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Final Electrical Specifications
LTC1688/LTC1689 52Mbps/100Mbps RS485 Hot Swapable Quad Drivers
March 1999
FEATURES
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DESCRIPTION
The LTC(R)1688/LTC1689 are ultrahigh speed, differential bus/line drivers that can operate at data rates up to 100Mbps. Propagation delay is guaranteed at 8ns 4ns over the full operating temperature range. These devices operate over the full RS485 common mode range (- 7V to 12V), and also meet RS422 requirements. The driver outputs are Hot Swap capable, maintaining backplane data integrity during board insertion and removal. The drivers feature three-state outputs, maintaining high impedance over the entire common mode range (- 7V to 12V). Outputs also remain high impedance during power-up and with the power off. A short-circuit feature detects bus contention and substantially reduces driver output current. Thermal shutdown circuitry protects the parts from excessive power dissipation. The LTC1688/LTC1689 operate from a single 5V or 3V supply and draw only 9mA of supply current.
, LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation.
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Ultrahigh Speed: 100Mbps Guaranteed Propagation Delay: 8ns 4ns Over Temperature 50Mbps Operation with VDD = 3V Low Channel-to-Channel Skew: 500ps Typ Low tPLH/tPHL Skew: 500ps Typ Hot SwapTM Capable Driver Outputs Maintain High Impedance in Three-State or with Power Off Short-Circuit Protected: 3mA Typ Output Current for an Indefinite Short Thermal Shutdown Protected Single 5V Supply Pin Compatible with LTC486/LTC487
APPLICATIONS
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High Speed RS485 Twisted-Pair Drivers High Speed Backplane Drivers Complementary Clock Drivers STS-1/OC-1 Data Drivers SCSI Drivers
TYPICAL APPLICATION
20ns Pulse Across 100 Feet of Category 5 UTP 50Mbps RS485 Data Connection
2V/DIV DRIVER INPUT CABLE DELAY
100 100
2V/DIV
RECEIVER
DRIVER
100 FT CATEGORY 5 UTP 1/4 LTC1688 1/4 LTC1518
1688/89 TA01
2V/DIV
5V/DIV
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 its circuits as described herein will not infringe on existing patent rights.
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DRIVER OUTPUT
RECEIVER INPUT
RECEIVER OUTPUT 20ns/DIV
1688/89 TA02
1
LTC1688/LTC1689 ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW DI1 1 DO1A 2 DO1B 3 EN (EN12*) 4 DO2B 5 DO2A 6 DI2 7 GND 8 16 VDD 15 DI4 14 DO4A 13 DO4B 12 ENB (EN34*) 11 DO3B 10 DO3A 9 DI3
Supply Voltage (VDD) ................................................ 7V Control Input Voltages .................. - 0.5V to VDD + 0.5V Control Input Currents .................... - 100mA to 100mA Driver Input Voltages .................... - 0.5V to VDD + 0.5V Driver Output Voltages ................................ - 7V to 12V Driver Input Currents ...................... - 100mA to 100mA Short-Circuit Duration (VOUT: - 7V to 10V) ...... Indefinite Operating Temperature Range .................... 0C to 70C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LTC1688CS LTC1689CS
S PACKAGE 16-LEAD PLASTIC SO *LTC1689 ONLY TJMAX = 150C, JA = 90C/ W
Consult factory for Industrial and Military grade parts.
