Download MAX3471 1.6µA, RS-485/RS-422, Half-Duplex, Differential Transceiver for Battery-Powered Systems ________________General Description

19-0497; Rev 0; 2/98
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
____________________________Features
♦ 1.6µA Supply Current with Receiver Enabled
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 µMAX package.
♦ 1/8-Unit-Load Receiver Input
________________________Applications
___________________Pin Configuration
♦ +2.5V to +5.5V Single-Supply Operation
♦ True Fail-Safe Receiver Input
♦ Available in µMAX Package
♦ -7V to +10V Common-Mode Input Voltage Range
_______________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX3471CUA
0°C to +70°C
8 µMAX
MAX3471EUA
-40°C to +85°C
8 µMAX
Remote Meter Reading
TOP VIEW
Battery-Powered Differential Communications
Level Translators
RO
1
8
VCC
RE
2
7
B
DE
3
6
A
DI
4
5
GND
MAX3471
µMAX
Typical Application Circuit
VCC
DI
VCC
VCC
B
B
A
A
0.1µF
DE
D
D
DE
RO
RE
B
R
GND
A
B
VCC
GND
DI
DE
RO RE
DI
R
VCC
RO
RE
GND
R
D
REMOTE UNIT
A
R
D
DI
CENTRAL UNIT
DE
RO RE
MAX3471
REMOTE UNIT
REMOTE UNIT
TYPICAL HALF-DUPLEX RS-485 NETWORK
________________________________________________________________ Maxim Integrated Products
1
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For small orders, phone 408-737-7600 ext. 3468.
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MAX3471
________________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.
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
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
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.
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 = +25°C.) (Note 1)
PARAMETER
SYMBOL
Differential Driver Output (no load)
VOD1
Differential Driver Output
(with load)
Change in Magnitude of
Differential Output Voltage
(Note 2)
Driver Common-Mode Output
Voltage
Change in Magnitude of
Common-Mode Voltage (Note 2)
VOD2
CONDITIONS
Figure 1
TYP
R = 750Ω (RS-422)
1.5
3.28
R = 27Ω (RS-485)
0.2
0.83
R = 27Ω (RS-485),
VCC = 5V, TA = +25°C
∆VOD
Figure 1, R = 750Ω or 27Ω
VOC
Figure 1, R = 750Ω or 27Ω
∆VOC
Figure 1, R = 750Ω or 27Ω
Input High Voltage
VIH
DE, DI, RE
Input Low Voltage
VIL
DE, DI, RE
DI Input Hysteresis
VHYS
MAX
UNITS
VCC
V
V
1.5
0.2
0.6 x VCC
0.2
0.7 x VCC
IIN1
DE, DI, RE
IIN2
DE = GND,
VCC = GND or 5.5V
Driver Short-Circuit Output
Current (Note 3)
IOSD
-7V ≤ VOUT ≤ 10V
Receiver Differential Threshold
Voltage
VTH
-7V ≤ VCM ≤ 10V
V
V
±0.001
±1
0.105
VIN = -7V
-0.075
VCC ≤ 3.6V
-60
60
VCC ≤ 5.5V
-130
130
-250
V
mV
VIN = 10V
-450
V
V
0.3 x VCC
100
Input Current (A and B),
Half Duplex
Input Current
MIN
Figure 1 (R = open)
-50
µA
mA
mA
mV
Receiver Input Hysteresis
∆VTH
VCM = 0
Receiver Output High Voltage
VOH
IO = -0.8mA, VID = -50mV
Receiver Output Low Voltage
VOL
IO = 2.2mA, VID = -450mV
0.4
V
Three-State Current at Receiver
Output
IOZR
0 ≤ VO ≤ VCC
±1
µA
Receiver Input Resistance
RIN
-7V ≤ VCM ≤ 10V
2
32
mV
VCC - 0.4
V
96
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kΩ
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
(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)
PARAMETER
Receiver Output Short-Circuit
Current
Supply Current
SYMBOL
IOSR
ICC
CONDITIONS
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
MIN
TYP
MAX
VCC ≤ 3.6V
-20
50
VCC ≤ 5.5V
-40
110
DE = VCC
50
60
DE = GND
1.6
2
DE = VCC
83
100
DE = GND
2.8
4
UNITS
mA
µA
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.)
