Maxim MAX3098EAESE ±15kv esd-protected, 32mbps, 3v/5v, triple rs-422/rs-485 receivers with fault detection Datasheet

19-1727; Rev 0; 7/00
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
Features
♦ Detects the Following RS-485 Faults:
Open-Circuit Condition
Short-Circuit Condition
Low Differential Voltage Signal
Common-Mode Range Violation
The fault circuitry includes a capacitor-programmable
delay to ensure that there are no erroneous fault conditions even at slow edge rates. Each receiver is capable
of accepting data at rates up to 32Mbps.
♦ Single +3V to +5.5V Operation
________________________Applications
♦ Independent and Universal Fault Outputs
RS-485/RS-422 Receivers for Motor-Shaft
Encoders
High-Speed, Triple RS-485/RS-422 Receiver with
Extended Electrostatic Discharge (ESD)
♦ ESD Protection
±15kV—Human Body Model
±15kV—IEC 1000-4-2, Air-Gap Discharge
Method
±8kV—IEC 1000-4-2, Contact Discharge Method
♦ -10V to +13.2V Extended Common-Mode Range
♦ Capacitor-Programmable Delay of Fault Indication
Allows Error-Free Operation at Slow Data Rates
♦ 32Mbps Data Rate
♦ 16-Pin QSOP is 40% Smaller than IndustryStandard 26LS31/32 Solutions
Ordering Information
Triple RS-485/RS-422 Receiver with Input Fault
Indication
PART
Telecommunications
PINPACKAGE
TEMP. RANGE
Embedded Systems
Typical Application Circuit
MAX3097ECEE
0°C to +70°C
16 QSOP
MAX3097ECSE
0°C to +70°C
16 SO
Ordering Information continued at end of data sheet.
ENCODED SIGNALS
Pin Configuration
A, A, B, B, Z, Z
TOP VIEW
MAX3097E
MAX3098E
RECEIVER
OUTPUTS
ALARM
OUTPUTS
DSP
8
MOTOR
MOTOR
CONTROLLER
A 1
16 VCC
A 2
15 ALARMA
B 3
14 OUTA
B 4
Z 5
MAX547
12-BIT D/A
MAX3097E
MAX3098E
Z 6
13 ALARMB
12 OUTB
11 ALARMZ
GND 7
10 OUTZ
DELAY 8
9
ALARMD
MOTOR DRIVER
QSOP/SO/DIP
________________________________________________________________ Maxim Integrated Products
1
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For small orders, phone 1-800-835-8769.
MAX3097E/MAX3098E
General Description
The MAX3097E/MAX3098E feature three high-speed RS485/RS-422 receivers with fault-detection circuitry and
fault-status outputs. The receivers’ inputs have fault
thresholds that detect when the part is not in a valid state.
The MAX3097E/MAX3098E indicate when a receiver
input is in an open-circuit condition, short-circuit condition, or outside the common-mode range. They also
generate a fault indication when the differential input
voltage goes below a preset threshold. See Ordering
Information or the Electrical Characteristics for threshold values.
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC).............................................................+7V
Receiver Input Voltage (A, A, B, B, Z, Z) .............................±25V
Output Voltage (OUT_, ALARM_)...............-0.3V to (VCC + 0.3V)
DELAY ........................................................-0.3V to (VCC + 0.3V)
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW
16-Pin SO (derate 8.7mW/°C above +70°C).................696mW
16-Pin Plastic DIP (derate 10.53mW/°C
above +70°C).............................................................762mW
Operating Temperature Ranges
MAX3097EC_E...................................................0°C to +70°C
MAX3098E_C_E .................................................0°C to +70°C
MAX3097E_E_E ..............................................-40°C to +85°C
MAX3098E_E_E ..............................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
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.
