|
|
PDF LTC1685CS8 Data sheet ( Hoja de datos )
| Número de pieza | LTC1685CS8 | |
| Descripción | 52Mbps/ Precision Delay/ RS485 Fail-Safe Transceiver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LTC1685CS8 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
LTC1685
52Mbps, Precision Delay,
RS485 Fail-Safe Transceiver
FEATURES
s Precision Propagation Delay Over Temperature:
Receiver/Driver: 18.5ns ±3.5ns
s High Data Rate: 52Mbps
s Low tPLH/tPHL Skew:
Receiver/Driver: 500ps Typ
s –7V to 12V RS485 Input Common Mode Range
s Guaranteed Fail-Safe Receiver Operation Over the
Entire Common Mode Range
s High Receiver Input Resistance: ≥ 22k, Even When
Unpowered
s Short-Circuit Protected
s Thermal Shutdown Protected
s Driver Maintains High Impedance in Three-State or
with Power Off
s Single 5V Supply
s Pin Compatible with LTC485
s 45dB CMRR at 26MHz
U
APPLICATIONS
s High Speed RS485/RS422 Transceivers
s Level Translator
s Backplane Transceiver
s STS-1/OC-1 Data Transceiver
s Fast-20, Fast-40 SCSI Transceivers
DESCRIPTION
The LTC®1685 is a high speed, precision delay RS485
transceiver that can operate at data rates as high as 52Mbps.
The device also meets the requirements of RS422.
A unique architecture provides very stable propagation
delays and low skew over a wide common mode and
ambient temperature range.
The driver and receiver feature three-state outputs, with
disabled driver outputs maintaining high impedance over
the entire common mode range. A short circuit feature
detects shorted outputs and substantially reduces driver
output current. A similar feature also protects the receiver
output from short circuits. Thermal shutdown circuitry
protects from excessive power dissipation.
The receiver has a fail-safe feature that guarantees a high
output state when the inputs are shorted or are left floating.
The LTC1685 RS485 transceiver guarantees receiver fail-
safe operation over the entire common mode range (– 7V
to 12V). Input resistance will remain ≥ 22k when the device
is unpowered or disabled.
The LTC1685 operates from a single 5V supply and draws
only 7mA of supply current.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
RO1
R
RE1
DE1
DI1 D
VCC1
GND1
Rt
RO2
R
RE2
DE2
DI2 D
VCC2
Rt
GND2
1685 TA01
2V/DIV
10Mbps Data Pulse
400ft Category 5 UTP
CABLE DELAY
DRIVER INPUT
1V/DIV
RECEIVER
INPUT
5V/DIV
100ns/DIV
RECEIVER
OUTPUT
1685 TA02
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
Driver Propagation Delay
vs Temperature
25
20
15
10
5
0
– 20 0 20 40 60 80 100
TEMPERATURE (°C)
1685 G07
Driver Propagation Delay
vs Driver Input Voltage
25
VDD = 5V
INPUT THRESHOLD = 1.5V
20 TA = 25°C
tHL
tLH
15
10
5
0
2.5 3.0 3.5 4.0 4.5 5.0
DRIVER INPUT VOLTAGE (V)
1685 G08
LTC1685
Driver Propagation Delay
vs Capacitive Load
19.0
TA = 25°C
18.5
18.0
17.5
17.0
16.5
16.0
5
15 25 50 75 100 150
LOAD CAPACITANCE (pF)
1685 G11
PIN FUNCTIONS
RO (Pin 1): Receiver Output. If A ≥ B by 300mV, then RO
will be high. If A ≤ B by 300mV, then RO will be low.
RE (Pin 2): Receiver Enable. RE = Low enables the
receiver. RE = High forces receiver output into high
impedance state. Do not float.
DE (Pin 3): Driver Enable. DE = High enables the driver.
DE = Low will force the driver output into a high impedance
state and the device will function as a line receiver if RE is
also low. Do not float.
DI (Pin 4): Driver Input. Controls the states of the A and
B outputs only if DE = High. If DE = Low, DI will have no
effect on A and B pins. Do not float.
GND (Pin 5): Ground.
A (Pin 6): Noninverting Receiver Input/Driver Output.
B (Pin 7): Inverting Receiver Input/Driver Output.
VDD (Pin 8): Positive Supply, 5V to ±5%. Bypass with
0.1µF ceramic capacitor.
5
5 Page 
LTC1685
APPLICATIONS INFORMATION
single-ended trace over an adjacent ground plane. Then
set the (bypassed) negative input of the receiver to roughly
2.5V. Note that single-ended operation might not reach
maximum speeds.
High Speed Differential SCSI (Fast-20, Fast-40 HVD)
The LTC1685’s high speed, tight propagation delay win-
dow and matched driver/receiver propagation delays make
it a natural choice as the external transceiver in high speed
differential SCSI applications. Note that the ±3.5ns propa-
gation delay window covers the entire commercial tem-
perature range. If, for example, a group of 16 transceivers
is placed on the same board, their temperature difference
will be much smaller. Hence, the difference in their propa-
gation delays should be even better than the ±3.5ns
specification (typically better than ±2ns). The LTC1685 is
the most efficient and reliable implementation that meets
the Fast-20 and Fast-40 HVD driver and receiver skew
specifications.
Power-Up Requirements
The LTC1685 has unique short-circuit protection that
shuts off the big output devices (and keeps them off) when
a short is detected. When the LTC1685 is powered up with
the driver outputs enabled (Figure 15 shows a typical
connection), the part will power up in short-circuit mode.
After power-up, the user must hold the DE pin of the
LTC1685 low for at least 200ns in order to start normal
operation. Note also that turning the termination power
on/off might induce the LTC1685 to see a “short.” Conse-
quently, the DE pin should be held low for 200ns after
cable termination power is turned on.
This requirement is solely due to the cable termination
(the 165Ω parallel resistance to both power and ground).
For applications whose connections to the cable are
made exclusively with RS485 devices, the cable can be
terminated only across the two signal wires (as in Figure
10). With cable distances covering under 25 meters, the
common mode range of the LTC1685 should be more
than sufficient to account for any ground differences
between any two communicating devices. The fact that
transmission is differential should greatly improve noise
RE
2
RO 1
TERM POWER
330Ω
4
DI
7
6
3
150Ω
DE 330Ω
LTC1685
TERM POWER RE
122Ω CABLE
330Ω
150Ω
2
1 RO
7
6
3
4
DI
EN 4 A 1
EN 12
2 B 330Ω
1/4 LTC1518
3
DE
LTC1685
RO 1685 F15
Figure 15. Fast-20, Fast-40 Differential SCSI Application
margin. Furthermore, the good high frequency CMRR of
the receiver will serve to reject any common mode
interference.
DE, DI Inputs
It is not necessary that the driver input (DI) have 0V to 3V
signal levels. The DI input can be driven by CMOS levels
(0V to 5V) and still achieve 40Mbps operation. However,
duty cycle will be slightly compromised when driven by a
CMOS device. Care should be taken to minimize the
ringing on the DI input in order to achieve a driver
propagation delay within the ±3.5ns window. This also
improves the package-to-package matching of propaga-
tion delays.
The DE pin should be held low for 200ns after the power-
up sequence has been completed. After fault conditions
such as an output short or thermal shutdown, the DE pin
should be held low for at least 200ns after the fault has
been removed. This is usually necessary only if the driver
outputs are connected to DC-biased cable terminations
(as in Figure 15).
Layout Considerations
A ground plane is recommended when using a high
frequency device like the LTC1685. A 0.1µF ceramic by-
pass capacitor less than 1/4 inch away from the VDD pin is
recommended. Good bypassing is especially needed when
operating at maximum frequency or when package-to-
package matching is very important. The PC board traces
connected to the “A” and “B” outputs must be kept as
symmetrical and short as possible to obtain the same
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1685CS8.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LTC1685CS8 | 52Mbps/ Precision Delay/ RS485 Fail-Safe Transceiver | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |