Page 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.
________________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 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 VCCor
below GND, internal circuitry prevents battery backcharging.
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,
Differ ential T ransceiver for Battery-Powered Systems
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
V
CC
B
A
GNDDI
DE
RE
RO
MAX3471
µMAX
TOP VIEW
___________________Pin Configuration
MAX3471
B
A
B
A
R
DI
V
CC
V
CC
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
V
CC
GND
V
CC
V
CC
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
Page 2
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential T ransceiver for Battery-Powered Systems
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS (Note 1)
DC ELECTRICAL CHARACTERISTICS
(VCC= +2.5V to +5.5V, TA= T
MIN
to T
MAX
, 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 (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
VIN= 10V
VIN= -7V -0.075
V
CC
≤ 5.5V
Figure 1
-130 130
Figure 1 (R = open)
IO = 2.2mA, VID= -450mV
IO = -0.8mA, VID= -50mV
V
CM
= 0
DE, DI, RE
-7V ≤ VCM≤ 10V
V
CC
≤ 3.6V
DE, DI, RE
Figure 1, R = 750Ω or 27Ω
Figure 1, R = 750Ω or 27Ω
DE = GND,
VCC= GND or 5.5V
Figure 1, R = 750Ω or 27Ω
DE, DI, RE
CONDITIONS
V0.4V
OL
Receiver Output Low Voltage
VVCC- 0.4V
OH
Receiver Output High Voltage
mV32∆V
TH
Receiver Input Hysteresis
mV-450 -250 -50V
TH
Receiver Differential Threshold
Voltage
mA
-60 60
I
OSD
Driver Short-Circuit Output
Current (Note 3)
mA
0.105
I
IN2
Input Current (A and B),
Half Duplex
µA±0.001 ±1I
IN1
Input Current
0.2 0.83
V
1.5 3.28
V
OD2
VV
CC
V
OD1
Differential Driver Output (no load)
Differential Driver Output
(with load)
mV100V
HYS
DI Input Hysteresis
V0.3 x V
CC
V
IL
Input Low Voltage
V0.7 x V
CC
V
IH
Input High Voltage
V0.2∆V
OC
Change in Magnitude of
Common-Mode Voltage (Note 2)
1.5
V0.2∆V
OD
Change in Magnitude of
Differential Output Voltage
(Note 2)
V0.6 x V
CC
V
OC
Driver Common-Mode Output
Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
R = 750Ω (RS-422)
R = 27Ω (RS-485)
R = 27Ω (RS-485),
V
CC
= 5V, TA= +25°C
0 ≤ VO≤ V
CC
µA±1I
OZR
Three-State Current at Receiver
Output
-7V ≤ VCM≤ 10V
kΩ
96R
IN
Receiver Input Resistance
-7V ≤ V
OUT
≤ 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.
Page 3
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential T ransceiver for Battery-Powered Systems
_______________________________________________________________________________________ 3
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC= +2.5V to +5.5V, TA= T
MIN
to T
MAX
, 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= T
MIN
to T
MAX
, 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: ∆V
OD
and ∆VOCare the changes in magnitude of VODand 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≤ V
CC
CONDITIONS
-20 50
UNITSMIN TYP MAXSYMBOLPARAMETER
V
CC
≤ 3.6V
mAI
OSR
Receiver Output Short-Circuit
Current
Figures 3 and 5, R
DIFF
= 1.5kΩ,
C
L1
= CL2= 100pF
Figures 3 and 5, R
DIFF
= 1.5kΩ,
C
L1
= CL2= 100pF
CONDITIONS
µs0.025t
DSKEW
Driver Output Skew
(t
DPLH
- t
DPHL
)
µs
Driver Input to Output
Propagation Delay
UNITSMIN TYP MAXSYMBOLPARAMETER
t
DPLH,
t
DPHL
1.40 2.00
Figures 3 and 5, R
DIFF
= 1.5kΩ,
C
L1
= CL2= 100pF
µs0.75 1.34 1.75tDR, t
DF
Driver Rise or Fall Time
Figures 4 and 6, CL= 100pF, S2 closed, S1 open µs1.5 6.00t
DZH
Driver Enable Time to Output
High
Figures 4 and 6, CL= 100pF, S1 closed, S2 open µs0.86 4.00t
DZL
Driver Enable Time to Output
Low
Figures 4 and 6, CL= 15pF, S1 closed, S2 open µs0.4 1.5t
DLZ
Driver Disable Time from Low
Figures 4 and 6, CL= 15pF, S2 closed, S1 open µs0.6 1.5t
DHZ
Driver Disable Time from High
Figures 7 and 9, CL= 15pF, |V
ID
|
= 2V
µs
6.4 12t
RPHL
Receiver Input to Output
Propagation Delay
Figures 7 and 9, |V
ID
|
= 2V
µs1.2t
RSKEW
Differential Receiver Skew
(t
RPLH
- t
RPHL
)
Figure 9, CL= 100pF kbps64f
MAX
Data Rate
Figures 2 and 8, CL= 15pF, S2 closed, S1 open ns85 500t
RZH
Receiver Enable Time to
Output High
Figures 2 and 8, CL= 15pF, S1 closed, S2 open ns50 200t
RLZ
Receiver Disable Time from Low
Figures 2 and 8, CL= 15pF, S2 closed, S1 open ns35 200t
RHZ
Receiver DisableTime from High
V
CC
≤ 5.5V -40 110
DE = V
CC
µAI
CC
Supply Current
V
CC
≤ 3.6V, no load,
RE = DI = GND or V
CC
,
V
A
= VB= 0
50 60
DE = GND 1.6 2
DE = V
CC
V
CC
≤ 5.5V, no load,
RE = DI = GND or V
CC
,
V
A
= VB= 0
