For free samples & the latest literature: https://www.doczj.com/doc/f93227951.html,, or phone 1-800-998-8800.For small orders, phone 408-737-7600 ext. 3468.
________________General Description
The MAX3471 half-duplex transceiver is intended for lithium battery-powered RS-485/RS-422 applications. It draws only 1.6μA (typical) supply current from a 3.6V supply with the receiver enabled and the driver dis-abled. 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 guar-antees a logic-high receiver output when the receiver inputs are open or shorted. This means that the receiv-er output will be a logic high if all transmitters on a ter-minated bus are disabled (high impedance). The MAX3471 has a 1/8-unit load input resistance. When driver outputs are enabled and pulled above V CC or below GND, internal circuitry prevents battery back-charging.
The MAX3471 is available in an 8-pin μMAX package.
________________________Applications
Remote Meter Reading
Battery-Powered Differential Communications Level Translators
____________________________Features
o 1.6μA Supply Current with Receiver Enabled o +2.5V to +5.5V Single-Supply Operation o True Fail-Safe Receiver Input o Available in μMAX Package o 1/8-Unit-Load Receiver Input
o -7V to +10V Common-Mode Input Voltage Range
MAX3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems
________________________________________________________________Maxim Integrated Products
1
___________________Pin Configuration
19-0497; Rev 0; 2/98
_______________Ordering Information
Typical Application Circuit
M A X 3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems 2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS (Note 1)
DC ELECTRICAL CHARACTERISTICS
(V CC = +2.5V to +5.5V, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +3.6V and T A = +25°C.) (Note 1)
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.
Supply Voltage (V CC ) ..............................................................7V Control Input Voltage (RE , DE)...................-0.3V to (V CC + 0.3V)Driver Input Voltage (DI).............................-0.3V to (V CC + 0.3V)Driver Output/Receiver Input Voltage (A, B).....................±10.5V Receiver Output Voltage (RO)....................-0.3V to (V CC + 0.3V)Continuous Power Dissipation
μMAX (derate 4.5mW/°C above +70°C)......................362mW
Operating Temperature Ranges
MAX3471CUA.....................................................0°C to +70°C MAX3471EUA..................................................-40°C to +85°C Storage Temperature Range.............................-65°C to +160°C Lead Temperature (soldering, 10sec).............................+300°C
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.
MAX3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems
_______________________________________________________________________________________3
DC ELECTRICAL CHARACTERISTICS (continued)
(V CC = +2.5V to +5.5V, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +3.6V and T A = +25°C.) (Note 1)
SWITCHING CHARACTERISTICS
(V CC = +2.5V to +5.5V, T A = T MIN to T MAX , unless otherwise noted. Typical values are at V CC = +3.6V and T A = +25°C.)
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:?V OD and ?V OC are the changes in magnitude of V OD and V OC , respectively, when the DI input changes state.Note 3:Maximum and minimum current levels apply to peak current just prior to foldback-current limiting.
M A X 3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems 4_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(V CC = +3.6V, T A = +25°C, unless otherwise noted.)
015510203540302545
0.40.60.8 1.00.2 1.2 1.4 1.6 1.8 2.0
OUTPUT CURRENT
vs. RECEIVER OUTPUT LOW VOLTAGE
OUTPUT LOW VOLTAGE (V)
O U T P U T C U R R E N T (m A )
042861210141816200
1.0 1.5
2.00.5 2.5
3.0 3.5
4.54.0
5.0
OUTPUT CURRENT vs. RECEIVER
OUTPUT HIGH VOLTAGE
OUTPUT HIGH VOLTAGE (V)
O U T P U T C U R R E N T (m A )
3.0
3.5
4.5
4.0
5.0
5.5
-50
-25
25
50
75
100
125
RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE
TEMPERATURE (°C)
R E C E I V E R O U T P U T V O L T A G E (V )
040208060
120100140
-50
25
-25
50
75
100
125
RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE
TEMPERATURE (°C)R E C E I V E R O U T P U T V O L T A G E (m V )
01.51.00.52.52.04.54.03.53.05.0-50
-25
25
50
75
100
125DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
TEMPERATURE (°C)D I F F E R E N T I A L O U T P U T V O L T A G E (V )
01051530352520400
1.0 1.5
2.0 2.50.5
3.0 3.5
4.0 4.5
5.0DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
DIFFERENTIAL OUTPUT VOLTAGE (V)
D R I V
E R O U T P U T C U R R E N T (m A )
0.60.40.2
1.00.81.81.61.41.2
2.0
-50
-25
25
50
75
100
125
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
TEMPERATURE (°C)
D I F F
E R E N T I A L O U T P U T V O L T A G E (V )
302010405060
