Datasheet

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LTC1688/LTC1689

16889fa

100Mbps RS485

Hot Swapable Quad Drivers

■

Ultrahigh Speed:

100Mbps

■

Guaranteed Propagation Delay: 8ns

4ns

Over Temperature

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Low Channel-to-Channel Skew: 500ps Typ

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Hot Swap

Capable

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50Mbps Operation with V

= 3V

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Low t

PLH

PHL

Skew: 500ps Typ

■

Driver Outputs Maintain High Impedance in

Three-State or with Power Off

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Short-Circuit Protected: 3mA Typ Output Current

for an Indefinite Short

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Thermal Shutdown Protected

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Single 5V or 3V Supply

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Pin Compatible with LTC486/LTC487

The LTC

1688/LTC1689 are ultrahigh speed, differential

bus/line drivers that can operate at data rates up to

100Mbps. Propagation delay is guaranteed at 8ns ±4ns

over the full operating temperature range. These devices

operate over the full RS485 common mode range (–7V

to 12V), and also meet RS422 requirements.

The driver outputs are Hot Swap capable, maintaining

backplane data integrity during board insertion and

removal. The drivers feature three-state outputs, maintain-

ing high impedance over the entire common mode range

(–7V to 12V). Outputs also remain high impedance during

power-up and with the power off. A short-circuit feature

detects bus contention and substantially reduces driver

output current. Thermal shutdown circuitry protects the

parts from excessive power dissipation.

The LTC1688 allows all four drivers to be enabled together,

while the LTC1689 allows two drivers at a time to be

enabled.

The LTC1688/LTC1689 operate from a single 5V or 3V

supply and draw only 9mA of supply current.

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High Speed RS485 Twisted-Pair Drivers

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High Speed Backplane Drivers

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Complementary Clock Drivers

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STS-1/OC-1 Data Drivers

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SCSI Drivers

Hot Swap is a trademark of Linear Technology Corporation.

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

20ns Pulse Across 100 Feet

of Category 5 UTP

20ns/DIV

2V/DIV

5V/DIV

1688/89 TA02

DRIVER INPUT

DRIVER OUTPUTS

RECEIVER INPUT

RECEIVER OUTPUT

CABLE DELAY

1688/89 TA01

RECEIVER

1/4 LTC1688

100Ω100Ω

1/4 LTC1518

100 FT CATEGORY 5 UTP

DRIVER

50Mbps RS485 Data Connection

DESCRIPTIO

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (12 pages)

