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19-0497; Rev 0; 2/98
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
________________General Description
The MAX3471 half-duplex transceiver is intended for lithium battery-powered RS-485/RS-422 applications. It draws only 1.6A (typical) supply current from a 3.6V supply with the receiver enabled and the driver disabled. Its wide 2.5V to 5.5V supply voltage guarantees operation over the lifetime of a lithium battery. This device features true fail-safe operation that guarantees a logic-high receiver output when the receiver inputs are open or shorted. This means that the receiver output will be a logic high if all transmitters on a terminated bus are disabled (high impedance). The MAX3471 has a 1/8-unit load input resistance. When driver outputs are enabled and pulled above VCC or below GND, internal circuitry prevents battery backcharging. The MAX3471 is available in an 8-pin MAX package.
____________________________Features
o 1.6A Supply Current with Receiver Enabled o +2.5V to +5.5V Single-Supply Operation o True Fail-Safe Receiver Input o Available in MAX Package o 1/8-Unit-Load Receiver Input o -7V to +10V Common-Mode Input Voltage Range
MAX3471
_______________Ordering Information
PART MAX3471CUA MAX3471EUA TEMP. RANGE 0C to +70C -40C to +85C PIN-PACKAGE 8 MAX 8 MAX
________________________Applications
Remote Meter Reading Battery-Powered Differential Communications Level Translators
___________________Pin Configuration
TOP VIEW
RO RE DE DI 1 2 3 4 8 VCC B A GND
MAX3471
7 6 5
MAX
Typical Application Circuit
VCC DI D DE RO RE R GND REMOTE UNIT DI VCC D DE R A B A GND VCC D DI DE R CENTRAL UNIT RO RE B A GND A R B B D DI RO RE VCC DE VCC 0.1F
RO RE
MAX3471
REMOTE UNIT REMOTE UNIT
TYPICAL HALF-DUPLEX RS-485 NETWORK ________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems MAX3471
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (VCC) ..............................................................7V Control Input Voltage (RE, DE)...................-0.3V to (VCC + 0.3V) Driver Input Voltage (DI).............................-0.3V to (VCC + 0.3V) Driver Output/Receiver Input Voltage (A, B).....................10.5V Receiver Output Voltage (RO)....................-0.3V to (VCC + 0.3V) Continuous Power Dissipation MAX (derate 4.5mW/C above +70C) ......................362mW Operating Temperature Ranges MAX3471CUA .....................................................0C to +70C MAX3471EUA ..................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
Note 1: All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device ground unless otherwise noted.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +2.5V to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.6V and TA = +25C.) (Note 1) PARAMETER Differential Driver Output (no load) Differential Driver Output (with load) SYMBOL VOD1 CONDITIONS Figure 1 (R = open) R = 750 (RS-422) VOD2 Figure 1 R = 27 (RS-485) R = 27 (RS-485), VCC = 5V, TA = +25C Figure 1, R = 750 or 27 1.5 0.2 3.28 0.83 1.5 V MIN TYP MAX VCC UNITS V
Change in Magnitude of Differential Output Voltage (Note 2) Driver Common-Mode Output Voltage Change in Magnitude of Common-Mode Voltage (Note 2) Input High Voltage Input Low Voltage DI Input Hysteresis Input Current Input Current (A and B), Half Duplex Driver Short-Circuit Output Current (Note 3) Receiver Differential Threshold Voltage Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Three-State Current at Receiver Output Receiver Input Resistance
VOD
0.2
V
VOC VOC VIH VIL VHYS IIN1 IIN2 IOSD VTH VTH VOH VOL IOZR RIN
Figure 1, R = 750 or 27 Figure 1, R = 750 or 27 DE, DI, RE DE, DI, RE 100 DE, DI, RE DE = GND, VCC = GND or 5.5V -7V VOUT 10V -7V VCM 10V VCM = 0 IO = -0.8mA, VID = -50mV IO = 2.2mA, VID = -450mV 0 VO VCC -7V VCM 10V 96 VCC - 0.4 VIN = 10V VIN = -7V VCC 3.6V VCC 5.5V -60 -130 -450 -250 32 0.001 0.7 x VCC
0.6 x VCC 0.2
V V V
0.3 x VCC 1 0.105 -0.075 60 130 -50
V mV A mA mA mV mV V
0.4 1
V A k
2
_______________________________________________________________________________________
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.5V to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.6V and TA = +25C.) (Note 1) PARAMETER Receiver Output Short-Circuit Current SYMBOL IOSR 0 VRO VCC VCC 3.6V, no load, RE = DI = GND or VCC, VA = VB = 0 VCC 5.5V, no load, RE = DI = GND or VCC, VA = VB = 0 CONDITIONS VCC 3.6V VCC 5.5V DE = VCC DE = GND DE = VCC DE = GND MIN -20 -40 50 1.6 83 2.8 TYP MAX 50 110 60 2 A 100 4 UNITS mA
