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LTC1483 Ultra-Low Power RS485 Low EMI Transceiver with Shutdown
FEATURES
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DESCRIPTIO
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Low Power: ICC = 120A Max with Driver Disabled ICC = 500A Max with Driver Enabled, No Load 1A Quiescent Current in Shutdown Mode Controlled Slew Rate Driver for Reduced EMI Single 5V Supply Drivers/Receivers Have 10kV ESD Protection - 7V to 12V Common-Mode Range Permits 7V Ground Difference Between Devices on the Data Line Thermal Shutdown Protection Power Up/Down Glitch-Free Driver Outputs Permit Live Insertion or Removal of Transceiver Driver Maintains High Impedance in Three-State or with the Power Off Up to 32 Transceivers on the Bus Pin Compatible with the LTC485
The LTC(R)1483 is an ultra-low power differential line transceiver designed for data transmission standard RS485 applications with extended common-mode range (- 7V to 12V). It will also meet the requirements of RS422. The LTC1483 features output drivers with controlled slew rate, decreasing the EMI radiated from the RS485 lines, and improving signal fidelity with misterminated lines. The CMOS design offers significant power savings over its bipolar counterparts without sacrificing ruggedness against overload or ESD damage. Typical quiescent current is only 80A while operating and less than 1A in shutdown. The driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common-mode range. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. I/O pins are protected against multiple ESD strikes of over 10kV. The LTC1483 is fully specified over the commercial and extended industrial temperature range and is available in 8-pin DIP and SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
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Battery-Powered RS485/RS422 Applications Low Power RS485/RS422 Transceiver Level Translator
TYPICAL APPLICATI
RO1 RE1 DE1 DI1 D R
VCC1 RTERM GND1
DI
A-B
RTERM RO2 RE2 DE2 DI2 D GND2
LTC1483 * TA01
R
VCC2
RO
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1483 TA02
UO
UO
1
LTC1483 ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW RO 1 RE 2 DE 3 DI 4 N8 PACKAGE 8-LEAD PDIP D R 8 7 6 5 VCC B A GND
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 Input Voltage .......................................... 14V Receiver Output Voltage ................ - 0.5V to VCC + 0.5V Operating Temperature Range LTC1483C........................................ 0C TA 70C LTC1483I .................................... - 40C TA 85C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LTC1483CN8 LTC1483IN8 LTC1483CS8 LTC1483IS8 S8 PART MARKING 1483 1483I
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 130C/ W (N8) TJMAX = 125C, JA = 150C/ W (S8)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VOD1 VOD2 VOD VOC VOC VIH VIL IIN1 IIN2 VTH VTH VOH VOL IOZR RIN ICC ISHDN IOSD1 IOSD2 IOSR PARAMETER Differential Driver Output Voltage (Unloaded) Differential Driver Output Voltage (with Load) Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common-Mode Output Voltage Change in Magnitude of Driver Common-Mode Output Voltage for Complementary Output States Input High Voltage Input Low Voltage Input Current Input Current (A, B) Differential Input Threshold Voltage for Receiver Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Three-State (High Impedance) Output Current at Receiver Receiver Input Resistance Supply Current Supply Current in Shutdown Mode Driver Short-Circuit Current, VOUT = HIGH Driver Short-Circuit Current, VOUT = LOW Receiver Short-Circuit Current
VCC = 5V, (Notes 2, 3) unless otherwise noted.