0431********OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE (V CC = 5V)
OUTPUT LOW VOLTAGE (V)O U T P U T C U R R E N T (m A
)
10520152530
046281012
OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE (V CC = 3.6V)
OUTPUT LOW VOLTAGE (V)
O U T P U T C U R R E N T (m A )
MAX3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems
_______________________________________________________________________________________5
010525201535403045-12-6
-4
-10
-8
-2
2
4
6
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE (V CC = 5V)
OUTPUT HIGH VOLTAGE (V)
O U T P U T C U R R E N T (m A )
05
15
10
2025
-12
-8
-6
-10
-4
-2
2
4
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE (V CC = 3.6V)
OUTPUT HIGH VOLTAGE (V)
O U T P U T C U R R E N T (m A )
201050403080706090
-50
25
-25
50
75
100
125
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (DE = V CC )
TEMPERATURE (°C)
S U P P L Y C U R R E N T (μA )
01.00.52.0
1.5
2.5
3.0-5025
50
-25
75
100
125
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (DE = GND)
TEMPERATURE (°C)
S U P P L Y C U R R E N T (μA )
0214356
-40
20
40
-20
60
80
100
RECEIVER PROPAGATION DELAY (t PLH ) vs. TEMPERATURE
TEMPERATURE (°C) P R O P A G A T I O N D E L A Y (μs )
0.7
0.90.8
1.11.01.41.31.21.5
-40
-20
20
40
60
80
100
DRIVER PROPAGATION DELAY (t DPHL , t DPLH ) vs. TEMPERATURE
TEMPERATURE (°C)
P R O P A G A T I O N D E L A Y (μs )
3.0
4.0
3.55.0
4.56.56.0
5.57.5
7.0-40
-20
20
40
60
80
100
RECEIVER PROPAGATION DELAY (t PHL ) vs. TEMPERATURE
TEMPERATURE (°C)
P R O P A G A T I O N D E L A Y (μs )
Typical Operating Characteristics (continued)
(V CC = +3.6V, T A = +25°C, unless otherwise noted.)
_______________Detailed Description
The MAX3471 half-duplex transceiver consumes only 1.6μA 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 hystere-sis. This filtering enhances noise immunity when differ-ential 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 set-ting 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 dis-abled, 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 mini-mum noise margin.
M A X 3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems 6
_______________________________________________________________________________________
______________________________________________________________Pin Description
RECEIVER PROPAGATION DELAY
MAX3471toc17
B DI (2V/div)(2V/div)A-B (2V/div)R O (2V/div)
A 1μs/div DRIVER PROPAGATION DELAY
MAX3471toc18
B DI (2V/div)
(2V/div)A-B (1V/div)
A 400ns/div
R = 1.5k ?, C L = 100pF
Ground
GND 5Noninverting Driver Output and Noninverting Receiver Input A 6Inverting Driver Output and Inverting Receiver Input B 7Positive Supply: +2.5V ≤V CC ≤+5.5V
V CC
8
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.DI 4Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high impedance when DE is low.
DE 3PIN Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high.
RE 2Receiver Output. When RE is low, if A - B ≥-50mV, RO will be high; if A - B ≤-450mV, RO will be low.RO 1FUNCTION
NAME Typical Operating Characteristics (continued)
(V CC = +3.6V, T A = +25°C, unless otherwise noted.)
__________ 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-485driver output specifications (1.5V with 54?differential ter-mination). 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 fol-lowing equation expresses this relationship conserva-tively:
Length = t RISE / (10 x 1.5ns/foot)
where t RISE is the transmitter’s rise time.
For example, the MAX3471’s rise time is typically 1.3μs,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 reflec-tions, if the waveform settles out before the UART sam-ples them.
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 cir-cuits over the whole common-mode voltage range (see Typical Operating Characteristics ).
MAX3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems
_______________________________________________________________________________________
7
Table 1. Transmitting
Table 2. Receiving
INPUTS
R E DE DI A X 111X 10000X Z D 1
X
Z D
B 01Z D Z D
OUTPUTS
1
000
INPUTS R E DE RO 0010001Z
A-B ≥-0.05V ≤-0.45V Open/Shorted
X
OUTPUT X = Don’t care
Z = Receiver output high impedance
Figure 1. Driver DC Test Load
Figure 2. Receiver Enable/Disable Timing Test Load Z D = Driver output disabled
Figure 3. Driver Test Circuit
M A X 3471
1.6μA, RS-485/RS-422, Half-Duplex,
Differential T ransceiver for Battery-Powered Systems 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?1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
Figure 4. Driver Enable/Disable Timing Test Load Figure 9. Receiver Propagation Delay and Maximum Data-Rate Test Circuit
Figure 5. Driver Differential Propagation Delay and Rise/Fall Times
Figure 6. Driver Enable and Disable Times
Figure 7. Receiver Propagation Delay
Figure 8. Receiver Enable and Disable Times
___________________Chip Information
TRANSISTOR COUNT: 351