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19-0740; Rev 0; 1/07
Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
General Description
The MAX13487E/MAX13488E +5V, half-duplex, 15kV ESD-protected RS-485/RS-422-compatible transceivers feature one driver and one receiver. The MAX13487E/ MAX13488E include a hot-swap capability to eliminate false transitions on the bus during power-up or live insertion. The MAX13487E/MAX13488E feature Maxim's proprietary AutoDirection control. This architecture makes the devices ideal for applications, such as isolated RS-485 ports, where the driver input is used in conjunction with the driver-enable signal to drive the differential bus. The MAX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 500kbps. The MAX13488E driver slew rate is not limited, allowing transmit speeds up to 16Mbps. The MAX13487E/MAX13488E feature a 1/4-unit load receiver input impedance, allowing up to 128 transceivers on the bus. These devices are intended for halfduplex communications. All driver outputs are protected to 15kV ESD using the Human Body Model. The MAX13487E/MAX13488E are available in an 8-pin SO package. The devices operate over the extended -40C to +85C temperature range.
Features
+5V Operation AutoDirection Enables Driver Automatically on Transmission Hot-Swappable for Telecom Applications Enhanced Slew-Rate Limiting Facilitates ErrorFree Data Transmission (MAX13487E) High-Speed Version (MAX13488E) Allows for Transmission Speeds Up to 16Mbps Extended ESD Protection for RS-485 I/O Pins 15kV Human Body Model 1/4-Unit Load, Allowing Up to 128 Transceivers on the Bus 8-Pin SO Package
MAX13487E/MAX13488E
Ordering Information/ Selector Guide
PART MAX13487EESA+ MAX13488EESA+ PINPACKAGE 8 SO 8 SO SLEW-RATE LIMITED Yes No PKG CODE S8-2 S8-2
+Denotes a lead-free package All devices operate over the -40C to +85C temperature range.
Applications
Isolated RS-485 Interfaces Utility Meters Industrial Controls Industrial Motor Drives Automated HVAC Systems
1 RO
Functional Diagram
MAX13487E MAX13488E
+ R RE 2 RE
VCC
8
3
SHDN COM
-
VDT
B7 A6
Pin Configuration and Typical Application Circuit appear at end of data sheet.
RI DI STATE MACHINE
+
DE 4 DI GND 5
D
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND.) Supply Voltage VCC ...............................................................+6V SHDN, RE, DI..............................................................-0.3V to +6 A, B........................................................................... -8V to +13V Short-Circuit Duration (RO, A, B) to GND ..................Continuous Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.9mW/C above +70C)..................471mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering 10s) ..................................+300C
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 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
PARAMETER DRIVER RDIFF = 100, Figure 1 Differential Driver Output Driver Common-Mode Output Voltage Driver Disable Threshold Input-High Voltage Input-Low Voltage Input Current Driver Short-Circuit Output Current (Note 3) Driver Short-Circuit Foldback Output Current (Note 3) RECEIVER Input Current (A and B) Receiver Differential Threshold Voltage Receiver Input Hysteresis Output-High Voltage Output-Low Voltage Tri-State Output Current at Receiver Receiver Input Resistance Receiver Output Short-Circuit Current IA, B VTH VTH VOH VOL IOZR RIN IOSR DI = VCC, VCC = GND or +5V -7V VCM +12V VA + VB = 0V IO = -1.6mA, VA - VB > VTH IO = 1mA, VA - VB < -VTH 0V VO VCC -7V VCM +12V 0V VRO VCC 48 7 95 VCC 1.5 0.4 1 VIN = +12V VIN = -7V -200 -200 25 +200 250 A mV mV V V A k mA VOD RDIFF = 54, Figure 1 No load VOC VDT VIH VIL IIN IOSD RL = 100 or 54, Figure 1 Figure 2 (Note 2) DI, SHDN, RE DI, SHDN, RE DI, SHDN, RE 0V VOUT +12V -7V VOUT 0V (VCC - 1V) VOUT +12V -7V VOUT 0V +50 -250 20 -20 +0.6 2.0 0.8 1 +250 mA -50 mA VCC / 2 2.0 1.5 VCC 3 +1 V V V V A VCC V SYMBOL CONDITIONS MIN TYP MAX UNITS
