View LTC2854NBSP_523887.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

FEATURES

LTC2854/LTC2855 3.3V 20Mbps RS485/RS422 Transceivers with Integrated Switchable Termination DESCRIPTIO
The LTC(R)2854 and LTC2855 are low power, 20Mbps RS485/RS422 transceivers operating on 3.3V supplies. The receiver includes a logic-selectable 120 termination, one-eighth unit load supporting up to 256 nodes per bus, and a failsafe feature that guarantees a high output state under conditions of floating or shorted inputs. The driver maintains a high output impedance over the entire common mode range when disabled or when the supply is removed. Excessive power dissipation caused by bus contention or a fault is prevented by current limiting all outputs and by a thermal shutdown. Enhanced ESD protection allows the LTC2854 to withstand 25kV (human body model) and the LTC2855 to withstand 15kV on the transceiver interface pins without latchup or damage.

Integrated, Logic-Selectable 120 Termination Resistor 3.3V Supply Voltage 20Mbps Maximum Data Rate No Damage or Latchup Up to 25kV HBM High Input Impedance Supports 256 Nodes Guaranteed Failsafe Receiver Operation Over the Entire Common Mode Range Current Limited Drivers and Thermal Shutdown Delayed Micropower Shutdown: 5A Maximum Power Up/Down Glitch-Free Driver Outputs Low Operating Current: 370A Typical in Receive Mode Compatible with TIA/EIA-485-A Specifications Available in 10-Pin 3mm x 3mm DFN, 12-Pin 4mm x 3mm DFN and 16-Pin SSOP Packages
APPLICATIO S

PRODUCT SELECTION GUIDE
PART NUMBER LTC2854 LTC2855 DUPLEX HALF FULL PACKAGE DFN-10 SSOP-16, DFN-12
Low Power RS485/RS422 Transceiver Level Translator Backplane Transceiver
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
LTC2854 RO RE TE DE DI D R
LTC2854 R RO RE TE DE D DI
120
120
2V/DIV
285455 TA01
LTC2854 120
285455 TA01b
R D
RO RE TE DE
DI
285455f
U
U
U
LTC2854 at 20Mbps into 54
DI
A B A-B
20ns/DIV
1
LTC2854/LTC2855 ABSOLUTE AXI U RATI GS (Note 1)
Operating Temperature (Note 4) LTC2854C, LTC2855C .............................. 0C to 70C LTC2854I, LTC2855I ............................ -40C to 85C Storage Temperature Range................... -65C to 125C Lead Temperature (Soldering, 10 sec) GN Package ...................................................... 300C Supply Voltage (VCC) ................................... -0.3V to 7V Logic Input Voltages (RE, DE, DI, TE)............ -0.3V to 7V Interface I/O: A, B, Y, Z ...................................... (VCC -15V) to +15V (A-B) or (B-A) with Terminator Enabled ..................6V Receiver Output Voltage (RO) ........ -0.3V to (VCC +0.3V)
PACKAGE/ORDER I FOR ATIO
TOP VIEW RO RO RE DE DI TE 1 2 3 4 5 11 10 VCC 9B 8A 7 NC 6 GND RE DE DI TE GND DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN EXPOSED PAD (PIN 11) PCB GND CONNECTION TJMAX = 125C, JA = 43C/W JC = 2.96C/W
1 2 3 4 5 6 13
DE PACKAGE 12-LEAD (4mm x 3mm) PLASTIC DFN EXPOSED PAD (PIN 13) PCB GND CONNECTION TJMAX = 125C, JA = 44C/W JC = 4.3C/W
ORDER PART NUMBER LTC2854CDD LTC2854IDD
DD PART* MARKING LCQG LCQG
ORDER PART NUMBER LTC2855CDE LTC2855IDE
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
2
U
U
W
WW U
W
TOP VIEW RO 12 V CC 11 A 10 B 9 8 7 Z Y NC RE DE DI TE GND NC NC
1 2 3 4 5 6 7 8
TOP VIEW
16 VCC 15 A 14 B 13 Z 12 Y 11 NC 10 NC 9
NC
GN PACKAGE 16-LEAD (NARROW 0.150) PLASTIC SSOP TJMAX = 125C, JA = 110C/W JC = 40C/W
DE PART* MARKING 2855 2855
ORDER PART NUMBER LTC2855CGN LTC2855IGN
GN PART MARKING 2855 2855I
285455f
LTC2854/LTC2855 ELECTRICAL CHARACTERISTICS
SYMBOL Driver |VOD| Differential Driver Output Voltage R = , VCC = 3V (Figure 1) R = 27, VCC = 3V (Figure 1) R = 50, VCC = 3.13V (Figure 1) R = 27 or R = 50 (Figure 1)

