Data Sheet
FEATURES
Operates with 3.3 V supply
EIA RS-422 and RS-485 compliant over full CM range 19 kΩ input impedance
Up to 50 transceivers on bus 20 Mbps data rate
Short-circuit protection
Specified over full temperature range Thermal shutdown
Interoperable with 5 V logic 840 μA supply current 2 nA shutdown current
Available in PDIP, SOIC, and TSSOP Meets IEC1000-4-4 (>1 kV) 8 ns skew
Upgrade for MAX3491, SN75ALS180
APPLICATIONS
Telecommunications DTE–DCE interface Packet switching Local area networks Data concentration Data multiplexers
Integrated services digital network (ISDN) AppleTalk
Industrial controls
GENERAL DESCRIPTION
The ADM3491-1 is a low power, differential line transceiver designed to operate using a single 3.3 V power supply. Low power consumption, coupled with a shutdown mode, makes it ideal for power-sensitive applications. It is suitable for commu-nication on multipoint bus transmission lines.
The ADM3491-1 is intended for balanced data transmission and complies with both Electronic Industries Association (EIA) Standards RS-485 and RS-422. It contains a differential line driver and a differential line receiver, making it suitable for full-duplex data transfer.
ADM3491-1
FUNCTIONAL BLOCK DIAGRAM
ADM3491-1ARORBREDEZDIDY100-43250Figure 1. The input impedance is 19 kΩ, allowing up to 50 transceivers to be connected on the bus. A thermal shutdown circuit prevents excessive power dissipation caused by bus contention or by
output shorting. This feature forces the driver output into a high impedance state if a significant temperature increase is detected in the internal driver circuitry during fault conditions. If the inputs are unconnected (floating), the receiver contains a fail-safe feature that results in a logic high output state. The ADM3491-1 is fabricated on BiCMOS, an advanced mixed technology process combining low power CMOS with fast switching bipolar technology.
ADM3491-1
TIMING SPECIFICATIONS
VCC = 3.3 V, TA = 25°C, unless otherwise noted. Table 2.
Parameter DRIVER
Differential Output Delay, TDD
Differential Output Transition Time
Propagation Delay Input to Output, TPLH, TPHL Driver Output to Output, TSKEW ENABLE/DISABLE
Driver Enable to Output Valid Driver Disable Timing
Driver Enable from Shutdown RECEIVER
Time to Shutdown
Propagation Delay Input to Output, TPLH, TPHL Skew, TPLH – TPHL Receiver Enable, TEN Receiver Disable, TDEN
Receiver Enable from Shutdown
Min
Typ
Max
Unit
Data Sheet
Test Conditions/ Comments
RL = 60 Ω, CL1 = CL2 = 15 pF, see Figure 18 RL = 60 Ω, CL1 = CL2 = 15 pF, see Figure 18 RL = 27 Ω, CL1 = CL2 = 15 pF, see Figure 19 RL = 54 Ω, CL1 = CL2 = 15 pF, see Figure 19
1 35 ns 1 8 15 ns 7 22 35 ns 8 ns
45 90 ns RL = 110 Ω, CL = 50 pF, see Figure 16
40 80 ns RL = 110 Ω, CL = 50 pF, see Figure 16 65 110 ns RL = 110 Ω, CL = 15 pF, see Figure 16
80 190 300 ns
25 65 90 ns
10 ns 25 50 ns 25 45 ns
500 ns CL = 15 pF, see Figure 21 CL = 15 pF, see Figure 21 CL = 15 pF, see Figure 17 CL = 15 pF, see Figure 17 CL = 15 pF, see Figure 17
VCC = 3.3 V ± 0.3 V, TA = TMIN to TMAX, unless otherwise noted. Table 3.
ParameterDRIVER
Differential Output Delay, TDD
Differential Output Transition Time
Propagation Delay Input to Output, TPLH, TPHL Driver Output to Output, TSKEW ENABLE/DISABLE
Driver Enable to Output Valid Driver Disable Timing
Driver Enable from Shutdown RECEIVER
Time to Shutdown
Propagation Delay Input to Output, TPLH, TPHL Skew, TPLH – TPHL Receiver Enable, TEN Receiver Disable, TDEN
Receiver Enable from Shutdown
Min Typ Max Unit Test Conditions/Comments1 2 7
70 ns 15 ns 70 ns 10 ns
RL = 60 Ω, CL1 = CL2 = 15 pF, see Figure 18
RL = 60 Ω, CL1 = CL2 = 15 pF, see Figure 18 RL = 27 Ω, CL1 = CL2 = 15 pF, see Figure 19 RL = 54 Ω, CL1 = CL2 = 15 pF, see Figure 19
8 22
45 110 ns RL = 110 Ω, CL = 50 pF, see Figure 16 40 110 ns RL = 110 Ω, CL = 50 pF, see Figure 16 65 110 ns RL = 110 Ω, CL = 15 pF, see Figure 16
50 190 500 ns
25 65 115 ns
20 ns
25 50 ns 25 50 ns
600 ns
CL = 15 pF, see Figure 21
CL = 15 pF, see Figure 21 CL = 15 pF, see Figure 17 CL = 15 pF, see Figure 17 CL = 15 pF, see Figure 17
Rev. C | Page 4 of 16
ADM3491-1
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
VCC1NC23456781615Data Sheet
NCABNCZYNC05234-003NC1RO2RE3DE4DI5GND6GND71413VCCVCCABZY05234-002ROREDEDINCGNDADM3491-1TOP VIEW(Not to Scale)14131211109ADM3491-1TOP VIEW(Not to Scale)12111098NCNCNC = NO CONNECTNC = NO CONNECTFigure 2. 14-Lead PDIP and 14-Lead SOIC Pin Configuration