CONDITIONS IO = 0 R = 50 (RS422) R = 27 (RS485), Figure 1 R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 DE, DI, RE DE, DI, RE DE, DI, RE 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 VO 2.4V - 7V VCM 12V No Load, Output Enabled No Load, Output Disabled DE = 0, RE = VCC - 7V VO 12V - 7V VO 12V 0V VO VCC
q q q q q q q q q q q q q q q q q q q q q q
MIN 2 1.5
TYP
MAX 5 5 0.2 3 0.2
UNITS V V V V V V V
2 0.8 2 1.0 - 0.8 - 0.2 45 3.5 0.4 1 12 25 300 80 1 35 35 7 500 120 10 250 250 85 0.2
2
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V A mA mA V mV V V A k A A A mA mA mA
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WW
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LTC1483
SWITCHI G CHARACTERISTICS
SYMBOL tPLH tPHL tSKEW t r , tf tZH tZL tLZ tHZ tPLH tPHL tSKD tZL tZH tLZ tHZ fMAX tSHDN tZH(SHDN) tZL(SHDN) tZH(SHDN) tZL(SHDN) PARAMETER Driver Input to Output Driver Input to Output Driver Output to Output Driver Rise or Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output Receiver Input to Output
tPLH - tPHL Differential Receiver Skew
Receiver Enable to Output Low Receiver Enable to Output High Receiver Disable from Low Receiver Disable from High Maximum Data Rate Time to Shutdown Driver Enable from Shutdown to Output High Driver Enable from Shutdown to Output Low Receiver Enable from Shutdown to Output High Receiver Enable from Shutdown to Output Low
The q denotes specifications which apply over the full operating temperature range. Note 1: Absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
350 300 THERMAL SHUTDOWN WITH DRIVER ENABLED 14 12
SUPPLY CURRENT (A)
DRIVER ENABLED 200 150 100 50 0 -50 -25 DRIVER DISABLED
tPLH - tPHL (ns)
250
10 8 6 4 2 0 -50 -25
OUTPUT CURRENT (mA)
0
25 50 75 100 125 150 175 TEMPERATURE (C)
1483 G01
UW
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VCC = 5V, (Notes 2, 3) unless otherwise noted.
MIN
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CONDITIONS RDIFF = 54, CL1 = CL2 = 100pF, (Figures 3, 5)
LTC1483 TYP
MAX 1200 1200
UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns kbits/s ns ns ns ns ns
150 150 100 150 100 100 150 150 30 30 140 140 13 20 20 20 20 250 50 200
600 1200 1500 1500 1500 1500 200 200 50 50 50 50 600 2000 2000 3500 3500
CL = 100pF (Figures 4, 6), S2 Closed CL = 100pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 4, 6), S2 Closed RDIFF = 54, CL1 = CL2 = 100pF, (Figures 3, 7)
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CRL = 15pF (Figures 2, 8), S1 Closed CRL = 15pF (Figures 2, 8), S2 Closed CRL = 15pF (Figures 2, 8), S1 Closed CRL = 15pF (Figures 2, 8), S2 Closed DE = 0, RE = CL = 100pF (Figures 4, 6), S2 Closed CL = 100pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 2, 8), S2 Closed CL = 15pF (Figures 2, 8), S1 Closed
q q q q q q q q q q
Note 2: 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. Note 3: All typicals are given for VCC = 5V and TA = 25C.
Receiver tPLH - tPHL vs Temperature
70 60 50 40 30 20 10 0 50 25 75 0 TEMPERATURE (C) 100 125
Driver Differential Output Voltage vs Output Current
TA = 25C
0
1
2 4 3 OUTPUT VOLTAGE (V)
5
1483 G03
1483 G02
3
LTC1483 TYPICAL PERFORMANCE CHARACTERISTICS
Driver Differential Output Voltage vs Temperature
2.5 2.4
DIFFERENTIAL VOLTAGE (V)
RL = 54
60
OUTPUT CURRENT (mA)
2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 -50
0 50 40 30 20 10
OUTPUT CURRENT (mA)
-25
50 25 0 75 TEMPERATURE (C)
PIN FUNCTIONS
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low), then if A > B by 200mV, RO will be high. If A < B by 200mV, then RO will be low. RE (Pin 2): Receiver Output Enable. A low enables the receiver output, RO. A high input forces the receiver output into a high impedance state. DE (Pin 3): Driver Outputs Enable. A high on DE enables the driver output. A, B and the chip will function as a line driver. A low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. If RE is high and DE is low, the part will enter a low power (1A) shutdown state. DI (Pin 4): Driver Input. If the driver outputs are enabled (DE high) then a low on DI forces the outputs A low and B high. A high on DI with the driver outputs enabled will force A high and B low. GND (Pin 5): Ground. A (Pin 6): Driver Output/Receiver Input. B (Pin 7): Driver Output/Receiver Input. VCC (Pin 8): Positive Supply. 4.75V < VCC < 5.25V.