The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V unless otherwise noted (Note 2).
PARAMETER CONDITIONS MIN TYP MAX VCC VCC VCC 0.2 UNITS V V V V
1.5 2
|VOD|
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 Driver Three-State (High Impedance) Output Current on Y and Z Maximum Driver Short-Circuit Current
VOC |VOC|
R = 27 or R = 50 (Figure 1) R = 27 or R = 50 (Figure 1)

3 0.2
V V
IOZD IOSD Receiver IIN
DE = OV, (Y or Z) = -7V, +12V (LTC2855) -7V (Y or Z) 12V (Figure 2)

10 180 -250 250 300 125 -100 96 125 0.2 25
A mA mA A A k V mV V
Receiver Input Current (A, B)
DE = TE = 0V, VCC = 0V or 3.3V, VIN = 12V (Figure 3) DE = TE = 0V, VCC = 0V or 3.3V, VIN = -7V, (Figure 3) RE = VCC or 0V, DE = TE = 0V, VIN = -7V, -3V, +3V, +7V, +12V (Figure 3) -7V B 12V B = 0V I(RO) = -4mA, A-B = 200mV, VCC = 3V I(RO) = 4mA, A-B = -200mV, VCC = 3V RE = VCC, 0V RO VCC 0V RO VCC TE = VCC, VAB = 2V, VB = -7V, 0V, 10V (Figure 8) VCC = 3.6V VCC = 3V

RIN VTH VTH VOH VOL IOZR IOSR RTERM Logic VIH VIL IINL Supplies ICCS ICCR ICCT ICCTR ICCTERM ICCTERMR
Receiver Input Resistance Receiver Differential Input Threshold Voltage Receiver Input Hysteresis Receiver Output HIGH Voltage Receiver Output LOW Voltage Receiver Three-State (High Impedance) Output Current on RO Receiver Short-Circuit Current Receiver Input Terminating Resistor

2.4 0.4 1 85 108 120 156
V A mA
Logic Input High Voltage Logic Input Low Voltage Logic Input Current Supply Current in Shutdown Mode Supply Current in Receive Mode Supply Current in Transmit Mode Supply Current with Both Driver and Receiver Enabled Supply Current in Termination Mode Supply Current in Receive and Termination Mode

2 0.8 0 0 370 450 450 110 450 10 5 900 1000 1000 180 950
V V A A A A A A A
DE = 0V, RE = VCC, TE = 0V DE = 0V, RE = 0V, TE = 0V No Load, DE = VCC, RE = VCC, TE = 0V No Load, DE = VCC, RE = 0V, TE = 0V DE = 0V, RE = VCC, TE = VCC DE = 0V, RE = 0V, TE = VCC

285455f
3
LTC2854/LTC2855 ELECTRICAL CHARACTERISTICS
SYMBOL ICCTERMT ICCTERMTR ESD Protection ESD Protection for RS485/RS422 Pins A, B on LTC2854, Human Body Model Y, Z, A, B on LTC2855, Human Body Model 25 15 kV kV PARAMETER Supply Current in Transmit and Termination Mode Supply Current with Driver, Receiver and Termination Enabled
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
CONDITIONS DE = VCC, RE = VCC, TE = VCC DE = VCC, RE = 0V, TE = VCC

