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PDF LTC2852 Data sheet ( Hoja de datos )
| Número de pieza | LTC2852 | |
| Descripción | 3.3V 20Mbps RS485/RS422 Transceivers | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n 3.3V Supply Voltage
n 20Mbps Maximum Data Rate
n No Damage or Latchup Up to ±15kV HBM
n High Input Impedance Supports 256 Nodes
(C, I-Grade)
n Operation Up to 125°C (H-Grade)
wwwn.DaGtuaaShraenete4Ue.dcoFmailsafe Receiver Operation Over the
Entire Common Mode Range
n Current Limited Drivers and Thermal Shutdown
n Delayed Micropower Shutdown: 5μA Maximum
(C, I-Grade)
n Power Up/Down Glitch-Free Driver Outputs
n Low Operating Current: 370μA Typical in Receive
Mode
n Compatible with TIA/EIA-485-A Specifications
n Available in 8-Pin and 10-Pin 3mm × 3mm DFN,
8-Pin and 10-Pin MSOP, and 8-Pin and 14-Pin SO
Packages
APPLICATIONS
n Low Power RS485/RS422 Transceiver
n Level Translator
n Backplane Transceiver
LTC2850/LTC2851/LTC2852
3.3V 20Mbps RS485/RS422
Transceivers
DESCRIPTION
The LTC®2850, LTC2851, and LTC2852 are low power,
20Mbps RS485/RS422 transceivers operating on 3.3V
supplies. The receiver has a one-eighth unit load supporting
up to 256 nodes per bus (C, I-Grade), 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 thermal shutdown.
Enhanced ESD protection allows these parts to withstand
up to ±15kV (human body model) on the transceiver
interface pins without latchup or damage.
PART NUMBER
LTC2850
LTC2851
LTC2852
DUPLEX
Half
Full
Full
PACKAGE
SO-8, MSOP-8, DFN-8
SO-8, MSOP-8, DFN-8
SO-14, MSOP-10, DFN-10
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
LTC2850
RO1
RE1 R
VCC1
DE1
DI1 D
GND1
RT
LTC2850
RO2
R
RE2
VCC2
RT
DE2
DI2 D
GND2
285012 TA01a
LTC2850 at 20Mbps Into 54Ω
DI
2V/DIV
A-B
A
B
20ns/DIV
285012 TA01b
285012fc
1
1 page  
LTC2850/LTC2851/LTC2852
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Supplies
ICCS
Supply Current in Shutdown Mode
ICCR Supply Current in Receive Mode
ICCT Supply Current in Transmit Mode
ICCTR
Supply Current with Both Driver and
Receiver Enabled
DE = 0V, RE = VCC,
LTC2850, LTC2852 (C and I-Grade)
LTC2850, LTC2852 (H-Grade)
DE = 0V, RE = 0V (LTC2850, LTC2852)
No Load, DE = VCC, RE = VCC (LTC2850,
LTC2852)
No Load, DE = VCC, RE = 0V
l
l
l
l
l
05
0 15
370 900
450 1000
450 1000
μA
μA
μA
μA
μA
www.DataSheet4U.com
SWITCHING CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 3.3V, unless otherwise noted. (Note 2)
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Driver
fMAX Maximum Data Rate
tPLHD, tPHLD Driver Input to Output
ΔtPD Driver Input to Output Difference
|tPLHD – tPHLD|
tSKEWD
Driver Output Y to Output Z
tRD, tFD
Driver Rise or Fall Time
tZLD, tZHD, Driver Enable or Disable Time
tLZD, tHZD
tZHSD, tZLSD Driver Enable from Shutdown
tSHDN
Time to Shutdown
(Note 3)
RDIFF = 54Ω, CL = 100pF (Figure 4)
RDIFF = 54Ω, CL = 100pF (Figure 4)
RDIFF = 54Ω, CL = 100pF (Figure 4)
RDIFF = 54Ω, CL = 100pF (Figure 4)
RL = 500Ω, CL = 50pF, RE = 0V (Figure 5)
(LTC2850, LTC2852)
RL = 500Ω, CL = 50pF, RE = VCC (Figure 5)
(LTC2850, LTC2852)
RL
or
= 500Ω,
(DE = 0V,
CRLE==5↑0)p(F,F(igDuEre=
↓,
5)
RE = VCC)
(LTC2850,
LTC2852)
l 20
l
l
l
l
l
l
l
Mbps
10 50
ns
1 6 ns
1 ±6 ns
4 12.5 ns
70 ns
8 μs
100 ns
Receiver
tPLHR, tPHLR Receiver Input to Output
tSKEWR
tRR, tFR
tZLR, tZHR,
tLZR, tHZR
tZHSR, tZLSR
Differential Receiver Skew
|tPLHR – tPHLR|
Receiver Output Rise or Fall Time
Receiver Enable/Disable
Receiver Enable from Shutdown
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)
(LTC2850, LTC2852)
RL = 1k, CL = 15pF, DE = 0V (Figure 7)
(LTC2850, LTC2852)
l
l
l
l
l
50 70
16
3 12.5
50
8
ns
ns
ns
ns
μs
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. High temperatures degrade operating lifetimes.
Operating lifetime is derated at temperatures greater than 105°C.
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.
Overtemperature protection activates at a junction temperature exceeding
150°C. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.
285012fc
5
5 Page 
LTC2850/LTC2851/LTC2852
APPLICATIONS INFORMATION
Receiver Input Resistance
The receiver input resistance from A or B to ground is
guaranteed to be greater than 96k (C, I-Grade). 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 specified in the RS485 standard. The
receiver input resistance from A or B to ground on high
temperature H-Grade parts is greater than 48k providing
wwwa.Doantea-Sqhueeatr4teUr.cuonmit load. The high input resistance of the
receiver is maintained whether it is enabled or disabled,
powered or unpowered.
Supply Current
The unloaded static supply currents in these devices are
very low, typically under 500μA for all modes of opera-
tion. In applications with resistively terminated cables,
the supply current is dominated by the driver load. For
example, when using two 120Ω terminators with a dif-
ferential driver output voltage of 2V, the DC load current
is 33mA, which is sourced by the positive voltage supply.
Power supply current increases with toggling data 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
RDIFF = 54Ω
70
60
CL = 1000pF
50
40 CL = 100pF
30
20
0.1
1 10
DATA RATE (Mbps)
100
285012 F13
Figure 13. Supply Current vs Data Rate
High Speed Considerations
A ground plane layout is recommended. A 0.1μF 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 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
the full-duplex devices, DI and A/B should not be routed
near the driver or receiver outputs.
The logic inputs 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/μs when transitioning. Good supply decoupling
and proper driver termination also reduce 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 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 transmis-
sion. In the flat region of the curve, maximum distance
285012fc
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC2852.PDF ] | |
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