83 100
DE = GND 2.8 4
Figures 2 and 8, CL= 15pF, S1 closed, S2 open ns70 500t
RZL
Receiver Enable Time to
Output Low
t
RPLH
5.2 12
Page 4
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential T ransceiver 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)
R
DIFF
= 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)
R
DIFF
= 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 (V
CC
= 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 (V
CC
= 3.6V)
MAX3471toc09
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
VCC = 3.6V
Page 5
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential T ransceiver 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 (V
CC
= 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 (V
CC
= 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 = V
CC
)
MAX3471toc12
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = 2.5V
DE = V
CC
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 (t
PLH
) vs. TEMPERATURE
MAS3471toc15
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 5V
VCC = 3.6V
CIRCUIT OF FIGURE 9
C
L
= 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
(t
DPHL
, t
DPLH
) vs. TEMPERATURE
MAX3471toc14
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 3.6V, R
DIFF
= 1.5kΩ
VCC = 5V, R
DIFF
= 1.5kΩ
VCC = 5V, R
DIFF
= 54Ω
VCC = 3.6V, R
DIFF
= 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 (t
PHL
) vs. TEMPERATURE
MAX3471toc16
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC = 3.6V
VCC = 5V
|VID| = 2V
C
L
= 100pF
Typical Operating Characteristics (continued)
(VCC= +3.6V, TA = +25°C, unless otherwise noted.)
Page 6
_______________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 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.
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential 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 = 1.5kΩ, C
L
= 100pF
GroundGND5
Noninverting Driver Output and Noninverting Receiver InputA6
Inverting Driver Output and Inverting Receiver InputB7
Positive Supply: +2.5V ≤ VCC≤ +5.5VV
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.
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
2
Receiver 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.)
Page 7
__________ 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 54Ω 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 = 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 reflections, if the waveform settles out before the UART samples 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 circuits over the whole common-mode voltage range (see
Typical Operating Characteristics
).
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential T ransceiver for Battery-Powered Systems
_______________________________________________________________________________________ 7
Table 1. Transmitting Table 2. Receiving
INPUTS
RREE
DE DI A
X 1 1 1
X 1 0 0
0 0 X Z
D
1 0 X Z
D
B
0
1
Z
D
Z
D
OUTPUTS
1
0 0
0
INPUTS
RREE
DE 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
C
L
RECEIVER
OUTPUT
V
CC
S1
TEST
POINT
Figure 2. Receiver Enable/Disable Timing Test Load
ZD= Driver output disabled
A
R
R
B
V
OD
V
OC
Figure 3. Driver Test Circuit
V
CC
DE
DI
DRIVER
C
A
V
O
R
DIFF
B
L1
C
L2
Page 8
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differ ential 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.
S2
12k
C
L
V
CC
S1
OUTPUT
UNDER TEST
Figure 4. Driver Enable/Disable Timing Test Load
A
B
C
L
RE
V
ID
RECEIVER
OUTPUT
RECEIVER
Figure 9. Receiver Propagation Delay and Maximum DataRate Test Circuit
10% 10%
A
0V
DI
V
CC
0V
V
O
V
DIFF
-V
O
B
t
DPLH
t
DR
t
DF
V
DIFF
= V
(A)
- V
(B)
t
DSKEW = (tDPLH - tDPHL
)
t
DPHL
V
O
1/2 V
O
1/2 V
O
90% 90%
V
CC
2
V
CC
2
Figure 5. Driver Differential Propagation Delay and Rise/Fall Times
0V
DE
V
CC
V
TEST
V
TEST
= 0.91V
CC
0V
A, B
V
OL
V
OH
V
OL +
0.5V
V
OH -
0.5V
A, B
t
DHZ
t
DLZ
t
DZL
t
DZH
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY LOW
V
CC
2
V
CC
2
V
CC
2
V
CC
2
Figure 6. Driver Enable and Disable Times
A
INPUT
OUTPUT
B
t
RPHL
|VID|
= 2V
t
RSKEW
= (t
RPLH
= t
RPHL
)
V
OL
V
OH
R
O
t
RPLH
1.4V 1.4V
Figure 7. Receiver Propagation Delay
0V
V
CC
0V
RO
V
CC
V
OL
V
OH
V
OL
+ 0.5V
V
OH
- 0.5V
RO
t
RHZ
t
RLZ
t
RZL
t
RZH
1.4V
1.4V
OUTPUT NORMALLY HIGH
OUTPUT NORMALLY LOW
V
CC
2
V
CC
2
RE
Figure 8. Receiver Enable and Disable Times
___________________Chip Information
TRANSISTOR COUNT: 351
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