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PDF LTC2859 Data sheet ( Hoja de datos )
| Número de pieza | LTC2859 | |
| Descripción | 20Mbps RS485 Transceivers | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC2859 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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FEATURES
LTC2859/LTC2861
20Mbps RS485 Transceivers
with Integrated Switchable
Termination
DESCRIPTION
■ Integrated, Logic-Selectable 120Ω Termination
Resistor
■ 20Mbps Max Data Rate
■ No Damage or Latchup to ESD: ±15kV HBM
■ High Input Impedance Supports 256 Nodes
■ 250kbps Low-EMI Mode
www■.DaGtuaaShraenette4Ue.dcoFmailsafe Receiver Operation Over the
Entire Common Mode Range
■ Current Limited Drivers and Thermal Shutdown
■ Delayed Micropower Shutdown (5μA Max)
■ Power Up/Down Glitch-Free Driver Outputs
■ Low Operating Current (900μA Max in Receive Mode)
■ Meets All TIA/EIA-485-A Specifications
■ Available in 10-Pin 3mm × 3mm DFN, 12-Pin
4mm × 3mm DFN and 16-Pin SSOP Packages
APPLICATIONS
■ Low Power RS485/RS422 Transceiver
■ Level Translator
■ Backplane Transceiver
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
The LTC®2859 and LTC2861 are low power, 20Mbps
RS485/422 transceivers operating on 5V supplies. The
receiver includes a logic-selectable 120Ω 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 features a logic-selectable low-EMI 250kbps
operating mode, and 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 LTC2859 and LTC2861
to withstand ±15kV (human body model) on the transceiver
interface pins without latchup or damage.
PRODUCT SELECTION GUIDE
PART NUMBER
LTC2859
LTC2861
DUPLEX
Half
Full
PACKAGE
DFN-10
SSOP-16, DFN-12
TYPICAL APPLICATION
RO R
RE
TE
DE
DI D
SLO
LTC2859
120Ω
LTC2859
120Ω
LTC2859
R RO
RE
TE
DE
D DI
SLO
2859/61 TA01
120Ω
R
D
RO RE TE DE DI SLO
LTC2859 at 20Mbps
DI
Y
Z
Y–Z
2V/DIV
20ns/DIV
285961 TA02
285961fb
1
1 page  
TEST CIRCUITS
GND
OR DI
VCC
DRIVER
Y
R
+
VOD
Z – R+
VOC
–
www.DataSheet4U.Fciogmure 1. Driver DC Characteristics
LTC2859/LTC2861
GND
OR DI
VCC
DRIVER
Y
Z
IOSD
+
–
–7V to +12V
2859/61 F01-2
Figure 2. Driver Output Short-Circuit Current
Y
DI
DRIVER
Z
RDIFF
CL
CL
VCC
DI
OV
Y, Z VO
tPLHD,
tPLHDS
1/2 VO
tPHLD,
tPHLDS
tSKEWD, tSKEWDS
(Y-Z)
90%
10%
0
tRD,
tRDS
Figure 3. Driver Timing Measurement
90%
0
10%
tFD,
tFDS
2859/61 F03
VCC
OR DI
GND
DRIVER
DE
Y
Z
RL
CL
GND
OR
VCC
RL
CL
VCC
OR
GND
DE
Y or Z
Z or Y
VCC
1/2 VCC
OV
VCC
VO
VOL
VOH
OV
tZLD,
tZLDS,
tZLSD,
tZLSDS
tZHD,
tZHDS,
tZHSD,
tZHSDS
1/2 VCC
1/2 VCC
Figure 4. Driver Enable and Disable Timing Measurement
tLZD,
tLZDS
tHZD,
tHZDS,
tSHDN,
tSHDNS
0.5V
0.5V
2859/61 F04
285961fb
5
5 Page 
LTC2859/LTC2861
APPLICATIONS INFORMATION
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 LTC2859/LTC2861 have a failsafe feature that guaran-
tees 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 for more than
about 3μs. The delay prevents signal zero crossings from
wwwb.DeiantgaSihneteertp4Ure.ctoemd as shorted inputs and causing RO to go
high inadvertently. 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 Hi-Z with leakage
of less than ±1μA 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 termina-
tion is disabled. This is 8X higher than the requirements
for 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 con-
nected 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.
Switchable Termination
Proper cable termination is very important for good
signal fidelity. If the cable is not terminated with its char-
acteristic impedance, reflections will result in distorted
waveforms.
The LTC2859/LTC2861 are the first RS485 transceivers to
offer integrated switchable termination resistors on the
receiver input pins. This provides the tremendous advan-
tage of being able to easily change, through logic control,
the proper line termination for optimal performance when
configuring transceiver networks.
When the TE pin is high, the termination resistor is en-
abled and the differential resistance from A to B is 120Ω.
Figure 10 shows the I/V characteristics between pins A
and B with the termination resistor enabled and disabled.
>96k
>96k
A
60Ω
60Ω
2859/61 F09
TE
B
Figure 9. Equivalent Input Resistance into A and B
(on the LTC2859, Valid if Driver is Disabled)
Figure 10. Curve Trace Between A and B
with Termination Enabled and Disabled
285961fb
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC2859.PDF ] | |
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