MAX3471
Supply Current
ICC
SWITCHING CHARACTERISTICS
(VCC = +2.5V to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.6V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay Driver Output Skew (tDPLH - tDPHL) Driver Rise or Fall Time Driver Enable Time to Output High Driver Enable Time to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output Propagation Delay Differential Receiver Skew (tRPLH - tRPHL) Data Rate Receiver Enable Time to Output Low Receiver Enable Time to Output High Receiver Disable Time from Low Receiver DisableTime from High SYMBOL tDPLH, tDPHL tDSKEW tDR, tDF tDZH tDZL tDLZ tDHZ tRPLH tRPHL tRSKEW fMAX tRZL tRZH tRLZ tRHZ CONDITIONS Figures 3 and 5, RDIFF = 1.5k, CL1 = CL2 = 100pF Figures 3 and 5, RDIFF = 1.5k, CL1 = CL2 = 100pF Figures 3 and 5, RDIFF = 1.5k, CL1 = CL2 = 100pF Figures 4 and 6, CL = 100pF, S2 closed, S1 open Figures 4 and 6, CL = 100pF, S1 closed, S2 open Figures 4 and 6, CL = 15pF, S1 closed, S2 open Figures 4 and 6, CL = 15pF, S2 closed, S1 open Figures 7 and 9, CL = 15pF, |VID| = 2V Figures 7 and 9, |VID| = 2V Figure 9, CL = 100pF Figures 2 and 8, CL = 15pF, S1 closed, S2 open Figures 2 and 8, CL = 15pF, S2 closed, S1 open Figures 2 and 8, CL = 15pF, S1 closed, S2 open Figures 2 and 8, CL = 15pF, S2 closed, S1 open 64 70 85 50 35 500 500 200 200 0.75 MIN TYP 1.40 0.025 1.34 1.5 0.86 0.4 0.6 5.2 6.4 1.2 1.75 6.00 4.00 1.5 1.5 12 12 MAX 2.00 UNITS s s s s s s s s s kbps ns ns ns ns
Note 1: All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device ground unless otherwise noted. Note 2: VOD and VOC are the changes in magnitude of VOD and VOC, respectively, when the DI input changes state. Note 3: Maximum and minimum current levels apply to peak current just prior to foldback-current limiting.
_______________________________________________________________________________________
3
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems MAX3471
__________________________________________Typical Operating Characteristics
(VCC = +3.6V, TA = +25C, unless otherwise noted.)
OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE
MAX3471toc01
OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE
MAX3471toc02
RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE
LOAD = 0.8mA RECEIVER OUTPUT VOLTAGE (V) 5.0 VCC = 5V 4.5
MAX3471toc03
45 40 OUTPUT CURRENT (mA) 35 30 25 20 15 10 5 0 0 VCC = 3.6V VCC = 5V
20 18 16 OUTPUT CURRENT (mA) 14 12 10 8 6 4 2 0 VCC = 3.6V VCC = 5V
5.5
4.0 VCC = 3.6V 3.5
3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT HIGH VOLTAGE (V) -50 -25 0 25 50 75 100 125 TEMPERATURE (C)
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 OUTPUT LOW VOLTAGE (V)
RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX3471toc04
DRIVER OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE
MAX3471toc05
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
DIFFERENTIAL OUTPUT VOLTAGE (V) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 RDIFF = 54 -50 -25 0 25 50 75 100 125 VCC = 3.6V VCC = 5V
MAX3471toc06
140 LOAD = 2.2mA RECEIVER OUTPUT VOLTAGE (mV) 120 100 80 60 VCC = 5V 40 20 0 -50 -25 0 25 50 75 100 VCC = 3.6V
40 DRIVER OUTPUT CURRENT (mA) 35 30 25 20 15 10 5 0 0 VCC = 3.6V VCC = 5V
2.0
125
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 DIFFERENTIAL OUTPUT VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX3471toc07
OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE (VCC = 5V)
MAX3471toc08
OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE (VCC = 3.6V)
VCC = 3.6V 25 OUTPUT CURRENT (mA) 20 15 10 5 0
MAX3471toc09
5.0 DIFFERENTIAL OUTPUT VOLTAGE (V) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -50 RDIFF = 1.5k VCC = 3.6V VCC = 5V
60 VCC = 5V 50 OUTPUT CURRENT (mA) 40 30 20 10 0
30
-25
0
25
50
75
100
125
0
1
2
3
4
5
6
7
8
9
10
0
2
4
6
8
10
12
TEMPERATURE (C)
OUTPUT LOW VOLTAGE (V)
OUTPUT LOW VOLTAGE (V)
4
_______________________________________________________________________________________
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +25C, unless otherwise noted.)
