Texas Instruments | PanelBus TFP401/401A Design Notes | Application notes | Texas Instruments PanelBus TFP401/401A Design Notes Application notes

Texas Instruments PanelBus TFP401/401A Design Notes Application notes
Application Note
SLLA136 – March 2003
TFP401, TFP401A Design Notes
Digital Visual Interface
ABSTRACT
The Texas Instruments TFP401 is one device in a family of TI PanelBusTM flat panel display
products that simplifies digital display systems design by offering value added flexibility and
reliability to the system designer. The TFP401 is a DVI compliant flat panel digital receiver that
supports display resolutions ranging from VGA to UXGA in 24-bit, true-color pixel format. The
TFP401 offers design flexibility in that it can be configured to drive one or two pixels per clock
and supports TFT or DSTN panels.
The TFP401 combines PanelBusTM circuit innovation with TI’s advanced 0.18-µm EPIC-5TM
CMOS process technology along with TI PowerPADTM package technology to achieve a reliable,
low-powered, low noise, high-speed digital solution to digital visual interfacing.
Fundamental Operation
The TFP401 is a DVI (Digital Visual Interface) compliant digital receiver that is used in digital flat
panel display systems to receive and decode T.M.D.S. encoded RGB pixel data streams. In a
digital display system a host, usually a PC or workstation, contains a DVI compliant transmitter
that receives 24-bit pixel data along with appropriate control signals and encodes them into a
high-speed low-voltage differential serial bit stream fit for transmission over a twisted-pair cable
to a display device. The display device, usually a flat-panel monitor, requires a DVI compliant
receiver like the TI TFP401 to decode the serial bit stream back to the same 24-bit pixel data
and control signals that originated at the host. This decoded data can then be applied directly to
the flat panel drive circuitry to produce an image on the display. Since the host and display can
be separated by distances up to 5 meters or more, serial transmission of the pixel data is
preferred. The TFP401 supports resolutions up to UXGA.
Routing High-Speed Differential Signal Traces
(RxC-, RxC+, Rx0-, Rx0+, Rx1-, Rx1+, Rx2-, Rx2+)
Trace impedance should be controlled for optimal performance. Each differential pair should be
equal in length and symmetrical and should have equal impedance to ground with a trace
separation of 2x to 4x Height. A differential trace separation of 4x Height yields about 6%
cross-talk(6% effect on impedance).
We recommend that differential trace routing should be side-by-side, though it is not important
that the differential traces be tightly coupled together because tight coupling is not achievable on
PCB traces. Typical ratios on PCB’s are only 20-50%, 99.9% is the value of a well balanced
twisted-pair cable.
Each differential trace should be as short as possible (< 2” preferably) with no 90° angles.
These high-speed transmission traces should be on layer 1 (top layer).
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SLLA136
RxC-, RxC+, Rx0-, Rx0+, Rx1-, Rx1+, Rx2-, Rx2+ signals all route directly from the DVI
connector pins to the device, no external components are needed.
DVI Connector Routing
Clear-out holes for connector pins should leave space between pins to allow continuous ground
through the pin field. Allow enough spacing in ground plane around signal pin vias however,
keep enough copper between vias to allow for ground current to flow between the vias. Avoid
creating a large ground-plane slot around the entire connector, minimizing the via capacitance is
the goal.
Data and Control Signal Output Routing
The trace length of data and control signals out of the receiver should be kept as close to equal
as possible. Trace separation should be ~5x Height. As a general rule, traces also should be
less than 2.8,” if possible (longer traces can be acceptable).
Calculation
ε
Delay = 85 * SQRT r
εr = 4.35 ; relative permitivity of 50% resin FR-4 @ 1GHz
Delay = 177 ps/inch
Length of rising edge = Tr(picoseconds)/Delay ;Tr = 3 ns
= 3000 ps/177 ps per inch
= 16.9 inches
Length of rising edge / 6 = Max length of trace for lumped circuit
16.9 / 6 = 2.8 inches.
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TFP401, TFP401A Design Notes
SLLA136
Power Supply De-Coupling
Use solid ground planes, tie ground planes together with as many vias as is practical. This will provide
a desirable return path for current. Each supply should be on separate split power planes, where each
power plane should be as large an area as possible. Connect PanelBus receiver power and ground
pins and all by-pass caps to appropriate power or ground plane with via. Vias should be as fat and
short as practical, the goal is to minimize the inductance.
DVDD
Place one 0.01-µF capacitor as close as possible between each DVDD device pin (Pins 6, 38,
67) and ground.
A 22-µF tantalum capacitor should be placed between the supply and 0.01-µF capacitors.
A ferrite bead should be used between the source and the 22-µF capacitor.
OVDD
Place one 0.01-µF capacitor as close as possible between each OVDD device pin (Pins 18, 29,
43, 57, 78) and ground.
A 22-µF tantalum capacitor should be placed between the supply and 0.01-µF capacitors.
A ferrite bead should be used between the source and the 22-µF capacitor.
AVDD
Place one 0.01-µF capacitor as close as possible between each AVDD device pin (Pins 82, 84,
88, 95) and ground.
A 22-µF tantalum capacitor should be placed between the supply and 0.01-µF capacitors.
A ferrite bead should be used between the source and the 22-µF capacitor.
PVCC
Place three 0.01-µF capacitors in parallel as close as possible between the PVDD device pin
(Pin 97) and ground.
A 22-µF tantalum capacitor should be placed between the supply and 0.01-µF capacitors.
A ferrite bead should be used between the source and the 22-µF capacitor.
TFP401, TFP401A Design Notes
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SLLA136
PanelBus Receiver
Ferrite Bead
Powe Supply Pin
Power supply
22uF
.01uF
PowerPadTM Connection
Designing boards for PowerPadTM connection is optional, there are benefits with the use of TI’s
PowerPadTM Technology.
Ground plane dimension for TI’s 100-Pin PZP package are 12 × 12 mm.
Maximum land area = 12 mm
Reference the following website for detailed PowerPadTM information:
http://www-s.ti.com/sc/techlit/slma002
.
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TFP401, TFP401A Design Notes
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