JAJS311D February   2008  – February 2020 TPS51200

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      単純化されたDDRアプリケーション
  4. 4 改訂履歴
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Sink and Source Regulator (VO Pin)
      2. 7.3.2  Reference Input (REFIN Pin)
      3. 7.3.3  Reference Output (REFOUT Pin)
      4. 7.3.4  Soft-Start Sequencing
      5. 7.3.5  Enable Control (EN Pin)
      6. 7.3.6  Powergood Function (PGOOD Pin)
      7. 7.3.7  Current Protection (VO Pin)
      8. 7.3.8  UVLO Protection (VIN Pin)
      9. 7.3.9  Thermal Shutdown
      10. 7.3.10 Tracking Start-up and Shutdown
      11. 7.3.11 Output Tolerance Consideration for VTT DIMM Applications
      12. 7.3.12 REFOUT (VREF) Consideration for DDR2 Applications
    4. 7.4 Device Functional Modes
      1. 7.4.1 Low Input Voltage Applications
      2. 7.4.2 S3 and Pseudo-S5 Support
  8. 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 Input Voltage Capacitor
        2. 8.2.2.2 VLDO Input Capacitor
        3. 8.2.2.3 Output Capacitor
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
      1. 8.3.1 3.3-VIN, DDR2 Configuration
      2. 8.3.2 2.5-VIN, DDR3 Configuration
      3. 8.3.3 3.3-VIN, LP DDR3 or DDR4 Configuration
      4. 8.3.4 3.3-VIN, DDR3 Tracking Configuration
      5. 8.3.5 3.3-VIN, LDO Configuration
      6. 8.3.6 3.3-VIN, DDR3 Configuration with LFP
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Design Considerations
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 デバイス・サポート
      1. 11.1.1 デベロッパー・ネットワークの製品に関する免責事項
      2. 11.1.2 開発サポート
        1. 11.1.2.1 評価基板
        2. 11.1.2.2 SPICEモデル
    2. 11.2 ドキュメントのサポート
      1. 11.2.1 関連資料
    3. 11.3 コミュニティ・リソース
    4. 11.4 商標
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 Glossary
  12. 12メカニカル、パッケージ、および注文情報

7.3.12 REFOUT (VREF) Consideration for DDR2 Applications

During TPS51200 tracking start-up, the REFIN voltage follows the rise of the VDDQ rail through a voltage divider, and REFOUT (VREF) follows REFIN once the REFIN voltage is greater than 0.39 V. When the REFIN voltage is lower than 0.39 V, VREF is 0 V.

The JEDEC DDR2 SDRAM Standard (JESD79-2E) states that VREF must track VDDQ/2 within ±0.3 V accuracy during the start-up period. To allow the TPS51200

device to meet the JEDEC DDR2 specification, a resistor divider can be used to provide the VREF signal to the DIMM. The resistor divider ratio is 0.5 to ensure that the VREF voltage equals VDDQ/2.

TPS51200 resitor_divider_tps51200.gifFigure 23. Resistor Divider Circuit

When selecting the resistor value, consider the impact of the leakage current from the DIMM VREF pin on the reference voltage. Use Equation 4 to calculate resistor values.

Equation 4. TPS51200 q_rref_slus812.gif

where

  • RREF is the resistor value
  • ∆VREF is the VREF DC variation requirement
  • IREF is the maximum total VREF leakage current from DIMMs

Consider the MT47H64M16 DDR2 SDRAM component from Micron as an example. The MT47H64M16 datasheet shows the maximum VREF leakage current of each DIMM is ±2 µA, and VREF(DC) variation must be within ±1% of VDDQ. In this DDR2 application, the VDDQ voltage is 1.8 V. Assuming one TPS51200 device needs to power 4 DIMMs, the maximum total VREF leakage current is ±8 µA. Based on the calculations, the resistor value should be lower than 4.5 kΩ. To ensure sufficient margin, 100 Ω is the suggested resistor value. With two 100-Ω resistors, the maximum VREF variation is 0.4 mV, and the power loss on each resistor is 8.1 mW.