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PRELIMINARY TECHNICAL DATA
a
Low-Current (1A) Shutdown Mode Slew Rate Control for Error-Free Data Transmission and Low EMI
Ultra-Low Power RS-485/RS-422 Transceiver with Low EMI and +/-10kV ESD Protection
Preliminary Technical Data
FEATURES Low Power - 120A Max ICC with Driver Disabled High Input Impedance -- Up to 256 Transceivers on Bus GENERAL DESCRIPTION
ADM1487
The ADM1487 is an ultra-low power RS-485/RS-422 transceiver consisting of one driver and one receiver per package. Quiescent operating current is typically 80A and 1A in shutdown mode. The driver and receiver both have three-state outputs. This allows multiple drivers to be connected to an RS-485/RS-422 bus, or several receiver outputs to be connected to a serial data bus. The driver will maintain a high-impedance output state even with power off, while the receiver features fail-safe operation that guarantees a logic high output if the inputs are left open-circuit. The device has slew-rate limited drivers to minimize electromagnetic interference (EMI) and reduce reflections caused by incorrectly terminated cables.
10kV ESD Protection (Human Body Model) on RS-485 I/O pins Thermal Protection of Driver Glitch-Free Driver Power-Up Allows Hot Connection Driver Maintains High Output Impedance with Power Off Wide Common-Mode Range Allows 7V Ground Differences Between Devices Pin-Compatible with Industry Standard 75176 APPLICATIONS Battery-Powered RS-485/RS-422 Systems Level Translation
FUNCTIONAL BLOCK DIAGRAM
RO RE DE DI
1
R
8 7 6
D
VCC B A GND
2 3 4
5
ADM1487
REV. PrC 08/02
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P Box 9106, Norwood, MA 02062-9106, U.S.A. .O. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2002
-1-
PRELIMINARY TECHNICAL DATA ADM1487
ADM1487 SPECIFICATIONS
DC ELECTRICAL CHARACTERISTICS (VCC = +5V 5%, TA = 0C TO +70C, UNLESS OTHERWISE NOTED)
Parameter Differential Driver Output Voltage,VOD1 Differential Driver Output Voltage, VOD2 Change in Magnitude of Driver Differential Output Voltage for Complementary Output States, Driver Common-Mode Output Voltage, VOC Change in Magnitude of Driver Common-Mode Output Voltage for Complementary Output States, |VOC| Input High Voltage (DE, DI, RE), VIH Input Low Voltage (DE, DI, RE), VIL Input Current (DE, DI, RE), IIN1 Input Current (A, B), IIN2 Differential Input Threshold Voltage for Receiver, VTH Receiver Input Hysteresis, VTH
Min
Typ
Max 5
Units V V V V
Test Conditions/Comments Unloaded, IO = 0 Figure 1, R = 50 Figure 1, R = 27 Figure 1, R = 27 (RS-422) (RS-485) or R = 50
2.0 1.5
5 0.2
VOD
3 0.2
V V
Figure 1, R = 27 R = 27
or R = 50
or R = 50
2 0.8 2 0.30 -0.15 -0.2 45 3.5 0.4 1 70 96 120 80 1 35 35 7 250 85 200 120 10 250 0.2
V V A mA mA V mV V V A k A A A mA mA mA DE = 0, VCC= 0V or 5.25V, VIN = 12V DE = 0, VCC = 0V or 5.25V, VIN = -7V -7V VCM 12V
VCM = 0V IO =-4mA, VID = 200mV IO = 4mA, VID = -200mV VCC = Max, 0.4V -7V VCM 12V Vo 2.4V
Receiver Output High Voltage, VOH Receiver Output Low Voltage, VOL Three-State (High Impedance) Output Current at Receive, IOZR Receiver Input Resistance, RIN Supply Current, ICC Supply Current in Shutdown Mode, ISHDN Driver Short-Circuit Ourrent, IOSD1 Driver Short-Circuit Ourrent, IOSD2 Receiver Short-Circuit Current, IOSR
No Load, Output Enabled No Load, Output Disabled DE = 0V, RE = VCC VOUT = HIGH, -7V VOUT = LOW, -7V 0V VO VOC VO Vo 12V 12V
-2-
Rev. PrC
PRELIMINARY TECHNICAL DATA
ADM1487
ADM1487 SPECIFICATIONS (continued)
ELECTRICAL CHARACTERISTICS (VCC = +5V 5%, TA = -40C TO +85C, UNLESS OTHERWISE NOTED)
