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________________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 VCC 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
♦1.6µA Supply Current with Receiver Enabled
♦+2.5V to +5.5V Single-Supply Operation
♦True Fail-Safe Receiver Input
♦Available in µMAX Package
♦1/8-Unit-Load Receiver Input
♦-7V to +10V Common-Mode Input Voltage Range
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
VCC
B
A
GNDDI
DE
RE
RO
MAX3471
µMAX
TOP VIEW
___________________Pin Configuration
MAX3471
B
A
B
A
R
DI
VCC
VCC GND
GND
REMOTE UNIT
DE
RO
D
RE R
DE
DI
RO
D
RE
R
DI DE
D
BA
RERO
TYPICAL HALF-DUPLEX RS-485 NETWORK
R
DI DE
D
BA
RERO
VCC GND
VCC
VCC 0.1µF
CENTRAL UNIT
REMOTE UNIT
REMOTE UNIT
19-0497; Rev 0; 2/98
PART
MAX3471CUA
MAX3471EUA -40°C to +85°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
8 µMAX
8 µMAX
_______________Ordering Information
Typical Application Circuit
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS (Note 1)
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= +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 (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
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
VIN = 10V
VIN = -7V -0.075
VCC ≤5.5V
Figure 1
-130 130
Figure 1 (R = open)
IO = 2.2mA, VID = -450mV
IO = -0.8mA, VID = -50mV
VCM = 0
DE, DI, RE
-7V ≤VCM ≤10V
VCC ≤3.6V
DE, DI, RE
Figure 1, R = 750Ωor 27Ω
Figure 1, R = 750Ωor 27Ω
DE = GND,
VCC = GND or 5.5V
Figure 1, R = 750Ωor 27Ω
DE, DI, RE
CONDITIONS
V0.4VOL
Receiver Output Low Voltage VVCC - 0.4VOH
Receiver Output High Voltage mV32∆VTH
Receiver Input Hysteresis
mV-450 -250 -50VTH
Receiver Differential Threshold
Voltage
mA
-60 60
IOSD
Driver Short-Circuit Output
Current (Note 3)
mA
0.105
IIN2
Input Current (A and B),
Half Duplex
µA±0.001 ±1IIN1
Input Current
0.2 0.83 V
1.5 3.28
VOD2
VVCC
VOD1
Differential Driver Output (no load)
Differential Driver Output
(with load)
mV100VHYS
DI Input Hysteresis V0.3 x VCC
VIL
Input Low Voltage V0.7 x VCC
VIH
Input High Voltage
V0.2∆VOC
Change in Magnitude of
Common-Mode Voltage (Note 2)
1.5
V0.2∆VOD
Change in Magnitude of
Differential Output Voltage
(Note 2)
V0.6 x VCC
VOC
Driver Common-Mode Output
Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
R = 750Ω(RS-422)
R = 27Ω(RS-485)
R = 27Ω(RS-485),
VCC = 5V, TA= +25°C
0 ≤VO≤VCC µA±1IOZR
Three-State Current at Receiver
Output
-7V ≤VCM ≤10V kΩ
96RIN
Receiver Input Resistance
-7V ≤VOUT ≤10V
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 Transceiver for Battery-Powered Systems
_______________________________________________________________________________________ 3
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= +25°C.) (Note 1)
SWITCHING CHARACTERISTICS
(VCC = +2.5V to +5.5V, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.6V and TA= +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: ∆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.
0 ≤VRO ≤VCC
CONDITIONS -20 50 UNITSMIN TYP MAXSYMBOLPARAMETER VCC ≤3.6V mAIOSR
Receiver Output Short-Circuit
Current
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF
CONDITIONS
µs0.025tDSKEW
Driver Output Skew
(tDPLH - tDPHL)
µs
Driver Input to Output
Propagation Delay
UNITSMIN TYP MAXSYMBOLPARAMETER
tDPLH,
tDPHL 1.40 2.00
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF µs0.75 1.34 1.75tDR, tDF
Driver Rise or Fall Time
Figures 4 and 6, CL= 100pF, S2 closed, S1 open µs1.5 6.00tDZH
Driver Enable Time to Output
High
Figures 4 and 6, CL= 100pF, S1 closed, S2 open µs0.86 4.00tDZL
Driver Enable Time to Output
Low
Figures 4 and 6, CL= 15pF, S1 closed, S2 open µs0.4 1.5tDLZ
Driver Disable Time from Low Figures 4 and 6, CL= 15pF, S2 closed, S1 open µs0.6 1.5tDHZ
Driver Disable Time from High
Figures 7 and 9, CL= 15pF, |VID|= 2V µs
6.4 12tRPHL
Receiver Input to Output
Propagation Delay
Figures 7 and 9, |VID|= 2V µs1.2tRSKEW
Differential Receiver Skew
(tRPLH - tRPHL)
Figure 9, CL= 100pF kbps64fMAX
Data Rate
Figures 2 and 8, CL= 15pF, S2 closed, S1 open ns85 500tRZH
Receiver Enable Time to
Output High
Figures 2 and 8, CL= 15pF, S1 closed, S2 open ns50 200tRLZ
Receiver Disable Time from Low Figures 2 and 8, CL= 15pF, S2 closed, S1 open ns35 200tRHZ
Receiver DisableTime from High
VCC ≤5.5V -40 110
DE = VCC
µAICC
Supply Current
VCC ≤3.6V, no load,
RE = DI = GND or VCC,
VA= VB= 0
50 60
DE = GND 1.6 2
DE = VCC
VCC ≤5.5V, no load,
RE = DI = GND or VCC,
VA= VB= 0
83 100
DE = GND 2.8 4
Figures 2 and 8, CL= 15pF, S1 closed, S2 open ns70 500tRZL
Receiver Enable Time to
Output Low
tRPLH 5.2 12
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
4_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(VCC = +3.6V, TA = +25°C, unless otherwise noted.)
