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19-5017; Rev 1; 4/10
High-ESD Profibus RS-485 Transceiver
General Description
The MAX14770E is a half-duplex, Q35kV high ESDprotected transceiver for PROFIBUS-DP and RS-485 applications. In addition, it can be used for RS-422/V.11 communications. The MAX14770E is designed to meet IEC 61158-2, TIA/EIA-422-B, TIA/EIA-485-A, V.11, and X.27 standards. The MAX14770E operates from a +5V supply and has true fail-safe circuitry that guarantees a logic-high receiver output when the receiver inputs are open or shorted. The MAX14770E features a 1/4 standard-unit load receiver input impedance, allowing up to 128 1/4 unit load transceivers on the bus. Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal-shutdown circuitry. The MAX14770E is available in 8-pin SO and tiny TDFN (3mm x 3mm) packages, and is specified over the extended (-40NC to +85NC) and automotive (-40NC to +125NC) temperature ranges. S +4.5V to +5.5V Supply Voltage S 20Mbps Data Rate S Short-Circuit Protected S True Fail-Safe Receiver S Thermal-Shutdown Protected S Hot Swappable S High ESD Protection 35kV Human Body Model (HBM) 20kV IEC 61000-4-2 Air Gap 10kV IEC 61000-4-2 Contact S -40NC to +125NC Automotive Temperature Range in Tiny 8-Pin (3mm x 3mm) TDFN
Features
S Meets EIA 61158-2 Type 3 PROFIBUS-DP
MAX14770E
Ordering Information
PART MAX14770EESA+T MAX14770EATA+T TEMP RANGE PINPACKAGE TOP MARK -- BMG
Applications
PROFIBUS-DP Networks Industrial Fieldbuses Motion Controllers RS-485 Networks Machine Encoders
-40NC to +85NC 8 SO -40NC to +125NC 8 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. *EP = Exposed pad.
Functional Diagram
RO RE
R A SHUTDOWN
Typical PROFIBUS-DP Operating Circuit appears at end of data sheet.
DE DI
B
D
MAX14770E
The PROFI BUS PROCESS FIELD BUS logo is a registered trademark of PROFIBUS and PROFINET International (PI).
_______________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
High-ESD Profibus RS-485 Transceiver MAX14770E
ABSOLUTE MAXIMUM RATINGS
(Voltages referenced to GND.) VCC .......................................................................-0.3V to +6.0V RE, RO.......................................................-0.3V to (VCC + 0.3V) DE, DI ...................................................................-0.3V to +6.0V A, B.....................................................................-8.0V to +13.0V Short-Circuit Duration (RO, A, B) to GND .................Continuous Continuous Power Dissipation (TA = +70NC) 8-Pin SOIC (derate 7.6mW/NC above +70NC) ............606mW 8-Pin TDFN (derate 24.4mW/NC above +70NC) ........1951mW Junction-to-Ambient Thermal Resistance (BJA) (Note 1) 8-Pin SO ....................................................................132NC/W 8-Pin TDFN..................................................................41NC/W Junction-to-Case Thermal Resistance (BJC) (Note 1) 8-Pin SO ......................................................................38NC/W 8-Pin TDFN....................................................................8NC/W Operating Temperature Range 8-Pin SO ......................................................... -40NC to +85NC 8-Pin TDFN................................................... -40NC to +125NC Storage Temperature Range............................ -65NC to +150NC Junction Temperature Range........................... -40NC to +150NC Lead Temperature (soldering, 10s) ................................+300NC Soldering Temperature (reflow) ........................................ 260NC
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic/thermal-tutorial.
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 = +5V Q10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V, TA = +25NC.) (Note 2) PARAMETER Power-Supply Range Supply Current Shutdown Supply Current DRIVER Differential Driver Output Differential Driver Peak-to-Peak Output Change in Magnitude of Differential Output Voltage Driver CommonMode Output Voltage Change in CommonMode Voltage Driver Short-Circuit Output Current (Note 5) Driver Short-Circuit Foldback Output Current (Note 5) |VOD| VODPP RL = 54I, DI = VCC or GND; Figure 1 Figure 2 (Note 3) 2.1 4.0 6.8 V V SYMBOL VCC ICC DE = 1, RE = 0 or DE = 0, RE = 0 or DE = 1, RE = 1; no load DE = 0, RE = 1 CONDITIONS MIN 4.5 2.5 TYP MAX 5.5 4 UNITS V mA
ISH
15
FA
DVOD
RL = 54I; Figure 1 (Note 4)
-0.2
0
+0.2
V
VOC DVOC
RL = 54I; Figure 1 RL = 54I; Figure 1 (Note 4) 0V P VOUT P +12V; output low -7V P VOUT P VCC; output high (VCC - 1V) P VOUT P +12V; output low -7V P VOUT P +1V; output high -250 -15 -0.2
1.8
3 +0.2 +250
V V
IOSD
mA
IOSDF
+15
mA
2
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High-ESD Profibus RS-485 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V Q10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V, TA = +25NC.) (Note 2) PARAMETER LOGIC INPUTS Driver Input High Voltage Driver Input Low Voltage Driver Input Hysteresis Driver Input Current Input Impedance in Hot Swap RECEIVER Input Current (A, B) Differential Input Capacitance Receiver Differential Threshold Voltage Receiver Input Hysteresis LOGIC OUTPUT Output High Voltage Output Low Voltage Three-State Receiver Output Current Receiver Input Resistance Receiver Output Short-Circuit Current Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis ESD Protection, A and B Pins ESD Protection, All Other Pins VOH VOL IOZR RIN IOSR IOUT = -1mA, VA - VB = VTH IOUT = 1mA, VA - VB = -VTH 0V P VOUT P VCC -7V P VCM P 12V 0V P VRO P VCC -1 48 -110 +110 VCC 1.5 0.4 +1 V V FA kI mA IA, IB CAB VTH DVTH DE = GND, VCC = VGND or +5.5V VIN = 12V VIN = -7V -200 8 -200 -125 15 -50 +250 FA pF mV mV VIH VIL VHYS IIN RDE RRE DE, DI, RE DE, DI, RE DE, DI, RE DE, DI, RE Figure 11 until the first low-to-high transition of DE occurs Figure 11 until the first high-to-low transition of RE occurs -1 50 +1 2.0 0.8 V V mV FA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX14770E
1
5.6
10
kW
Between A and B, DE = RE = GND at 6MHz -7V P VCM P 12V VCM = 0V
PROTECTION SPECIFICATIONS VTS VTSH HBM IEC 61000-4-2 Air-Gap Discharge to GND IEC 61000-4-2 Contact Discharge to GND HBM +160 15 35 20 10 2 kV kV NC NC
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3
High-ESD Profibus RS-485 Transceiver MAX14770E
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V Q10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V, TA = +25NC.) (Note 2) PARAMETER Driver Propagation Delay Differential Driver Output Skew |tDPLH - tDPHL| Driver Output Transition Skew |tt(MLH)|, |tt(MHL)| Driver Differential Output Rise or Fall Time Maximum Data Rate Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Driver Enable Skew Time Driver Disable Skew Time Driver Enable from Shutdown to Output High Driver Enable from Shutdown to Output Low Time to Shutdown Receiver Propagation Delay Receiver Output Skew tDZH tDZL tDLZ tDHZ |tZL - tZH| |tLZ - tHZ| RL = 500I, CL = 50pF; Figure 6 RL = 500I, CL = 50pF; Figure 7 RL = 500I, CL = 50pF; Figure 7 RL = 500I, CL = 50pF, Figure 6 RL = 500I, CL = 50pF; Figures 6 and 7 RL = 500I, CL = 50pF; Figures 6 and 7 SYMBOL tDPLH tDPHL tDSKEW CONDITIONS MIN TYP MAX UNITS DRIVER SWITCHING CHARACTERISTICS RL = 54I, CL = 50pF; Figures 3 and 4 28 ns
RL = 54I, CL = 50pF; Figures 3 and 4
1.2
ns
tTSKEW
RL = 54I, CL = 50pF; Figures 3 and 5
2
ns
tLH, tHL
RL = 54I, CL = 50pF; Figures 3 and 4 20
15
ns Mbps
50 50 40 40 8 8
ns ns ns ns ns ns
tDZL(SHDN)
RL = 500I, CL = 50pF; Figure 7 (Note 6)
100
Fs
tDZH(SHDN) tSHDN tRPLH tRPHL tRSKEW
RL = 500I, CL = 50pF; Figure 6 (Note 6) (Note 6) 50
100 800
Fs ns
RECEIVER SWITCHING CHARACTERISTICS CL = 15pF; Figures 8 and 9 (Note 7) CL = 15pF; Figures 8 and 9 (Notes 7, 8) 28 2 ns ns
4
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High-ESD Profibus RS-485 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V Q10%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V, TA = +25NC.) (Note 2) PARAMETER Maximum Data Rate Receiver Enable to Output High Receiver Enable to Output Low Receiver Disable Time from Low Receiver Disable Time from High Receiver Enable from Shutdown to Output High Receiver Enable from Shutdown to Output Low Time to Shutdown Note Note Note Note 2: 3: 4: 5: tRZH tRZL tRLZ tRHZ S2 closed; RL = 1kI, CL = 15pF; Figure 10 S1 closed; RL = 1kI, CL = 15pF; Figure 10 S1 closed; RL = 1kI, CL = 15pF; Figure 10 S2 closed; RL = 1kI, CL = 15pF; Figure 10 S1 closed; RL = 1kI, CL = 15pF; Figure 10 (Notes 6, 7) S2 closed; RL = 1kI, CL = 15pF; Figure 10 (Notes 6, 7) (Note 6) 50 SYMBOL CONDITIONS MIN 20 30 30 30 30 TYP MAX UNITS Mbps ns ns ns ns
MAX14770E
tRZL(SHDN)
100
Fs
tRZH(SHDN) tSHDN
100 800
Fs ns
Devices are production tested at TA = +25NC. Specifications over temperature limits are guaranteed by design. VODPP is the difference in VOD, with the DI at high and DI at low. DVOD and DVOC are the changes in |VOD| and |VOC|, respectively, with the DI at high and DI at low. The short-circuit output current applies to peak current just prior to foldback current limiting; the short-circuit foldback output current applies during current limiting to allow a recovery from bus contention. Note 6: Shutdown is enabled by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns, the device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 800ns, the device is guaranteed to have entered shutdown. Note 7: Capacitive load includes test probe and fixture capacitance. Note 8: Guaranteed by characterization, not production tested.
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5
High-ESD Profibus RS-485 Transceiver MAX14770E
VCC A RL 2 VOD RL 2 B DI DE VCC A 110I B VOC 195I VOD 195I
Figure 1. Driver DC Test Load
Figure 2. VODPP Swing Under Profibus Equivalent Load Test
VCC DE DI A B VID RL CL
Figure 3. Driver Timing Test Circuit
VCC DI 0 1.5V
f = 1MHz, tLH P 3ns, tHL P 3ns 1.5V 1/2 VO
tDPLH B A 1/2 VO VO VO VDIFF 0 -VO 20% tLH tDSKEW = |tDPLH - tDPHL| 80%
tDPHL
VDIFF = VA - VB 80%
20% tHL
Figure 4. Driver Propagation Delays 6 ______________________________________________________________________________________
High-ESD Profibus RS-485 Transceiver MAX14770E
50% A tt(MLH) B 50% 50% tt(MHL) 50%
Figure 5. Driver Transition Skew
A 0 OR VCC DI D B DE GENERATOR 50I
S1 CL 50pF
OUT RL = 500I DE tDZH, tDZH(SHDN) 1.5V tDHZ 1.5V 0.25V OUT
VCC 0 VOH 0
Figure 6. Driver Enable and Disable Times
VCC RL = 500I S1 OUT
0 OR VCC DI D
A B
DE GENERATOR 50I
VCC DE VCC OUT VOL tDZL, tDZL(SHDN) 1.5V tDLZ 1.5V 0.25V 0
Figure 7. Driver Enable and Disable Times
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7
High-ESD Profibus RS-485 Transceiver MAX14770E
A ATE VID B R RECEIVER OUTPUT
Figure 8. Receiver Propagation Delay Test Circuit
t = 1MHz, tLH P 3ns, tHL P 3ns
A B VOH RO VOL tRPHL VCC 2
1V -1V
tRPLH VCC 2 tRSKEW = |tRPHL - tRPLH|
Figure 9. Receiver Propagation Delays
+1.5V -1.5V
S3 VID R RO
R 1kI CL 15pF
S1 S2
VCC
RE GENERATOR 50I
VCC RE 1.5V tRZH, tRZH (SHDN) RO 0 S1 OPEN S2 CLOSED S3 = +1.5V 1.5V RE tRZL, tRZL(SHDN) VOH VCC 2 0 VCC RE 1.5V 0 tRHZ RO 0.25V VOH VCC 2 RO
VCC S1 CLOSED S2 OPEN S3 = -1.5V
0
VCC
VOL VCC 1.5V
S1 OPEN S2 CLOSED S3 = +1.5V RE
S1 CLOSED S2 OPEN S3 = -1.5V
0 tRLZ VCC
0
RO
0.25V
VOL
Figure 10. Receiver Enable and Disable Times 8 ______________________________________________________________________________________
High-ESD Profibus RS-485 Transceiver
Typical Operating Characteristics
(VCC = +5V, TA = +25NC, unless otherwise noted.)
NO-LOAD DC SUPPLY CURRENT vs. TEMPERATURE
MAX14770E toc01
MAX14770E
SUPPLY CURRENT vs. DATA RATE
MAX14770E toc02
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX14770E toc03
2.5 NO-LOAD SUPPLY CURRENT (mA) 2.0 1.5 1.0 0.5 0
DE = VCC
60 55 50 SUPPLY CURRENT (mA) 45 40 35 30 25 20 15 10 5 0 0 5,000 10,000 DATA RATE (kbps) 15,000
3.0 SHUTDOWN SUPPLY CURRENT (A) 2.5 2.0 1.5 1.0 0.5 0
PROFIBUS EQUIVALENT LOAD
DE = GND
NO LOAD
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
20,000
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
RECEIVER OUTPUT RO CURRENT vs. OUTPUT LOW VOLTAGE
MAX14770E toc04
RECEIVER OUTPUT RO CURRENT vs. OUTPUT HIGH VOLTAGE
MAX14770E toc05
RECEIVER PROPAGATION DELAY vs. TEMPERATURE
RECEIVER PROPAGATION DELAY (ns)
MAX14770E toc06
60 50 OUTPUT CURRENT (mA) 40 30 20 10 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
60 50 OUTPUT CURRENT (mA) 40 30 20 10 0
25 20 15 10 5 0
4.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
OUTPUT LOW VOLTAGE (V)
OUTPUT HIGH VOLTAGE (V)
DRIVER PROPAGATION DELAY vs. TEMPERATURE
MAX14770E toc07
DIFFERENTIAL OUTPUT VOLTAGE VOD vs. OUTPUT CURRENT
MAX14770E toc08
DIFFERENTIAL OUTPUT VOLTAGE VOD vs. TEMPERATURE
DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
RL = 54, CL = 50pF
20 15 10 5 0
DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER PROPAGATION DELAY (ns)
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 20 40 60
RL = 54
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
80
OUTPUT CURRENT (mA)
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MAX14770E toc09
25
4.0
2.8
9
High-ESD Profibus RS-485 Transceiver MAX14770E
Typical Operating Characteristics (continued)
(VCC = +5V, TA = +25NC, unless otherwise noted.)
DRIVER OUTPUT CURRENT vs. OUTPUT LOW VOLTAGE
MAX14770E toc10
DRIVER OUTPUT CURRENT vs. OUTPUT HIGH VOLTAGE
MAX14770E toc11
DRIVER DIFFERENTIAL SKEW tDSKEW vs. TEMPERATURE
RL = 54, CL = 50pF
MAX14770E toc12 MAX14770E toc15
140 120 OUTPUT CURRENT (mA) 100 80 60 40 20 0 0 3 6 9
140 120 OUTPUT CURRENT (mA) 100 80 60 40 20 0
5 4 3 2 1 0
12
-7
-5
-3
-1
1
3
DRIVER OUTPUT SKEW (ns)
5
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
OUTPUT LOW VOLTAGE (V)
OUTPUT HIGH VOLTAGE (V)
DRIVER OUTPUT TRANSITION SKEW vs. TEMPERATURE
MAX14770E toc13
DRIVER OUTPUT RISE AND FALL TIME vs. TEMPERATURE
MAX14770E toc14
DRIVER ENABLE TO OUTPUT HIGH tDZH
DI = VCC, RL = 500, CL = 50pF
5 DRIVER OUTPUT TRANSITION SKEW (ns) 4 3 2 1 0
RL = 54, CL = 50pF
16 14 12 TIME (ns) 10 8 6 4 2 0
RL = 54, CL = 50pF
FALL TIME
RISE TIME
DE 2V/div
A 2V/div -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) 10ns/div
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
DRIVER ENABLE TO OUTPUT LOW tDZL
DI = VCC, RL = 500, CL = 50pF
MAX14770E toc16
DRIVER DISABLE TIME FROM LOW tDLZ
DI = VCC, RL = 500, CL = 50pF
MAX14770E toc17
DRIVER DISABLE TIME FROM HIGH tDHZ
DI = VCC, RL = 500, CL = 50pF
MAX14770E toc18
DE 2V/div
DE 2V/div
DE 2V/div
B 2V/div 10ns/div 10ns/div
B 2V/div 10ns/div
A 2V/div
10
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High-ESD Profibus RS-485 Transceiver
Pin Configurations
TOP VIEW
+ +
MAX14770E
RO RE
1 2
8 VCC 7B
RO RE DE DI
1 2 3 4
8 7
VCC B A GND
DE 3 DI 4
MAX14770E
6
A
MAX14770E
*EP
6 5
5 GND
SO
TDFN (3mm x 3mm)
*CONNECT EXPOSED PAD TO GND.
Pin Description
PIN 1 2 3 NAME RO RE DE FUNCTION Receiver Output. When RE is low and (A - B) R -50mV, RO is high; if (A - B) P -200mV, RO is low. Receiver Enable. Drive RE low to enable RO; RO is high impedance when RE is high. Drive RE high and DE low to enter low-power shutdown mode. Driver Enable. Drive DE high to enable driver output. The driver outputs are high impedance when DE is low. Drive RE high and DE low to enter low-power shutdown mode. Driver Input. With DE high, a low on DI forces the noninverting output, A, low and the inverting output, B, high. Similarly, a high on DI forces the noninverting output, A, high and the inverting output, B, low. Ground Noninverting Receiver Input and Noninverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply. Bypass VCC to GND with a 0.1FF ceramic capacitor as close as possible to the device. Exposed Pad (TDFN Only). Connect EP to GND.
4 5 6 7 8 --
DI GND A B VCC EP
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11
High-ESD Profibus RS-485 Transceiver MAX14770E
Detailed Description
The MAX14770E is a half-duplex, Q35kV high ESDprotected transceiver for PROFIBUS-DP, RS-485, and RS-422 communications. The device features true failsafe circuitry that 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 (see the True Fail-Safe section). The MAX14770E supports data rates up to 20Mbps. The MAX14770E operates from a single +4.5V to +5.5V supply. Drivers are output short-circuit current limited. Thermal-shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal-shutdown circuitry places the driver outputs into a high-impedance state. The MAX14770E has a hotswap input structure that prevents disturbances on the differential signal lines when the MAX14770E is powered up (see the Hot-Swap Capability section). The MAX14770E 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 done by having the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A - B) is greater than or equal to -50mV, RO is logic-high. If (A - B) is less than or equal to -200mV, RO is 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 receiver thresholds of the MAX14770E, this results in a logic-high with a 50mV minimum noise margin. The -50mV to -200mV threshold complies with the Q200mV EIA/TIA-485 standard.
