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19-5131; Rev 0; 2/10
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
General Description
The MAX14840E/MAX14841E are +3.3V ESD-protected transceivers intended for half-duplex RS-485 communication up to 40Mbps. These transceivers are optimized for high speeds over extended cable runs while minimizing tolerance to noise. The MAX14840E features symmetrical fail-safe and larger receiver hysteresis, providing improved noise rejection and improved recovered signals in high-speed and long cable applications. The MAX14841E has true failsafe receiver inputs guaranteeing a logic-high receiver output when inputs are shorted or open. The MAX14840E/MAX14841E transceivers draw 1.5mA (typ) supply current when unloaded or when fully loaded with the drivers disabled. Hot-swap capability eliminates undesired transitions on the bus during power-up or hot insertion. The MAX14840E/MAX14841E are available in 8-pin SO and small, 8-pin (3mm x 3mm) TDFN-EP packages. Both devices operate over the -40NC to +125NC automotive temperature range.
S Half-Duplex RS-485 Transceivers S +3.3V Supply Voltage S 40Mbps Maximum Data Rate S Large (170mV) Receiver Hysteresis on
Features
MAX14840E/MAX14841E
MAX14840E
S Symmetrical Fail-Safe Receiver Input on
MAX14840E
S Fail-Safe Receiver Input (MAX14841E) S Hot-Swap Capability S Short-Circuit Protected Outputs S Thermal Self-Protection S Low 10A (max) Shutdown Current S Extended ESD Protection for RS-485 I/O Pins
35kV Human Body Model (HBM) 20kV Air-Gap Discharge per IEC 61000-4-2 12kV Contact Discharge per IEC 61000-4-2
S Automotive -40C to +125C Operating
Temperature Range
S Available in Industry-Standard 8-Pin SO or
Applications
Motion Controllers Fieldbus Networks Industrial Control Systems Backplane Buses HVAC Networks
PART MAX14840EASA+ MAX14840EATA+ MAX14841EASA+ MAX14841EATA+ FAIL SAFE Symmetrical Symmetrical True True
Space-Saving, 8-Pin TDFN-EP (3mm x 3mm) Packages
Ordering Information/Selector Guide
TEMP RANGE -40NC to +125NC -40NC to +125NC -40NC to +125NC -40NC to +125NC PIN-PACKAGE 8 SO 8 TDFN-EP* 8 SO 8 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
_______________________________________________________________ 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.
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
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 SO (derate 7.6mW/NC above +70NC) ............... 606mW 8-Pin TDFN (derate 24.4mW/NC above +70NC) ....... 1951mW Junction-to-Case Thermal Resistance (BJC) (Note 1) 8-Pin SO .......................................................................38NC/W 8-Pin TDFN ....................................................................8NC/W Junction-to-Ambient Thermal Resistance (BJA) (Note 1) 8-Pin SO ....................................................................132NC/W 8-Pin TDFN ..................................................................41NC/W Operating Temperature Range ...................... -40NC to +125NC Junction Temperature .................................................. +150NC Storage Temperature Range ......................... -65NC 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.com/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.
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3) PARAMETER POWER SUPPLY Supply Voltage VCC DE = RE = VCC, or DE = RE = GND, or DE = VCC, RE = GND, DI = VCC or GND, no load DE = GND and RE = VCC RL = 54I, Figure 1 RL = 54I, Figure 1 (Note 4) RL = 54I, Figure 1 RL = 54I, Figure 1 (Note 4) A/B output, IOUT = -20mA A/B output, IOUT = 20mA 0V P VOUT P +12V, output low -7V P VOUT P VCC, output high DE = GND, VCC = GND or +3.6V VIN = +12V VIN = -7V -800 12 250 1000 -0.2 2.2 0.8 250 1.5 -0.2 0 VCC/2 +0.2 3 0.2 3.0 3.6 V SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Current
ICC
1.5
4
mA