0
15
5
10
20
35
40
30
25
45
0 0.4 0.6 0.8 1.00.2 1.2 1.4 1.6 1.8 2.0
OUTPUT CURRENT
vs. RECEIVER OUTPUT LOW VOLTAGE
MAX3471toc01
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 3.6V
VCC = 5V
0
4
2
8
6
12
10
14
18
16
20
0 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
MAX3471toc02
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 3.6V
VCC = 5V
3.0
3.5
4.5
4.0
5.0
5.5
-50 0-25 25 50 75 100 125
RECEIVER OUTPUT HIGH
VOLTAGE vs. TEMPERATURE
MAX3471toc03
TEMPERATURE (°C)
RECEIVER OUTPUT VOLTAGE (V)
LOAD = 0.8mA
VCC = 5V
VCC = 3.6V
0
40
20
80
60
120
100
140
-50 0 25-25 50 75 100 125
RECEIVER OUTPUT LOW
VOLTAGE vs. TEMPERATURE
MAX3471toc04
TEMPERATURE (°C)
RECEIVER OUTPUT VOLTAGE (mV)
LOAD = 2.2mA
VCC = 3.6V
VCC = 5V
0
1.5
1.0
0.5
2.5
2.0
4.5
4.0
3.5
3.0
5.0
-50 -25 0 25 50 75 100 125
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
MAX3471toc07
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE (V)
RDIFF = 1.5kΩ
VCC = 3.6V
VCC = 5V
0
10
5
15
30
35
25
20
40
0 1.0 1.5 2.0 2.50.5 3.0 3.5 4.0 4.5 5.0
DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
MAX3471toc05
DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER OUTPUT CURRENT (mA)
VCC = 3.6V
VCC = 5V
0
0.6
0.4
0.2
1.0
0.8
1.8
1.6
1.4
1.2
2.0
-50 -25 0 25 50 75 100 125
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
MAX3471toc06
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE (V)
RDIFF = 54Ω
VCC = 3.6V
VCC = 5V
0
30
20
10
40
50
60
0 431 2 5 6 7 8 9 10
OUTPUT CURRENT vs. DRIVER
OUTPUT LOW VOLTAGE (VCC = 5V)
MAX3471toc08
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 5V
0
10
5
20
15
25
30
0 4 62 8 10 12
OUTPUT CURRENT vs. DRIVER
OUTPUT LOW VOLTAGE (VCC = 3.6V)
MAX3471toc09
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 3.6V
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
_______________________________________________________________________________________
5
0
10
5
25
20
15
35
40
30
45
-12 -6 -4-10 -8 -2 0 2 4 6
OUTPUT CURRENT vs. DRIVER
OUTPUT HIGH VOLTAGE (VCC = 5V)
MAX3471toc10
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 5V
0
5
15
10
20
25
-12 -8 -6-10 -4 -2 0 2 4
OUTPUT CURRENT vs. DRIVER
OUTPUT HIGH VOLTAGE (VCC = 3.6V)
MAX3471toc11
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 3.6V
0
20
10
50
40
30
80
70
60
90
-50 0 25-25 50 75 100 125
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (DE = VCC)
MAX3471toc12
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = 2.5V
DE = VCC
VCC = 3.6V
VCC = 5.5V
VCC = 5.0V
0
1.0
0.5
2.0
1.5
2.5
3.0
-50 25 50-25 0 75 100 125
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (DE = GND)
MAX3471toc13
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = 2.5V
DE = GND
VCC = 3.6V
VCC = 5.5V
VCC = 5.0V
0
2
1
4
3
5
6
-40 20 40-20 0 60 80 100
RECEIVER PROPAGATION
DELAY (tPLH) vs. TEMPERATURE
MAS3471toc15
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 5V
VCC = 3.6V
CIRCUIT OF FIGURE 9
CL = 100pF
|VID| = 2V
0.7
0.9
0.8
1.1
1.0
1.4
1.3
1.2
1.5
-40 0-20 20 40 60 80 100
DRIVER PROPAGATION DELAY
(tDPHL, tDPLH) vs. TEMPERATURE
MAX3471toc14
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 3.6V, RDIFF = 1.5kΩ
VCC = 5V, RDIFF = 1.5kΩ
VCC = 5V, RDIFF = 54Ω
VCC = 3.6V, RDIFF = 54Ω
CL1 = CL2 = 100pF
3.0
4.0
3.5
5.0
4.5
6.5
6.0
5.5
7.5
7.0
-40 0-20 20 40 60 80 100
RECEIVER PROPAGATION
DELAY (tPHL) vs. TEMPERATURE
MAX3471toc16
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 3.6V
VCC = 5V
|VID| = 2V
CL = 100pF
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +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.