MIN
TYP 470 470
MAX 1000 1000
UNITS A A
SWITCHING CHARACTERISTICS
SYMBOL Driver fMAX tPLHD, tPHLD tPD tSKEWD tRD, tFD tZLD, tZHD, tLZD, tHZD tZHSD, tZLSD tSHDN Receiver tPLHR, tPHLR tSKEWR tRR, tFR tZLR, tZHR, tLZR, tHZR tZHSR, tZLSR tRTEN, tRTZ Receiver Input to Output Differential Receiver Skew |tPLHR-tPHLR| Receiver Output Rise or Fall Time Receiver Enable/Disable Receiver Enable from Shutdown Termination Enable or Disable Time Maximum Data Rate Driver Input to Output Driver Input to Output Difference |tPLHD-tPHLD| Driver Output Y to Output Z Driver Rise or Fall Time Driver Enable or Disable Time Driver Enable from Shutdown Time to Shutdown PARAMETER
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V, TE = 0V unless otherwise noted (Note 2).
CONDITIONS Note 3 RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RDIFF = 54, CL = 100pF (Figure 4) RL = 500, CL = 50pF, RE = 0 (Figure 5) RL = 500, CL = 50pF, RE = VCC (Figure 5) (DE = , RE = VCC) or (DE = 0, RE (Figure 5) )

MIN 20
TYP
MAX
UNITS Mbps
10 1 1 4
50 6 6 12.5 70 8 100
ns ns ns ns ns s ns
CL = 15pF, VCM = 1.5V, |VAB| = 1.5V, tR and tF < 4ns (Figure 6) CL = 15pF (Figure 6) CL = 15pF (Figure 6) RL = 1k, CL =15pF, DE = VCC (Figure 7) RL = 1k, CL = 15pF, DE = 0V (Figure 7) VB = 0V, VAB = 2V, RE = VCC, DE = 0V (Figure 8)