Parameter Differential Driver Output Voltage, VOD1 Differential Driver Output Voltage, VOD2 Driver Common-Mode Output Voltage, VOC Differential Input Threshold Voltage for Receiver, VTH Receiver Input Hysteresis, Supply Current, ICC Supply Current in Shutdown Mode, ISHDN Driver Input to Output High, tDPLH Driver Input to Output Low, tDPHL Driver Output to Output, tSKEW Driver Rise or Fall Time, tDR, tDF Receiver Input to Output High, tRPLH Receiver Input to Output Low, tRHL Differential Receiver Skew, tSKD |tRPLH-tRPHL| Maximum Data Rate, fMAX VTH
Min
Typ
Max 5
Units Test Conditions/Comments V V V V V mV Unloaded, IO = 0 Figure 1, R = 50 Figure 1, R = 27 Figure 1, R = 27 -7V VCM 12V (RS-422) (RS-485) or R = 50
2.0 1.5
5 3
-0.2 45 120 80 1 150 150 100 150 30 30 140 140 13 250
0.2
VCM = 0V No Load, Output Enabled No Load, Output Disabled DE = 0V, RE = VCC Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 4, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 4, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 4, RDIFF= 54 , CL1 = CL2 = 100pF
200 120 10 1200 1200 600 2000 250 250
A A A ns ns ns ns ns ns ns kbps
SWITCHING CHARACTERISTICS (VCC = +5V 5%, TA = -40C TO +85C, UNLESS OTHERWISE NOTED)
Parameter Driver Input to Output High, tDPLH Driver Input to Output, tDPHL Driver Output to Output, tSKEW Driver Rise or Fall Time, tDR, tDF Driver Enable to Output High, tDZH Driver Enable to Output Low, tDZL Driver Disable Time from Low, tDLZ
Min 150 150
Typ
Max 1200 1200
Units Test Conditions/Comments ns ns ns ns ns ns ns Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 2, 3, RDIFF= 54 , CL1 = CL2 = 100pF Figures 5, 6, CL = 100pF, S2 Closed Figures 5, 6, CL = 100pF, S1 Closed Figures 5, 6, CL = l5pF, S1 Closed
250 150 100 100 150
600 1200 1500 1500 1500
Rev. PrC
-3-
PRELIMINARY TECHNICAL DATA ADM1487
ADM1487 SPECIFICATIONS (continued)
SWITCHING CHARACTERISTICS (VCC = +5V 5%, TA = -40C TO +85C, UNLESS OTHERWISE NOTED)
Parameter Driver Disable Time from High, tDHZ Receiver Input to Output, tRPLH Receiver Input to Output Low, tRPHL DifferentialReceiverSkew, tSKD |tPLH-tPHL| Receiver Enable to Output Low, tRZL Receiver Enable to Output High, tRZH Receiver Disable from Low, tRLZ Receiver Disable from High, tRHZ Maximum Data Rate, fMAX Time to Shutdown, tSHDN Driver Enable from Shutdown to Output High, tDZH(SHDN) Driver Enable from Shutdown to Output Low, tDZL(SHDN) Receiver Enable from Shutdown to Output High, tRZH(SHDN) Receiver Enable from Shutdown to Output Low, tRZL(SHDN)
NOTES
1 2
Min 150 30 30
Typ
Max 1500
Units Test Conditions/Comments ns ns ns ns Figures 5, 6, CL= l5pF, S2 Closed Figures.2, 4, RDIFF= 54 , CL1 = CL2 = 100pF Figures.2, 4, RDIFF= 54 , CL1 = CL2 = 100pF Figures.2, 4, RDIFF= 54 , CL1 = CL2 = 100pF Figures 7, 8, CRL = l5pF, S1 Closed Figures 7, 8, CRL = l5pF, S2 Closed Figures 7, 8, CRL = l5pF, S1 Closed Figures 7, 8, CRL = l5pF, S2 Closed
140 140 13 20 20 20 20
250 250
50 50 50 50
ns ns ns ns kbps
250 50 200 600 2000 2000 2000 2000
ns ns ns ns ns
DE = 0, RE = low to high transition Figures 5, 6, CL = 100pF, S2 Closed Figures 5, 6, CL = 100pF, S1 Closed Figures 7, 8, CL = l5pF, S2 Closed Figures 7, 8, CL = l5pF, S1 Closed
Absolute maximum ratings are those beyond which the safety of the device cannot be guaranfeed. All currents into device pins are positive; all currents out ot device pins are negative. All voltages are referenced to device ground unless otherwise specified. 3 All typicals are given for Vcc = 5V and Tp = 25C. 4 The ADM1487 is not tested and is not quality-assurance sampled at -40C and at 85C. These specifications are guaranteed by design, correlation, andlor inference from 0C, 25C and/or 70C tests.
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
RO RE DE DI 1 2 3 4 8 VCC
Supply Voltage (Vcc) . . . . . . . . . . . . . . . . . . . . . . . . . . 12V Control Input Voltage . . . . . . . . . . . -0.5V to Vcc + 0.5V Driver Input Voltage . . . . . . . . . . . -0.5V to Vcc + 0.5V Driver Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . 14V Receiver InputVoltage . . . . . . . . . . . . . . . . . . . . . . . . 14V Receiver Output Voltage . . . . . . . . . -0.5V to Vcc + 0.5V 70C Operating Temperature Range . . . . . . 0C TA Lead Temperature (Soldering, 10 sec) . . . . . . . . . 300C
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ADM1487
TOP VIEW (Not to Scale)
7B 6A 5 GND
ORDERING INFORMATION
Model ADM1487JN ADM1487JR
Temperature Range 0C to +70C 0C to +70C
Package Option 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO
THERMAL CHARACTERISTICS
8-Pin Plastic DIP Package JA = tbd K/Watt, JC = tbd K/Watt 8-Pin Plastic SO Package JA = tbd K/Watt, JC = tbd K/Watt -4-
ADM1487AN -40C to +85C ADM1487AR -40C to +85C
Rev. PrC
PRELIMINARY TECHNICAL DATA
ADM1487
ADM1487 TEST CIRCUITS AND TIMING
A R VOD R
S1 TEST POINT VCC
A
VOC
OUTPUT UNDER TEST CRL 15pF
500V
S2
Figure 1. Driver DC Load Test Circuit
3V
Figure 5. Test Load for Driver Enable/Disable Time Test
DE DI A D B VOD2 RDIFF CL2 CL1 R B 15pF A, B VOL RO DE 0V 5V tDZL(SHDN), tDZL 2.3V OUTPUT NORMALLY LOW tDLZ VOL+ 0.5V A 3V 1.5V f = 1MHz, tr # 10ns, tf # 10ns
Figure 2. Driver/Receiver Timing Test Circuit
3V DI 0V tDPLH B V0 A V0/2 V0 0V -V0 VDIFF = VA - VB 10% 90% tDR tSKEW = |tDPLH-tDPHL| 90% tDF 10% tDPHL 1.5V f = 1MHz, tr # 10ns, tf # 10ns
VOH A, B VOL
2.3 V t
OUTPUT NORMALLY HIGH tDHZ
VOH- 0.5V
DZH(SHDN), tDZH
Figure 6. Driver Enable and Disable Times
VCC
TEST POINT
1kV
VDIFF
S1 RO CRL 15pF S2
Figure 3. Driver Propagation Delays
A VOD2 B -VOD2 VOH RO VOL
3V
f = 1MHz, tr # 10ns, tf # 10ns
1kV
tRPHL
tRPLH 1.5V
Figure 7. Test Load for Receiver Enable/Disable Time Test
RE 0V 5V RO 1.5 V 5V RO 0V tRZL(SHDN), tRZL OUTPUT NORMALLY LOW tRLZ 0.5V 0.5V tRHZ f = 1MHz, tr # 10ns, tf # 10ns 1.5 V
Figure 4. Receiver Propagation Delays
OUTPUT NORMALLY HIGH 1.5 V tRZH(SHDN), tRZH
Figure 8. Receiver Enable and Disable Delay Times
Rev. PrC
-5-
PRELIMINARY TECHNICAL DATA ADM1487
ADM1487 TYPICAL PERFORMANCE CHARACTERISTICS
A
AW
A
I IT
NG
T DA
AW
A
I IT
NG
AT D
A AI N TI G
T DA
A
AW
TPC1. No-load Supply Current vs. Temperature
TPC2. Output Current vs. Receiver Output High Voltage
TPC3. Output Current vs. Receiver Output Low Voltage
AW
AI
N TI
G
T DA
A AI N TI G
T DA
A AI N TI G
T DA
A
AW
AW
TPC4. Receiver Output High Voltage vs. Temperature PIN FUNCTION DESCRIPTION
TPC5. Receiver Output Low Voltage vs. Temperature
TPC6. Shutdown Current vs. Temperature
Pin Mnemonic 1 2 3 4 5 6 7 8 RO RE DE DI GND A B VCC
Description Receiver Output. When RE is low and A - B (more positive than) 200mV, RO will be high. When RE is low and A - B (more negative than) -200mV, RO will be low. Receiver Output Enable. Take RE low to enable RO; RO is high impedance when RE is high. Take RE high and DE low to enter low-power shutdown mode. Driver Output Enable. Take DE high to enable driver outputs. These outputs are high impedance when DE is low. Take RE high and DE low to enter low-power shutdown mode. Driver Input. With DE high, a low on DI forces non-inverting output low and inverting output high. Similarly, a high on DI forces non-inverting output high and inverting output low. Ground Non-Inverting Receiver Input and Non-Inverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply 4.75V =VCC =5.25V -6- Rev. PrC
PRELIMINARY TECHNICAL DATA
ADM1487
DEVICE TRUTH TABLES TRANSMITTING RECEIVING
INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X Z 0 1
OUTPUTS Y 1 0 High-Z RE 0 0 0 1
INPUTS DE X X X 0 A-B 0.2V -0.2V Open/shorted X
OUTPUT RO 1 0 1 Shutdown*
High-Z
Shutdown*
X = Don't care
CIRCUIT DESCRIPTION
*In shutdown mode, driver and receiver outputs high impedance
SHUTDOWN MODE
The ADM1487 is a differential input, differential output transceiver designed RS-485/RS-422 serial data communications over twisted-pair cables. It is a half-duplex device intended for alternate transmission and reception of data over a single twisted-pair cable, and the driver outputs and receiver inputs are internally linked and brought out to a single pair of pins. Its principal features include ultra-low power operation, a controlled slew-rate driver that minimizes electromagnetic interference (EMI) and signals reflections due to incorrectly terminated lines, and high input impedance that allows up to 256 receivers to be connected to a bus.
THREE-STATE BUS CONNECTION
If RE is taken high while DE is taken low, the device will enter a low-power shutdown mode, in which the supply current is typically 1A. If the driver outputs are active immediately before shutdown (DE high), the supply current will not drop to 1 until the driver outputs have settled to their three-state mode, which can take up to 2.6s worst-case. If DE is already low and shutdown is entered by taking RE high, the supply current will drop to 1A very quickly. When RE is taken low and/or DE is takem high, the device will wake up within 3.5s. If shutdown mode is not used, the fact that DE is activehigh and RE is active-low offers a convenient way of switching the device between transmit and receive, by tying DE and RE together. This is useful, for example, in applications using half duplex operation and where several receiver outputs are connected to a serial bus. The device is guaranteed not to enter shutdown mode if DE and RE are driven in this way. If DE is low and RE is high for less than 50ns the device will not enter shutdown. If DE is low and RE is high for greater than 600ns, the device is guaranteed to enter shutdown.
RECEIVER INPUTS
The ADM1487 has a Driver Enable pin (DE) that enables the driver outputs when taken high or puts the driver outputs into a high-impedance state when taken low. This allows several driver outputs to be connected to an RS-422/ RS-485 bus. Similarly, the device has a (active-low) Receiver Enable pin (RE). Taking this low enables the receiver, while taking it high puts the receiver outputs into a high-impedance state. This allows several receiver outputs to be connected to a serial data bus. The input impedance of the device is 96k , which is 8 times higher than the standard RS-485 load of 12k . A standard driver can driver 32 standard loads, so up to 256 ADM1487 receivers, or a combination of ADM1487 and other devices up to 32 unit loads, may be connected to an RS-422/RS485 bus driven by a single driver.
LOW POWER OPERATION
The ADM1487 receiver has an input common-mode range covering the entire RS-485 range of -7V to 12V. Internal 96k input resistors from each line terminal to ground provide a 1/8 unit load to the RS485 bus. Differential signals greater than 200mV within the specified input common-mode range are converted to a TTLcompatible logic signal at the receiver output. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the line is terminated or the receiver inputs are shorted together, the receiver output will retain the last valid line signal due to the 45mV of hysteresis incorporated in the receiver circuit. If the receiver inputs are left floating (unterminated), an internal pull-up of 10A at the A input will force the receiver output to a guranteed high output state.
DRIVER OUTPUT STAGE
The ADM1487 draws very little supply current (typically 80A) when the driver outputs are disabled or unloaded. This will increase by up to 72A if the driver outputs are enabled (but unloaded) and applying the maximum output swing of 5V across the receiver input resistors. However, in practical applications with the device driving and RS-485/RS422 cable or bus, the current drain is dominated by the current sourced into the line termination resistors and any other devices on the bus. With a half-termination (120 load) between the driver outputs, the load current can be in excess of 13mA as the drivers force a minimum of 1.5V across the line, and can be greater than 25mA with a fully terminated 60 line attached. Rev. PrC
The RS-485 specification requires that a transceiver withstand common-mode voltages of up to 12V above or -7V below system ground at the RS-485 line connections. In addition, the transceiver must be protected against both ESD and latch-up. This precludes the use of conventional -7-
PRELIMINARY TECHNICAL DATA ADM1487
CMOS outout stages, which include parasitic diodes from their driver outputs to each supply rail and can latch up when these diodes conduct.