ELECTRICAL CHARACTERISTICS
(VCC = +3V to +5.5V, TA = TMIN to TMAX , unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
Supply Voltage Range
Supply Current
Receiver Differential Threshold
Voltage (Note 1)
Receiver Input Hysteresis
SYMBOL
VCC
ICC
No load
VTH
-10V ≤ VCM ≤ 13.2V
∆VTH
-10V ≤ VCM ≤ 13.2V
Output High Voltage
VOH
Output Low Voltage
VOL
Receiver Input Resistance
RIN
Input Current
(A , A , B , B (Z , Z )
Output Short-Circuit Current
CONDITIONS
IIN
IOSR
MIN
3
TYP
MAX
5.5
UNITS
V
3.1
4.0
mA
+200
mV
-200
40
VCC = 4.75V, IO = -4mA, VID = 200mV
VCC - 1.5
VCC = 3.0V, IO = -1mA, VID = 200mV
VCC - 1.0
mV
V
VCC = 4.75V, IO = +4mA, VID = -200mV
0.4
VCC = 3.0V, IO = +1mA, VID = -200mV
0.4
-10V ≤ VCM ≤ 13.2V
VCC = 0 or 5.5V
90
160
VIN = 13.2V
(Note 2)
0.07
0.14
VIN = -10V
(Note 2)
-0.05
-0.11
V
kΩ
mA
0 ≤ VRO ≤ VCC
±105
mA
FAULT DETECTION
2
MAX3097E Fault-Detection
Receiver Differential Threshold
Voltage (Note 3)
FDIFH
MAX3098EA Fault-Detection
Receiver Differential Threshold
Voltage (Note 3)
FDIFH
High limit
275
475
Low limit
-475
-275
High limit
0.12
0.20
Low limit
-0.20
-0.12
VCM = 0
FDIFL
mV
VCM = 0
FDIFL
V
_______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
(VCC = +3V to +5.5V, TA = TMIN to TMAX , unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MAX3098EB Fault-Detection
Receiver Differential Threshold
Voltage (Note 3)
FDIFH
Fault-Detection Common-Mode
Voltage Range (Note 4)
FCMH
High limit
FCML
Low limit
MIN
TYP
MAX
High limit
70
250
Low limit
-250
-70
VCM = 0
mV
FDIFL
DELAY Current Source
13.2
-10
VCC = 5V, VDELAY = 0
DELAY Threshold
UNITS
9
10
11
VCC = 3V
1.55
1.73
1.90
VCC = 5V
3.1
3.29
3.5
V
µA
V
ESD PROTECTION
ESD Protection
(A, A, B, B, Z, Z)
Human Body Model
±15
IEC1000-4-2 (Air-Gap Discharge)
±15
IEC1000-4-2 (Contact Discharge)
±8
kV
SWITCHING CHARACTERISTICS
(VCC = +3V to +5.5V, VID = ±3.0V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
Propagation Delay from Input to
Output
Receiver Skew |tPLH - tPHL|
SYMBOL
tPLH, tPHL
tSKEW
Channel-to-Channel
Propagation Delay Skew
Maximum Data Rate
fMAX
CONDITIONS
CL = 15pF,
Figures 1, 2
MIN
TYP
MAX
VCC = 4.5V to 5.5V
75
VCC = 3.0V to 3.6V
85
UNITS
ns
CL = 15pF, Figures 1, 2
±10
ns
CL = 15pF, Figures 1, 2
±10
ns
CL = 15pF, Figure 1
32
Mbps
FAULT DETECTION
Differential Fault Propagation
Delay to Output (Note 5)
tDFLH
µs
1.2
tDFHL
Minimum Differential Slew Rate
to Avoid False Alarm Output
Common-Mode Fault
Propagation Delay to Output
(Note 5)
15
CLF = 15pF, Figures 1, 3
MAX3097E (Note 6)
1.0
MAX3098E (Note 7)
0.33
V/µs
tCMFLH
15
CL = 15pF, Figures 1, 4
tCMFHL
µs
1.5
VCM is the common-mode input voltage. VID is the differential input voltage.
VIN is the input voltage at pins A, A, B, B, Z, Z.
A differential terminating resistor is required for proper function of open-circuit fault detection (see Applications Information).
See Applications Information for a discussion of the receiver common-mode voltage range and the operating conditions for
fault indication.
