SNLS498A November   2015  – December 2015 DS90CR286AT-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 LVDS Receivers
        1. 7.3.1.1 Input Termination
      2. 7.3.2 Phase Locked Loop (PLL)
      3. 7.3.3 Serial LVDS-to-Parallel LVCMOS Converter
      4. 7.3.4 LVCMOS Drivers
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power Down Mode
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Bit Resolution and Operating Frequency Compatibility
        2. 8.2.2.2 Data Mapping between Receiver and Endpoint Panel Display
        3. 8.2.2.3 RSKM Interoperability
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The DS90CR286AT-Q1 is designed for a wide variety of data transmission applications. The use of serialized LVDS data lines in these applications allows for efficient signal transmission over a narrow bus width, thereby reducing cost, power, and space. The DS90CR286AT-Q1 is designed for PCB board chip-to-chip OpenLDI-to-RGB (LVDS-to-parallel) bridge conversion. LVDS data transmission over cable interconnect is not recommended for this device. Users designing a sub-system with a compatible OpenLDI transmitter and DS90CR286AT-Q1 receiver must ensure an acceptable skew margin budget (RSKM).

8.2 Typical Application

DS90CR286AT-Q1 typ_blk_diagram.gif Figure 22. Typical DS90CR286AT-Q1 Application Block Diagram

8.2.1 Design Requirements

For this design example, ensure that the following requirements are observed.

Table 1. DS90CR286AT-Q1 Design Parameters

DESIGN PARAMETER DESIGN REQUIREMENTS
Operating Frequency LVDS clock must be within 20-66 MHz.
Bit Resolution No higher than 24 bpp. The maximum supported resolution is 8-bit RGB.
Bit Data Mapping Determine the appropriate mapping required by the panel display following the DS90CR286AT-Q1 outputs.
RSKM (Receiver Skew Margin) Ensure that there is acceptable margin between Tx pulse position and Rx strobe position.
Input Termination for RxIN± 100 Ω ± 10% resistor across each LVDS differential pair. Place as close as possible to IC input pins.
RxIN± Board Trace Impedance Design differential trace impedance with 100 Ω ± 5%.
LVCMOS Outputs If unused, leave pins floating. Series resistance on each LVCMOS output optional to reduce reflections from long board traces. If used, 33 Ω series resistance is typical.
DC Power Supply Coupling Capacitors Use a 0.1 µF capacitor to minimize power supply noise. Place as close as possible to Vcc pins.

8.2.2 Detailed Design Procedure

To begin the design process with the DS90CR286AT-Q1, determine the following:

  • Operating Frequency
  • Bit Resolution of the Panel
  • Bit Mapping from Receiver to Endpoint Panel Display
  • RSKM Interoperability with Transmitter Pulse Position Margin

8.2.2.1 Bit Resolution and Operating Frequency Compatibility

The bit resolution of the endpoint panel display reveals whether there are enough bits available in the DS90CR286AT-Q1 to output the required data per pixel. The DS90CR286AT-Q1 has 28 parallel LVCMOS outputs and can therefore provide a bit resolution up to 24 bpp (bits per pixel). In each clock cycle, the remaining bits are the three control signals (HSync, VSync, DE) and one spare bit.

The number of pixels per frame and the refresh rate of the endpoint panel display indicate the required operating frequency of the receiver clock. To determine the required clock frequency, refer to the following formula:

Equation 1. f_Clk = [H_Active + H_Blank] × [V_Active + V_Blank] × f_Vertical

where

  • H_Active = Active Display Horizontal Lines
  • H_Blank = Blanking Period Horizontal Lines
  • V_Active = Active Display Vertical Lines
  • V_Blank = Blanking Period Vertical Lines
  • f_Vertical = Refresh Rate (in Hz)
  • f_Clk = Operating Frequency of LVDS clock