50 1 3
70 6 12.5 50 8 100
ns ns ns ns s s
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to device ground unless otherwise specified.
Note 3: Maximum data rate is guaranteed by other measured parameters and is not tested directly. Note 4: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure.
285455f
4
LTC2854/LTC2855 TEST CIRCUITS
Y GND DI OR VCC DRIVER Z + VOD - R Y GND OR DI VCC IOSD DRIVER Z
R
+ VOC -
+ -
285455 F01-2
-7V to +12V
Figure 1. Driver DC Characteristics
Figure 2. Driver Output Short-Circuit Current
IIN
A OR B RECEIVER B OR A
285455 F03
VIN
+ -
V RIN = IN IIN
Figure 3. Receiver Input Current and Input Resistance
VCC Y DI CL DRIVER RDIFF CL Z
285455 F04a
DI 0V
tPLHD tSKEWD
tPHLD
Y, Z
VO
1/2 VO
90% Y-Z 10% 0 tRD 0
90% 10% tFD
285455 F04b
Figure 4. Driver Timing Measurement
VCC Y VCC OR GND DI CL DRIVER RL DE Z CL VCC OR GND
285455 F05a
RL
GND OR VCC
DE 0V VCC Y OR Z VOL VOH Z OR Y 0V VO
1/2 VCC tZLD, tZLSD 1/2 VCC tLZD 0.5V 0.5V tHZD, tSHDN
285455 F05b
1/2 VCC tZHD, tZHSD
Figure 5. Driver Enable and Disable Timing Measurements
285455f
5
LTC2854/LTC2855 TEST CIRCUITS
tR VAB/2 VCM VAB/2 B A RECEIVER RO CL
285455 F06a
tF 90% 10% tPLHR tPHLR 1/2 VCC 90% 10% tFR
285455 F06b
VAB A-B -VAB VCC RO 0 VO
90% 0 10%
90% 1/2 VCC 10% tRR
tSKEWR = tPLHR - tPHLR
Figure 6. Receiver Propagation Delay Measurements
VCC RE 0V 0V OR VCC A RECEIVER VCC OR 0V B RE RO CL RL VCC OR GND VCC RO VOL VOH RO DI = 0V OR VCC
285455 F07a
1/2 VCC tZLR, tZLSR VO 1/2 VCC tLZR 0.5V 0.5V
285455 F05b
1/2 VCC 0V tZHR, tZHSR tHZR
Figure 7. Receiver Enable and Disable Timing Measurements
IA A RO RECEIVER
RTERM = VAB IA TE VAB IA
VCC 1/2 VCC 0V 90% 10% tRTEN tRTZ
+ -
B
TE
+ -
VB
285455F07
Figure 8. Termination Resistance and Timing Measurements
285455f
6
LTC2854/LTC2855 TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Skew vs Temperature
2 VAB = 1.5V CL = 15pF RECEIVER SKEW (ns) 1 DRIVER SKEW (ns) RDIFF = 54 CL = 100pF
1
PROP DELAY (ns)
0
-1 -40 -20
0
20
40
60
TEMPERATURE (C)
285455 G01
RTERM vs Temperature
135 130 125 120 115 110 105 100 -40 -20 0 0 20 40 60 80 100 120
285455 G04
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
RESISTANCE ()
TEMPERATURE (C)
Receiver Output Voltage vs Output Current (Source and Sink)
70 SOURCE 3 OUTPUT VOLTAGE (V) 65 60 55 50 45 40 SINK 0 0 1 2 3 4 5 6
285455 G07
SUPPLY CURRENT (mA)
PROP DELAY (ns)
2
1
OUTPUT CURRENT (mA)
UW
80
TA = 25C, VCC = 3.3V, unless otherwise noted. Driver Propagation Delay vs Temperature
18 16 14 12 10 9 RDIFF = 54 CL = 100pF
Driver Skew vs Temperature
0
-1
6 4 -40 -20
100 120
-40 -20
0
20
40
60
80
100 120
285455 G02
0
20
40
60
80
100 120
285455 G03
TEMPERATURE (C)
TEMPERATURE (C)
Driver Output Low/High Voltage vs Output Current
3 VOH 3
Driver Differential Output Voltage vs Temperature
RDIFF = RDIFF = 100 2 RDIFF = 54
2
1
VOL
1
0
10
20
30
40
50
60
70
0 -40 -20
0
20
40
60
80
100 120
285455 G06
OUTPUT CURRENT (mA)
285455 G05
TEMPERATURE (C)
Receiver Propagation Delay vs Temperature
VAB = 1.5V CL = 15pF 60 50 40 30 20 10
Supply Current vs Data Rate
CL = 100pF
RDIFF = 54
RDIFF = 100
RDIFF = 0 20 40 60 80 100 120
285455 G08
35 -40 -20
0 0.1 1 10 DATA RATE (Mbps) 100
285455 G09
TEMPERATURE (C)
285455f
7
LTC2854/LTC2855 PIN FUNCTIONS
(DD/DE/GN)
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low) and A > B by 200mV, then RO will be high. If A < B by 200mV, then RO will be low. If the receiver inputs are open, shorted, or terminated without a signal, RO will be high. RE (Pin 2): Receiver Enable. A low enables the receiver. A high input forces the receiver output into a high impedance state. DE (Pin 3): Driver Enable. A high on DE enables the driver. A low input will force the driver outputs into a high impedance. If RE is high with DE and TE low, the part will enter a low power shutdown state. DI (Pin 4): Driver Input. If the driver outputs are enabled (DE high), then a low on DI forces the driver positive output low and negative output high. A high on DI, with the driver outputs enabled, forces the driver positive output high and negative output low.