FU CTIO TABLES
LTC1483 Transmitting
INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X 0 1 Z Z* OUTPUTS B A 1 0 Z Z* RE 0 0 0 1
*Shutdown mode for LTC1483
4
UW
100 125
1483 G04
Driver Output Low Voltage vs Output Current
70 TA = 25C
0 -10 -20 -30 -40 -50 -60 -70 -80
Driver Output High Voltage vs Output Current
TA = 25C
0
1
2 OUTPUT VOLTAGE
3
4
1483 G05
-90 0 1 3 2 OUTPUT VOLTAGE (V) 4 5
1483 G06
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LTC1483 Receiving
INPUTS DE 0 0 0 0 A-B 0.2V - 0.2V Inputs Open X OUTPUTS RO 1 0 1 Z*
*Shutdown mode for LTC1483
LTC1483
TEST CIRCUITS
A R VOD R B
LTC1483 * F01
RECEIVER OUTPUT
TEST POINT
S1
1k VCC
VOC
CRL
1k
S2
LTC1483 * F02
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
3V DE A DI B RDIFF CL2 CL1 A RO B RE
LTC1483 * F03
S1 OUTPUT UNDER TEST 500 S2 CL
LTC1483 * F04
VCC
15pF
Figure 3. Driver/Receiver Timing Test Circuit
Figure 4. Driver Timing Test Load
SWITCHI G TI E WAVEFOR S
3V DI 0V t PLH B VO A VO 0V -VO 1/2 VO 10% tr tSKEW 90% VDIFF = V(A) - V(B) tf t SKEW 90% 10%
LTC1483 * F05
1.5V
Figure 5. Driver Propagation Delays
3V DE 0V 5V A, B VOL VOH A, B 0V 2.3V 1.5V
Figure 6. Driver Enable and Disable Times
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tr 10ns, tf 10ns t PHL
1.5V 1/2 VO
tr 10ns, tf 10ns t ZL(SHDN), t ZL t LZ
1.5V
2.3V
OUTPUT NORMALLY LOW
0.5V
OUTPUT NORMALLY HIGH t HZ
0.5V
LTC1483 * F06
t ZH(SHDN), t ZH
5
LTC1483
SWITCHI G TI E WAVEFOR S
VOH RO VOL t PHL VOD2 A-B -VOD2 0V 1.5V OUTPUT tr 10ns, tf 10ns INPUT t PLH 0V
LTC1483 * F07
Figure 7. Receiver Propagation Delays
3V RE 0V 5V RO 1.5V tr 10ns, tf 10ns t ZL(SHDN), tZL 1.5V OUTPUT NORMALLY LOW t LZ 0.5V 1.5V
RO 0V
Figure 8. Receiver Enable and Disable Times
APPLICATIO S I FOR ATIO
Basic Theory of Operation
Traditionally RS485 transceivers have been designed using bipolar technology because the common-mode range of the device must extend beyond the supplies and the device must be immune to ESD damage and latch-up. Unfortunately, most bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption. The LTC1483 is a CMOS RS485/RS422 transceiver which features ultra-low power consumption without sacrificing ESD and latch-up immunity. The LTC1483 uses a proprietary driver output stage, which allows a common-mode range that extends beyond the power supplies while virtually eliminating latch-up and providing excellent ESD protection. Figure 9 shows the LTC1483 output stage while Figure 10 shows a conventional CMOS output stage. When the conventional CMOS output stage of Figure 10 enters a high impedance state, both the P-channel (P1) and the N-channel (N1) are turned off. If the output is then driven above VCC or below ground, the P+/N-well diode
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1.5V
1.5V
OUTPUT NORMALLY HIGH t HZ
0.5V
LTC1483 * F08
t ZH(SHDN), tZH
(D1) or the N+/P-substrate diode (D2) respectively will turn on and clamp the output to the supply. Thus, the output stage is no longer in a high impedance state and is not able to meet the RS485 common-mode range requirement. In addition, the large amount of current flowing through either diode will induce the well-known CMOS latch-up condition, which could destroy the device.
