Application note MLX75605 DownloadLink 5578

Rev: 1.1
Application Note MLX75605CA
Revision
1.0
1.1
Date
15/10/2008
26/10/2008
Author
ADE
CVA
Change
Creation
Addition of footprint dimensions
Introduction
This document describes the connections between MLX75605 MOST150 Fiber Optics
Transceivers and MOST control part. It explains how to connect the different pins, their
role, necessary external components, and some layout recommendations.
Pin List and Descriptions
DATAOUT+
DATAOUTRX
VCC_RX1
GND_RX1
RESERVED2
VDD_RX2
GND_RX2
STATUS
GP3_RX
SHIELD
SHIELD
SHIELD
SHIELD
TX
RESERVED1
GP2_TX
VCC_TX1
VCC_TX2
GND_TX1
GND_TX2
DATAIN+
DATAI-
Author: ADE
GP4_RX
GP1_TX
/RST
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MELEXIS CONFIDENTIAL AND PROPRIETARY
26/10/2008
Rev: 1.1
Pin Number Pin name
Description
1
DataOUT Plus
LVDS Positive Output. Routing
To LVDS Plus input of MOST
should be mirrored together
controller
with minus input.
2
DataOUT Minus
LVDS Negative Output Routing
To LVDS minus input of MOST
should be mirrored together
controller
with plus input.
3
VCC_Rx1
Supply voltage for Receiver
Connected to Rx VDD
4
GND_Rx1
Ground for Receiver
Connected to Rx GND
5
STATUS
Indicates if modulated light is
received within operation
frequency range. If the
received light power level and
frequency is greater than
threshold, then voltage on the
status pin is «LOW».
With the status pin the power
supply of the whole MOST
devices can be switched ON.
Connected to Status input of
controller
6
Shield
Shield pin connected to die
pad of package
Connected to Sh_GND
7
Shield
Shield pin connected to die
pad of package
Connected to Sh_GND
8
Reserved1
Connect to GND through 0ohm resistor.
Used for factory test purpose.
M3dB function
Connected to possible M3dB
function of controller (Not
available on MLX75605CA
revision)
9
VCC_Tx1
Supply voltage for Transmitter
Connected to Tx VDD
10
GND_Tx1
Ground for Transmitter
Connected to Tx GND
11
DataIN Plus
LVDS Negative Input
From LVDS minus output of
MOST controller
12
DataIN Minus
LVDS Positive Input
From LVDS plus output of
MOST controller
13
/RST
Optical Output power disabling.
Connected to /RST of MOST
Active-low logic signal disables controller
the optical output
14
Tx_GP1
Currently used for Test output
pin.
Should be left unconnected
Should be floating
15
GND_Tx2
Ground for Transmitter
Connected to Tx GND
16
VCC_TX2
Supply voltage for Transmitter
Connected to Tx VDD
Author: ADE
Connection
2
MELEXIS CONFIDENTIAL AND PROPRIETARY
26/10/2008
Rev: 1.1
17
Tx_GP2
Factory Test input.
Should left unconnected.
Should be floating
18
Shield
Shield pin connected to die
pad of package
Connected to Sh_GND
19
Shield
Shield pin connected to die
pad of package
Connected to Sh_GND
20
GP3_RX
Factory test output. Automatic
Gain Control analog output
Should be left unconnected
Should be floating. (Connected
to 10nF for MLX75603CA only)
21
GND_Rx2
Ground for Receiver
Connected to Rx GND
22
VCC_Rx2
Supply voltage for Receiver
Connected to Rx VDD
23
Reserved2
Connect to VCC_RX2 through
0-ohm resistor.
Used for factory test purpose.
Connected to Rx VDD.
24
GP4_RX
Should left unconnected.
Should be floating
Author: ADE
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MELEXIS CONFIDENTIAL AND PROPRIETARY
26/10/2008
Rev: 1.1
Schematics
VDD
_Tx
VDD_
Rx
10uF
100
10uF
DATAOUT+
DATAOUT-
LVDS
Outputs
M3dB
MOST
CONTROLLER
Including supply
control
LVDS
Outputs
VDD_RX2
STATUS
GP3_RX
GND_RX2
SHIELD
SHIELD
SHIELD
SHIELD
10nF
TX
RESERVED1
GP2_TX
VCC_TX1
VCC_TX2
100nF GND_TX1
DATAIN+
DATAI-
Author: ADE
RESERVED2
RX
100nF VCC_RX1
GND_RX1
100
/RST
GP4_RX
4
26/10/2008
MELEXIS CONFIDENTIAL AND PROPRIETARY
GND_TX2
GP1_TX
/RST
Rev: 1.1
External Components
- To guarantee correct impedance matching between controller and transceiver, it is
necessary to add 100ohms between both LVDS I/Os. To maximize their efficiency, the
resistors have to be placed close to the LVDS receiver buffer. This means that, for data
coming from transceiver, resistor has to be placed close to the MOST controller and for
data arriving at transceiver, resistor should be placed close to this one.
- As Transmitter can be disabled by supply shut down, Receiver and transmitter supplies
have to be fully decoupled.
- 10uF has can be used for global decoupling.
- Then, 100nF bypass capacitors can be connected for each device: one for Receiver
chipset and one for transmitter. It is recommended that, these capacitors are with low
equivalent serial resistance, in order to increase decoupling efficiency with high current.
These capacitors have to be placed close to the device to minimize routing impact.
- For MLX75605CA only, a 10nF decoupling capacitor should be added on pin #20. This
capacitor should be considered as a containment action for a small design weakness in
Automatic Gain control on the receiver chip.
Layout Recommendations
-
-
It is important to decouple supply lines to the maximum. This means that, supply
lines have to be routed in a star configuration.
For VDD side, it is recommended to short both VCC from each device,
respectively transmitter and receiver, together routing under the device. Pinout of
supply and ground lines have been made such a way that, they face each other.
This allows direct connection with the shortest route.
For GND side, it is advised to fully decouple ground from transmitter and ground
from receiver to guarantee no cross talk.
A ground plate has been placed all around FOT and especially around LVDS
High speed tracks to fully isolate them.
Moreover, device allows shield to be grounded to Ground plate. This allows
optimizing EMc performance.
Author: ADE
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MELEXIS CONFIDENTIAL AND PROPRIETARY
26/10/2008
Rev: 1.1
Footprint – recommendation
All dimensions given in mm.
11x means that this dimension is repeated 11 times in this footprint drawing (only the
bottom half of the drawing)
Due to the symmetry axis this is also valid for the upper half of the drawing
24x means that this dimension is repeated 24 times in this footprint drawing (for the
bottom half as well as for the upper half of the drawing)
Author: ADE
6
MELEXIS CONFIDENTIAL AND PROPRIETARY
26/10/2008
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