Shutdown Supply Current DRIVER Differential Driver Output Change in Magnitude of Differential Output Voltage Driver Common-Mode Output Voltage Change in Common-Mode Voltage Single-Ended Driver Output High Single-Ended Driver Output Low Driver Short-Circuit Output Current RECEIVER Input Current (A and B) Differential Input Capacitance
ISH VOD DVOD VOC DVOC VOH VOL |IOSD|
10
FA V V V V V V mA
IA,B CA,B
FA pF
Between A and B, DE = GND, f = 2MHz
2
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3) PARAMETER Receiver Differential Threshold Voltage (MAX14840E Only) Receiver Input Hysteresis (MAX14840E Only) Receiver Differential Threshold Voltage (MAX14841E Only) Receiver Input Hysteresis (MAX14841E Only) LOGIC INTERFACE Input High Voltage Input Low Voltage Input Hysteresis Input Current Input Impedance on First Transition Output High Voltage Output Low Voltage Three-State Output Current at Receiver Receiver Output Short-Circuit Current PROTECTION Thermal Shutdown Threshold Thermal Shutdown Hysteresis ESD Protection: A, B to GND ESD Protection: All Other Pins TTS TTSH IEC 61000-4-2 Air Gap Discharge IEC 61000-4-2 Contact Discharge HBM HBM 160 15 Q20 Q12 Q35 Q2 kV kV NC NC VOH VOL IOZR IOSR VIH VIL VHYS IIN DE, DI RE DE, DI, RE DE, DI, RE DE, DI, RE DE, RE RE = GND, IO = -1mA, VA - VB > 200mV RE = GND, IO = 1mA, VA - VB < -200mV RE = VCC, 0V P VO P VCC 0V P VRO P VCC -1 -95 -1 1 VCC 1.5 0.4 +1 +95 50 +1 10 2.0 2.0 0.8 5.5 V V mV FA kI V V FA mA VTH DVTH SYMBOL VTHF VTHR CONDITIONS -7V P VCM P 12V, VOD falling -7V P VCM P 12V, VOD rising VCM = 0V -7V P VCM P 12V VCM = 0V MIN -200 10 20 -200 170 -105 10 -10 TYP MAX -10 200 UNITS mV mV mV mV mV
MAX14840E/MAX14841E
SWITCHING CHARACTERISTICS
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3) PARAMETER DRIVER Propagation Delay Differential Driver Output Skew |tDPLH - tDPHL| Driver Differential Output Rise or Fall Time tDPLH tDPHL tDSKEW tHL, tLH RL = 54I, CL = 50pF, Figures 2 and 3 (Note 5) RL = 54I, CL = 50pF, Figures 2 and 3 (Notes 5, 8) RL = 54I, CL = 50pF, Figures 2 and 3 (Notes 5, 8) 5 5 12 12 20 20 2 7.5 ns ns ns SYMBOL CONDITIONS MIN TYP MAX UNITS
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3
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
SWITCHING CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3) PARAMETER 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 from Shutdown to Output Low Driver Enable from Shutdown to Output High Time to Shutdown RECEIVER Propagation Delay Receiver Output Skew 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 Low Receiver Enable from Shutdown to Output High Time to Shutdown tRPLH tRPHL tRSKEW DRMAX tRZH tRZL tRLZ tRHZ RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) CL = 15pF, Figures 6 and 7 (Note 5) CL = 15pF, Figures 6 and 7 (Notes 5, 8) 40 20 20 20 20 4 4 50 800 25 25 2 ns ns Mbps ns ns ns ns Fs Fs ns SYMBOL DRMAX tDZH tDZL tDLZ tDHZ tDZL(SHDN) tDZH(SHDN) tSHDN RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) RL = 110I, CL = 50pF, Figures 4 and 5 (Notes 5, 6) (Note 7) 50 CONDITIONS MIN 40 30 30 30 30 4 4 800 TYP MAX UNITS Mbps ns ns ns ns Fs Fs ns
tRZL(SHDN) RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) tRZH(SHDN) RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6) tSHDN (Note 7)
Note 2: All devices are 100% production tested at TA = +25NC. Specifications for all temperature limits are guaranteed by design. Note 3: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device ground, unless otherwise noted. Note 4: DVOD and DVOC are the changes in VOD and VOC, respectively, when the DI input changes state. Note 5: Capacitive load includes test probe and fixture capacitance. Note 6: The timing parameter refers to the driver or receiver enable delay when the device has exited the initial hot-swap protect state and is in normal operating mode. Note 7: Shutdown is enabled by driving RE high and DE low. The device is guaranteed to have entered shutdown after tSHDN has elapsed. Note 8: Parameter is guaranteed by characterization and not production tested.
