SLUSF63B may   2023  – july 2023 TPSM843A26

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  VIN Pins and VIN UVLO
      2. 7.3.2  Internal Bypassing (BP5)
      3. 7.3.3  Enable and Adjustable UVLO
        1. 7.3.3.1 Internal Sequence of Events During Start-up
      4. 7.3.4  Switching Frequency Selection
      5. 7.3.5  Switching Frequency Synchronization to an External Clock
        1. 7.3.5.1 Internal PWM Oscillator Frequency
        2. 7.3.5.2 Loss of Synchronization
        3. 7.3.5.3 Interfacing the SYNC/FSEL Pin
      6. 7.3.6  Remote Sense Amplifier and Adjusting the Output Voltage
      7. 7.3.7  Loop Compensation Guidelines
        1. 7.3.7.1 Output Filter Inductor Tradeoffs
        2. 7.3.7.2 Ramp Capacitor Selection
        3. 7.3.7.3 Output Capacitor Selection
        4. 7.3.7.4 Design Method for Good Transient Response
      8. 7.3.8  Soft Start and Prebiased Output Start-up
      9. 7.3.9  MSEL Pin
      10. 7.3.10 Power Good (PG)
      11. 7.3.11 Output Overload Protection
        1. 7.3.11.1 Positive Inductor Current Protection
        2. 7.3.11.2 Negative Inductor Current Protection
      12. 7.3.12 Output Overvoltage and Undervoltage Protection
      13. 7.3.13 Overtemperature Protection
      14. 7.3.14 Output Voltage Discharge
    4. 7.4 Device Functional Modes
      1. 7.4.1 Forced Continuous-Conduction Mode
      2. 7.4.2 Discontinuous Conduction Mode During Soft Start
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 1.0-V Output, 1-MHz Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Switching Frequency
          2. 8.2.1.2.2  Output Inductor Selection
          3. 8.2.1.2.3  Output Capacitor
          4. 8.2.1.2.4  Input Capacitor
          5. 8.2.1.2.5  Adjustable Undervoltage Lockout
          6. 8.2.1.2.6  Output Voltage Resistors Selection
          7. 8.2.1.2.7  Bootstrap Capacitor Selection
          8. 8.2.1.2.8  BP5 Capacitor Selection
          9. 8.2.1.2.9  PG Pullup Resistor
          10. 8.2.1.2.10 Current Limit Selection
          11. 8.2.1.2.11 Soft-Start Time Selection
          12. 8.2.1.2.12 Ramp Selection and Control Loop Stability
          13. 8.2.1.2.13 MSEL Pin
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
      3. 8.4.3 Thermal Performance
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.7.2 Ramp Capacitor Selection

The TPSM843A26 uses input voltage, duty cycle, and low-side FET current information to generate an internal ramp. The ramp amplitude is determined by an internal ramp generation capacitor, CRAMP. Three different values for CRAMP can be selected with a resistor to AGND on the MSEL pin (see Section 7.3.9). The capacitor options are 1 pF, 2 pF, and 4 pF. A larger ramp capacitor results in a smaller ramp amplitude, which results in a higher control loop bandwidth. The following figures show how the loop changes with each ramp setting for the schematic in Figure 8-1.

Many applications perform best with a CRAMP value of 4 pF, however, the user must measure the loop gain and phase to determine the optimum CRAMP value for their specific application.

  1. First, calculate the RAMP time constant using Equation 5 and Table 7-4.
    Equation 5.  τCRAMP=CRAMP × 106Lookup1 - Lookup2  ×  VOUTVIN
    Table 7-4 RAMP Selection Lookup Values
    fSW (kHz)Lookup1 ValueLookup2 Value
    5000.3720.297
    7500.5480.445
    10000.7190.594
    15001.040.891
    22001.461.31
  2. Next, calculate the RAMP capacitor voltage to ensure the capacitor chosen for CRAMP does not result in a ramp amplitude of greater than 1.25 V, which ensures the ramp does not saturate to ground during a load transient.
    Equation 6. VCRAMP=VIN × (tON + 100 ns)τCRAMP
  • A larger CRAMP capacitance results in highest loop gain.
  • A smaller CRAMP capacitance requires fewer output capacitors, and results in a higher crossover frequency.

Figure 7-6 and Figure 7-7 show how the loop changes with each ramp setting for the schematic in Section 8.

GUID-20230420-SS0I-D97Z-M5GR-VSQBK8Z3DL0F-low.svgFigure 7-6 Loop Gain vs Ramp Settings
GUID-20230420-SS0I-KN69-DCLC-J5LTTZ0J64N9-low.svgFigure 7-7 Loop Phase vs Ramp Settings