Figure 3. 16-Lead TSSOP Pin Configuration
Table 5. Pin Function Descriptions Pin Number Mnemonic PDIP/SOIC TSSOP 1, 8 2, 7, 9, 10, 13, 16 NC 2 3 4 5 6, 7 9 10 11 12 13, 14 3 4 5 6 8 11 12 14 15 1 RO RE DE DI GND Y Z B A VCC Description No Connect. Receiver Output. High when A > B by 200 mV; low when A < B by 200 mV. Receiver Output Enable. When RE is low, the receiver output RO is enabled. When RE is high, the output is high impedance. If RE is high and DE is low, the ADM3491-1 enters a shutdown state. Driver Output Enable. A high level enables the driver differential outputs, Y and Z. A low level places the part in a high impedance state. Driver Input. When the driver is enabled, a logic low on DI forces Y low and Z high; a logic high on DI forces Y high and Z low. Ground Connection, 0 V. Noninverting Driver Output Y. Inverting Driver Output Z. Inverting Receiver Input B. Noninverting Receiver Input A. Power Supply, 3.3 V ± 0.3 V. Rev. C | Page 6 of 16
Data Sheet TEST CIRCUITS
R/2VOD05234-004ADM3491-1
DIR/2VOCCL1DRLDIFF05234-006VCCVOUTCL2Figure 14. Driver Voltage Measurement Test Circuit Figure 18. Driver Differential Output Delay Test Circuit
Rev. C | Page 9 of 16
Data Sheet
ADM3491-1
As with any transmission line, it is important that reflections be minimized. This can be achieved by terminating the extreme ends of the line using resistors equal to the characteristic impedance of the line. Stub lengths of the main line should also be kept as short as possible. A properly terminated transmission line appears purely resistive to the driver.
THEORY OF OPERATION
DIFFERENTIAL DATA TRANSMISSION
Differential data transmission is used to reliably transmit data at high rates over long distances and through noisy environments. Differential transmission nullifies the effects of ground shifts and noise signals that appear as common-mode voltages on the line. The two main standards approved by the EIA specify the electrical characteristics of transceivers used in differential data transmission: ?
RS-422 standard specifies data rates up to 10 MBaud and line lengths up to 4000 ft. A single driver can drive a transmission line with up to 10 receivers.
RS-485 standard was defined to cater to true multipoint communications. This standard meets or exceeds all the requirements of RS-422, but also allows multiple drivers and receivers to be connected to a single bus. An extended common-mode range of ?7 V to +12 V is defined.
RECEIVER OPEN-CIRCUIT FAIL-SAFE FEATURE
The receiver input includes a fail-safe feature that guarantees a logic high on the receiver when the inputs are open circuit or floating.
3.3V0.1μF3.3V0.1μF?
REROVCCARBYZVCCDEDIDThe most significant differentiator of the RS-485 standard is that the drivers can be disabled, thereby allowing more than one to be connected to a single line. Only one driver should be enabled at a time, but the RS-485 standard contains additional specifications to guarantee device safety in the event of line contention.
Table 6. Comparison of RS-422 and RS-485 Interface Standards
Specification
Transmission Type
Maximum Cable Length
Minimum Driver Output Voltage Driver Load Impedance Receiver Input Resistance Receiver Input Sensitivity Receiver Input Voltage Range
RS-422 Differential 4000 ft. ±2 V 100 Ω 4 kΩ min ±200 mV ?7 V to +7 V
RS-485 Differential 4000 ft. ±1.5 V 54 Ω
12 kΩ min ±200 mV ?7 V to +12 V
ADM3491-1ZDIDYRS-485/RS-422 LINKBAADM3491-1RORREDEGNDGND05234-026
Figure 26. ADM3491-1 Full-Duplex Data Link
Table 7. Transmitting Truth Table Inputs Outputs RE DE DI Z Y X 1 1 0 1 X 1 0 1 0 0 0 X Hi-Z Hi-Z 1 0 X Hi-Z Hi-Z
Table 8. Receiving Truth Table CABLE AND DATA RATE
The transmission line of choice for RS-485 communications is a
twisted pair. Twisted pair cable tends to cancel common-mode noise and also causes cancellation of the magnetic fields gener-ated by the current flowing through each wire, thereby reducing the effective inductance of the pair.
The ADM3491-1 is designed for bidirectional data communica-tions on multipoint transmission lines. A typical application showing a multipoint transmission network is illustrated in Figure 26. Only one driver can transmit at a particular time, but multiple receivers can be enabled simultaneously.
Inputs Outputs RO RE DE A–B 0 X ≥ +0.2 V 0 0 X ≤ ?0.2 V 0 0 X Inputs O/C 1 1 X X Hi-Z
Rev. C | Page 11 of 16
MEMORY存储芯片ADM3485EARZ-REEL中文规格书 - 图文