VCC SD3 P1
VCC P1
D1
D1
OUTPUT LOGIC SD4
LOGIC
OUTPUT
N1
D2
N1
D2
LTC1483 * F09
LTC1483 * F10
Figure 9. LTC1483 Output Stage
Figure 10. Conventional CMOS Output Stage
LTC1483
APPLICATIO S I FOR ATIO
The LTC1483 output stage of Figure 9 eliminates these problems by adding two Schottky diodes, SD3 and SD4. The Schottky diodes are fabricated by a proprietary modification to the standard N-well CMOS process. When the output stage is operating normally, the Schottky diodes are forward biased and have a small voltage drop across them. When the output is in the high impedance state and is driven above VCC or below ground, the parasitic diode D1 or D2 still turns on, but SD3 or SD4 will reverse bias and prevent current from flowing into the N-well or the substrate. Thus the high impedance state is maintained even with the output voltage beyond the supplies. With no minority carrier current flowing into the N-well or substrate, latch-up is virtually eliminated under power-up or power-down conditions. The LTC1483 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively. The output will be clamped to either VCC or ground by a Zener voltage plus a Schottky diode drop, but this voltage is well beyond the RS485 operating range. An ESD cell protects output against multiple 10kV human body model ESD strikes. Because the ESD injected current in the N-well or substrate consists of majority carriers, latch-up is prevented by careful layout techniques. Slew Rate The LTC1483 is designed for systems that are sensitive to electromagnetic radiation. The part features a slew rate limited driver that reduces high frequency electromagnetic emissions, while improving signal fidelity by reducing reflections due to misterminated cables. Figures 11 and 12 show the spectrum of the signal at the driver output for a standard slew rate RS485 driver and the slew rate limited LTC1483. The LTC1483 shows significant reduction of the high frequency harmonics. Because the driver is slew rate limited, the maximum operating frequency is limited to 250kbits/s. Low Power Operation The LTC1483 is designed to operate with a quiescent current of 120A max. With the driver in three-state ICC will
LOG MAGNITUDE (dBVRMS)
LOG MAGNITUDE (dBVRMS)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights.
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20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 0 1 2 3 4 5 FREQUENCY (MHz)
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Figure 11. Typical RS485 Driver Output Spectrum Transmitting at 150kHz
20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 0 1 2 3 4 5 FREQUENCY (MHz)
Figure 12. Slew Rate Limited LTC1483 Driver Output Spectrum Transmitting at 150kHz
drop to this 120A level. With the driver enabled there will be additional current drawn by the internal 12k resistor. Under normal operating conditions this additional current is overshadowed by the current drawn by the external bus impedance.
7
LTC1483
APPLICATIO S I FOR ATIO
Shutdown Mode
Both the receiver output (RO) and the driver outputs (A, B) can be placed in three-state mode by bringing RE high and DE low respectively. In addition, the LTC1483 will enter shutdown mode when RE is high and DE is low. In shutdown the LTC1483 typically draws only 1A of supply current. In order to guarantee that the part goes into shutdown, RE must be high and DE must be low for at least 600ns simultaneously. If this time duration is less
PACKAGE DESCRIPTION
0.300 - 0.325 (7.620 - 8.255)
Dimension in inches (millimeters) unless otherwise noted. N Package 8-Lead Plastic DIP
0.045 - 0.065 (1.143 - 1.651) 0.130 0.005 (3.302 0.127) 8 0.400* (10.160) MAX 7 6 5
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.005 (0.127) MIN 0.100 0.010 (2.540 0.254) 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076) 0.015 (0.380) MIN
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254)
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
0.014 - 0.019 (0.355 - 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.016 - 0.050 0.406 - 1.270
RELATED PARTS
PART NUMBER LTC485 LTC1480 LTC1481 LTC1485 LTC1487 DESCRIPTION 5V Low Power RS485 Interface Transceiver 3.3V Ultra-Low Power RS485 Transceiver 5V Ultra-Low Power RS485 Transceiver with Shutdown 5V Differential Bus Transceiver 5V Ultra-Low Power RS485 with Low EMI Shutdown and High Input Impendance COMMENTS Low Power World's First 3V Powered 485 Transceiver with Low Power Consumption Lowest Power Highest Speed High Input Impendance/Low EMI/Lowest Power
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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than 50ns the part will not enter shutdown mode. Toggling either RE or DE will wake the LTC1483 back up within 3.5s. If the slow slew rate driver was active immediately prior to shutdown, the supply current will not drop to 1A until the driver outputs have reached a steady state; this can take as long as 2.6s under worst case conditions. If the driver was disabled prior to shutdown the supply current will drop to 1A immediately.
0.255 0.015* (6.477 0.381) 1 2 3 4
N8 0695
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S Package 8-Lead Plastic SOIC
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
0.050 (1.270) BSC
1
2
3
4
SO8 0695
LT/GP 1094 10K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

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