DC ELECTRICAL CHARACTERISTICS
SYMBOL VOD1 VOD2 VOD PARAMETER Differential Driver Output (Unloaded) Differential Driver Output (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 Three-State (High Impedance) Output Current Supply Current of Entire Device Driver Short-Circuit Current, VOUT = HIGH Driver Short-Circuit Current, VOUT = LOW Differential Driver Output (Unloaded) Differential Driver Output (With Load) Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage CONDITIONS IOUT = 0 R = 50 (RS422) R = 25 (RS485), Figure 1 R = 25 or 50, Figure 1
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MIN
TYP
MAX VDD
UNITS V V V V
VDD = 5V per Driver, TA = 25C, Unless Otherwise Noted (Note 2) 2 1.5
3.0 0.2
VOC VOC
R = 25 or 50, Figure 1 R = 25 or 50, Figure 1
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3 0.2
VIH VIL IIN1 IOZ IDD IOSD1 IOSD2 VOD1 VOD2 VOD
EN, ENB, EN12, EN34, DI EN, ENB, EN12, EN34, DI EN, ENB, EN12, EN34, DI VOUT = - 7V to 12V, VDD = 5V No Load, Digital Input Pins = 0V or VDD VOUT = - 7V to 10V VOUT = - 7V to 10V IOUT = 0 R = 50 (RS422) R = 25 (RS485), Figure 1 R = 25 or 50, Figure 1
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2 0.8 1 2 9 200 16 20 20 VDD 1.5 0.65 0.1 2.0
VDD = 3V per Driver, TA = 25C, Unless Otherwise Noted (Note 2)
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VOC
R = 25 or 50, Figure 1
1.3
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V V V V A A mA mA mA V V V V V
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LTC1688/LTC1689
DC ELECTRICAL CHARACTERISTICS
SYMBOL VOC PARAMETER Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Input High Voltage Input Low Voltage Input Current Three-State (High Impedance) Output Current Supply Current of Entire Device Driver Short-Circuit Current, VOUT = HIGH Driver Short-Circuit Current, VOUT = LOW CONDITIONS R = 25 or 50, Figure 1 MIN TYP 0.1 MAX UNITS V
VIH VIL IIN1 IOZ IDD IOSD1 IOSD2
EN, ENB, EN12, EN34, DI EN, ENB, EN12, EN34, DI EN, ENB, EN12, EN34, DI (Note 3) VOUT = - 7V to 10V (Note 3) No Load, Digital Input Pins = 0V or VDD VOUT = - 7V to 8V (Note 3) VOUT = - 7V to 8V (Note 3)
q q q q
1.4 0.5 1 1 5 200
V V A A mA 10 10 mA mA
q q
SWITCHING CHARACTERISTICS
SYMBOL tPLH, tPHL tSKEW tr, tf tZH tZL tLZ t HZ CL(MAX) PARAMETER Driver Input-to-Output Propagation Delay Driver Output-to-Output Skew Driver Rise/Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable from Low Driver Disable from High Maximum Output Capacitive Load Maximum Data Rate Maximum Driver Input Rise/Fall Time VDD = 3V, TA = 25C, Unless Otherwise Noted (Note 2) tPLH, tPHL tSKEW tr, tf tZH tZL tLZ t HZ CL(MAX) Driver Input-to-Output Propagation Delay Driver Output-to-Output Skew Driver Rise/Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable from Low Driver Disable from High Maximum Output Capacitive Load Maximum Data Rate Maximum Driver Input Rise/Fall Time (Note 3)
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VDD = 5V, TA = 25C, Unless Otherwise Noted (Note 2) RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 CL = 25pF, S2 Closed, Figures 3, 5 CL = 25pF, S1 Closed, Figures 3, 5 CL = 15pF, S1 Closed, Figures 3, 5 CL = 15pF, S2 Closed, Figures 3, 5 (Note 3) (Note 3) (Note 3) RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 RDIFF = 50, CL1 = CL2 = 25pF, Figures 2, 4 CL = 25pF, S2 Closed, Figures 3, 5 CL = 25pF, S1 Closed, Figures 3, 5 CL = 15pF, S1 Closed, Figures 3, 5 CL = 15pF, S2 Closed, Figures 3, 5 (Note 3)
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The q denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
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CONDITIONS
MIN 4
TYP 8 500 2 10 10 25 25
MAX 12
UNITS ns ps ns
35 35 65 65 200
ns ns ns ns pF Mbps ns ns ns ns ns ns ns ns
100 500 11 1 4 25 25 50 50 200 50 500
pF Mbps ns
Note 2: All currents into the device pins are positive; all currents out of the device pins are negative. Note 3: Guaranteed by design or correlation, but not tested.
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LTC1688/LTC1689 TYPICAL PERFORMANCE CHARACTERISTICS
Propagation Delay vs Temperature
250
VDD = 5V 8
PROPAGATION DELAY (ns)
6 5 4 3 2 1 0 -20 -10 0
SUPPLY CURRENT (mA)
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PIN FUNCTIONS
DI1 (Pin 1): Driver 1 Input. Do not float. DO1A (Pin 2): Driver 1 Noninverting Output. DO1B (Pin 3): Driver 1 Inverting Output. EN (Pin 4, LTC1688): High True Enable Pin. A low on Pin 4 and a high on Pin 12 will put all driver outputs into a high impedance state. See Function Tables for details. Do not float. EN12 (Pin 4, LTC1689): Enables Drivers 1 and 2. A low on Pin 4 will put the outputs of drivers 1 and 2 into a high impedance state. See Function Tables for details. Do not float. DO2B (Pin 5): Driver 2 Inverting Output. DO2A (Pin 6): Driver 2 Noninverting Output. DI2 (Pin 7): Driver 2 Input. Do not float. GND (Pin 8): Ground Connection. A good ground plane is recommended for all applications. DI3 (Pin 9): Driver 3 Input. Do not float. DO3A (Pin 10): Driver 3 Noninverting Output. DO3B (Pin 11): Driver 3 Inverting Output. ENB (Pin 12, LTC1688): Low True Enable Pin. A low on Pin 4 and a high on Pin 12 will put all driver outputs into a high impedance state. See Function Tables for details. Do not float. EN34 (Pin 12, LTC1689): Enables Drivers 3 and 4. A low on Pin 12 will put the outputs of drivers 3 and 4 into a high impedance state. See Function Tables for details. Do not float. DO4B (Pin 13): Driver 4 Inverting Output. DO4A (Pin 14): Driver 4 Noninverting Output. DI4 (Pin 15): Driver 4 Input. Do not float. VDD (Pin 16): Power Supply Input. This pin should be bypassed with a 0.1F ceramic capacitor as close to the pin as possible. Recommended: VDD = 5V 5%.
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Supply Current vs Data Rate
VDD = 5V TA = 25C 200 4 DRIVERS SWITCHING
150
100 1 DRIVER SWITCHING 50
0
10 20 30 40 50 60 70 80 TEMPERATURE (C)
1688/89 G01
1
2
5 3 6 4 DATA RATE (Mbps)
7
8
1688/89 G02
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LTC1688/LTC1689
FU CTIO TABLES
LTC1688
INPUTS DI H L H L X EN H H X X L ENB X X L L H OUTA H L H L HI-Z OUTPUTS OUTB L H L H HI-Z DI H L X
TEST CIRCUITS
EN (EN12)
A R VOD R B
Figure 1. Driver DC Test Load
SWITCHI G TI E WAVEFOR S
3V DI 0V tPLH B VO A 1/2 VO VO - VO 10% tr 90% tSKEW VDIFF = V(A) - V(B) 1/2 VO tSKEW 90% 10% tf
1688/89 F04
1.5V
Figure 4. Driver Propagation Delays
3V EN 0V tZL 5V A, B VOL VOH A, B 0V tZH tHZ 1/2 VDD OUTPUT NORMALLY LOW tLZ 0.5V 1.5V f = 1MHz; tr 3ns; tf 3ns 1.5V
1/2 VDD
Figure 5. Driver Enable and Disable Times
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LTC1689
INPUTS EN12/EN34 H H L OUTA H L HI-Z OUTPUTS OUTB L H HI-Z
CL1 A DI
VOC
S1 VDD OUTPUT UNDER TEST 500
DRIVER B
RDIFF
CL2
1688/89 TC01
CL
1688/89 TC02
S2
ENB (EN34)
1688/89 TC03
Figure 2. Driver Timing Test Circuit
Figure 3. Driver Timing Test Load #2
f = 1MHz; tr < 3ns; tf < 3ns
1.5V tPHL
OUTPUT NORMALLY HIGH
0.5V
1688/89 F05
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LTC1688/LTC1689
APPLICATIONS INFORMATION
The LTC1688/LTC1689 family of RS485 quad differential drivers employs a novel architecture and fabrication process that allows ultra high speed operation (100Mbps) and Hot Swap capability while maintaining the ruggedness of RS485 operation (three-state outputs can float from - 7V to 12V with a single 5V supply). Unlike typical CMOS drivers whose propagation delay can vary as much as 500%, the propagation delay of the LTC1688/LTC1689 drivers will only vary by 50% (a narrow 4ns window). This performance is achieved by designing the input stage of each driver to have minimum propagation delay shift over temperature and from part to part. 50Mbps with 3V Operation The LTC1688/LTC1689 are designed to operate with a 3V power supply and still achieve 50Mbps operation. However, all DC and AC specifications will be reduced (see Electrical Characteristics table). Figure 6 shows an LTC1689 driving an LTC1520 over 100 feet of Category 5 UTP. Both parts are operating at 3V supply.
LTC1689 OUTPUT 2V/DIV FAR END OF CABLE 2V/DIV
LTC1520 OUTPUT 5V/DIV
20ns/DIV
1688/89 F06
Figure 6
Hot Swap Capability With the LTC1688/LTC1689 outputs disabled but connected to the transmission line, the user can turn on/off the power to the LTC1688/LTC1689 without inducing a differential signal on the transmission line. Due to capacitive coupling, however, there can be a small amount of common mode charge injected into both disabled outputs, which is not seen as a differential signal (see Figure 7). The disabled outputs can be hooked/unhooked to a transmission line without disturbing the existing data.
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Figure 7. Common Mode Charge Injection During Hot Swapping
Output Short-Circuit Protection In addition to 100Mbps operation and Hot Swap capability, the LTC1688/LTC1689 employ voltage sensing shortcircuit protection that reduces short-circuit current by over an order of magnitude. For a given input polarity, this circuitry determines what the correct output level should be. If the output level is different from the expected, the circuitry shuts off the big output devices. Much smaller devices are instead turned on, thus producing a much smaller short-circuit output current (3mA typical). For example, if the driver input is > 2V, it expects the "A" output to be > 3.25V and the "B" output to be less than 1.75V. If the "A" output is subsequently shorted to a voltage below VDD/2, this circuitry shuts off the big outputs and turns on 3mA current sources instead (the converse applies to the "B" output). Note that these 3mA current sources are active only during a short-circuit fault. During normal operation, the regular output drivers can sink/source > 50mA. A time-out period of about 50ns is required before a shortcircuit fault is detected. This circuitry might falsely detect a short under excess output capacitive load (> 200pF). Additionally, a short might go undetected if there is too much resistance (user inserted or cable parasitic) between the physical short and the actual driver output. For cables with the recommended RS485 termination (no DC bias on the cable, see Figure 8), the LTC1688/LTC1689 will automatically come out of short-circuit mode once the physical short has been removed.
LTC1688/LTC1689
APPLICATIONS INFORMATION
DE TERM POWER 330
1/4 LTC1519
LTC1688
100
100
1/4 LTC1518
Figure 8. Multipoint Transmission
Cable Termination The recommended cable termination for use with the LTC1688/LTC1689 is a single resistor across the two ends of a transmission cable (see Figure 8). When PC traces are used as the transmission line, its characteristic impedance should be chosen close to 100 in order to better match the specified timing characteristics of the LTC1688/ LTC1689. Category 5 unshielded twisted pair can be used over short distances at the maximum data rates (100Mbps). For point-to-point configurations (see Figure 9), a single resistor across the cable at the receiver end is sufficient. A single resistor termination lowers power consumption and increases the differential output signal.
LTC1689
100
LTC1518
Figure 9. Point-to-Point Transmission
Enable Pins For cable terminations with a DC bias (such as High Voltage Differential SCSI, see Figure 10), the driver outputs must be disabled for at least 200ns after power-up. This ensures that the driver outputs do not disturb the cable upon power-up. It also ensures the correct output start-up conditions. When there is an output short fault condition and the cable has a DC biased termination, such as Figure 10, the driver outputs must be disabled for at least 200ns after the short has been removed. Recall that for transmission lines that have the recommended RS485 single resistor termination (Figures 8 and 9), the LTC1688/ LTC1689 will come out of a short-circuit fault condition automatically without having to disable the outputs.