Note 5: Applies to the individual channel immediate-fault outputs (ALARM_) and the general delayed-fault output (ALARMD) when
there is no external capacitor at DELAY.
Note 6: Equivalent pulse test: 1.3V / (tDFLH - tDFHL) ≥ SRD.
Note 7: Equivalent pulse test: 0.62V / (tDFLH - tDFHL) ≥ SRD.
Note 1:
Note 2:
Note 3:
Note 4:
_______________________________________________________________________________________
3
MAX3097E/MAX3098E
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Typical values are at VCC = +5V and TA = +25°C.)
VCC = 5V
VCC = 3V
1
10
100
1000
50
VCC = 5.0V
40
10,000
4
VCC = 5.0V
3
VCC = 3.3V
2
1
0
-40
-20
0
20
40
60
-40
80
-20
0
20
40
60
TEMPERATURE (°C)
RECEIVER OUTPUT LOW VOLTAGE
vs. OUTPUT CURRENT
RECEIVER OUTPUT HIGH VOLTAGE
vs. OUTPUT CURRENT
DELAYED ALARM OUTPUT
3.5
3.0
VCC = 3.3V
2.0
1.5
1.0
MAX3097E/8E toc05
VCC = 5.0V
5
OUTPUT HIGH VOLTAGE (V)
MAX3097E/8E toc04
VCC = 5.0V
6
CH 1
VCC = 3.3V
3
CH 2
GND
CH 3
GND
2
1
0
-45 -40 -35 -30 -25 -20 -15 -10 -5
OUTPUT CURRENT (mA)
0
GND
4
0.5
0
80
MAX3097E/8E toc06
TEMPERATURE (°C)
4.5
4
NO LOAD
CAPACITANCE (pF)
5.0
2.5
VCC = 3.3V
30
1
4.0
60
5
SUPPLY CURRENT (mA)
100
MAX3097E/8E toc02
1000
70
RECEIVER PROPAGATION DELAY (ns)
MAX3097E/8Etoc01
ALARMD OUTPUT DELAY (µs)
10,000
10
SUPPLY CURRENT vs.
TEMPERATURE
RECEIVER PROPAGATION DELAY
vs. TEMPERATURE
MAX3097E/8E toc03
ALARMD OUTPUT DELAY
vs. CAPACITANCE
OUTPUT LOW VOLTAGE (V)
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
0
5
10
15
20
OUTPUT CURRENT (mA)
25
30
20µs/div
CH1: VA, 5V/div
CH2: VALARMA, 5V/div
CH3: VALARMD, 5V/div
VA = GND, CDELAY = 270pF
_______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
COMMON-MODE VOLTAGE FAULT
(HIGH SIDE)
GND
CH 1
CH 2
GND
CH 2
GND
CH 3
MAX3097E/8E toc08
MAX3097E/8E toc07b
MAX3097E/8E toc07a
CH 1
GND
CH 1
GND
GND
CH 2
GND
GND
2ms/div
CH1: VA + AC(60Hz), 10V/div
CH2: VOUTA, 5V/div
CH3: VALARMA, 5V/div
VCC = 3V
2ms/div
CH1: VA + AC(60Hz), 10V/div
CH2: VOUTA, 5V/div
CH3: VALARMA, 5V/div
VCC = 3V
FAULT-DETECTION RECEIVER DIFFERENTIAL
THRESHOLD VOLTAGE SHIFT vs.
COMMON-MODE VOLTAGE
CH 2
12
GND
THRESHOLD SHIFT (mV)
MAX3097E/8E toc09
SLEW-RATE FAULT
CH 1
100µs/div
CH1: VA, 200mV/div
CH2: VALARMA, 5V/div
VA = GND
MAX3097E/8E toc10
CH 3
MAX3097E
LOW DIFFERENTIAL INPUT FAULT
COMMON-MODE VOLTAGE FAULT
(LOW SIDE)
8
MAX3097E
4
0
MAX3098E
GND
-4
-8
CH1: VA, 5V/div
CH2: VALARMA, 5V/div
SLEW RATE = 0.05V/µs
VA = GND
-10
-5
0
5
10
COMMON-MODE VOLTAGE (V)
_______________________________________________________________________________________
5
MAX3097E/MAX3098E
Typical Operating Characteristics (continued)
(Typical values are at VCC = +5V and TA = +25°C.)
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
MAX3097E/MAX3098E
Pin Description
6
PIN
NAME
1
A
Noninverting Receiver A Input
FUNCTION
2
A
Inverting Receiver A Input
3
B
Noninverting Receiver B Input
4
B
Inverting Receiver B Input
5
Z
Noninverting Receiver Z Input
6
Z
Inverting Receiver Z Input
7
GND
8
DELAY
Ground
Programmable Delay Terminal. Connect a capacitor from DELAY to GND to set the
ALARMD output delay time. To obtain a minimum delay, leave DELAY unconnected. See
Capacitance vs. ALARMD Output Delay in the Typical Operating Characteristics.
9
ALARMD
Delayed Fault Output. This output is the logic OR of ALARMA, ALARMB, and ALARMZ.
Place a capacitor from the DELAY pin to GND to set the delay (see Setting Delay Time). A
high logic level indicates a fault condition on at least one receiver input pair. A low level on
this pin indicates no fault condition is present.
10
OUTZ
Z Receiver Output. If VZ - V Z ≥ +200mV, OUTZ will be high. If VZ - V Z ≤ -200mV, OUTZ will
be low. If Z or Z exceeds the receiver’s input common-mode voltage range, the ALARMZ
output will be high and OUTZ will be indeterminate.
11
ALARMZ
Z Fault Output. When ALARMZ is high, OUTZ is indeterminate. Tables 1 and 2 show all the
possible states for which an alarm is set.
12
OUTB
B Receiver Output. If VB - V B ≥ +200mV, OUTB will be high. If VB - V B ≤ -200mV, OUTB will
be low. If B or B exceeds the input receiver’s common-mode voltage range, the ALARMB
output will be high and OUTB will be indeterminate.
13
ALARMB
B Fault Output. When ALARMB is high, OUTB is indeterminate. Tables 1 and 2 show all the
possible states for which an alarm is set.
14
OUTA
A Receiver Output. If VA - V A ≥ +200mV, OUTA will be high. If VA - V A ≤ -200mV, OUTA will
be low. If A or A exceeds the receiver’s input common-mode voltage range, the ALARMA
output will be high and OUTA will be indeterminate.
15
ALARMA
A Fault Output. When ALARMA is high, OUTA is indeterminate. Tables 1 and 2 show all the
possible states for which an alarm is set.
16
VCC
Power Supply
_______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
The MAX3097E/MAX3098E feature high-speed, triple
RS-485/RS-422 receivers with fault-detection circuitry
and fault-status outputs. The fault outputs are active
push-pull, requiring no pull-up resistors. The fault circuitry includes a capacitor-programmable delayed
FAULT_ output to ensure that there are no erroneous
fault conditions even at slow edge rates (see Delayed
Fault Output). The receivers operate at data rates up to
32Mbps.
The MAX3097E/MAX3098E are designed for motorshaft encoders with standard A, B, and Z outputs (see
Using the MAX3097E/MAX3098E as Shaft Encoder
Receivers). The devices provide an alarm for open-circuit conditions, short-circuit conditions, data nearing
the minimum differential threshold conditions, data
below the minimum threshold conditions, and receiver
inputs outside the input common-mode range. Tables 1
and 2 are functional tables for each receiver.
