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LTC1690 Datasheet(PDF) 8 Page - Linear Technology |
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LTC1690 Datasheet(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LTC1690 3 1 5 6 D 120 Ω 2 1 8 7 R DRIVER LTC1690 5V LTC1690 RECEIVER 120 Ω SHIELD 2 4 7 8 R 3 4 6 5 D RECEIVER DRIVER 1690 F06 SHIELD 0.01 µF 5V 0.01 µF Figure 6. Typical Application APPLICATIONS INFORMATION A typical application is shown in Figure 6. 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 con- nected to the ends of the wire. However, the wires must be terminated at the ends with a resistor equal to their characteristic impedance, typically 120 Ω. Because only one driver can be connected on the bus, the cable need only be terminated at the receiving end. The optional shields around the twisted pair are connected to GND at one end and help reduce unwanted noise. The LTC1690 can be used as a line repeater as shown in Figure 7. If the cable is longer that 4000 feet, the LTC1690 is inserted in the middle of the cable with the receiver output connected back to the driver input. Receiver Fail-Safe Some encoding schemes require that the output of the receiver maintains a known state (usually a logic 1) when data transmission ends and all drivers on the line are forced into three-state. The receiver of the LTC1690 has a fail-safe feature which guarantees the output to be in a logic 1 state when the receiver inputs are left floating or shorted together. This is achieved without external com- ponents by designing the trip-point of the LTC1690 to be within – 200mV to –10mV. If the receiver output must be a logic 0 instead of a logic 1, external components are required. The LTC1690 fail-safe receiver is designed to reject fast –7V to 12V common mode steps at its inputs. The slew rate that the receiver will reject is typically 400V/ µs, but –7V to 12V steps in 10ns can be tolerated if the frequency of the common mode step is moderate (<600kHz). Driver-Receiver Crosstalk The driver outputs generate fast rise and fall times. If the LTC1690 receiver inputs are not terminated and floating, switching noise from the LTC1690 driver can couple into the receiver inputs and cause the receiver output to glitch. This can be prevented by ensuring that the receiver inputs are terminated with a 100 Ω or 120Ω resistor, depending on the type of cable used. A cable capacitance that is greater than 10pF ( ≈1ft of cable) also prevents glitches if no termination is present. The receiver inputs should not be driven typically above 8MHz to prevent glitches. |
Similar Part No. - LTC1690_15 |
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Similar Description - LTC1690_15 |
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