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
6_______________________________________________________________________________________
______________________________________________________________Pin Description
RECEIVER PROPAGATION DELAY
MAX3471toc17 B
DI
(2V/div)
(2V/div)
A-B
(2V/div)
RO
(2V/div)
A
1µs/div
DRIVER PROPAGATION DELAY
MAX3471toc18
B
DI
(2V/div)
(2V/div)
A-B
(1V/div)
A
400ns/div
R = 1.5kΩ, CL = 100pF
GroundGND5 Noninverting Driver Output and Noninverting Receiver InputA6 Inverting Driver Output and Inverting Receiver InputB7 Positive Supply: +2.5V ≤VCC ≤+5.5VVCC
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.
DI4
Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high impedance when
DE is low.
DE3
PIN
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.
RO1
FUNCTIONNAME
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +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-485
driver output specifications (1.5V with 54Ωdifferential 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 = tRISE / (10 x 1.5ns/foot)
where tRISE 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 Transceiver for Battery-Powered Systems
_______________________________________________________________________________________ 7
Table 1. Transmitting Table 2. Receiving
INPUTS
RREEDE DI A
X 1 1 1
X 1 0 0
0 0 X ZD
1 0 X ZD
B
0
1
ZD
ZD
OUTPUTS
1
0 0
0
INPUTS
RREEDE RO
0 0 1
0
0 0 1
Z
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
S2
1k
CL
RECEIVER
OUTPUT
VCC
S1
TEST
POINT
Figure 2. Receiver Enable/Disable Timing Test Load
ZD= Driver output disabled
A
R
R
B
VOD
VOC
DE
DI
A
B
DRIVER VO
VCC
RDIFF
CL1
CL2
Figure 3. Driver Test Circuit
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver 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.
S2
12k
CL
VCC
S1
OUTPUT
UNDER TEST
Figure 4. Driver Enable/Disable Timing Test Load
A
B
CL
RE
VID RECEIVER
OUTPUT
RECEIVER
Figure 9. Receiver Propagation Delay and Maximum Data-
Rate Test Circuit
10% 10%
A
0V
DIVCC
0V
VO
VDIFF -VO
B
tDPLH
tDR tDF
VDIFF = V(A) - V(B)
tDSKEW = (tDPLH - tDPHL)
tDPHL
VO
1/2 VO1/2 VO
90% 90%
VCC
2 VCC
2
Figure 5. Driver Differential Propagation Delay and Rise/Fall Times
0V
DEVCC
VTEST
VTEST = 0.91VCC
0V
A, B
VOL
VOH
VOL + 0.5V
VOH - 0.5V
A, B
tDHZ
tDLZ
tDZL
tDZH
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY LOW
VCC
2
VCC
2
VCC
2
VCC
2
Figure 6. Driver Enable and Disable Times
AINPUT
OUTPUT
B
tRPHL
|VID| = 2V
tRSKEW = (tRPLH = tRPHL)
VOL
VOH
RO
tRPLH
1.4V 1.4V
Figure 7. Receiver Propagation Delay
0V
VCC
0V
RO
VCC
VOL
VOH
VOL + 0.5V
VOH - 0.5V
RO
tRHZ
tRLZ
tRZL
tRZH
1.4V
1.4V
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY LOW
VCC
2 VCC
2
RE
Figure 8. Receiver Enable and Disable Times
___________________Chip Information
TRANSISTOR COUNT: 351
