SLUS609J May   2004  – January 2018 TPS51116

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1. 3.1 Typical Application
  4. 4 Revision History
  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 Dissipation Ratings
    5. 6.5 Thermal Information
    6. 6.6 Electrical Characteristics
    7. 6.7 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  VDDQ SMPS, Light Load Condition
      2. 7.3.2  Low-Side Driver
      3. 7.3.3  High-Side Driver
      4. 7.3.4  Current Sensing Scheme
      5. 7.3.5  PWM Frequency and Adaptive On-Time Control
      6. 7.3.6  VDDQ Output Voltage Selection
      7. 7.3.7  VTT Linear Regulator and VTTREF
      8. 7.3.8  Controling Outputs Using the S3 and S5 Pins
      9. 7.3.9  Soft-Start Function and Powergood Status
      10. 7.3.10 VDDQ and VTT Discharge Control
      11. 7.3.11 Current Protection for VDDQ
      12. 7.3.12 Current Protection for VTT
      13. 7.3.13 Overvoltage and Undervoltage Protection for VDDQ
      14. 7.3.14 Undervoltage Lockout (UVLO) Protection, V5IN (PWP), V5FILT (RGE)
      15. 7.3.15 Input Capacitor, V5IN (PWP), V5FILT (RGE)
      16. 7.3.16 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 VDDQ SMPS, Dual PWM Operation Modes
      2. 7.4.2 Current Mode Operation
      3. 7.4.3 D-CAP™ Mode Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 DDR3 Application With Current Mode
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Pin Connections
        2. 8.2.2.2 Choose the inductor
        3. 8.2.2.3 Choose rectifying (low-side) MOSFET
        4. 8.2.2.4 Choose output capacitance
        5. 8.2.2.5 Determine f0 and calculate RC
        6. 8.2.2.6 Calculate CC2
        7. 8.2.2.7 Calculate CC.
        8. 8.2.2.8 Determine the value of R1 and R2.
      3. 8.2.3 Application Curves
    3. 8.3 DDR3 Application With D−CAP™ Mode
      1. 8.3.1 Design Requirements
      2. 8.3.2 Detailed Design Procedure
        1. 8.3.2.1 Pin Connections
        2. 8.3.2.2 Choose the Components
      3. 8.3.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    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

7.4.3 D-CAP™ Mode Operation

Figure 37 shows a simplified schematic of a buck converter application operating in D-CAP™ mode.

TPS51116 figb_lus609.gifFigure 37. Linearizing the Modulator

The PWM comparator compares the VDDQSNS voltage divided by R1 and R2 with internal reference voltage, and determines the timing to turn on the high-side MOSFET. The gain and speed of the comparator is high enough to maintain the voltage at the beginning of each on cycle (or the end of off cycle) substantially constant. The DC output voltage may have line regulation due to ripple amplitude that slightly increases as the input voltage increase.

f0, must be lower than 1/3 of the switching frequency.Equation 16 defines the 0-dB frequency calculation.

Equation 16. TPS51116 Q_f0b_lus609_.gif

Because the 0-dB frequency, f0 is determined solely by the output capacitor characteristics, loop stability of D-CAP™ mode is determined by the capacitor’s chemistry. For example, specialty polymer capacitors (SP-CAP) have CO in the order of several 100 μF and ESR in range of 10 mΩ. These makes f0 on the order of 100 kHz or less and the loop is then stable. However, ceramic capacitors have f0 at more than 700 kHz, which is not suitable for this operational mode.

Although D-CAP™ mode design provides many advantages such as ease-of-use, minimum external components configuration and extremely short response time, due to not employing an error amplifier in the loop, sufficient amount of feedback signal needs to be provided by external circuit to reduce jitter level.

The required signal level is approximately 15 mV at comparing point. This gives VRIPPLE = (VOUT/0.75) x 15 (mV) at the output node. The output capacitor’s ESR should meet this requirement.

The external components selection is simple for applications that operate in D-CAP™ mode.

  1. Choose inductor. Inductor selection for DCAP mode operation is the same as for current mode operation. Please refer to the instructions in the Current Mode Operation section.
  2. Choose output capacitor(s).Organic semiconductor capacitor(s) or specialty polymer capacitor(s) are recommended. Determine ESR to meet required ripple voltage above. Equation 17 shows an approximation calculation.
    3. Equation 17. TPS51116 Q_esr_lus609.gif