Hot-Swap Capability
Hot-Swap Inputs When circuit boards are inserted into a hot or powered backplane, disturbances to the enable inputs and differential receiver inputs can lead to data errors. Upon initial circuit board insertion, the processor undergoes its power-up sequence. During this period, the processor output drivers are high impedance and are unable to drive the DE and RE inputs of the MAX14770E to a defined logic level. Leakage currents up to 10FA from the highimpedance output of a controller could cause DE and RE to drift to an incorrect logic state. Additionally, parasitic circuit board capacitance could cause coupling of VCC or GND to DE and RE. These factors could improperly enable the driver or receiver. However, the MAX14770E has hot-swap inputs that avoid these potential problems. When VCC rises, an internal pulldown circuit holds DE low and RE high. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hot-swap-tolerable inputs. Hot-Swap Input Circuitry The MAX14770E DE and RE enable inputs feature hot-swap capability. At the input, there are two NMOS devices, M1 and M2 (Figure 11). When VCC ramps from 0, an internal 15Fs timer turns on M2 and sets the SR latch that also turns on M1. Transistors M2, a 1mA current sink, and M1, a 100FA current sink, pull DE to GND through a 5.6kI resistor. M2 is designed to pull DE to the disabled state against an external parasitic capacitance up to 100pF that can drive DE high. After 15Fs, the timer deactivates M2 while M1 remains on, holding DE low against three-state leakages that can drive DE high. M1 remains on until an external source overcomes the required input current. At this time, the SR latch resets and M1 turns off. When M1 turns off, DE reverts to a standard, high-impedance CMOS input. Whenever VCC drops below 1V, the hot-swap input is reset. For RE, there is a complementary circuit employing two PMOS devices pulling RE to VCC.
True Fail-Safe
Table 1. Functional Table (Transmitting)
TRANSMITTING INPUTS RE X X 0 1 X = Don't care. DE 1 1 0 0 DI 1 0 X X B 0 1 High-Z OUTPUTS A 1 0 High-Z
High-Z and shutdown
Table 2. Functional Table (Receiving)
RECEIVING INPUTS RE 0 0 0 1 1 X = Don't care. 12 DE X X X 1 0 A-B R -0.05V P -0.2V Open/shorted X X OUTPUT RO 1 0 1 High-Z High-Z and shutdown
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High-ESD Profibus RS-485 Transceiver
The MAX14770E features thermal-shutdown circuitry. The internal switch turns off when the junction temperature exceeds +160NC (typ) and immediately goes into a fault mode. The device exits thermal shutdown after the junction temperature cools by 15NC (typ).
Thermal-Shutdown Protection
Applications Information
The standard RS-485 receiver input impedance is one unit load, and a standard driver can drive up to 32 unit loads. The MAX14770E transceiver has a 1/4 unit load receiver, which allows up to 128 transceivers connected in parallel on one communication line. Connect any combination of these devices, and/or other RS-485 devices, for a maximum of 32 unit loads to the line. Low-power shutdown mode is initiated by bringing both RE high and DE low. In shutdown, the devices draw only 15FA (max) of supply current. RE and DE can be driven simultaneously; the devices are guaranteed not to enter shutdown if RE is high and DE is low for less than 50ns. If the inputs are in this state for at least 800ns, the devices are guaranteed to enter shutdown.
128 Transceivers on the Bus
Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. The first, a foldback current limit on the output stage, provides immediate protection against short circuits over the whole common-mode voltage range (see the Typical Operating Characteristics). The second, a thermal-shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature exceeds +160NC (typ). The MAX14770E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figure 12 shows a typical network applications circuit. To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible.
Driver Output Protection
MAX14770E
Typical Application
Low-Power Shutdown Mode
The MAX14770E is designed for driving PROFIBUS-DP termination networks. With a worst-case loading of two termination networks with 220I termination impedance and 390I pullups/pulldowns, the drivers can drive V(A - B) > 2.1V output.
