Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsInterface ICsInterface IC - transceivers LTC485CS8 RS485 1/1 SOIC 8

LTC485

sn 485LTC485ffs

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Low Power RS485

Interface Transceiver

The LTC

485 is a low power differential bus/line trans-

ceiver designed for multipoint data transmission standard

RS485 applications with extended common mode range

(12V to –7V). It also meets the requirements of RS422.

The CMOS design offers significant power savings over its

bipolar counterpart without sacrificing ruggedness against

overload of ESD damage.

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.

The LTC485 is fully specified over the commercial and

extended industrial temperature range.

■

Low Power: I

= 300µA Typ

■

Designed for RS485 Interface Applications

■

Single 5V supply

■

–7V to 12V Bus Common Mode Range Permits

±7V Ground Difference Between Devices on the Bus

■

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

■

Combined Impedance of a Driver Output and

Receiver Allows Up to 32 Transceivers on the Bus

■

70mV Typical Input Hysteresis

■

30ns Typical Driver Propagation Delays

with 5ns Skew

■

Pin Compatible with ±60V Protected LT1785 and

52Mbps LTC1685

■

Low Power RS485/RS422 Transceiver

■

Level Translator

CC1

GND1

RO1

RE1

DE1

DI1

CC2

GND2

RO2

RE2

DE2

DI2

LTC485 • TA01

Driver Outputs

LTC485 • TA02

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

Summary of content (12 pages)

PAGE 1
LTC485 Low Power RS485 Interface Transceiver U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Low Power: ICC = 300µA Typ Designed for RS485 Interface Applications Single 5V supply – 7V to 12V Bus Common Mode Range Permits ±7V Ground Difference Between Devices on the Bus 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 Combined Impedance of a Driver Output and Receiver Allows
PAGE 2
LTC485 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ....................................................... 12V Control Input Voltages ................... – 0.5V to VCC + 0.5V Driver Input Voltage ....................... – 0.5V to VCC + 0.5V Driver Output Voltage ........................................... ±14V Receiver Input Voltage .......................................... ±14V Receiver Output Voltages .............. – 0.5V to VCC + 0.
PAGE 3
LTC485 U SWITCHI G CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.VCC = 5V ±5%, unless otherwise noted.
PAGE 4
LTC485 U W TYPICAL PERFOR A CE CHARACTERISTICS Receiver Output Low Voltage vs Temperature Driver Differential Output Voltage vs Output Current 0.9 TA = 25°C OUTPUT CURRENT (mA) 0.6 0.5 0.4 0.3 0.2 0.1 56 48 40 32 24 16 2.1 2.0 1.9 1.8 1.7 1.6 1.5 –50 0 25 50 0 75 TEMPERATURE (°C) –25 100 125 1 0 4 3 2 OUTPUT VOLTAGE (V) LTC485 • TPC03 40 30 20 10 –84 –72 –60 –48 –36 –24 3 2 OUTPUT VOLTAGE (V) 4 1.61 1.60 1.59 1.58 1.57 1.55 –50 0 1 0 1.62 1.56 –12 0 1.
PAGE 5
LTC485 U U U PI FU CTIO S RO (Pin 1): Receiver Output. If the receiver output is enabled(RE low), then if A > B by 200mV, 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 and B, and the chip will function as a line driver.
PAGE 6
LTC485 U W W SWITCHI G TI E WAVEFOR S 3V f = 1MHz, t r ≤ 10ns, t f ≤ 10ns 1.5V DI 1.5V 0V t ZL 5V t LZ A, B 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL VOH A, B 0V t HZ t ZH LTC485 • F06 Figure 6. Driver Enable and Disable Times VOH 1.5V R f = 1MHz, t r ≤ 10ns, t f ≤ 10ns t PHL VOD2 A, B –VOD2 1.5V OUTPUT VOL 0V t PLH INPUT LTC485 • F07 Figure 7. Receiver Propagation Delays 3V 1.5V RE f = 1MHz, t r ≤ 10ns, t f ≤ 10ns 1.5V 0V t ZL 5V t LZ R R 1.
PAGE 7
LTC485 U U W U APPLICATIO S I FOR ATIO Basic Theory of Operation Previous RS485 transceivers have been designed using bipolar technology because the common-mode range of the device must extend beyond the supplies and the device must be immune to ESD damage and latchup. Unfortunately, the bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption.
PAGE 8
LTC485 U U W U APPLICATIO S I FOR ATIO The LTC485 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively. The output will be clamped to either VCC or ground by a Zener voltage plus a Schottky diode drop, but this voltage is way beyond the RS485 operating range. This clamp protects the MOS gates from ESD voltages well over 2000V.
PAGE 9
LTC485 U U W U APPLICATIO S I FOR ATIO LTC485 Line Length vs Data Rate The maximum line length allowable for the RS422/RS485 standard is 4000 feet. Figures 17 and 18 show that the LTC485 is able to comfortably drive 4000 feet of wire at 110kHz. RO 100Ω C A LTC485 D B TTL IN NOISE GENERATOR LTC485 TTL OUT COMMON MODE VOLTAGE (A + B)/2 4000 FT 26AWG TWISTED PAIR DI LTC485 • F17 Figure 14. Line Length Test Circuit Figure 17.
PAGE 10
LTC485 U TYPICAL APPLICATIO S Typical RS485 Network Rt Rt LTC485 • TA03 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) CORNER LEADS OPTION (4 PLCS) 0.023 – 0.045 (0.584 – 1.143) HALF LEAD OPTION 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION 0.005 (0.127) MIN 0.405 (10.287) MAX 8 7 6 5 0.025 (0.635) RAD TYP 0.220 – 0.310 (5.588 – 7.874) 1 0.300 BSC (0.762 BSC) 2 3 4 0.200 (5.080) MAX 0.015 – 0.060 (0.381 – 1.524) 0.008 – 0.
PAGE 11
LTC485 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference 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 0.100 (2.54) BSC (0.457 ± 0.
PAGE 12
LTC485 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC486/LTC487 Low Power Quad RS485 Drivers 110µA Supply Current LTC488/LTC489 Low Power Quad RS485 Receivers 7mA Supply Current LTC490/LTC491 Low Power Full-Duplex RS485 Transceivers 300µA Supply Current LTC1480 3.