Test Circuits and Waveforms
CLF
A
ALARMA
OR (FAULT OUTPUT)
ALARMD
+3V
VID
VA
RISE/FALL TIMES ≤2ns
OV
OV
tPLH
tPHL
-3V
OUTA
VID
VOH
CL
A
VCC/2
RO
VA
VCC/2
VOL
Figure 1. Typical Receiver Test Circuit
Figure 2. Propagation Delay
+3.0V
FCMH
VIN
OV
FDIFH
OV
VID
FCML
FDIFL
-3.0V
VOH
ALARM OR ALARMD
VOL
tDFHL
tDFLH
VCC/2
Figure 3. Fault-Detection Timing
VCC/2
tCMFLH
VOH
ALARM OR ALARMD
VOL
tCMFHL tCMFLH
VCC/2
VCC/2
tCMFHL
VCC/2
VCC/2
Figure 4. Common-Mode Fault Propagation Delay
_______________________________________________________________________________________
7
MAX3097E/MAX3098E
Detailed Description
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
Table 1. MAX3097E Alarm Function Table (Each Receiver)
INPUTS
VID
(DIFFERENTIAL
INPUT VOLTAGE)
OUTPUTS
COMMON-MODE
VOLTAGE
OUT_
ALARM_
ALARMD
t ≥ DELAY
(NOTE 1)
FAULT CONDITION
≥0.475V
1
0
0
Normal Operation
<0.475V and ≥0.275V
1
Indeterminate
Indeterminate
Indeterminate
<0.275V and ≥0.2V
1
1
1
Low Input Differential Voltage
Indeterminate
(Note 2)
1
1
Low Input Differential Voltage
≤-0.2V and >-0.275V
0
1
1
Low Input Differential Voltage
≤-0.275V and
>-0.475V
0
Indeterminate
Indeterminate
≤-0.475V
0
0
0
Indeterminate
(Note 3)
1
1
≤0.2V and ≥-0.2V
X
≤13.2V and ≥-10V
<-10V or >+13.2V
Indeterminate
Outside Common-Mode
Voltage Range
X = Don’t care
Note 1: ALARMD indicates fault for any receiver.
Note 2: Receiver output may oscillate with this differential input condition.
Note 3: See Applications Information for conditions leading to input range fault condition.
Table 2. MAX3098EA Alarm Function Table (Each Receiver)
INPUTS
VID
(DIFFERENTIAL
INPUT VOLTAGE)
OUTPUTS
COMMON-MODE
VOLTAGE
OUT_
ALARM_
ALARMD
t ≥ DELAY
(NOTE 1)
FAULT CONDITION
≥0.2V
1
0
0
Normal Operation
<0.2V and ≥0.12V
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
(Note 2)
1
1
Low Input Differential Voltage
≤-0.12V and ≥ -0.2V
Indeterminate
Indeterminate
Indeterminate
Indeterminate
≤-0.2V
0
0
0
Normal Operation
Indeterminate
(Note 3)
1
1
Outside Common-Mode Voltage
Range
<0.12V and ≥ -0.12V
X
≤13.2V and ≥10V
<-10V or
>+13.2V
X = Don’t care; for B-grade functionality, replace VID input values in Table 2 with B-grade parameters from Electrical Characteristics.
Note 1: ALARMD indicates fault for any receiver.
Note 2: Receiver output may oscillate with this differential input condition.
Note 3: See Applications Information for conditions leading to input range fault condition.
8
_______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
ESD protection can be tested in several ways. The
receiver inputs are characterized for protection to the
following:
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method specified
in IEC 1000-4-2 (formerly IEC 801-2)
• 15kV using the Air-Gap Discharge method specified
in IEC 1000-4-2 (formerly IEC 801-2)
ESD Test Conditions
ESD performance depends on a number of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
Human Body Model
Figure 5a shows the Human Body Model, and Figure
5b shows the current waveform it generates when discharged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the device through a
1.5kΩ resistor.
RD
1.5k
RC
1MΩ
CHARGE-CURRENT
LIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
Machine Model
The Machine Model for ESD testing uses a 200pF storage capacitor and zero-discharge resistance. It mimics
the stress caused by handling during manufacturing
and assembly. All pins (not just RS-485 inputs) require
this protection during manufacturing. Therefore, the
Machine Model is less relevant to the I/O ports than are
the Human Body Model and IEC 1000-4-2.
IP 100%
90%
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
IEC 1000-4-2
Since January 1996, all equipment manufactured and/or
sold in the European community has been required to
meet the stringent IEC 1000-4-2 specification. The IEC
1000-4-2 standard covers ESD testing and performance
of finished equipment; it does not specifically refer to integrated circuits. The MAX3097E/MAX3098E help you
design equipment that meets Level 4 (the highest level)
of IEC 1000-4-2, without additional ESD-protection components.
The main difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2. Because series resistance is
lower in the IEC 1000-4-2 ESD test model (Figure 6a), the
ESD-withstand voltage measured to this standard is generally lower than that measured using the Human Body
Model. Figure 6b shows the current waveform for the
±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge test.
The Air-Gap test involves approaching the device with a
charge probe. The Contact Discharge method connects
the probe to the device before the probe is energized.
Ir
AMPERES
DEVICE
UNDER
TEST
36.8%
10%
0
0
Figure 5a. Human Body ESD Test Model
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
tRL
TIME
tDL
CURRENT WAVEFORM
Figure 5b. Human Body Model Current Waveform
_______________________________________________________________________________________
9
MAX3097E/MAX3098E
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against ESD
encountered during handling and assembly. The
MAX3097E/MAX3098E receiver inputs have extra protection against static electricity found in normal operation. Maxim’s engineers developed state-of-the-art
structures to protect these pins against ±15kV ESD
without damage. After an ESD event, the MAX3097E/
MAX3098E continue working without latchup.
___________Applications Information
RC
50MΩ to 100MΩ
Using the MAX3097E/MAX3098E as Shaft
Encoder Receivers
The MAX3097E/MAX3098E are triple RS-485 receivers
designed for shaft encoder receiver applications. A
shaft encoder is an electromechanical transducer that
converts mechanical rotary motion into three RS-485
differential signals. Two signals, A (A and A) and B (B
and B) provide incremental pulses as the shaft turns,
while the index signal, Z (Z and Z) occurs only once
per revolution to allow synchronization of the shaft to a
known position. Digital signal processing (DSP) techniques are used to count the pulses and provide feedback of both shaft position and shaft velocity for a
stable positioning system.
CHARGE-CURRENT
LIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Detecting Faults
Detecting Short Circuits
In Figure 8, if wires A and A are shorted together, then A
and A will be at the same potential, so the difference in
the voltage between the two will be approximately 0. This
causes fault A to trigger since the difference between A A is less than the differential fault threshold.
Detecting Open-Circuit Conditions
Detecting an open-circuit condition is similar to detecting a short-circuit condition and relies on the terminating resistor being across A and A. For example, if the
wire drops out of the A terminal, A pulls A through the
terminating resistor to look like the same signal. In this
condition, VID is approximately 0 and a fault occurs.
10
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 6a. IEC 1000-4-2 ESD Test Model
I
100%
90%
Shaft encoders typically transmit RS-485 signals over
twisted-pair cables since the signal often has to travel
across a noisy electrical environment (Figure 7).
Signal integrity from the shaft encoder to the DSP is
essential for reliable system operation. Degraded signals could cause problems ranging from simple miscounts to loss of position. In an industrial environment,
many problems can occur within the three twisted
pairs. The MAX3097E/MAX3098E can detect various
types of common faults, including a low-input-level signal, open-circuit wires, short-circuit wires, and an input
signal outside the common-mode input voltage range
of the receiver.
Cs
150pF
RD
330Ω
IPEAK
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
10%
tr = 0.7ns to 1ns
t
30ns
60ns
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
A
A
B
B
Z
Z
Figure 7. Typical Shaft Encoder Output
______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
Detecting Low Input Differential
Due to cable attenuation on long wire runs, it is possible that V ID < 200mV, and incorrect data will be
received. In this condition, a fault will be indicated.
Delayed Fault Output
The delayed fault output provides a programmable
blanking delay to allow transient faults to occur without
triggering an alarm. Such faults may occur with slow
signals triggering the receiver alarm through the zero
crossover region.
Figure 9 shows the delayed alarm output.