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TERM POWER 330 150
DI
1/4 LTC1688
150
1/4 LTC1518
330
1/4 LTC1518
330
1688/89 F10
1688/89 F08
Figure 10. DC-Biased Termination (Recommended for SCSI Applications Only)
High Speed Twisted-Pair Transmission Data rates up to 100Mbps can be transmitted over short distances using Category 5 UTP (unshielded twisted pair). The cable distance will determine the maximum data rate. Figures 11 and 12 show an LTC1688 driving the LT1720 dual UltraFastTM comparator. An 8ns pulse is propagated over 25 feet of Category 5 UTP. Notice the high frequency attenuation.
UltraFast is a trademark of Linear Technology Corporation.
2V/DIV
DRIVER INPUT
2V/DIV
DRIVER OUTPUT
1688/89 F09
2V/DIV COMPARATOR INPUT
5V/DIV
LT1720 OUTPUT
10ns/DIV
1688/89 F11
Figure 11. 8ns Pulse Over 25 Feet Category 5 UTP with LT1720 Comparator
DRIVER
100 25 FT CATEGORY 5 UTP
100
+
RECEIVER
-
1/4 LTC1688 1/2 LT1720
1688/89 F12
Figure 12. 100Mbps RS485 Data Connection with LT1720
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LTC1688/LTC1689
APPLICATIONS INFORMATION
High Speed Backplane Transmission The LTC1688/LTC1689 can be used in backplane point-topoint and multipoint applications. At high data rates, signals should be routed differentially and PC traces should be terminated (see Figure 13). Note that the RS485 specification calls for characteristic impedances near 100, therefore, PC trace transmission lines should be designed with an impedance close to 100. If trace impedance is
1/4 LTC1688 BACKPLANE DRIVER RECEIVER 1/4 LTC1520
TRANSMISSION LINE
Figure 13. Backplane Transmission
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S Package 16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.386 - 0.394* (9.804 - 10.008) 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 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 0.004 - 0.010 (0.101 - 0.254) 16 15 14 13 12 11 10 9
0.016 - 0.050 0.406 - 1.270
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
RELATED PARTS
PART NUMBER LTC486/LTC487 LT 1394 LTC1518/LTC1519 LTC1520 LTC1685 LTC1686/LTC1687 LT1720
(R)
DESCRIPTION Low Power Quad RS485 Drivers 7ns UltraFast Single Supply Comparator High Speed, Precision Quad RS485 Receivers High Speed, Precision Quad Differential Line Receiver High Speed, Precision RS485 Transceiver High Speed, Precision RS485 Full-Duplex Transceivers Dual 4.5ns UltraFast Single Supply Comparator
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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much less than 100, and the trace is double terminated, the part will experience excess heating. The propagation delay could then fall outside the specified window. Layout Considerations A ground plane is recommended when using high frequency devices like the LTC1688/LTC1689. A 0.1F ceramic bypass capacitor less than 0.25 inch away from the VDD pin is also recommended. Special care should be taken to route the differential outputs very symmetrically in order to obtain the same parasitic capacitances and thus maintain good propagation delay skew. Parasitic capacitance from each input to its corresponding outputs should also be minimized. Any excess capacitance could result in slower operation or even instability.
1688/89 F13
0.050 (1.270) TYP
S16 0695
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COMMENTS 110A Typ Supply Current, 10Mbps, - 7V to 12V Common Mode Range 6mA Typ Supply Current, Ground Sensing on Single Supply 52Mbps, Pin Compatible with LTC488/LTC489 Single Supply, 18ns Propagation Delay, 100mV Threshold 52Mbps, Pin Compatible with LTC485 52Mbps, Pin Compatible with LTC490/LTC491 4mA per Comparator, Optimized for 3V or 5V Operation
16889i LT/TP 0399 4K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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