In each frame, there is a blanking period associated with horizontal rows and vertical columns that are not actively displayed on the panel. These blanking period pixels must be included to determine the required clock frequency. Consider the following example to determine the required LVDS clock frequency:

  • H_Active = 640
  • H_Blank = 40
  • V_Active = 480
  • V_Blank = 41
  • f_Vertical = 59.95 Hz

Thus, the required operating frequency is determined below:

Equation 2. [640 + 40] x [480 + 41] x 59.95 = 21239086 Hz ≈ 21.24 MHz

Since the operating frequency for the PLL in the DS90CR286AT-Q1 ranges from 20-66 MHz, the DS90CR286AT-Q1 can support a panel display with the aforementioned requirements.

If the specific blanking interval is unknown, the number of pixels in the blanking interval can be approximated to 20% of the active pixels. The following formula can be used as a conservative approximation for the operating LVDS clock frequency:

Equation 3. f_Clk ≈ H_Active x V_Active x f_Vertical x 1.2

Using this approximation, the operating frequency for the example in this section is estimated below:

Equation 4. 640 x 480 x 59.95 x 1.2 = 22099968 Hz ≈ 22.10 MHz

8.2.2.2 Data Mapping between Receiver and Endpoint Panel Display

Ensure that the LVCMOS outputs are mapped to align with the endpoint display RGB mapping requirements following the deserializer. Two popular mapping topologies for 8-bit RGB data are shown below:

  1. LSBs are mapped to RxIN3±.
  2. MSBs are mapped to RxIN3±.

The following tables depict how these two popular topologies can be mapped to the DS90CR286AT-Q1 outputs.

Table 2. 8-Bit Color Mapping with LSBs on RxIN3±

LVDS INPUT CHANNEL LVDS BIT STREAM POSITION LVCMOS OUTPUT CHANNEL COLOR MAPPING COMMENTS
RxIN0 TxIN0 RxOUT0 R2
TxIN1 RxOUT1 R3
TxIN2 RxOUT2 R4
TxIN3 RxOUT3 R5
TxIN4 RxOUT4 R6
TxIN6 RxOUT6 R7 MSB
RxIN1 TxIN7 RxOUT7 G2
TxIN8 RxOUT8 G3
TxIN9 RxOUT9 G4
TxIN12 RxOUT12 G5
TxIN13 RxOUT13 G6
TxIN14 RxOUT14 G7 MSB
TxIN15 RxOUT15 B2
TxIN18 RxOUT18 B3
RxIN2 TxIN19 RxOUT19 B4
TxIN20 RxOUT20 B5
TxIN21 RxOUT21 B6
TxIN22 RxOUT22 B7 MSB
TxIN24 RxOUT24 HSYNC Horizontal Sync
TxIN25 RxOUT25 VSYNC Vertical Sync
TxIN26 RxOUT26 DE Data Enable
RxIN3 TxIN27 RxOUT27 R0 LSB
TxIN5 RxOUT5 R1
TxIN10 RxOUT10 G0 LSB
TxIN11 RxOUT11 G1
TxIN16 RxOUT16 B0 LSB
TxIN17 RxOUT17 B1
TxIN23 RxOUT23 GP General Purpose

Table 3. 8-Bit Color Mapping with MSBs on RxIN3±

LVDS INPUT CHANNEL LVDS BIT STREAM POSITION LVCMOS OUTPUT CHANNEL COLOR MAPPING COMMENTS
RxIN0 TxIN0 RxOUT0 R0 LSB
TxIN1 RxOUT1 R1
TxIN2 RxOUT2 R2
TxIN3 RxOUT3 R3
TxIN4 RxOUT4 R4
TxIN6 RxOUT6 R5
RxIN1 TxIN7 RxOUT7 G0 LSB
TxIN8 RxOUT8 G1
TxIN9 RxOUT9 G2
TxIN12 RxOUT12 G3
TxIN13 RxOUT13 G4
TxIN14 RxOUT14 G5
TxIN15 RxOUT15 B0 LSB
TxIN18 RxOUT18 B1
RxIN2 TxIN19 RxOUT19 B2
TxIN20 RxOUT20 B3
TxIN21 RxOUT21 B4
TxIN22 RxOUT22 B5
TxIN24 RxOUT24 HSYNC Horizontal Sync
TxIN25 RxOUT25 VSYNC Vertical Sync
TxIN26 RxOUT26 DE Data Enable
RxIN3 TxIN27 RxOUT27 R6
TxIN5 RxOUT5 R7 MSB
TxIN10 RxOUT10 G6
TxIN11 RxOUT11 G7 MSB
TxIN16 RxOUT16 B6
TxIN17 RxOUT17 B7 MSB
TxIN23 RxOUT23 GP General Purpose

In situations where the DS90CR286AT-Q1 must support 18 bpp, Table 2 is commonly used. With this mapping, MSBs of RGB data are retained on RXIN0±, RXIN1±, and RXIN2± while the two LSBs for the original 8-bit RGB resolution are ignored from RxIN3±.

8.2.2.3 RSKM Interoperability

One of the most important factors when designing the receiver into a system application is assessing how much RSKM (Receiver Skew Margin) is available. In each LVDS clock cycle, the LVDS data stream carries seven serialized data bits. Ideally, the Transmit Pulse Position for each bit will occur every (n x T)/7 seconds, where n = Bit Position and T = LVDS Clock Period. Likewise, ideally the Receive Strobe Position for each bit will occur every ((n + 0.5) x T)/7 seconds. However, due to the effects of clock jitter and ISI, both LVDS transmitter and receiver in real systems will have a minimum and maximum pulse and strobe position, respectively, for each bit position. This concept is illustrated in Figure 23:

DS90CR286AT-Q1 RSKM_TI_Notation_1.gif Figure 23. RSKM Measurement Example

All left and right margins for Bits 0-6 must be considered in order to determine the absolute minimum for the whole LVDS bit stream. This absolute minimum corresponds to the RSKM.

To improve RSKM performance between LVDS transmitter and receiver, designers may either advance or delay the LVDS clock compared to the LVDS data. Moving the LVDS clock compared to the LVDS data can improve the Rx strobe position compared to the Tx pulse position of the transmitter.

If there is less left bit margin than right bit margin, the LVDS clock can be delayed so that the Rx strobe position for incoming data appears to be delayed. If there is less right bit margin than left bit margin, all the LVDS data pairs can be delayed uniformly so that the LVDS clock and Rx strobe position for incoming data appear to advance. To delay an LVDS data or clock pair, designers can either add more PCB trace length or install a capacitor between the LVDS transmitter and receiver. It is important to note that when using these techniques, all serialized bit positions are shifted right or left uniformly.

When designing the DS90CR286AT-Q1 receiver with a third-party OpenLDI transmitter, users must calculate the skew margin budget (RSKM) based on the Tx pulse position and the Rx strobe position to ensure error-free transmission. For more information about calculating RSKM, refer to Application Note SNLA249.

8.2.3 Application Curves

The following application curves are examples taken with a DS90C385 serializer interfacing to a DS90CR286AT-Q1 deserializer in nominal temperature (25ºC) at an operating frequency of 66 MHz.

DS90CR286AT-Q1 clock_lvds_data.gif Figure 24. LVDS RxIN0± aligned with LVCMOS RxCLKOUT
DS90CR286AT-Q1 RisingEdge_to_RxStrobe.gif Figure 26. RxOUT and RxCLKOUT Timing Diagram
DS90CR286AT-Q1 LVDS_CLK_v_LVCMOS_CLK.gif Figure 25. LVDS CLKIN aligned with LVCMOS RxCLKOUT
DS90CR286AT-Q1 PRBS7_66MHz_AdjacentChannels.gif Figure 27. PRBS-7 Output on RxOUT Channels