TE (Pin 5): Internal Termination Resistance Enable. A high input will connect a termination resistor (120 typical) between pins A and B. GND (Pins 6,11/6,13/6): Ground. Pins 11 and 13 are backside thermal pad, connected to Ground. Y (Pins NA/8/12): Positive Driver Output for LTC2855. Z (Pins NA/9/13): Negative Driver Output for LTC2855. B (Pins 9/10/14): Negative Receiver Input (and Negative Driver Output for LTC2854). A (Pins 8/11/15): Positive Receiver Input (and Positive Driver Output for LTC2854). VCC (Pins 10/12/16): Positive Supply. VCC = 3.0V < VCC < 3.6V. Bypass with 0.1F ceramic capacitor.
285455f
8
LTC2854/LTC2855 FUNCTION TABLES
LTC2854
DE 0 0 0 0 1 1 1 1 LOGIC INPUTS RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE RECEIVE RECEIVE WITH TERM SHUTDOWN TERM ONLY TRANSMIT WITH RECEIVE TRANSMIT WITH RECEIVE AND TERM TRANSMIT TRANSMIT WITH TERM A, B RIN RTERM RIN RTERM DRIVEN DRIVEN DRIVEN DRIVEN RO DRIVEN DRIVEN HIGH-Z HIGH-Z DRIVEN DRIVEN HIGH-Z HIGH-Z TERMINATOR OFF ON OFF ON OFF ON OFF ON
LTC2855
DE 0 0 0 0 1 1 1 1 LOGIC INPUTS RE 0 0 1 1 0 0 1 1 TE 0 1 0 1 0 1 0 1 MODE RECEIVE RECEIVE WITH TERM SHUTDOWN TERM ONLY TRANSMIT WITH RECEIVE TRANSMIT WITH RECEIVE AND TERM TRANSMIT TRANSMIT WITH TERM A, B RIN RTERM RIN RTERM RIN RTERM RIN RTERM Y, Z HIGH-Z HIGH-Z HIGH-Z HIGH-Z DRIVEN DRIVEN DRIVEN DRIVEN RO DRIVEN DRIVEN HIGH-Z HIGH-Z DRIVEN DRIVEN HIGH-Z HIGH-Z TERMINATOR OFF ON OFF ON OFF ON OFF ON
BLOCK DIAGRAMS
LTC2854
VCC
LTC2855
VCC
RE DE
SLEEP/SHUTDOWN LOGIC AND DELAY
A 25kV 120 RTERM
RE DE
SLEEP/SHUTDOWN LOGIC AND DELAY
A (15kV) 120 RTERM
125k RIN RO RECEIVER
TE
125k RIN RO RECEIVER
TE
125k RIN
B 25kV
125k RIN
B (15kV)
DI
DRIVER
DI
DRIVER
Z (15kV) Y (15kV)
GND
GND
285455 BD
285455f
9
LTC2854/LTC2855 APPLICATIO S I FOR ATIO
Driver The driver provides full RS485/RS422 compatibility. When enabled, if DI is high, Y-Z is positive for the full-duplex device (LTC2855) and A-B is positive for the half-duplex device (LTC2854). When the driver is disabled, both outputs are highimpedance. For the full-duplex LTC2855, the leakage on the driver output pins is guaranteed to be less than 10A over the entire common mode range of -7V to +12V. On the half-duplex LTC2854, the impedance is dominated by the receiver input resistance, RIN. Driver Overvoltage and Overcurrent Protection The driver outputs are protected from short-circuits to any voltage within the Absolute Maximum range of (VCC -15V) to +15V. The typical peak current in this condition does not exceed 180mA. If a high driver output is shorted to a voltage just above VCC , a reverse current will flow into the supply. When this voltage exceeds VCC by about 1.4V, the reverse current turns off. Preventing the driver from turning off with outputs shorted to output voltages just above VCC keeps the driver active even for receiver loads that have a positive common mode with respect to the driver -- a valid condition. The worst-case peak reverse short-circuit current can be as high as 300mA in extreme cold conditions. If this current cannot be absorbed by the supply, a 3.6V Zener diode can be added in parallel with the supply to sink this current. All devices also feature thermal shutdown protection that disables the driver and receiver in case of excessive power dissipation (see Note 4).
>96k A 60 TE 60 >96k
285455 F09
Figure 9. Equivalent Input Resistance into A and B (on the LTC2854, Valid if Driver is Disabled)
285455f
10
U
Receiver and Failsafe With the receiver enabled, when the absolute value of the differential voltage between the A and B pins is greater than 200mV, the state of RO will reflect the polarity of (A-B). The LTC2854/LTC2855 have a failsafe feature that guarantees the receiver output to be in a logic-high state when the inputs are either shorted, left open, or terminated (externally or internally), but not driven. This failsafe feature is guaranteed to work for inputs spanning the entire common mode range of -7V to +12V. The receiver output is internally driven high (to VCC) or low (to ground) with no external pull-up needed. When the receiver is disabled the RO pin becomes high-Z with leakage of less than 1A for voltages within the supply range. Receiver Input Resistance The receiver input resistance from A or B to ground is guaranteed to be greater than 96k when the termination is disabled. This is 8X higher than the requirements for the RS485 standard and thus this receiver represents a one-eighth unit load. This, in turn, means that 8X the standard number of receivers, or 256 total, can be connected to a line without loading it beyond what is called out in the RS485 standard. The input resistance of the receivers is unaffected by enabling/disabling the receiver and by powering/unpowering the part. The equivalent input resistance looking into A and B is shown in Figure 9. The termination resistor cannot be enabled by TE if the device is unpowered or in thermal shutdown mode.
