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PDF DS25MB200 Data sheet ( Hoja de datos )
| Número de pieza | DS25MB200 | |
| Descripción | Dual 2.5 Gbps 2:1/1:2 CML Mux/Buffer | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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April 9, 2008
DS25MB200
Dual 2.5 Gbps 2:1/1:2 CML Mux/Buffer with Transmit Pre-
Emphasis and Receive Equalization
General Description
The DS25MB200 is a dual signal conditioning 2:1 multiplexer
and 1:2 fan-out buffer designed for use in backplane redun-
dancy applications. Signal conditioning features include input
equalization and programmable output pre-emphasis that en-
able data communication in FR4 backplanes up to 2.5 Gbps.
Each input stage has a fixed equalizer to reduce ISI distortion
from board traces. All output drivers have 4 selectable steps
www.DoaftparSeh-eemetp4hUa.csiosmto compensate for transmission losses from
long FR4 backplanes and reduce deterministic jitter. The pre-
emphasis levels can be independently controlled for the line-
side and switch-side drivers. The internal loopback paths from
switch-side input to switch-side output enable at-speed sys-
tem testing. All receiver inputs are internally terminated with
100Ω differential terminating resistors. All drivers are inter-
nally terminated with 50Ω to VCC.
Features
■ 0.6–2.5 Gbps low jitter operation
■ Fixed input equalization
■ Programmable output pre-emphasis
■ Independent switch and line side pre-emphasis controls
■ Programmable switch-side loopback modes
■ On-chip terminations
■ HBM ESD rating 6 kV on all pins
■ +3.3V supply
■ Lead-less LLP-48 package (7mm x 7mm x 0.8mm, 0.5mm
pitch)
■ —40°C to +85°C operating temperature range
Applications
■ Backplane or cable driver
■ Redundancy and signal conditioning applications
Functional Block Diagram
© 2008 National Semiconductor Corporation 201823
20182333
www.national.com
1 page  
Pin Name Pin Number I/O
Description
POWER
VCC 2, 8, 14, 20, P VCC = 3.3V ± 5%.
29, 35, 38,
Each VCC pin should be connected to the VCC plane through a low inductance path, typically with a
44 via located as close as possible to the landing pad of the VCC pin.
It is recommended to have a 0.01 μF or 0.1 μF, X7R, size-0402 bypass capacitor from each VCC
pin to ground plane.
GND
5, 11, 17, 32, P Ground reference. Each ground pin should be connected to the ground plane through a low
41 inductance path, typically with a via located as close as possible to the landing pad of the GND pin.
GND
DAP
P Die Attach Pad (DAP) is the metal contact at the bottom side, located at the center of the LLP-48
package. It should be connected to the GND plane with at least 4 via to lower the ground impedance
and improve the thermal performance of the package.
Functional Description
The DS25MB200 is a signal conditioning 2:1 multiplexer and
a 1:2 buffer designed to support port redundancy up to 2.5
wwGwbp.Ds.aEtaaSchheienpt4uUt .sctoamge has a fixed equalizer that provides
equalization to compensate about 5 dB of transmission loss
from a short backplane trace (about 10 inches backplane).
The output driver has pre-emphasis (driver-side equalization)
to compensate the transmission loss of the backplane that it
is driving. The driver conditions the output signal such that the
lower frequency and higher frequency pulses reach approxi-
mately the same amplitude at the end of the backplane, and
minimize the deterministic jitter caused by the amplitude dis-
parity. The DS25MB200 provides 4 steps of user-selectable
pre-emphasis ranging from 0, −3, −6 and –9 dB to handle
different lengths of backplane. Figure 1 shows a driver pre-
emphasis waveform. The pre-emphasis duration is 188 ps
nominal, corresponds to 0.47 bit-width at 2.5 Gbps. The pre-
emphasis levels of switch-side and line-side can be individu-
ally programmed.
The high speed inputs are self-biased to about 1.5V and are
designed for AC coupling. The inputs are compatible to most
AC coupling differential signals such as LVDS, LVPECL and
CML. See Figure 6 for details.
TABLE 1. LOGIC TABLE FOR MULTIPLEX CONTROLS
MUX_S0
0
1 (default)
MUX_S1
0
1 (default)
Mux Function
MUX_0 select switch_B input, SIB_0±.
MUX_0 select switch_A input, SIA_0±.
Mux Function
MUX_1 select switch_B input, SIB_1±.
MUX_1 select switch_A input, SIA_0±.
TABLE 2. LOGIC TABLE FOR LOOPBACK CONTROLS
LB0A
0
1 (default)
LB0B
0
1 (default)
LB1A
0
1 (default)
LB1B
0
1 (default)
Loopback Function
Enable loopback from SIA_0± to SOA_0±.
Normal mode. Loopback disabled.
Loopback Function
Enable loopback from SIB_0± to SOB_0±.
Normal mode. Loopback disabled.
Loopback Function
Enable loopback from SIA_1± to SOA_1±.
Normal mode. Loopback disabled.
Loopback Function
Enable loopback from SIB_1± to SOB_1±.
Normal mode. Loopback disabled.
5 www.national.com
5 Page 
Application Information
The DS25MB200 input equalizer provides equalization to
compensate about 5 dB of transmission loss from a short
backplane transmission line. For characterization purposes,
a 25-inch FR4 coupled micro-strip board trace is used in place
of the short backplane link. The 25-inch microstrip board trace
has approximately 5 dB of attenuation between 375 MHz and
1.875 GHz, representing closely the transmission loss of the
short backplane transmission line. The 25-inch microstrip is
connected between the pattern generator and the differential
inputs of the DS25MB200 for AC measurements.
Trace Length
25 inches
Finished Trace
Width W
8.5 mil
Separation between
Dielectric Constant
Dielectric Height H
Traces
εR
11.5 mil
6 mil
3.8
Loss Tangent
0.022
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FIGURE 7. Application Diagram (showing data paths of port 0)
20182344
11 www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet DS25MB200.PDF ] | |
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