IOSDF
2
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
PARAMETER POWER SUPPLY Supply Voltage Supply Current Shutdown Supply Current ESD PROTECTION ESD Protection (A, B) ESD Protection (All Other Pins) Air Gap Discharge IEC61000-4-2 (MAX13487E) Human Body Model Human Body Model 15 15 2 kV kV VCC ICC ISHDN SHDN = 1, RE = 0, no load SHDN = 0 4.75 5.25 4.5 10 V mA A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX13487E/MAX13488E
SWITCHING CHARACTERISTICS--MAX13487E
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER DRIVER Driver Propagation Delay Driver Differential Output Rise or Fall Time Maximum Data Rate Driver Disable Delay Driver Enable from Shutdown to Output High Driver Enable from Shutdown to Output Low Time to Shutdown RECEIVER Receiver Propagation Delay Receiver Output Skew Maximum Data Rate Receiver Enable to Output High Receiver Enable to Output Low Receiver Disable Time from High Receiver Disable Time from Low Receiver Enable from Shutdown to Output High tRZH tRZL tRHZ tRLZ tRZH
(SHDN)
SYMBOL tDPLH tDPHL tHL tLH tDDD
CONDITIONS
MIN 200 200 200 200 500
TYP
MAX 1000 1000 900 900 2500 5.5 5.5
UNITS
RL = 110, CL = 50pF, Figures 2 and 3 RL = 110, CL = 50pF, Figures 2 and 3
ns ns kbps ns s s ns
Figure 3
tDZH(SHDN) Figure 4 tDZL(SHDN) Figure 4 tSHDN tRPLH tRPHL tRSKEW 50 340
700 80 80 13
CL = 15pF, Figures 5 and 6 CL = 15pF, Figure 6 500 Figure 7 Figure 7 Figure 7 Figure 7 Figure 8
ns ns kbps ns ns ns ns ns
50 50 50 50 2200
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
SWITCHING CHARACTERISTICS--MAX13487E (continued)
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Receiver Enable from Shutdown to Output Low Receiver Enable Delay Time to Shutdown SYMBOL tRZL
(SHDN)
CONDITIONS Figure 8 Figure 3
MIN
TYP
MAX 2200 70
UNITS ns ns ns
tRED tSHDN
50
340
700
SWITCHING CHARACTERISTICS--MAX13488E
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER DRIVER Driver Propagation Delay Driver Differential Output Rise or Fall Time Maximum Data Rate Driver Disable Delay Driver Enable from Shutdown to Output High Driver Enable from Shutdown to Output Low Time to Shutdown RECEIVER Receiver Propagation Delay Receiver Output Skew Maximum Data Rate Receiver Enable to Output High Receiver Enable to Output Low Receiver Disable Time from High Receiver Disable Time from Low Receiver Enable from Shutdown to Output High tRZH tRZL tRHZ tRLZ tRZH
(SHDN)
SYMBOL tDPLH tDPHL tHL tLH tDDD
CONDITIONS
MIN
TYP
MAX 50 50 15 15
UNITS
RL = 110, CL = 50pF, Figures 2 and 3 RL = 110, CL = 50pF, Figures 2 and 3 16 Figure 3
ns ns Mbps
70 2.2 2.2 50 340 700 80 80 13 16 50 50 50 50 2200
ns s s ns
tDZH(SHDN) Figure 4 tDZL(SHDN) Figure 4 tSHDN tRPLH tRPHL tRSKEW
CL = 15pF, Figures 5 and 6 CL = 15pF, Figure 6 Figure 7 Figure 7 Figure 7 Figure 7 Figure 8
ns ns Mbps ns ns ns ns ns
4
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
SWITCHING CHARACTERISTICS--MAX13488E (continued)
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Receiver Enable from Shutdown to Output Low Receiver Enable Delay Time to Shutdown SYMBOL tRZL (SHDN) tRED tSHDN Figure 8 Figure 3 50 340 CONDITIONS MIN TYP MAX 2200 70 700 UNITS ns ns ns
MAX13487E/MAX13488E
Note 1: All currents into the device are positive. All currents out of the device are negative. All voltages referred to device ground, unless otherwise noted. Note 2: This is a differential voltage from A to B that the driving device must see on the bus to disable its driver. Note 3: The short-circuit output current applied 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.