B
W
U
U
LTC2854/LTC2855 APPLICATIO S I FOR ATIO
Switchable Termination Proper cable termination is very important for good signal fidelity. If the cable is not terminated with its characteristic impedance, reflections will result in distorted waveforms. The LTC2854/LTC2855 are the first 3.3V RS485/RS422 transceivers to offer integrated switchable termination resistors on the receiver input pins. This provides the advantage of being able to easily change, through logic control, the line termination for optimal performance when configuring transceiver networks.
RESISTANCE ()
Figure 10. Curve Trace Between A and B with Termination Enabled and Disabled
185 170 MAGNITUDE () 155 140 125 110 95 80 10 -1 10 0 FREQUENCY (MHz) MAGNITUDE PHASE
Figure 12. Termination Magnitude and Phase vs Frequency
U
When the TE pin is high, the termination resistor is enabled and the differential resistance from A to B is 120. Figure 10 shows the I/V characteristics between pins A and B with the termination resistor enabled and disabled. The resistance is maintained over the entire RS485 common mode range of -7V to +12V as shown in Figure 11. The integrated termination resistor has a high frequency response which does not limit performance at the maximum specified data rate. Figure 12 shows the magnitude and phase of the termination impedance vs frequency.
150 VAB = 2V 140 130 120 110 100 -10 -5 5 10 0 COMMON MODE VOLTAGE (V) 15
285455 F11
W
U
U
Figure 11. Typical Resistance of the Enabled Terminator vs Voltage on B Pin
30 15 0 PHASE ()
285455f
-15 -30 - 45 - 60 - 75 101
285455 F12
11
LTC2854/LTC2855 APPLICATIO S I FOR ATIO
Supply Current The unloaded static supply currents in the LTC2854/ LTC2855 are very low --typically under 500A for all modes of operation. In applications with resistively terminated cables, the supply current is dominated by the driver load. For example, when using two 120 terminators with a differential driver output voltage of 2V, the DC current is 33mA, which is sourced by the positive voltage supply. This is true whether the terminators are external or internal such as in the LTC2854/LTC2855. Power supply current increases with toggling rate due to capacitive loading and this term can increase significantly at high data rates. Figure 13 shows supply current vs data rate for two different capacitive loads for the circuit configuration of Figure 4.
80 70 SUPPLY CURRENT (mA) 60 50 40 30 20 0.1 1 10 DATA RATE (Mbps) 100
285455 F13
RDIFF = 54
C L = 1000pF
C L = 100pF
Figure 13. Supply Current vs Data Rate
10k
High Speed Considerations A ground plane layout is recommended for the LTC2854/ LTC2855. A 0.1F bypass capacitor less than one-quarter inch away from the VCC pin is also recommended. The PC board traces connected to signals A/B and Z/Y (LTC2855) should be symmetrical and as short as possible to maintain good differential signal integrity. To minimize capacitive effects, the differential signals should be separated by more than the width of a trace and should not be routed on top of each other if they are on different signal planes. Care should be taken to route outputs away from any sensitive inputs to reduce feedback effects that might cause noise, jitter, or even oscillations. For example, in
CABLE LENGTH (FT) 1k LTC2854/LTC2855 MAX DATA RATE 100 RS485/RS422 MAX DATA RATE 10 10k 100k 1M 10M DATA RATE (bps) 100M
285455 F14
12
U