VCC S CH O T T KY RE V E RS E -BIA S E D W H E N O UT P UT > V CC +V D P A RA S ITIC DIO DE D P
CURRENT LIMIT AND THERMAL SHUTDOWN
P A RA S IT IC D IO D E D P
S C HO TT K Y R E V ER S E -B IAS E D W HE N O U TP U T < GND - VD
The ADM1487 incorporates two protection mechanisms to guard the drivers against short-circuits, bus contention or other fault conditions. The first is a current-limited output stage that protects the driver against short-circuits over the entire common-mode voltage range by limiting the output current to about 70mA. Under extreme fault condtions where the current limit is not effective, a thermal shutdown circuit puts the driver outputs into a high-impedance state if the die temperature exceeds 150C, and does not turn them back on until the temperature has fallen to 130C.
ENHANCED ESD PROTECTION
Figure 9. ADM1487 Driver Output Stage
The ADM1487 output includes Schottky diodes in series with the positive supply to the drain of the P-channel output device and in series with the drain of the N-channel output device. These diodes prevent the P-channel's parasitic diode from conducting when the output voltage exceeds VCC and prevent the N-channel's parasitic diode from conducting when the output voltage falls below ground.
SLEW RATE CONTROL
All Analog Devices parts incorporate protection against electrostatic discharge (ESD) to protect the devices during handling, assembly and normal operation. In addition, the ADM1487 has enhanced ESD protection up to 10kV on the A and B I/O pins to protect against severe operational conditions such as line transients, connection and disconnection.
APPLICATION INFORMATION
The driver output stage of the ADM1487 has a controlled slew rate to minmize signal reflections on incorrectly terminated lines and to reduce electromagnetic interference (EMI).
Figure 10 shows a typical application of the ADM1487. This is a half-duplex RS-485/RS-422 network. Up to 254 additional ADM1487s can be connected along the cable (termination resistors are only required at each end).
RECEIVER OUTPUT (RO) RECEIVER ENABLE (RE) DRIVER ENABLE (DE) DATA IN (DI)
1
R
8 7 6
D
ADM1487
B
2 3 4
+5V (VCC ) CABLE TERMINATED AT ENDS 100n
RT
5 6 7
D
4 3 2
DI
DE
RE
RT
A
BABA
5
+5V (VCC)
R 8 ADM1487 1 RO
100n
ADDITIONAL ADM1487s
Figure 10. Typical Half-Duplex RS-485/RS-422 Network
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic Dual-In-Line Package (N-8)
0. 43 0 (10 . 92 ) 0. 34 8 (8.84 )
8 5
8-Pin SO Package (R-8)
0. 19 6 8 (5 . 00 ) 0. 18 9 0 (4 . 80 )
0. 28 0 (7.11 ) 0. 24 0 (6.10 )
14
85
0. 24 4 0 (6 . 20 )
0. 15 7 4 (4 . 00 )
1 4
0. 32 5 (8. 25 ) P IN 1 0. 06 0 (1. 52 ) 0. 01 5 (0. 38 ) 0. 30 0 (7. 62 ) 0. 19 5 (4. 95 ) 0. 11 5 (2. 93 )
0. 22 8 4 (5 . 80 )
0. 14 9 7 (3 . 80 )
0.21 0 (5. 33 ) MAX 0. 16 0 (4.06 ) 0. 11 5 (2.93 ) 0. 02 2 (0.5 58 ) 0.1 0 0 0.07 0 (1. 77 ) 0. 01 4 (0.3 56 ) (2 .54 ) 0.04 5 (1. 15 ) BS C
0.1 3 0 (3 .30 ) M IN S E A TI N G PLANE
PIN 1
0. 10 2 (2.59 ) 0. 09 4 (2.39 )
0. 01 9 6 (0 .50 ) 0. 00 9 9 (0 .25 )
x 45
0. 01 5 (0. 3 81 ) 0. 00 8 (0. 2 04 )
0. 00 9 8 (0 .25 ) 0. 00 4 0 (0 .10 ) S E A TI N G PL A N E 0. 0 5 00 (1 . 27 ) BSC 0. 01 9 2 (0 . 49 ) 0. 01 3 8 (0 . 35 ) 0. 00 9 8 (0 .25 ) 0. 00 7 5 (0 .19 ) 8 0
0. 05 0 0 (1 .27 ) 0. 01 6 0 (0 .41 )
-8-
Rev. PrC

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