Typical Operating Characteristics
(VCC = +5.0V, TA = +25C, unless otherwise noted.)
OUTPUT CURRENT vs. RECEIVER OUTPUT-HIGH VOLTAGE
MAX13487Etoc01 MAX13487Etoc02
SUPPLY CURRENT vs. TEMPERATURE
4.0 NO LOAD 3.8 SUPPLY CURRENT (mA) 35
OUTPUT CURRENT vs. RECEIVER OUTPUT-LOW VOLTAGE
MAX13487Etoc03
60 50 OUTPUT CURRENT (mA) 40 30 20 10 0
28 OUTPUT CURRENT (mA)
3.6
21
3.4
14
3.2
7
3.0 -40 -15 10 35 60 85 TEMPERATURE (C)
0 0 1 2 3 4 5 OUTPUT-HIGH VOLTAGE (V)
0
1
2
3
4
5
OUTPUT-LOW VOLTAGE (V)
RECEIVER OUTPUT-HIGH VOLTAGE vs. TEMPERATURE
MAX13487Etoc04
RECEIVER OUTPUT-LOW VOLTAGE vs. TEMPERATURE
MAX13487Etoc05
DIFFERENTIAL OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE
MAX13487Etoc06
5.4 IO = 1mA 5.2 OUTPUT-HIGH VOLTAGE (V) 5.0 4.8 4.6 4.4 4.2 4.0 -40 -15 10 35 60
0.5 IO = 1mA OUTPUT-HIGH VOLTAGE (V) 0.4
80
0.3
OUTPUT CURRENT (mA) -40 -15 10 35 60 85
60
40
0.2
0.1
20
0 85 TEMPERATURE (C) TEMPERATURE (C)
0 0 1 2 3 4 5 OUTPUT VOLTAGE (V)
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Typical Operating Characteristics (continued)
(VCC = +5.0V, TA = +25C, unless otherwise noted.)
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX13487Etoc07
OUTPUT CURRENT vs. TRANSMITTER OUTPUT-HIGH VOLTAGE
MAX13487Etoc08
OUTPUT CURRENT vs. TRANSMITTER OUTPUT-LOW VOLTAGE
MAX13487Etoc09
3.0 RDIFF = 54 DIFFERENTIAL OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 0 -40 -15 10 35 60
120 100 OUTPUT CURRENT (mA) 80 60 40 20 0
120 100 OUTPUT CURRENT (mA) 80 60 40 20 0
85
-7 -6 -5 -4 -3 -2 -1 0
1
2
3
4
5
0
2
4
6
8
10
12
TEMPERATURE (C)
OUTPUT-HIGH VOLTAGE (V)
OUTPUT-LOW VOLTAGE (V)
SHUTDOWN CURRENT vs. TEMPERATURE
MAX13487Etoc10
DRIVER PROPAGATION vs. TEMPERATURE (MAX13487E)
MAX13487Etoc11
DRIVER PROPAGATION vs. TEMPERATURE (MAX13487E)
RL = 110 tDPLH
MAX13487Etoc12
10 9 SHUTDOWN CURRENT (A) 8 7 6 5 4 3 2 1 0 -40 -15 10 35 60
1000 DRIVER PROPAGATION DELAY (ns)
600 DRIVER PROPAGATION DELAY (ns) 500 400 300 200 100 0
RL = 10k
800 tDPLH 600
400
tDPHL
200 tDPHL 0
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
DRIVER PROPAGATION vs. TEMPERATURE (MAX13488E)
MAX13487Etoc13
DRIVER PROPAGATION vs. TEMPERATURE (MAX13488E)
RL = 110
MAX13487Etoc14
RECEIVER PROPAGATION vs. TEMPERATURE (MAX13487E)
MAX13487Etoc15
30 DRIVER PROPAGATION DELAY (ns) 25 20 15 10
RL = 10k
30 DRIVER PROPAGATION DELAY (ns) 25 20 15 10
60
PROPAGATION DELAY (ns)
45
30
tRPHL
tDPLH 5 tDPHL 0 -40 -15 10 35 60 85 TEMPERATURE (C)
tDPLH 5 tDPHL 0 -40 -15 10 35 60 85 TEMPERATURE (C)
15 tRPLH 0 -40 -15 10 35 60 85 TEMPERATURE (C)
6
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Typical Operating Characteristics (continued)
(VCC = +5.0V, TA = +25C, unless otherwise noted.)
