參數(shù)資料
型號: MAX3468EPA
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 通用總線功能
英文描述: +5V, Fail-Safe, 40Mbps, Profibus RS-485/ RS-422 Transceivers
中文描述: LINE TRANSCEIVER, PDIP8
封裝: PLASTIC, DIP-8
文件頁數(shù): 9/14頁
文件大?。?/td> 309K
代理商: MAX3468EPA
M
+5V, Fail-Safe, 40Mbps, Profibus RS-485/
RS-422 Transceivers
_______________________________________________________________________________________
9
Detailed Description
The MAX3465
MAX3469 high-speed transceivers for
RS-485/RS-422 communication contain one driver and
one receiver. These devices feature true fail-safe cir-
cuitry, which guarantees a logic-high receiver output
when the receiver inputs are open or shorted, or when
they are connected to a terminated transmission line
with all drivers disabled (see the
True Fail-Safe
sec-
tion). The MAX3465
MAX3469
s driver slew rates allow
transmit speeds up to 40Mbps.
The MAX3468 and MAX3469 are half-duplex trans-
ceivers, while the MAX3465, MAX3466, and MAX3467
are full-duplex transceivers. All of these parts operate
from a single +5V supply. Drivers are output short-cir-
cuit current limited. Thermal-shutdown circuitry protects
drivers against excessive power dissipation. When acti-
vated, the thermal-shutdown circuitry places the driver
outputs into a high-impedance state. The MAX3465
and MAX3468 devices have a hot-swap input structure
that prevents disturbances on the differential signal
lines when a circuit board is plugged into a hot back-
plane (see the
Hot-Swap Capability
section). All
devices have output levels that are compatible with
Profibus standards.
True Fail-Safe
The MAX3465
MAX3469 guarantee a logic-high receiv-
er output when the receiver inputs are shorted or open,
or when they are connected to a terminated transmis-
sion line with all drivers disabled. This is done by set-
ting the receiver threshold between -50mV and
-200mV. If the differential receiver input voltage (A - B)
is greater than or equal to -50mV, RO is logic high. If
A - B is less than or equal to -200mV, RO is logic low. In
the case of a terminated bus with all transmitters dis-
abled, the receiver
s differential input voltage is pulled
to 0V by the termination. With the receiver thresholds of
the MAX3465
MAX3469, this results in a logic high with
a 50mV minimum noise margin. Unlike previous true
fail-safe devices, the -50mV to -200mV threshold com-
plies with the ±200mV EIA/TIA-485 standard.
Hot-Swap Capability
Hot-Swap Inputs
When circuit boards are inserted into a
hot
or pow-
ered backplane, disturbances to the enable and differ-
ential receiver inputs can lead to data errors. Upon
initial circuit board insertion, the processor undergoes
its power-up sequence. During this period, the proces-
sor output drivers are high impedance and are unable
to drive the DE input of the MAX3465/MAX3468 to a
defined logic level. Leakage currents up to 10μA from the
high-impedance output could cause DE to drift to an
incorrect logic state. Additionally, parasitic circuit board
capacitance could cause coupling of V
CC
or GND to DE.
These factors could improperly enable the driver.
When V
CC
rises, an internal pulldown circuit holds DE
low for around 15μs. After the initial power-up
sequence, the pulldown circuit becomes transparent,
resetting the hot-swap-tolerable input.
Hot-Swap Input Circuitry
The MAX3465/MAX3468 enable inputs feature hot-swap
capability. At the input there are two NMOS devices, M1
and M2 (Figure 4). When V
CC
ramps from 0, an internal
15μs timer turns on M2 and sets the SR latch, which
also turns on M1. Transistors M2, a 2mA current sink,
and M1, a 100μA current sink, pull DE to GND through a
5.6k
resistor. M2 is designed to pull DE to the disabled
state against an external parasitic capacitance up to
100pF that can drive DE high. After 15μs, the timer
deactivates M2 while M1 remains on, holding DE low
against three-state leakages that can drive DE high. M1
remains on until an external source overcomes the
required input current. At this time, the SR latch resets
and M1 turns off. When M1 turns off, DE reverts to a
standard, high-impedance CMOS input. Whenever V
CC
drops below 1V, the hot-swap input is reset.
For
RE
there is a complementary circuit employing two
PMOS devices pulling to V
CC
.
V
CC
TIMER
TIMER
EN
DE
(HOT SWAP)
15
μ
s
100
μ
A
M1
M2
5.6k
2mA
Figure 4. Simplified Structure of the Driver Enable Pin (DE)
相關(guān)PDF資料
PDF描述
MAX3469CPA +5V, Fail-Safe, 40Mbps, Profibus RS-485/ RS-422 Transceivers
MAX3471CUA 1.6レA, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
MAX3471EUA 1.6レA, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
MAX3471 Programmable 27-Bit Display Serial Interface Receiver 80-BGA MICROSTAR JUNIOR -40 to 85
MAX3491E 3.3V-Powered, 【15kV ESD-Protected, 12Mbps and Slew-Rate-Limited True RS-485/RS-422 Transceivers
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX3468EPA+ 功能描述:RS-422/RS-485 接口 IC 5V Fail-Safe 40Mbps Profibus Tcvr RoHS:否 制造商:Maxim Integrated 數(shù)據(jù)速率:1136 Kbps 工作電源電壓:3 V to 5.5 V 電源電流:5.9 mA 工作溫度范圍:- 40 C to + 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-28 封裝:Tube
MAX3468ESA 功能描述:RS-422/RS-485 接口 IC RoHS:否 制造商:Maxim Integrated 數(shù)據(jù)速率:1136 Kbps 工作電源電壓:3 V to 5.5 V 電源電流:5.9 mA 工作溫度范圍:- 40 C to + 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-28 封裝:Tube
MAX3468ESA+ 功能描述:RS-422/RS-485 接口 IC 5V Fail-Safe 40Mbps Profibus Tcvr RoHS:否 制造商:Maxim Integrated 數(shù)據(jù)速率:1136 Kbps 工作電源電壓:3 V to 5.5 V 電源電流:5.9 mA 工作溫度范圍:- 40 C to + 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-28 封裝:Tube
MAX3468ESA+T 功能描述:RS-422/RS-485 接口 IC 5V Fail-Safe 40Mbps Profibus Tcvr RoHS:否 制造商:Maxim Integrated 數(shù)據(jù)速率:1136 Kbps 工作電源電壓:3 V to 5.5 V 電源電流:5.9 mA 工作溫度范圍:- 40 C to + 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-28 封裝:Tube
MAX3468ESA-T 功能描述:RS-422/RS-485 接口 IC RoHS:否 制造商:Maxim Integrated 數(shù)據(jù)速率:1136 Kbps 工作電源電壓:3 V to 5.5 V 電源電流:5.9 mA 工作溫度范圍:- 40 C to + 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-28 封裝:Tube