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE (VCC = 3.6V)
MAX3471toc11 MAX3471toc10
MAX3471
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE (VCC = 5V)
45 40 OUTPUT CURRENT (mA) 35 30 25 20 15 10 5 0 -12 -10 -8 -6 -4 -2 0 2 4 6 OUTPUT HIGH VOLTAGE (V) 0 VCC = 5V 25
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (DE = VCC)
80 SUPPLY CURRENT (A) 70 60 50 40 30 20 10 0 DE = VCC -50 -25 0 25 50 75 100 125 VCC = 2.5V VCC = 3.6V VCC = 5.5V VCC = 5.0V
MAX3471toc12
90
VCC = 3.6V 20 OUTPUT CURRENT (mA)
15
10
5
-12
-10
-8
-6
-4
-2
0
2
4
OUTPUT HIGH VOLTAGE (V)
TEMPERATURE (C)
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (DE = GND)
MAX3471toc13
DRIVER PROPAGATION DELAY (tDPHL, tDPLH) vs. TEMPERATURE
1.4 PROPAGATION DELAY (s) 1.3 1.2 1.1 1.0 0.9 0.8 CL1 = CL2 = 100pF 0.7 VCC = 5V, RDIFF = 54 VCC = 3.6V, RDIFF = 54 VCC = 3.6V, RDIFF = 1.5k VCC = 5V, RDIFF = 1.5k
MAX3471toc14
3.0 2.5 SUPPLY CURRENT (A) 2.0 VCC = 3.6V 1.5 1.0 0.5 DE = GND 0 -50 -25 0 25 50 75 100 VCC = 2.5V VCC = 5.5V VCC = 5.0V
1.5
125
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
RECEIVER PROPAGATION DELAY (tPLH) vs. TEMPERATURE
MAS3471toc15
RECEIVER PROPAGATION DELAY (tPHL) vs. TEMPERATURE
7.0 PROPAGATION DELAY (s) 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 VCC = 5V VCC = 3.6V
MAX3471toc16
6 VCC = 3.6V 5 PROPAGATION DELAY (s) 4 VCC = 5V 3 2 1 0 -40 CIRCUIT OF FIGURE 9 CL = 100pF |VID| = 2V -20 0 20 40 60 80
7.5
|VID| = 2V
CL = 100pF -40 -20 0 20 40 60 80 100
100
TEMPERATURE (C)
TEMPERATURE (C)
_______________________________________________________________________________________
5
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems MAX3471
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +25C, unless otherwise noted.)
RECEIVER PROPAGATION DELAY
MAX3471toc17
DRIVER PROPAGATION DELAY
MAX3471toc18
B (2V/div) A DI (2V/div) A-B (2V/div) RO (2V/div)
A (2V/div) B DI (2V/div)
A-B (1V/div)
1s/div
400ns/div R = 1.5k, CL = 100pF
______________________________________________________________Pin Description
PIN 1 2 3 4 5 6 7 8 NAME RO RE DE DI GND A B VCC FUNCTION Receiver Output. When RE is low, if A - B -50mV, RO will be high; if A - B -450mV, RO will be low. Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high. Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high impedance when DE is low. Driver Input. With DE high, a low on DI forces the noninverting output low and the inverting output high. Similarly, a high on DI forces the noninverting output high and the inverting output low. Ground Noninverting Driver Output and Noninverting Receiver Input Inverting Driver Output and Inverting Receiver Input Positive Supply: +2.5V VCC +5.5V
_______________Detailed Description
The MAX3471 half-duplex transceiver consumes only 1.6A from a single +3.6V supply. Its wide 2.5V to 5.5V supply voltage guarantees operation over the lifetime of a lithium battery. This device contains one driver and one receiver. Its true fail-safe receiver input 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. Reduced-slew-rate drivers minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 64kbps.
