14

LTC1484

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 differ-

ence 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 0.13

µs and 0.4µs. Using smaller valued

pull-up and pull-down resistors to equalize the positive

and negative voltage swings needed to trip the receivers

will reduce the difference in delay and increase the maxi-

mum data rate. With 220

Ω resistors, both rising and

falling edge delays are 2.2

µswhendrivinga1000-footSTP

cable as shown in Figure 12b.

The fail-safe feature of the LTC1484 receiver allows a

CDMA system to function without the A and B pull-up and

pull-down resistors. However, if the resistors are left out,

noise margin will be reduced to as low as 15mV and

propagation delays will increase significantly. Operation in

this mode is not recommended.

Since DE and RE are tied together, the part never shuts

down. The receiver inputs are never floating (due to the

apply to this application. The whole system can be changed

to actively transmit only a “1” by swapping the pull-up and

connecting the 1k resistor as a pull-down. In this configu-

ration the driver is noninverting and the receiver output RO

truly follows DE.

MS8 Package

8-Lead Plastic MSOP

(LTC DWG # 05-08-1660)

MSOP (MS8) 1098

* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,

PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

0.021

± 0.006

(0.53

± 0.015)

0

° – 6° TYP

SEATING

PLANE

0.007

(0.18)

0.040

± 0.006

(1.02

± 0.15)

0.012

(0.30)

REF

0.006

± 0.004

(0.15

± 0.102)

0.034

± 0.004

(0.86

± 0.102)

0.0256

(0.65)

BSC

12

3

4

0.193

± 0.006

(4.90

± 0.15)

8

7 6

5

0.118

± 0.004*

(3.00

± 0.102)

0.118

± 0.004**

(3.00

± 0.102)