the full duplex LTC2855, DI and A/B should not be routed near the driver or receiver outputs. The logic inputs of the LTC2854/LTC2855 have 150mV of hysteresis to provide noise immunity. Fast edges on the outputs can cause glitches in the ground and power supplies which are exacerbated by capacitive loading. If a logic input is held near its threshold (typically 1.5V), a noise glitch from a driver transition may exceed the hysteresis levels on the logic and data input pins causing an unintended state change. This can be avoided by maintaining normal logic levels on the pins and by slewing inputs through their thresholds by faster than 1V/s when transitioning. Good supply decoupling and proper line termination also reduces glitches caused by driver transitions. Cable Length vs Data Rate For a given data rate, the maximum transmission distance is bounded by the cable properties. A typical curve of cable length vs data rate compliant with the RS485/RS422 standards is shown in Figure 14. Three regions of this curve reflect different performance limiting factors in data transmission. In the flat region of the curve, maximum distance is determined by resistive losses in the cable. The downward sloping region represents limits in distance and data rate due to AC losses in the cable. The solid vertical line represents the specified maximum data rate in the RS485/RS422 standards. The dashed lines at 20Mbps show the maximum data rates of the LTC2854/LTC2855.
Figure 14. Cable Length vs Data Rate (RS485/ RS422 Standards Shown in Vertical Solid Line)
285455f
W
U
U
LTC2854/LTC2855 TYPICAL APPLICATION
Failsafe "0" Application (Idle State = Logic "0")
VCC 100k RO I1 R LTC2854 B "A"
A DI I2 D
"B"
285455 TA03
PACKAGE DESCRIPTIO
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
U
DD Package 10-Lead Plastic DFN (3mm x 3mm) (Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10 3.00 0.10 (4 SIDES) 1.65 0.10 (2 SIDES)
(DD) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
285455f
13
LTC2854/LTC2855 PACKAGE DESCRIPTIO U
DE/UE Package 12-Lead Plastic DFN (4mm x 3mm)
(Reference LTC DWG # 05-08-1695)
0.70 0.05 PACKAGE OUTLINE 0.25 0.05 3.30 0.05 (2 SIDES) 0.50 BSC 4.00 0.10 (2 SIDES) R = 0.05 TYP 3.00 0.10 (2 SIDES) 1.70 0.05 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER 0.75 0.05 6 0.25 0.05 3.30 0.05 (2 SIDES) 1 0.50 BSC
(UE12/DE12) DFN 0905 REV C
3.60 0.05 1.70 0.05 2.20 0.05 (2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 0.40 0.10 12
7
PIN 1 TOP MARK (NOTE 6)
0.200 REF
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
285455f
14
LTC2854/LTC2855 PACKAGE DESCRIPTION
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.045 .005
.189 - .196* (4.801 - 4.978) 16 15 14 13 12 11 10 9
.009 (0.229) REF
.254 MIN
.150 - .165
.229 - .244 (5.817 - 6.198)
.0165 .0015
.150 - .157** (3.810 - 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1 .015 .004 x 45 (0.38 0.10)
.007 - .0098 (0.178 - 0.249) 0 - 8 TYP .0532 - .0688 (1.35 - 1.75)
23
4
56
7
8
.004 - .0098 (0.102 - 0.249)
.016 - .050 (0.406 - 1.270)
NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE
.008 - .012 (0.203 - 0.305) TYP
.0250 (0.635) BSC
GN16 (SSOP) 0204
*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
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.
285455f
15
LTC2854/LTC2855 TYPICAL APPLICATION
Multi-Node Network with End Termination Using the LTC2854
TE = 0V
TE = 0V
D R R
D
LTC2854
LTC2854
LTC2854 R TE = 3.3V
LTC2854 R TE = 3.3V
D
D
285455 TA04
RELATED PARTS
PART NUMBER LTC485 LTC491 LTC1480 LTC1483 LTC1485 LTC1487 LTC1520 LTC1535 LTC1685 LT1785 DESCRIPTION Low Power RS485 Interface Transceiver Differential Driver and Receiver Pair 3.3V Ultralow Power RS485 Transceiver Ultralow Power RS485 Low EMI Transceiver Differential Bus Transceiver Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance 50Mbps Precision Quad Line Receiver Isolated RS485 Full-Duplex Transceiver 52Mbps RS485 Transceiver with Precision Delay 60V Fault Protected RS485 Transceiver COMMENTS ICC = 300A (Typ) ICC = 300A 3.3V Operation Controlled Driver Slew Rate 10Mbps Operation Up to 256 Transceivers on the Bus Channel-to-Channel Skew 400ps (Typ) 2500VRMS Isolation in Surface Mount Package Propagation Delay Skew 500ps (Typ) 60V Tolerant, 15kV ESD Up to 256 Transceivers on the Bus 5V Integrated, Switchable, 120 Termination Resistor, 15kV ESD
LTC2856/LTC2857/ 20Mbps and Slew Rate-Limited, 15kV RS485/RS422 LTC2858 Transceiver LTC2859/LTC2861 20Mbps RS485 Transceiver with Integrated Swtichable Termination
285455f
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0107 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

▲Up To Search▲

Price & Availability of LTC2854NBSP

	To Download LTC2854NBSP Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .