SLVS939B June   2009  – December 2014 TPS55332-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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  Input Voltage (VIN)
      2. 7.3.2  Output Voltage (Vout)
      3. 7.3.3  Regulated Supply Voltage (VReg)
      4. 7.3.4  Over-Current Protection (SW)
      5. 7.3.5  Oscillator Frequency (RT)
      6. 7.3.6  Enable / Shutdown (EN)
      7. 7.3.7  Reset Delay (Cdly)
      8. 7.3.8  Reset Pin (RST)
      9. 7.3.9  Boost Capacitor (BOOT)
      10. 7.3.10 Soft Start (SS)
      11. 7.3.11 Synchronization (SYNC)
      12. 7.3.12 Regulation Voltage (VSENSE)
      13. 7.3.13 Reset Threshold (RST_TH)
      14. 7.3.14 Slew Rate Control (Rslew)
      15. 7.3.15 Thermal Shutdown
      16. 7.3.16 Loop Control Frequency Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 DCM Operation
      2. 7.4.2 CCM Operation
      3. 7.4.3 Loop Compensation For Stability Criteria
  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  Output Capacitor (Co)
        2. 8.2.2.2  Output Inductor Selection (Lo) for CCM
        3. 8.2.2.3  Output Diode
        4. 8.2.2.4  Input Capacitor CI
        5. 8.2.2.5  Output Voltage And Feedback Resistor Selection
        6. 8.2.2.6  Reset Threshold Resistor Selection
        7. 8.2.2.7  Soft Start Capacitor
        8. 8.2.2.8  Loop Compensation Calculation
        9. 8.2.2.9  Loop Compensation Response
        10. 8.2.2.10 Output Inductor Selection (LO) For DCM
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Inductor
      2. 10.1.2 Input Filter Capacitors
      3. 10.1.3 Feedback
      4. 10.1.4 Traces And Ground Plane
    2. 10.2 Layout Example
    3. 10.3 Power Dissipation
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

10 Layout

10.1 Layout Guidelines

The recommended guidelines for PCB layout of the TPS55332 device are described in the following sections.

10.1.1 Inductor

Use a low EMI inductor with a ferrite type shielded core. Other types of inductors may be used, however they must have low EMI characteristics and be located away from the low power traces and components in the circuit.

10.1.2 Input Filter Capacitors

Input ceramic filter capacitors should be located in close proximity of the VIN terminal. Surface mount capacitors are recommended to minimize lead length and reduce noise coupling. Also low ESR and max input ripple current requirements must be satisfied.

10.1.3 Feedback

Route the feedback trace such that there is minimum interaction with any noise sources associated with the switching components. Recommended practice is to ensure the inductor is placed away from the feedback trace to prevent EMI noise sourcing.

10.1.4 Traces And Ground Plane

All power (high current) traces should be as thick and short as possible. The inductor and output capacitors should be as close to each other as possible. This reduces EMI radiated by the power traces due to high switching currents.

In a two sided PCB it is recommended to have ground planes on both sides of the PCB to help reduce noise and ground loop errors. The ground connection for the input and output capacitors and IC ground should be connected to this ground plane.

In a multi-layer PCB, the ground plane is used to separate the power plane (high switching currents and components are placed) from the signal plane (where the feedback trace and components are placed) for improved performance.

Also arrange the components such that the switching current loops curl in the same direction. Place the high current components such that during conduction the current path is in the same direction. This prevents magnetic field reversal caused by the traces between the two half cycles, helping to reduce radiated EMI.

The power ground terminal for the power FET must also be terminated to the ground plane in the shortest trace possible.

10.2 Layout Example

m0148-01_lvs939.gifFigure 15. PCB Layout Example
top_layer_slvs939.gifFigure 16. Top Layer
bottom_layer_slvs939.gifFigure 17. Bottom Layer

10.3 Power Dissipation

The power dissipation losses are applicable for continuous conduction mode operation (CCM).

Equation 29. PCON = Io2 × RdsON × (1 – Vi/Vo)  (conduction losses)
Equation 30. PSW = ½ × Vo × Io/(1 – D) × (tr + tf) × ƒSW  (switching losses)
Equation 31. PGate = Vdrive × Qg × ƒsw (gate drive losses), where Qg = 1 × 10-9 (nC)
Equation 32. PIC = Vi × Iq-normal  (supply losses)
Equation 33. PTotal = PCON + PSW + PGate + PIC (watts)

Where:

Vo = Output voltage
Vi = Input voltage
Io = Output current
tr = FET switching rise time (tr max = 40 ns)
tf = FET switching fall time
Vdrive = FET gate drive voltage (typically Vdrive = 6 V and Vdrive max = 8 V)
ƒsw = Switching frequency
D = Duty cycle

For given operating ambient temperature, TAmb:

Equation 34. TJ = TAmb + Rth × PTotal

For a given max junction temperature of TJ-Max = 150°C:

Equation 35. TAmb-Max = TJ-Max – Rth × PTotal

Where:

PTotal = Total power dissipation (watts)
TAmb = Ambient temperature in °C
TJ = Junction temperature in °C
TAmb-Max = Maximum ambient temperature in °C
TJ-Max = Maximum junction temperature in °C
Rth = Thermal resistance of package in (°C/W)

Other factors NOT included in the information above which affect the overall efficiency and power losses are inductor ac and dc losses, and trace resistance and losses associated with the copper trace routing connection.

g012_lvs939.gif
Power de-rating based on JEDEC JESD 51-5 standard board with thermal vias and high-k profile.
Figure 18. Power Dissipation