RECEIVER PROPAGATION vs. TEMPERATURE (MAX13488E)
MAX13487Etoc16
DRIVER PROPAGATION (500kbps) (MAX13487E)
MAX13487Etoc17
DRIVER PROPAGATION (16Mbps) (MAX13488E)
MAX13487Etoc18
40
RECEIVER PROPAGATION (ns)
30 tRPLH 20 tRPHL
DI 2V/div
DI 2V/div
10
A-B 5V/div WAVEFORM INTENSITY: 68% -40 -15 10 35 60 85 400ns/div 10ns/div
A-B 5V/div
0 TEMPERATURE (C)
RECEIVER PROPAGATION (16Mbps) (MAX13488E)
MAX13487Etoc19
DRIVING 16nF (19.2kbps) (MAX13487E)
B 2V/div
MAX13487Etoc20
DI 2V/div
A 2V/div
RO 2V/div
A-B 5V/div
10ns/div
10s/div
DRIVING 16nF (19.2kbps) (MAX13488E)
MAX13487Etoc21
DRIVING 16nF (750kbps) (MAX13488E)
MAX13487Etoc22
DI 2V/div
DI 2V/div
A-B 5V/div
A-B 5V/div
10s/div
400ns/div
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Test Circuits and Waveforms
A RDIFF RL 2 DI A VID B RDIFF 2 VOC VCC GND RL CL
VOD
CL
B
Figure 1. Driver DC Test Load
Figure 2. Driver-Timing Test Circuit
VCC DI 0 1.5V
RE = VCC
f = 1MHz, tLH 3ns, tHL 3ns 1.5V 1/2 VO
tDPLH B VO A 1/2 VO RO O VO VDIFF 0 -VO tLH 10% (RO PULLED LOW) tDDD, tRED
tDPHL
VDIFF = V(A) - V(B) 90% 90% 10% tHL
Figure 3. Driver Propagation Delays
8
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
Test Circuits and Waveforms (continued)
MAX13487E/MAX13488E
VCC SHDN 0 tDZL(SHDN) A, B OUTPUT UNDER TEST CL 500 S1 S2 VCC VOL A, B 2.3V 0 tDZH(SHDN) 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH 1.5V
Figure 4. Driver Enable and Disable Times
B ATE VID A R RECEIVER OUTPUT
Figure 5. Receiver-Propagation-Delay Test Circuit
A B
f = 1MHz, tLH 3ns, tHL 3ns
1V -1V
tRPHL VOH RO VOL 1.5V tRSKEW = | tRPHL - tRPLH |
tRPLH
1.5V
Figure 6. Receiver Propagation Delays
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Test Circuits and Waveforms (continued)
VCC RE 0 tRZL(SHDN), tRZL VCC RO 0 VCC RO 0 DI = 0V tRZH(SHDN), tRZH tRHZ 2.3V 2.3V VOH + 0.5V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH VOH + 0.5V tRHZ 1.5V 1.5V
Figure 7. Receiver Enable and Disable Times
VCC SHDN 0 tRZL(SHDN) VCC 500 RO CL S1 S2 RO 0 tRZH(SHDN) DI = 1 VCC RO 0 VCC 2.3V 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH 1.5V
Figure 8. Receiver Enable Time from Shutdown
10
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
Pin Description
PIN 1 2 3 NAME RO RE SHDN FUNCTION Receiver Output. When receiver is enabled and V(A) - V(B) > +200mV, RO is high. If V(A) - V(B) < -200mV, RO is low. Receiver Output Enable. Drive RE low to enable the RO. Drive RE high to let the AutoDirection circuit control the receiver. RE is a hot-swap input (see the Hot-Swap Capability section for more details). Shutdown. Drive SHDN high to let the device operate in normal operation. Drive SHDN low to put the part in shutdown. Driver Input. Drive DI low to force noninverting output low and inverting output high. Drive DI high to force noninverting output high and inverting output low. DI is an input to the internal state machine that automatically enables and disables the driver. See the Function Tables and General Description for more information. DI is a hot-swap input (see the Hot-Swap Capability section for more details). Ground Noninverting Receiver Input and Noninverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply, VCC = +5V 5%. Bypass VCC to GND with a 0.1F capacitor.
MAX13487E/MAX13488E
4
DI
5 6 7 8
GND A B VCC
Function Tables
TRANSMITTING INPUTS SHDN 1 1 1 1 0 DI 0 1 1 1 X A-B > VDT X False False True X ACTION Turn driver ON If driver was OFF, keep it OFF If driver was ON, keep it ON Turn driver OFF X RECEIVING INPUTS SHDN 1 1 1 1 1 0 RE 0 0 1 1 1 X A-B +200mV -200mV X >+200mV -200mV X DRIVER STATE X X ON OFF OFF X RECEIVER STATE ON ON OFF ON ON X OUTPUT RO 1 0 HIGH IMPEDANCE 1 0 SHUTDOWN A 0 HIGH IMPEDANCE 1 HIGH IMPEDANCE SHUTDOWN OUTPUTS B 1 HIGH IMPEDANCE 0 HIGH IMPEDANCE
X = Don't care, shutdown mode, driver, and receiver outputs are in high impedance.
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Detailed Description
The MAX13487E/MAX13488E half-duplex, high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. The MAX13487E/ MAX13488E feature a hot-swap capability allowing line insertion without erroneous data transfer (see the HotSwap Capability section). The MAX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission up to 500kbps. The MAX13488E driver slew rate is not limited, making data throughput of up to 16Mbps possible. important factor when sizing these resistors is to guarantee that the idle voltage on the bus (A-B) is greater than 200mV in order to remain compatible with standard RS-485 receiver thresholds. Idle State When not transmitting data, the MAX13487E/ MAX13488E require the DI input be driven high to remain in the idle state. A conventional RS-485 transceiver has DE and RE inputs that are used to enable and disable the driver and receiver. However, the MAX13487E/MAX13488E does not have a DE input, and instead uses an internal state machine to enable and disable the drivers. DI must be driven high in order to go to the idle state.
AutoDirection Circuitry
Internal circuitry in the MAX13487E/MAX13488E, in conjunction with an external pullup resistor on A and pulldown resistor on B (see Typical Operation Circuit), act to automatically disable or enable the driver and receiver to keep the bus in the correct state. This AutoDirection circuitry consists of a state machine and an additional receive comparator that determines whether this device is trying to drive the bus, or another node on the network is driving the bus. The internal state machine has two inputs: * DI * The current state of A-B (determined by a dedicated differential comparator) The state machine also has two outputs: * DRIVER_ENABLE--Internal signal that enables and disables the driver * RECEIVER_ENABLE--Internal signal that is the inverse of the DRIVER_ENABLE signal, but it can be overridden by an external pin When DI is low, the device always drives the bus low. When DI is high, the device drives the bus for a short time, then disables the driver and allows the external pullup/pulldown resistors to hold the bus in the high state (A-B > 200mV). During each low-to-high transition of DI, the driver stays enabled until (A-B) > VDT, and then disables the driver, letting the pullup/pulldown resistors hold the A and B lines in the correct state. Pullup and Pulldown Resistors The pullup and pulldown resistors on the A and B lines are required for proper operation of the device although their exact value is not critical. They function to hold the bus in the high state (A-B > 200mV) following a low-to-high transition. Sizing of these resistors is determined in the same way as when using any other RS-485 driver and depends on how the line is terminated and how many nodes are on the bus. The most
12
Hot-Swap Capability
Hot-Swap Inputs When circuit boards are inserted into a hot or powered back plane, differential disturbances to the data bus can lead to data errors. Upon initial circuit-board insertion, the data communication processor undergoes its own power-up sequence. During this period, the processor's logic-output drivers are high impedance and are unable to drive the DI and RE inputs of these devices to a defined logic level. Leakage currents up to 10A from the high-impedance state of the processor's logic drivers could cause standard CMOS enable inputs of a transceiver to drift to an incorrect logic level. Additionally, parasitic circuit-board capacitance could cause coupling of VCC or GND to the enable inputs. Without the hot-swap capability, these factors could improperly enable the transceiver's driver. To overcome both these problems, two different pullup switches (strong and weak) are turned on during the power-up. When VCC rises, an internal power-up signal enables a strong pullup circuit. It holds DI and RE high with 1mA for 15s. Once the timeout is expired, this strong pullup is switched off. A weak pullup (100A) remains active to overcome leakage on the pin. This second weak pullup disappears as soon as the microcontroller forces a low state on these pins. Therefore, in normal operation (after the first activation), these pins can be considered as high-impedance pins (CMOS inputs) without any pullup circuitry. The AutoDirection state machine is initialized, forcing the driver disabled. The receiver is enabled in AutoDirection mode. Hot-Swap Input Circuitry The enable inputs feature hot-swap capability. At the input there are two pMOS devices, M1 and M2 (Figure 9). When VCC ramps from zero, an internal 15s timer turns
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
on M2 and sets the SR latch, which also turns on M1. Transistors M2, a 1.5mA current source, and M1, a 500A current source, pull RE to VCC through a 5k resistor. M2 is designed to pull RE to the disabled state against an external parasitic capacitance up to 100pF that can drive RE high. After 15s, the timer deactivates M2 while M1 remains on, holding DI high against three-state leakages that can drive RE low. 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, RE reverts to a standard, high-impedance CMOS input. Whenever VCC drops below 1V, the hot-swap input is reset. DI has similar hot-swap circuitry.
MAX13487E/MAX13488E
VCC 15s TIMER SR LATCH TIMER
15kV ESD Protection
As with all Maxim devices, 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 MAX13487E/MAX13488E have extra protection against static electricity. Maxim's engineers have developed state-of-the-art structures to protect these pins against ESD of 15kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the MAX13487E/MAX13488E keep working without latchup or damage. ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the MAX13487E/MAX13488E are characterized for protection to the following limits: * 15kV using the Human Body Model * 15kV using the Air Gap Discharge Method specified in 61000-4-2 (MAX13487E only) ESD Test Conditions ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results. Human Body Model Figure 10a shows the Human Body Model, and Figure 10b 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 test device through a 1.5k resistor. IEC 61000-4-2 The IEC 61000-4-2 standard covers ESD testing and performance of finished equipment. However, it does not specifically refer to integrated circuits. The MAX13487E/MAX13488E help you design equipment to
5k RE 100A 500A M1 VCC M2
RE (HOT SWAP)
Figure 9. Simplified Structure of the Receiver Enable Pin (RE)
meet IEC 61000-4-2 without the need for additional ESD-protection components. The major difference between tests done using the Human Body Model 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 Human Body Model. Figure 10c shows the IEC 61000-4-2 model, and Figure 10d shows the current waveform for IEC 61000-4-2 ESD Contact Discharge test. Machine Model The machine model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. The objective is to emulate the stress caused when I/O pins are contacted by handling equipment during test and assembly. Of course, all pins require this protection, not just RS-485 inputs and outputs. The Air-Gap test involves approaching the device with a charged probe. The Contact-Discharge method connects the probe to the device before the probe is energized.
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13
Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
RC 1M CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1500 DISCHARGE RESISTANCE DEVICE UNDER TEST HIGHVOLTAGE DC SOURCE RC 50M TO 100M CHARGE-CURRENTLIMIT RESISTOR RD 330 DISCHARGE RESISTANCE DEVICE UNDER TEST
Cs 100pF
STORAGE CAPACITOR
Cs 150pF
STORAGE CAPACITOR
Figure 10a. Human Body ESD Test Model
Figure 10c. ICE 61000-4-2 ESD Test Model
I 100% 90% IPEAK
IP 100% 90% AMPS 36.8% 10% 0 0 tRL TIME
Ir
PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
10% tDL CURRENT WAVEFORM tr = 0.7ns TO 1ns 30ns 60ns t
Figure 10b. Human Body Current Waveform
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
Applications Information
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12k (1-unit load), and the standard driver can drive up to 32-unit loads. The MAX13487E/MAX13488E have a 1/4unit load receiver input impedance (48k), allowing up to 128 transceivers to be connected in parallel on one communication line. Any combination of these devices, as well as other RS-485 transceivers with a total of 32unit loads or fewer, can be connected to the line.
Low-Power Shutdown Mode
Low-power shutdown mode is initiated by bringing SHDN low. In shutdown, the devices draw a maximum of 10A of supply current. The devices are guaranteed not to enter shutdown if SHDN is low for less than 50ns. If the inputs are in this state for at least 700ns, the devices are guaranteed to enter shutdown. Enable times tZH and tZL (see the Switching Characteristics section) assume the devices were not in a lowpower shutdown state. Enable times t ZH(SHDN) and tZL(SHDN) assume the devices were in shutdown state. It takes drivers and receivers longer to become enabled from low-power shutdown mode (tZH(SHDN), tZL(SHDN)) than from driver/receiver-disable mode (tZH, tZL).
Reduced EMI and Reflections
The MAX13487E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps.
Line Length
The RS-485/RS-422 standard covers line lengths up to 4000ft.
14
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
VCC VCC
DI SHDN RO RE
D
Rt VCC R
Rt VCC R
D
DI SHDN RO RE
MAX13487E MAX13488E
D
R
R
D
DI
SHDN
RO
RE
DI SHDN
RO
RE
Figure 11. Typical Half-Duplex RS-485 Network
Typical Applications
The MAX13487E/MAX13488E transceivers are designed for half-duplex, bidirectional data communications on multipoint bus transmission lines. Figure 11 shows a typical network application. To minimize reflections, terminate the line at both ends in its characteristic impedance, and keep stub lengths off the main line as short as possible. The slew-rate-limited MAX13487E is more tolerant of imperfect termination.
Circuit shows an isolated RS-485 interface using the MAX13487E/MAX13488E. The transceiver is powered separately from the controlling circuitry. The AutoDirection feature of the MAX13487E/MAX13488E (see the AutoDirection Circuitry section), replaces an external relay allowing faster switching speeds, no contact bounce, better reliability, and better electrical isolation. The MAX13487E/MAX13488E only require two optocouplers to electrically isolate the transceiver.
Isolated RS-485 Interface
An isolated RS-485 interface electrically isolates different nodes on the bus to protect the bus from problems due to high common-mode voltages that exceed the RS-485 common-mode voltage range, conductive noise, and ground loops. The Typical Application
Chip Information
PROCESS: BiCMOS
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15
Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control MAX13487E/MAX13488E
Pin Configurations/Typical Application Circuit
VSYS RXD VISO
VCC 0.1F RO + 1 2 3 4 D R 8 7 6 5 GND B Rt A VCC
VISO VISO VSYS
RE SHDN DI
TXD
SO
16
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Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX13487E/MAX13488E
INCHES DIM A A1 B C e E H L MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050
MILLIMETERS MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 1.27
N
E
H
VARIATIONS:
1
INCHES
MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC
TOP VIEW
DIM D D D
MIN 0.189 0.337 0.386
MAX 0.197 0.344 0.394
D A e B A1 L C
0-8
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL DOCUMENT CONTROL NO. REV.
21-0041
B
1 1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Boblet
SOICN .EPS

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