PAGE 1
LTC1688/LTC1689 100Mbps RS485 Hot Swapable Quad Drivers U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Ultrahigh Speed: 100Mbps Guaranteed Propagation Delay: 8ns ±4ns Over Temperature Low Channel-to-Channel Skew: 500ps Typ Hot SwapTM Capable 50Mbps Operation with VDD = 3V Low tPLH/tPHL Skew: 500ps Typ Driver Outputs Maintain High Impedance in Three-State or with Power Off Short-Circuit Protected: 3mA Typ Output Current for an Indefinite Short Thermal Shutdown Protected Single 5V or 3V Supply Pin Compati
PAGE 2
LTC1688/LTC1689 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VDD) ................................................ 7V Enable Input Voltages ................. – 0.5V to (VDD + 0.5V) Enable Input Currents ..................... – 100mA to 100mA Driver Input Voltages .................. – 0.5V to (VDD + 0.5V) Driver Output Voltages ................. (– 12V + VDD) to 12V Driver Input Currents ......................
PAGE 3
LTC1688/LTC1689 DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
PAGE 4
LTC1688/LTC1689 U W TYPICAL PERFORMANCE CHARACTERISTICS Propagation Delay vs Temperature Propagation Delay vs Load Capacitance 14 14 VDD = 3V 10 8 VDD = 5V 6 4 VDI = 0V TO 3V RDIFF = 50Ω CL = 25pF 2 VDD = 3V 12 PROPAGATION DELAY (ns) PROPAGATION DELAY (ns) 12 10 VDD = 5V 8 6 4 VDI = 0V TO 3V RDIFF = 50Ω TA = 25°C 2 0 0 0 20 40 60 80 TEMPERATURE (°C) 0 100 10 20 30 40 50 LOAD CAPACITANCE (pF) 60 1688/89 G02 1688/89 G01 Three-State Output Current Supply Current vs Data Rate 250 4.
PAGE 5
LTC1688/LTC1689 U U U PIN FUNCTIONS DI1 (Pin 1): Driver 1 Input. Do not float. DI3 (Pin 9): Driver 3 Input. Do not float. DO1A (Pin 2): Driver 1 Noninverting Output. DO3A (Pin 10): Driver 3 Noninverting Output. DO1B (Pin 3): Driver 1 Inverting Output. DO3B (Pin 11): Driver 3 Inverting Output. EN (Pin 4, LTC1688): High True Enable Pin, enables all four drivers. A low on Pin 4 and a high on Pin 12 will put all driver outputs into a high impedance state. See Function Tables for details. Do not float.
PAGE 6
LTC1688/LTC1689 U W W SWITCHI G TI E WAVEFOR S 3V DI f = 1MHz; tr < 3ns; tf < 3ns 1.5V 1.5V 0V tPLH tPHL B VO A tSKEW 1/2 VO VO 1/2 VO 90% tSKEW 90% 10% VDIFF = V(A) – V(B) 10% – VO 1688/89 F04 tf tr Figure 4. Driver Propagation Delays 3V EN f = 1MHz; tr ≤ 3ns; tf ≤ 3ns 1.5V 1.5V 0V tZL 5V A, B VOL VOH A, B tLZ 1/2 VDD OUTPUT NORMALLY LOW 1/2 VDD OUTPUT NORMALLY HIGH 0.5V 0.5V 0V tZH 1688/89 F05 tHZ Figure 5.
PAGE 7
LTC1688/LTC1689 U U W U APPLICATIONS INFORMATION Hot Swap Capability With the LTC1688/LTC1689 outputs disabled but connected to the transmission line, the user can turn on/off the power to the LTC1688/LTC1689 without inducing a differential signal on the transmission line. Due to capacitive coupling, however, there can be a small amount of common mode charge injected into both disabled outputs, which is not seen as a differential signal (see Figure 7).
PAGE 8
LTC1688/LTC1689 U U W U APPLICATIONS INFORMATION Cable Termination Enable Pins The recommended cable termination for use with the LTC1688/LTC1689 is a single resistor across the two ends of a transmission cable (see Figure 8). When PC traces are used as the transmission line, its characteristic impedance should be chosen close to 100Ω in order to better match the specified timing characteristics of the LTC1688/ LTC1689.
PAGE 9
LTC1688/LTC1689 U W U U APPLICATIONS INFORMATION High Speed Twisted-Pair Transmission High Speed Backplane Transmission Data rates up to 100Mbps can be transmitted over short distances using Category 5 UTP (unshielded twisted pair). The cable distance will determine the maximum data rate. Figures 11 and 12 show an 8ns pulse propagating over 25 feet of Category 5 UTP. Notice how the cable attenuates the signal.
PAGE 10
LTC1688/LTC1689 U W U U APPLICATIONS INFORMATION Layout Considerations A ground plane is recommended when using high frequency devices like the LTC1688/LTC1689. A 0.1µF ceramic bypass capacitor less than 0.25 inch away from the VDD pin is also recommended. Special care should be taken to route the differential outputs very symmetrically in order to obtain the same parasitic capacitances and thus maintain good propagation delay skew.
PAGE 11
LTC1688/LTC1689 U W U U APPLICATIONS INFORMATION DRIVER INPUT DRIVER INPUT CABLE DELAY CABLE DELAY RECEIVER INPUT 2V/DIV RECEIVER INPUT 2V/DIV RECEIVER OUTPUT 500ns/DIV RECEIVER OUTPUT 1µs/DIV 1688/89 F18 Figure 18. 1000 Feet, 5Mbps, LTC1518 Receiver 1688/89 F19 Figure 19. 1000 Feet, 1Mbps, LTC1518 Receiver DRIVER INPUT DRIVER INPUT CABLE DELAY CABLE DELAY RECEIVER INPUT RECEIVER INPUT 2V/DIV 2V/DIV RECEIVER OUTPUT 100ns/DIV RECEIVER OUTPUT 50ns/DIV 1688/89 F20 Figure 20.
PAGE 12
LTC1688/LTC1689 U PACKAGE DESCRIPTION S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .386 – .394 (9.804 – 10.008) NOTE 3 .045 ±.005 .050 BSC 16 N 15 14 13 12 11 10 9 N .245 MIN .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 1 .030 ±.005 TYP 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 2 1 .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 3 4 5 7 6 8 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.