TYP
MAX
UNITS
Driver Input to Output
Propagation Delay
PARAMETER
SYMBOL
tDPLH,
tDPHL
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF
CONDITIONS
MIN
1.40
2.00
µs
Driver Output Skew
(tDPLH - tDPHL)
tDSKEW
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF
0.025
Driver Rise or Fall Time
tDR, tDF
Figures 3 and 5, RDIFF = 1.5kΩ,
CL1 = CL2 = 100pF
0.75
µs
1.34
1.75
µs
Driver Enable Time to Output
High
tDZH
Figures 4 and 6, CL = 100pF, S2 closed, S1 open
1.5
6.00
µs
Driver Enable Time to Output
Low
tDZL
Figures 4 and 6, CL = 100pF, S1 closed, S2 open
0.86
4.00
µs
Driver Disable Time from Low
tDLZ
Figures 4 and 6, CL = 15pF, S1 closed, S2 open
0.4
1.5
µs
Driver Disable Time from High
tDHZ
Figures 4 and 6, CL = 15pF, S2 closed, S1 open
0.6
1.5
µs
Receiver Input to Output
Propagation Delay
tRPLH
5.2
12
6.4
12
Differential Receiver Skew
(tRPLH - tRPHL)
tRPHL
tRSKEW
Figures 7 and 9, CL = 15pF, |VID| = 2V
1.2
Figures 7 and 9, |VID| = 2V
µs
µs
Data Rate
fMAX
Figure 9, CL = 100pF
64
kbps
Receiver Enable Time to
Output Low
tRZL
Figures 2 and 8, CL = 15pF, S1 closed, S2 open
70
500
ns
Receiver Enable Time to
Output High
tRZH
Figures 2 and 8, CL = 15pF, S2 closed, S1 open
85
500
ns
Receiver Disable Time from Low
tRLZ
Figures 2 and 8, CL = 15pF, S1 closed, S2 open
50
200
ns
Receiver DisableTime from High
tRHZ
Figures 2 and 8, CL = 15pF, S2 closed, S1 open
35
200
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.
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3
MAX3471
DC ELECTRICAL CHARACTERISTICS (continued)
__________________________________________Typical Operating Characteristics
(VCC = +3.6V, TA = +25°C, unless otherwise noted.)
OUTPUT CURRENT vs. RECEIVER
OUTPUT HIGH VOLTAGE
30
VCC = 5V
20
15
VCC = 3.6V
VCC = 5V
12
10
8
6
10
4
5
2
VCC = 3.6V
4.5
4.0
VCC = 3.6V
3.5
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
-50
-25
0
25
50
75
100
125
OUTPUT HIGH VOLTAGE (V)
TEMPERATURE (°C)
RECEIVER OUTPUT LOW
VOLTAGE vs. TEMPERATURE
DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
VCC = 3.6V
80
60
VCC = 5V
40
30
25
20
15
5
0
0
0
25
50
75
100
VCC = 3.6V
10
20
-25
VCC = 5V
MAX3471toc06
1.0
0.8
VCC = 3.6V
0.6
0.4
RDIFF = 54Ω
-50
-25
60
VCC = 5V
3.5
VCC = 3.6V
2.5
2.0
1.5
1.0
25
50
75
100
125
OUTPUT CURRENT vs. DRIVER
OUTPUT LOW VOLTAGE (VCC = 3.6V)
30
VCC = 3.6V
25
OUTPUT CURRENT (mA)
50
OUTPUT CURRENT (mA)
VCC = 5V
0
TEMPERATURE (°C)
OUTPUT CURRENT vs. DRIVER
OUTPUT LOW VOLTAGE (VCC = 5V)
MAX3471toc07
5.0
3.0
VCC = 5V
1.2
DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER DIFFERENTIAL
OUTPUT VOLTAGE vs. TEMPERATURE
4.0
1.4