4
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
Test and Timing Diagrams
A RL 2 VOD RL 2 B VCC DE DI A B VOD RL CL
MAX14840E/MAX14841E
VOC
Figure 1. Driver DC Test Load
Figure 2. Driver Timing Test Circuit
VCC 1.5V 0 tDPLH B
f = 1MHz, tLH = 3ns, tHL = 3ns 1.5V
tDPHL
A VOD VO VOD 0 -VO 10% tLH tHL 10% 90% VOD = [VA - VB] 90%
tDSKEW = tDPLH - tDPHL
Figure 3. Driver Propagation Delays
A GND OR VCC DI D B DE GENERATOR 50I
S1 CL 50pF
OUT RL = 110I DE tDZH, tDZH(SHDN) 1.5V tDHZ 1.5V 0.25V OUT
VCC 0 VOH 0
Figure 4. Driver Enable and Disable Times (tDZH, tDHZ) _______________________________________________________________________________________ 5
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
Test and Timing Diagrams (continued)
VCC RL = 110I S1 OUT
0 OR VCC
DI
A D B DE
GENERATOR
50I
VCC DE VCC OUT VOL tDZL, tDZL(SHDN) 1.5V tDLZ 1.5V 0.25V 0
Figure 5. Driver Enable and Disable Times (tDLZ, tDZL)
A ATE VID B R
RECEIVER OUTPUT
Figure 6. Receiver Propagation Delay Test Circuit
A B VOH RO VOL tRPHL VCC 2
f = 1MHz, tLH P 3ns, tHL P 3ns
1V -1V
tRPLH VCC 2 tRSKEW = tRPHL - tRPLH
Figure 7. Receiver Propagation Delays
6
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
Test and Timing Diagrams (continued)
+1.5V -1.5V S3 VID R RO R 1kI CL 15pF S1 S2
MAX14840E/MAX14841E
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 8. Receiver Enable and Disable Times
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7
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
Typical Operating Characteristics
(VCC = +3.3V, TA = +25NC, unless otherwise noted.)
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE
MAX14840E toc01
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX14840E toc02
SUPPLY CURRENT vs. DATA RATE
MAX14840E toc03
4
4
100 80 SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
SUPPLY CURRENT (A)
3
3
54I LOAD
60 40 20 0 0 10 20 DATA RATE (Mbps) 30 40
2
2
NO LOAD
1
1
RE = GND AND DE = VCC, OR RE = VCC AND DE = VCC
0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C) 0 -40 -15 10 35 60
RE = VCC DE = GND
85 110 125
TEMPERATURE (C)
RECEIVER OUTPUT HIGH VOLTAGE vs. OUTPUT CURRENT
MAX14840E toc04
RECEIVER OUTPUT LOW VOLTAGE vs. OUTPUT CURRENT
MAX14840E toc05
DIFFERENTIAL DRIVER OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX14840E toc06
5 4 3 2 1 0 0 5 10 15 20
5 4 3 2 1 0
5 4 3 2 1 0
VRO (V)
VOD (V)
VRO (V)
25
0
3
6
9
12
15
18
21
24
27
0
20
40 IOD (mA)
60
80
IRO (mA)
IRO (mA)
DIFFERENTIAL DRIVER OUTPUT VOLTAGE vs. TEMPERATURE
MAX14840E toc07
DRIVER OUTPUT CURRENT vs. OUTPUT HIGH VOLTAGE
MAX14840E toc08
DRIVER OUTPUT CURRENT vs. OUTPUT LOW VOLTAGE
120 OUTPUT CURRENT (mA) 100 80 60 40 20 0 0 2 4 6 8 10 12 OUTPUT LOW VOLTAGE (V)
MAX14840E toc09
DIFFERENTIAL DRIVER OUTPUT VOLTAGE (V)
4
100 80 OUTPUT CURRENT (mA) 60 40 20
140
3
2
1
RL = 54I
0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C) 0 -7 -5 -3 -1 1 3 5 OUTPUT HIGH VOLTAGE (V)
8
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = +25NC, unless otherwise noted.)