Profibus Termination
VCC 15Fs TIMER TIMER
DE
5.6kI
DRIVER ENABLE (HOT SWAP) 100FA M1 1mA M2
Figure 11. Simplified Structure of the Driver Enable Pin (DE)
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13
High-ESD Profibus RS-485 Transceiver MAX14770E
DI D DE RO RE R A B A B A A R 120I B 120I B D DI RO RE DE
MAX14770E
D
R
D
R
DI
DE
RO RE
DI
DE
RO RE
Figure 12. Typical Half-Duplex RS-485 Network
RC 1MI CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE CS 100pF
RD 1.5kI DISCHARGE RESISTANCE STORAGE CAPACITOR DEVICE UNDER TEST
IP 100% 90% AMPERES 36.8% 10% 0 0 tRL
IR
PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
TIME tDL CURRENT WAVEFORM
Figure 13. Human Body ESD Test Model
Figure 14. Human Body Current Waveform
ESD protection structures are incorporated on all pins to protect against electrostatic discharges up to Q2kV (HBM) encountered during handling and assembly. A and B are further protected against high ESD up to Q35kV (HBM) without damage. The A and B pins are also protected against Q20kV Air-Gap and Q10kV Contact IEC61000-4-2 ESD events. The ESD structures withstand high ESD both in normal operation and when the device is powered down. After an ESD event, the MAX14770E continues to function without latchup. ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results.
Extended ESD Protection
Figure 13 shows the HBM. Figure 14 shows the current waveform it generates when discharged into a lowimpedance state. This model consists of a 100pF capacitor charged to the ESD voltage of interest that is then discharged into the device through a 1.5kI resistor. The IEC 61000-4-2 standard covers ESD testing and performance of finished equipment. It does not specifically refer to integrated circuits. The MAX14770E is specified for Q20kV Air-Gap Discharge and Q10kV Contact Discharge IEC 61000-4-2 on the A and B pins. The main difference between tests done using the HBM and IEC 61000-4-2 is higher peak current in IEC 61000-4-2. Because series resistance is lower in the IEC 61000-4-2
Human Body Model
IEC 61000-4-2
ESD Test Conditions
14
_____________________________________________________________________________________
High-ESD Profibus RS-485 Transceiver MAX14770E
RC 50MI TO 100MI CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE CS 150pF RD 330I DISCHARGE RESISTANCE STORAGE CAPACITOR DEVICE UNDER TEST
100% 90%
IPEAK 10% tR = 0.7ns TO 1ns t 30ns 60ns
Figure 15. IEC61000-4-2 ESD Test Model
Figure 16. IEC61000-4-2 ESD Generator Current Waveform
Typical PROFIBUS-DP Operating Circuit
VCC RO RE A SHUTDOWN DE DI D B 390I 220I 220I SHUTDOWN B R RE RO A R 390I VCC 390I D DI DE
0.1FF
0.1FF
390I
MAX14770E
GND GND
MAX14770E
ESD test model (Figure 15), the ESD-withstand voltage measured to this standard is generally lower than that measured using the HBM. Figure 16 shows the current waveform for the Q10kV IEC 61000-4-2 Level 4 ESD Contact Discharge test. The Air-Gap Discharge test involves approaching the device with a charged probe. The Contact Discharge method connects the probe to the device before the probe is energized.
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+," "#," or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PACKAGE TYPE 8 SO 8 TDFN-EP
PACKAGE CODE S8+4 T833+2
DOCUMENT NO. 21-0041 21-0137
Chip Information
PROCESS: BiCMOS
______________________________________________________________________________________
15
High-ESD Profibus RS-485 Transceiver MAX14770E
Revision History
REVISION NUMBER 0 1 REVISION DATE 10/09 4/10 Initial release Switched the position of the pins DE and DI (TDFN) in the Pin Configurations. DESCRIPTION PAGES CHANGED -- 11
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.
16
(c)
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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