 1.2k R D 4 3 2 1 1484 F11 1k RO1 DE1 DE3 RO3 1k Figure 11. Transmit “0” CDMA Application receiver output and expects to see perfect agreement between the two data streams. (Note that the driver inverts the data, so the transmitted and received data streams are actually opposites.
PAGE 14
LTC1484 U W U U APPLICATIONS INFORMATION longer delay for the falling edge is due to the larger voltage range the line must swing (typically > 2V compared to 370mV) before the receiver trips high again. The difference in delay affects the duty cycle of the received data and depends on cable capacitance. For a 1-foot STP cable, the delays drop to 0.13µs and 0.4µs.
PAGE 15
LTC1484 U PACKAGE DESCRIPTION Dimensions in inches (millimeters), unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.400* (10.160) MAX 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) ) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) 0.100 (2.
PAGE 16
LTC1484 U TYPICAL APPLICATIO Fail-Safe “0” Application (Idle State = Logic “0”) 5V I1 RO RE LTC1484 RE R DE DE DI RO I2 DI VCC B A “A” “B” D GND 1484 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 5V Low Power RS485 Interface Transceiver Low Power LTC1480 3.