ALARMD performs a logic OR of ALARMA, ALARMB,
and ALARMZ (Figure 10). A NOR gate drives an Nchannel MOSFET so that in normal operation with no
faults, the current source (10µA typ) is shunted to
ground. Upon activation of any alarm from receiver A,
B, or Z, the MOSFET is turned off, allowing the current
source to charge CDELAY. When VDELAY exceeds the
DELAY threshold, the comparator output, ALARMD,
goes high. ALARMD is reset when all receiver alarms
go low, quickly discharging CDELAY to ground.
Setting Delay Time
ALARMD’s delay time is set with a single capacitor
connected from DELAY to GND. The delay comparator
threshold varies with supply voltage, and the CDELAY
value can be determined for a given time delay period
from the Capacitance vs. ALARMD Output Delay graph
in the Typical Operating Characteristics or using the
following equations:
tD = 15 + 0.33 x CDELAY (for VCC = 5V)
and
tD = 10 + 0.187 x CDELAY (for VCC = 3V)
where tD is in µs and CDELAY is in pF.
DELAY
CURRENT
SOURCE
A
A
NORMAL OPERATION
SHORT CIRCUIT A TO A
ALARMA
ALARMB
ALARMZ
NMOS
DELAY
COMPARATOR
ALARMD
CDELAY*
(EXTERNAL)
Figure 8. Short-Circuit Detection
G1
tDLY
ALARMA
ALARM_
DELAY THRESHOLD
DELAY
ALARMB
ALARMD
tD
tD
*The capacitor (CDELAY) charges up slowly, but discharges rapidly.
If the duration of an ALARM_ pulse is less than tDLY, no alarm
output will be present at ALARMD.
ALARMD
Figure 9. Delayed Alarm Output
Figure 10. ALARMD Simplified Schematic
______________________________________________________________________________________
11
MAX3097E/MAX3098E
Common-Mode Range
The MAX3097E/MAX3098E contain circuitry that detects if the input stage is going outside its useful common-mode range. If the received data could be
unreliable, a fault signal is triggered.
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
Ordering Information (continued)
PART
TEMP. RANGE
Functional Diagram
PINPACKAGE
VCC
MAX3097ECPE
0°C to +70°C
16 Plastic DIP
MAX3097EEEE
-40°C to +85°C
16 QSOP
A
MAX3097EESE
-40°C to +85°C
16 SO
A
MAX3097EEPE
-40°C to +85°C
16 Plastic DIP
MAX3098EACEE
0°C to +70°C
16 QSOP
MAX3098EACSE
0°C to +70°C
16 SO
MAX3098EACPE
0°C to +70°C
16 Plastic DIP
MAX3098EAEEE
-40°C to +85°C
16 QSOP
MAX3098EAESE
-40°C to +85°C
16 SO
MAX3098EAEPE
-40°C to +85°C
16 Plastic DIP
MAX3098EBCEE
0°C to +70°C
16 QSOP
MAX3098EBCSE
0°C to +70°C
16 SO
MAX3098EBCPE
0°C to +70°C
16 Plastic DIP
MAX3098EBEEE
-40°C to +85°C
16 QSOP
MAX3098EBESE
-40°C to +85°C
16 SO
MAX3098EBEPE
-40°C to +85°C
16 Plastic DIP
ALARMA
OUTA
ALARMB
B
OUTB
B
ALARMZ
Z
OUTZ
Z
ALARMD
MAX3097E
MAX3098E
DELAY
GND
Chip Information
TRANSISTOR COUNT: 675
PROCESS: CMOS
12
______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
SOICN.EPS
______________________________________________________________________________________
13
MAX3097E/MAX3098E
Package Information
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
QSOP.EPS
MAX3097E/MAX3098E
Package Information (continued)
14
______________________________________________________________________________________
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
PDIPN.EPS
______________________________________________________________________________________
15
MAX3097E/MAX3098E
Package Information (continued)
MAX3097E/MAX3098E
±15kV ESD-Protected, 32Mbps, 3V/5V,
Triple RS-422/RS-485 Receivers with Fault Detection
NOTES
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.
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© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.