Datasheet

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LTC490

490fb

Differential Driver and

Receiver Pair

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Low Power: I

= 300µA Typical

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Designed for RS485 or RS422 Applications

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Single 5V Supply

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–7V to 12V Bus Common Mode Range

Permits ±7V Ground Difference Between Devices

on the Bus

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Thermal Shutdown Protection

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Power-Up/-Down Glitch-Free Driver Outputs Permit

Live Insertion or Removal of Package

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Driver Maintains High Impedance with the

Power Off

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Combined Impedance of a Driver Output and

Receiver Allows up to 32 Transceivers on the Bus

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70mV Typical Input Hysteresis

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28ns Typical Driver Propagation Delays with

5ns Skew for 2.5MB Operation

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Pin Compatible with the SN75179

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Available in 8-Lead PDIP and SO Packages

The LTC

490 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 or ESD damage.

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.

Both AC and DC specifications are guaranteed from 0°C to

70°C and 4.75V to 5.25V supply voltage range.

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Low Power RS485/RS422 Transceiver

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Level Translator

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

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

LTC490 • TA01

120Ω 120Ω

4000 FT BELDEN 9841

RECEIVER

LTC490

DRIVER

RECEIVER

LTC490

DRIVER

Summary of content (12 pages)

PAGE 1
LTC490 Differential Driver and Receiver Pair U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Low Power: ICC = 300µA Typical Designed for RS485 or RS422 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 Package Driver Maintains High Impedance with the Power Off Combined Impedance of a Driver Output and Receiver Allows up to 32 T
PAGE 2
LTC490 W W W AXI U U U W PACKAGE/ORDER I FOR ATIO U ABSOLUTE RATI GS (Note 1) Supply Voltage (VCC) ............................................... 12V Driver Input Currents ........................... – 25mA to 25mA Driver Input Voltages ...................... –0.5V to VCC + 0.5V Driver Output Voltages .......................................... ±14V Receiver Input Voltages ......................................... ±14V Receiver Output Voltages ............... –0.5V to VCC + 0.
PAGE 3
LTC490 U SWITCHI G CHARACTERISTICS The ● denotes the specificatiions which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
PAGE 4
LTC490 U W TYPICAL PERFOR A CE CHARACTERISTICS Driver Skew vs Temperature 5 1.61 4 1.59 1.57 350 3 2 1.55 –50 0 50 TEMPERATURE (°C ) 1 –50 100 0 50 TEMPERATURE (°C ) LTC490 • TPC04 1.5 –50 OUTPUT VOLTAGE (V) TIME (ns) 100 5 LTC490 • TPC07 3 –50 100 LTC490 • TPC06 0.8 I = 8mA 0.6 0.4 0.2 4 0 50 TEMPERATURE (°C ) 0 50 TEMPERATURE (°C ) Receiver Output Low Voltage vs Temperature 6 1.7 320 310 –50 100 7 2.1 1.9 330 Receiver tPLH-tPHL vs Temperature RO = 54Ω 2.
PAGE 5
LTC490 U U U PI FU CTIO S VCC (Pin 1): Positive Supply; 4.75V ≤ VCC ≤ 5.25V. Y (Pin 5): Driver Output. R (Pin 2): Receiver Output. If A > B by 200mV, R will be high. If A < B by 200mV, then R will be low. Z (Pin 6): Driver Output. D (Pin 3): Driver Input. A low on D forces the driver outputs Y low and Z high. A high on D will force Y high and Z low. A (Pin 8): Receiver Input. B (Pin 7): Receiver Input. GND (Pin 4): Ground Connection.
PAGE 6
LTC490 U W U U APPLICATIO S I FOR ATIO Typical Application A typical connection of the LTC490 is shown in Figure 5. Two twisted-pair wires connect two driver/receiver pairs for full duplex data transmission. Note that the driver and receiver outputs are always enabled. If the outputs must be disabled, use the LTC491. There are no restrictions on where the chips are connected, and it isn’t necessary to have the chips connected at the ends of the wire.
PAGE 7
LTC490 U W U U APPLICATIO S I FOR ATIO less flexible, more bulky, and more costly than twisted pairs. Many cable manufacturers offer a broad range of 120Ω cables designed for RS485 applications. terrible losses at high data rates (>100kbs), and greatly reduce the maximum cable length. At low data rates however, they are acceptable and much more economical. Losses in a transmission line are a complex combination of DC conductor loss, AC losses (skin effect), leakage and AC losses in the dielectric.
PAGE 8
LTC490 U W U U APPLICATIO S I FOR ATIO cable is lightly loaded (470Ω), the signal reflects in phase and increases the amplitude at the driver output. An input frequency of 30kHz is adequate for tests out to 4000 feet of cable. AC Cable Termination Cable termination resistors are necessary to prevent unwanted reflections, but they consume power.
PAGE 9
LTC490 U TYPICAL APPLICATIO S RS232 Receiver RS232 IN RX RECEIVER 5.6k 1/2 LTC490 LTC490 • TA02 RS232 to RS485 Level Transistor with Hysteresis R = 220k Y 10k RS232 IN DRIVER 5.
PAGE 10
LTC490 U PACKAGE DESCRIPTIO N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 8.255 +0.889 –0.381 ) .045 – .065 (1.143 – 1.651) .130 ± .005 (3.302 ± 0.127) .065 (1.651) TYP .100 (2.54) BSC .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) N8 1002 NOTE: 1.
PAGE 11
LTC490 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 3 4 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1.
PAGE 12
LTC490 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 LTC1480 3.