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
TEMPERATURE (°C)
4.5
1.6
0
0
125
1.8
0.2
MAX3471toc08
100
35
2.0
DIFFERENTIAL OUTPUT VOLTAGE (V)
120
40
MAX3471toc05
MAX3471toc04
LOAD = 2.2mA
40
30
20
20
15
10
5
10
0.5
VCC = 5V
OUTPUT LOW VOLTAGE (V)
140
-50
5.0
3.0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
DRIVER OUTPUT CURRENT (mA)
0
RDIFF = 1.5kΩ
0
0
0
-50
-25
0
25
50
75
TEMPERATURE (°C)
4
LOAD = 0.8mA
0
0
RECEIVER OUTPUT VOLTAGE (mV)
14
MAX3471toc03
16
5.5
MAX3471toc09
25
18
OUTPUT CURRENT (mA)
35
MAX3471toc02
40
OUTPUT CURRENT (mA)
20
MAX3471toc01
45
RECEIVER OUTPUT HIGH
VOLTAGE vs. TEMPERATURE
RECEIVER OUTPUT VOLTAGE (V)
OUTPUT CURRENT
vs. RECEIVER OUTPUT LOW VOLTAGE
DIFFERENTIAL OUTPUT VOLTAGE (V)
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
100
125
0
1
2
3
4
5
6
7
OUTPUT LOW VOLTAGE (V)
8
9
10
0
2
4
6
8
OUTPUT LOW VOLTAGE (V)
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10
12
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
30
25
20
15
10
SUPPLY CURRENT (µA)
20
15
10
80
VCC = 5.5V
70
VCC = 5.0V
MAX3471toc12
VCC = 3.6V
OUTPUT CURRENT (mA)
35
90
MAX3471toc11
VCC = 5V
60
50
VCC = 3.6V
40
30
VCC = 2.5V
20
5
10
5
0
-6
-4
-2
0
2
4
-12
6
-10
-8
-6
-4
-2
0
2
VCC = 5.5V
25
1.5
VCC = 5.0V
2.0
VCC = 3.6V
1.5
VCC = 2.5V
VCC = 3.6V, RDIFF = 1.5kΩ
1.4
PROPAGATION DELAY (µs)
SUPPLY CURRENT (µA)
0
50
75
100
125
DRIVER PROPAGATION DELAY
(tDPHL, tDPLH) vs. TEMPERATURE
MAX3471toc13
3.0
1.0
-25
TEMPERATURE (°C)
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (DE = GND)
2.5
-50
4
OUTPUT HIGH VOLTAGE (V)
OUTPUT HIGH VOLTAGE (V)
0.5
MAX3471toc14
-8
VCC = 5V, RDIFF = 1.5kΩ
1.3
1.2
1.1
VCC = 5V, RDIFF = 54Ω
1.0
VCC = 3.6V, RDIFF = 54Ω
0.9
0.8
CL1 = CL2 = 100pF
DE = GND
0
0.7
-50
-25
0
25
50
75
100
125
-40
-20
0
TEMPERATURE (°C)
RECEIVER PROPAGATION
DELAY (tPLH) vs. TEMPERATURE
VCC = 3.6V
4
VCC = 5V
3
2
-20
0
20
80
100
7.0
VCC = 3.6V
6.5
6.0
5.5
5.0
VCC = 5V
4.5
4.0
CIRCUIT OF FIGURE 9
CL = 100pF
|VID| = 2V
-40
60
7.5
PROPAGATION DELAY (µs)
5
0
40
RECEIVER PROPAGATION
DELAY (tPHL) vs. TEMPERATURE
MAS3471toc15
6
1
20
TEMPERATURE (°C)
MAX3471toc16
-12 -10
DE = VCC
0
0
PROPAGATION DELAY (µs)
OUTPUT CURRENT (mA)
25
MAX3471toc10
45
40
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (DE = VCC)
OUTPUT CURRENT vs. DRIVER
OUTPUT HIGH VOLTAGE (VCC = 3.6V)
OUTPUT CURRENT vs. DRIVER
OUTPUT HIGH VOLTAGE (VCC = 5V)
|VID| = 2V
3.5
CL = 100pF
3.0
40
60
TEMPERATURE (°C)
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
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5
MAX3471
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +25°C, unless otherwise noted.)
MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
Typical Operating Characteristics (continued)
(VCC = +3.6V, TA = +25°C, unless otherwise noted.)
DRIVER PROPAGATION DELAY
RECEIVER PROPAGATION DELAY
MAX3471toc17
MAX3471toc18
B
A
(2V/div)
(2V/div)
A
B
DI
(2V/div)
DI
(2V/div)
A-B
(2V/div)
RO
(2V/div)
A-B
(1V/div)
400ns/div
1µs/div
R = 1.5kΩ, CL = 100pF
______________________________________________________________Pin Description
PIN
NAME
FUNCTION
1
RO
Receiver Output. When RE is low, if A - B ≥ -50mV, RO will be high; if A - B ≤ -450mV, RO will be low.
2
RE
Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high.
3
DE
Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high impedance when
DE is low.
4
DI
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.
5
GND
6
A
Noninverting Driver Output and Noninverting Receiver Input
7
B
Inverting Driver Output and Inverting Receiver Input
8
VCC
Ground
Positive Supply: +2.5V ≤ VCC ≤ +5.5V
_______________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 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.
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1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
Table 2. Receiving
INPUTS
OUTPUTS
INPUTS
OUTPUT
RE
DE
DI
B
A
RE
DE
A-B
RO
X
1
1
0
1
0
0
≥ -0.05V
1
X
1
0
1
0
0
0
≤ -0.45V
0
0
0
X
ZD
ZD
0
0
Open/Shorted
1
1
0
X
ZD
ZD
1
0
X
Z
ZD = Driver output disabled
MAX3471
Table 1. Transmitting
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 54Ω differential termination). See the Typical Operating Characteristics.
A
R
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 1.3µs,
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).
VOD
R
VOC
B
Figure 1. Driver DC Test Load
VCC
S1
RECEIVER
OUTPUT
TEST
POINT
VCC
DE
1k
CL1
A
DI
CL
S2
Figure 2. Receiver Enable/Disable Timing Test Load
VO
DRIVER
RDIFF
B
CL2
Figure 3. Driver Test Circuit
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MAX3471
1.6µA, RS-485/RS-422, Half-Duplex,
Differential Transceiver for Battery-Powered Systems
V CC
DI
0V
VCC
S1
V CC
2
V CC
2
t DPLH
12k
B
OUTPUT
UNDER TEST
t DPHL
VO
A
1/2 V O
1/2 V O
CL
V DIFF = V (A) - V (B)
VO
VDIFF 0V
-VO
S2
90%
10%
90%
t DR
10%
t DF
t DSKEW = (t DPLH - t DPHL )
Figure 4. Driver Enable/Disable Timing Test Load
V CC
DE
0V
V CC
2
V CC
2
t DZL
t DLZ
V CC
2 OUTPUT NORMALLY LOW
V TEST
A, B
VOL
VOL + 0.5V
1.4V
1.4V
OUTPUT
t RPHL
t RPLH
A
INPUT
VOH - 0.5V
V CC
2
t DZH
t DHZ
| V ID | = 2V
t RSKEW = (t RPLH = t RPHL )
V TEST = 0.91V CC
Figure 7. Receiver Propagation Delay
Figure 6. Driver Enable and Disable Times
V CC
RE
0V
V OH
RO
V OL
B
OUTPUT NORMALLY HIGH
VOH
A, B
0V
Figure 5. Driver Differential Propagation Delay and Rise/Fall Times
V CC
2
V CC
2
t RZL
t RLZ
VCC
RO
VOL
1.4V
OUTPUT NORMALLY LOW
VOH
RO
0V
OUTPUT NORMALLY HIGH
A
RECEIVER
OUTPUT
RECEIVER
CL
VOL + 0.5V
VOH - 0.5V
1.4V
t RZH
B
VID
t RHZ
RE
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
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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