DRIVER PROPAGATION DELAY vs. TEMPERATURE
MAX14840E toc10
MAX14840E/MAX14841E
DIFFERENTIAL DRIVER SKEW (tDSKEW) vs. TEMPERATURE
MAX14840E toc11
DRIVER OUTPUT RISE AND FALL TIME vs. TEMPERATURE
RL = 54I, CL = 50pF
8 6 4 2 0
MAX14840E toc12
25 DRIVER PROPAGATION DELAY (ns) 20 15 10 5
2.0
10
RL = 54I, CL = 50pF
DRIVER OUTPUT SKEW (ns) 1.5
tDPLH
tDPHL
1.0
0.5
TIME (ns)
RISE TIME
FALL TIME
RL = 54I, CL = 50pF
0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C) 0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C) -40 -15 10 35 60 85 110 125
TEMPERATURE (C)
DRIVER OUTPUT TRANSITION SKEW (tDSKEW) vs. TEMPERATURE
DRIVER OUTPUT TRANSITION SKEW (ns) RECEIVER PROPAGATION DELAY (ns)
RECEIVER PROPAGATION DELAY vs. TEMPERATURE
MAX14840E toc13 MAX14840E toc14
4
25 20 15 10
RL = 54I, CL = 50pF
3
2
tRPLH
1
tRPHL
5
CL = 50pF
0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C) 0 -40 -15 10 35 60 85 110 125 TEMPERATURE (C)
DRIVER/RECEIVER PROPAGATION DELAY
MAX14840E toc15
RECEIVER INPUT CAPACITANCE vs. FREQUENCY
60 CAPACITANCE (pF) 50 40 30 20 10 0 100 1000 10,000 100,000 FREQUENCY (kHz)
MAX14840E toc16
70 DI 5V/div
A/B 2V/div
RO 5V/div
10ns/div
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9
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
Pin Configurations
TOP VIEW
VCC 8 B 7 A 6 GND 5 RO 1 2 3 4 8 VCC B A GND
MAX14840E MAX14841E
+
1 RO 2 RE 3 DE *EP 4 DI
RE DE DI
MAX14840E MAX14841E
7 6 5
SO
TDFN
*CONNECT EXPOSED PAD (EP) TO GND.
Pin Descriptions
PIN 1 2 NAME RO RE Receiver Output. See the Function Table. Active-Low Receiver-Output 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. RE is a hot-swap input (see the Hot-Swap Capability section for details). Driver-Output Enable. Drive DE high to enable driver outputs. These outputs are high impedance when DE is low. Drive RE high and DE low to enter low-power shutdown mode. DE is a hot-swap input (see the Hot-Swap Capability section for details). Driver Input. With DE high, a low on DI forces the A output low and the B output high. Similarly, a high on DI forces the A output high and the B output low. Ground Noninverting Receiver Input and Noninverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply Voltage Input. Bypass VCC with a 0.1FF ceramic capacitor to GND. Exposed Pad (TDFN Only). Connect EP to GND. FUNCTION
3
DE
4 5 6 7 8 --
DI GND A B VCC EP
10
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
Function Table
TRANSMITTING INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X RECEIVING (MAX14840E) INPUTS RE 0 0 0 1 1 DE X X X 1 0 A-B R 200mV P -200mV Open/Shorted X X RECEIVING (MAX14841E) INPUTS RE 0 0 0 1 1 X = Don't care. Note: Shutdown mode, driver, and receiver outputs are in high impedance. DE X X X 1 0 A-B R -10mV P -200mV Open/Shorted X X OUTPUTS RO 1 0 1 High Impedance Shutdown (see note) OUTPUTS RO 1 0 Previous State High Impedance Shutdown (see note) B 0 1 High Impedance Shutdown (see note) OUTPUTS A 1 0 High Impedance
MAX14840E/MAX14841E
Functional Diagram
VCC
MAX14840E MAX14841E
RO RE
R B
SHUTDOWN
DE DI D
A
GND
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11
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
Detailed Description
The MAX14840E/MAX14841E are +3.3V ESD-protected RS-485 transceivers intended for high-speed, half-duplex communications. A hot-swap capability eliminates false transitions on the bus during power-up or hot insertion. The MAX14840E features symmetrical fail-safe and larger receiver hysteresis, providing improved noise rejection and improved recovered signals in high-speed and long cable applications. The MAX14841E has true failsafe receiver inputs guaranteeing a logic-high receiver output when inputs are shorted or open. All devices have a 1-unit load receiver input impedance, allowing up to 32 transceivers on the bus. The MAX14840E/MAX14841E transceivers draw 1.5mA (typ) supply current when unloaded or when fully loaded with the drivers disabled. At high data rates and with long cable lengths, the signal at the end of the cable is attenuated and distorted due to the lowpass characteristic of the transmission line. Under these conditions, fail-safe RS-485 receivers, which have offset threshold voltages, produce recovered signals with uneven mark-space ratios. The MAX14840E has symmetrical receiver thresholds, as shown in Figure 9. This produces near even mark-space ratios at the receiver's output (RO). The MAX14840E also has higher receiver hysteresis than the MAX14841E and most other RS-485 transceivers. This results in higher receiver noise tolerance. Symmetrical fail safe means that the receiver's output (RO) remains at the same logic state that it was before the differential input voltage VOD went to 0V. Under normal conditions, where UART signaling is used, this means that the state on the line prior to all drivers being disabled is a logic-high (i.e., a UART STOP bit). The MAX14841E 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 the case if the receiver input threshold is between -10mV and -200mV. RO is logic-high if the differential receiver input voltage VOD is greater than or equal to -10mV.
