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LTC1484IS8#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
13
LTC1484
R
D
1
1k
RO4 DE4
67
2
58
5V
34
R
D
1
1k
RO2DE2
67
120Ω
2
5
8
5V
5V
34
1.2k
1484 F11
1.2k
120Ω
5V
1.2k
1.2k
R
D
1
1k
RO3
DE3
RO1
DE1
67
2
5
8
5V
34
R
D
1
1k
67
2
5
8
5V
34
receiver output and expects to see perfect agreement
between the two data streams. (Note that the driver inverts
the data, so the transmitted and received data streams are
actually opposites.) If the simultaneously transmitted and
received data streams differ (usually detected by compar-
ing RO and DE with an XOR), it signals the presence of a
second, active driver. The first driver falls silent, and the
second driver seizes control.
If the LTC1484 is connected as shown in Figure 11, the
overhead of XORing the transmitted and received data in
hardware or software is eliminated. DE and RE are con-
nected together so the receiver is disabled and its output
three-stated whenever a “0” is transmitted. A 1k pull-up
ensures a “1” at the receiver output during this condition.
The receiver is enabled when the driver is disabled. During
this interval the receiver output should also be “1”. Thus,
under normal operation the receiver output is always “1”.
If a “0” is detected, it indicates the presence of a second
active driver attempting to seize control of communica-
tions.
The maximum frequency at which the system in Figure 11
can operate is determined by the cable capacitance, the
values of the pull-up and pull-down resistors and receiver
propagation delay. The external resistors take a longer
time to pull the line to a “1” state due to higher source
resistance compared to an active driver, thereby affecting
the duty cycle of the receiver output at the far end of the
line.
Figure 11. Transmit “0” CDMA Application
APPLICATIONS INFORMATION
WUU
U
(b)
Figure 12a shows a 100kHz DE1 waveform for an LTC1484
driving a 1000-foot shielded twisted-pair (STP) cable and
the A2, B2 and RO2 waveforms of a receiving LTC1484 at
the far end of the cable. The propagation delay between
DE1 of the driver and RO2 at the far end of the line is 1.8µs
at the rising edge and 3.7µs at the falling edge of DE1. The
(a)
Figure 12. LTC1484 Driving a 1000 Foot STP Cable
1484 F12a
1484 F12b
B2
A2
RO2
DE1
DE1
B2
A2
RO2
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 0.13µs 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 220Ω resistors, both rising and
falling edge delays are 2.2µs when driving a 1000-foot STP
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
external bias resistors) so that the t
DZR
timing does not
apply to this application. The whole system can be changed
to actively transmit only a “1” by swapping the pull-up and
pull-down resistors in Figure 11, shorting DI to V
CC
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.
APPLICATIONS INFORMATION
WUU
U
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters), unless otherwise noted.
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)
15
LTC1484
PACKAGE DESCRIPTION
U
Dimensions in inches (millimeters), unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
N8 1098
0.100
(2.54)
BSC
0.065
(1.651)
TYP
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
0.020
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
0.125
(3.175)
MIN
12
3
4
876
5
0.255 ± 0.015*
(6.477 ± 0.381)
0.400*
(10.160)
MAX
0.009 – 0.015
(0.229 – 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.325
+0.035
–0.015
+0.889
–0.381
8.255
()
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.016 – 0.050
(0.406 – 1.270)
0.010 – 0.020
(0.254 – 0.508)
×
45
°
0
°
– 8
°
TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 1298
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
1
2
3
4
0.150 – 0.157**
(3.810 – 3.988)
8
7
6
5
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
*
**
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC1484IS8#PBF

Mfr. #:
Buy LTC1484IS8#PBF
Manufacturer:
Analog Devices Inc.
Description:
RS-485 Interface IC L Pwr RS485 Tran w/ Rcv Fail-Safe
Lifecycle:
New from this manufacturer.
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