Receiver Input Filtering
The MAX3471 receiver operates at up to 64kbps and incorporates input filtering in addition to input hystere6
sis. This filtering enhances noise immunity when differential signals have very slow rise and fall times. The MAX3471 guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is accomplished by setting the receiver threshold between -50mV and -450mV. If the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is a logic high. If A-B is less than or equal to -450mV, RO is a logic low. In the case of a terminated bus with all transmitters disabled, the receiver's differential input voltage is pulled to 0V by the termination. With the MAX3471's receiver thresholds, this results in a logic high with a 50mV minimum noise margin.
_______________________________________________________________________________________
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems
Table 1. Transmitting
INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X B 0 1 ZD ZD OUTPUTS A 1 0 ZD ZD RE 0 0 0 1
Table 2. Receiving
INPUTS DE 0 0 0 0 A-B -0.05V -0.45V Open/Shorted X OUTPUT RO 1 0 1 Z
MAX3471
ZD = Driver output disabled
X = Don't care Z = Receiver output high impedance
__________ Applications Information
Transceivers on the Bus
The MAX3471 is optimized for the unterminated bus normally used in slow, low-power systems. With a +2.5V supply, the part is guaranteed to drive up to eight standard loads (for example, 64 other MAX3471s or 56 MAX3471s plus one standard load). Drive capability increases significantly with supply. For example, with a +5V supply, the MAX3471 typically meets the RS-485 driver output specifications (1.5V with 54 differential termination). See the Typical Operating Characteristics.
Reduced EMI and Reflections
The MAX3471 is slew-rate limited, minimizing EMI and reducing reflections caused by improperly terminated cables. In general, the rise time of a transmitter directly relates to the length of an unterminated stub, which can be driven with only minor waveform reflections. The following equation expresses this relationship conservatively: Length = tRISE / (10 x 1.5ns/foot) where tRISE is the transmitter's rise time. For example, the MAX3471's rise time is typically 1.3s, which results in excellent waveforms with a stub length up to 82 feet. In general, systems operate well with longer unterminated stubs, even with severe reflections, if the waveform settles out before the UART samples them.
A R VOD R B VOC
Driver Output Protection
Excessive output current and power dissipation caused by faults or bus contention are prevented by foldback current limiting. A foldback current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics).
Figure 1. Driver DC Test Load
VCC VCC
S1 RECEIVER OUTPUT TEST POINT 1k
DE A DI DRIVER B VO RDIFF CL2 CL1
CL S2
Figure 2. Receiver Enable/Disable Timing Test Load
Figure 3. Driver Test Circuit
7
_______________________________________________________________________________________
1.6A, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems MAX3471
V CC DI 0V V CC 2 t DPLH B A 1/2 V O CL S2 VO VDIFF 0V -VO 10% t DR t DSKEW = (t DPLH - t DPHL ) 90% V DIFF = V (A) - V (B) 90% t DF 10% 1/2 V O t DPHL V CC 2
S1 12k OUTPUT UNDER TEST
VCC
VO
Figure 4. Driver Enable/Disable Timing Test Load
Figure 5. Driver Differential Propagation Delay and Rise/Fall Times
V CC DE 0V
V CC 2 t DZL t DLZ
V CC 2 V OH RO V OL A B VOH - 0.5V t DZH t DHZ INPUT
V TEST A, B VOL VOH A, B 0V
V CC 2 OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH V CC 2
1.4V t RPHL
OUTPUT
1.4V t RPLH
VOL + 0.5V
V TEST = 0.91V CC
|V ID | = 2V t RSKEW = (t RPLH = t RPHL )
Figure 6. Driver Enable and Disable Times
Figure 7. Receiver Propagation Delay
V CC RE 0V
V CC 2 t RZL t RLZ
V CC 2 VID
B A RECEIVER CL RE RECEIVER OUTPUT
VCC RO VOL VOH RO 0V
1.4V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH
VOL + 0.5V
VOH - 0.5V 1.4V t RZH t RHZ
Figure 9. Receiver Propagation Delay and Maximum DataRate Test Circuit
___________________Chip Information
Figure 8. Receiver Enable and Disable Times
TRANSISTOR COUNT: 351
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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