True Fail Safe (MAX14841E)
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 powerup sequence. During this period, the processor output drivers are high impedance and are unable to drive the DE and RE inputs of the MAX14840E/MAX14841E to a defined logic level. Leakage currents up to 10FA from the high-impedance 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 MAX14840E/MAX14841E have 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.
Symmetrical Fail Safe (MAX14840E)
RO
-200mV VTHF
-10mV +10mV VTHP VTHP
+200mV
VOD
Figure 9. Symmetrical Hysteresis
12
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers
How-Swap Input Circuitry The MAX14840E/MAX14841E DE and RE enable inputs feature hot-swap capability. At the input, there are two nMOS devices, M1 and M2 (Figure 10). When VCC ramps from 0V, 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 15s, 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. ESD protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver outputs and receiver inputs of the MAX14840E family of devices have extra protection against static electricity. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the MAX14840E/MAX14841E keep working without latchup or damage. ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the MAX14840E/ MAX14841E are characterized for protection to the following limits: * Q35kV HBM * Q20kV using the Air Gap Discharge method specified in IEC 61000-4-2 * Q12kV using the Contact Discharge method specified in IEC 61000-4-2
35kV ESD Protection
MAX14840E/MAX14841E
VCC 15Fs TIMER TIMER
DE
5.6kI
DRIVER ENABLE (HOT SWAP) 100FA M1 1mA M2
Figure 10. Simplified Structure of the Driver Enable Pin (DE)
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13
40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results.
ESD Test Conditions
Figure 11 shows the HBM, and Figure 12 shows the current waveform it generates when discharged into a low-impedance state. This model consists of a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5kI resistor. The IEC 61000-4-2 standard covers ESD testing and performance of finished equipment. However, it does not specifically refer to integrated circuits. The MAX14840E/ MAX14841E family of devices helps you design equipment to meet IEC 61000-4-2, without the need for additional ESD protection components.
Human Body Model
The major 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 model. Hence, the ESD withstand voltage measured to IEC 61000-4-2 is generally lower than that measured using the HBM. Figure 13 shows the IEC 61000-4-2 model, and Figure 14 shows the current waveform for IEC 61000-4-2 ESD Contact Discharge test.
Applications Information
The MAX14840E and MAX14841E are high-performance RS-485 transceivers supporting data rates up to 40Mbps. Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. Current limit on the output stage provides
RC 50M TO 100M CHARGE CURRENT LIMIT RESISTOR RD 330 DISCHARGE RESISTANCE DEVICE UNDER TEST
IEC 61000-4-2
High-Speed Operation
Driver Output Protection
RC 1MI CHARGE CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE CS 100pF
RD 1.5kI DISCHARGE RESISTANCE STORAGE CAPACITOR DEVICE UNDER TEST HIGHVOLTAGE DC SOURCE
Cs 150pF
STORAGE CAPACITOR
Figure 11. Human Body ESD Test Model
Figure 13. IEC 61000-4-2 ESD Test Model
IP 100% 90% AMPERES 36.8% 10% 0 0 tRL
IR
PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
IPEAK
I 100% 90%
10% TIME tDL CURRENT WAVEFORM tR = 0.7ns TO 1ns 30ns 60ns t
Figure 12. Human Body current Waveform
Figure 14. IEC 61000-4-2 ESD Generator Current Waveform
14
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40Mbps, +3.3V, RS-485 Half-Duplex Transceivers MAX14840E/MAX14841E
120 DI D DE RO RE R R D R A B A B A A R RO RE B 120 B D DI DE
MAX14840E MAX14841E
DI
D
DE
RO RE
DI
DE
RO RE
Figure 15. Typical Half-Duplex RS-485 Network
immediate protection against short circuits over the whole common-mode voltage range (see the Typical Operating Characteristics). Additionally, a thermal shutdown circuit forces the driver outputs into a high-impedance state if the die temperature exceeds +160NC (typ). Low-power shutdown mode is initiated by bringing RE high and DE low. In shutdown, the devices draw less than 10FA of supply current. RE and DE can be driven simultaneously; the parts 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 parts are guaranteed to enter shutdown. The MAX14840E/MAX14841E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figure 15 shows a typical network application circuit. To minimize reflections, terminate the line at both ends with its characteristic impedance and keep stub lengths off the main line as short as possible.
Chip Information
PROCESS: BiCMOS
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
Low-Power Shutdown Mode
Typical Applications
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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