SLVSB38C March   2011  – August 2016 TPS62242-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 Typical Characteristics
  7. Parameter Measurement Information
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Undervoltage Lockout
      2. 8.3.2 Enable
      3. 8.3.3 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Soft Start
      2. 8.4.2 Power Save Mode
        1. 8.4.2.1 100% Duty Cycle Low Dropout Operation
      3. 8.4.3 Short-Circuit Protection
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Output Filter Design (Inductor and Output Capacitor)
          1. 9.2.2.1.1 Inductor Selection
          2. 9.2.2.1.2 Output Capacitor Selection
          3. 9.2.2.1.3 Input Capacitor Selection
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Third-Party Products Disclaimer
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9 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.

9.1 Application Information

The TPS62242-Q1 device is a high-efficiency synchronous step-down DC-DC converter featuring power save mode.

9.2 Typical Application

TPS62242-Q1 ai4_fix18_lvsb38.gif Figure 7. Fixed 1.2 V

9.2.1 Design Requirements

The device operates over an input voltage range from 2 V to 6 V.

9.2.2 Detailed Design Procedure

Table 2 shows the list of components for the Application Curves. Users must verify and validate these components for suitability with their application before using the components.

Table 2. List of Components

VALUE COMPONENT REFERENCE PART NUMBER MANUFACTURER
4.7 μF, 6.3 V. X5R Ceramic CIN GRM188R60J475K Murata
10 μF, 6.3 V. X5R Ceramic COUT GRM188R60J106M Murata
22 pF, COG Ceramic C1 Murata
2.2 μH, 110 mΩ L1 LPS3015 Coilcraft

9.2.2.1 Output Filter Design (Inductor and Output Capacitor)

The TPS62242-Q1 device is designed to operate with inductors in the range of 1.5 μH to 4.7 μH and with output capacitors in the range of 4.7 μF to 22 μF. The device is optimized for operation with a 2.2-μH inductor and 10μF output capacitor.

Larger or smaller inductor values can be used to optimize the performance of the device for specific operation conditions. For stable operation, the L and C values of the output filter may not fall below 1-μH effective Inductance and 3.5-μF effective capacitance. Selecting larger capacitors is less critical, because the corner frequency of the L-C filter moves to lower frequencies with fewer stability problems.

9.2.2.1.1 Inductor Selection

The inductor value has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation current (Table 3). The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VI or VO.

The inductor selection also has an impact on the output voltage ripple in the PFM mode. Higher inductor values lead to lower-output voltage ripple and higher PFM frequency, and lower inductor values lead to a higher-output voltage ripple with lower PFM frequency.

Equation 2 calculates the maximum inductor current in PWM mode under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 3. This is the recommendation because during heavy-load transients the inductor current rises above the calculated value.

Equation 2. TPS62242-Q1 q3_delta_lvs762_.gif
Equation 3. TPS62242-Q1 q4_ilmax_lvs762.gif

where

  • ƒ = Switching frequency (2.25-MHz typical)
  • L = Inductor value
  • ΔIL = Peak-to-Peak inductor ripple current
  • ILmax = Maximum inductor current

A more conservative approach is to select the inductor current rating just for the maximum switch current limit ILIMF of the converter.

Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output current capability.

The total losses of the coil strongly impact the efficiency of the DC-DC conversion and consist of both the losses in the DC resistance (R(DC)) and the following frequency-dependent components:

  • The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)
  • Additional losses in the conductor from the skin effect (current displacement at high frequencies)
  • Magnetic field losses of the neighboring windings (proximity effect)
  • Radiation losses

Table 3. List of Inductors

INDUCTANCE (μH) DIMENSIONS (mm) PART NUMBER MANUFACTURER
2 2.5 × 2 × 1 MIPS2520D2R2 FDK
2 2.5 × 2 × 1.2 MIPSA2520D2R2 FDK
2.2 2.5 × 2 × 1 KSLI-252010AG2R2 Hitachi Metals
2.2 2.5 × 2 × 1.2 LQM2HPN2R2MJ0L Murata
2.2 3 × 3 × 1.4 LPS3015 Coilcraft

9.2.2.1.2 Output Capacitor Selection

The advanced fast-response voltage-mode control scheme of the TPS62242-Q1 device allows the use of tiny ceramic capacitors. Ceramic capacitors with low-ESR values have the lowest-output voltage ripple and are recommended. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequencies.

At nominal load current, the device operates in PWM mode and the RMS ripple current is calculated as in Equation 4:

Equation 4. TPS62242-Q1 q5_irmsc_lvs762.gif

At nominal load current, the device operates in PWM mode and the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor as in Equation 5:

Equation 5. TPS62242-Q1 q6_deltav_lvs762.gif

At light load currents, the converter operates in power save mode and the output voltage ripple depends on the output capacitor and inductor value. Larger output capacitor and inductor values minimize the voltage ripple in PFM mode and tighten DC output accuracy in PFM mode.

9.2.2.1.3 Input Capacitor Selection

The buck converter has a natural pulsating input current; therefore, a low-ESR input capacitor is required for best input voltage filtering and minimizing the interference with other circuits caused by high-input voltage spikes. For most applications, a 4.7-μF to 10-μF ceramic capacitor is recommended (Table 4). Because ceramic capacitors lose up to 80% of their initial capacitance at 5 V, TI recommends using a 10-μF input capacitor for input voltages greater than 4.5 V. The input capacitor can be increased without any limit for better input voltage filtering.

Take care when using only small ceramic input capacitors. When a ceramic capacitor is used at the input, and the power is being supplied through long wires, such as from a wall adapter, a load step at the output, or VIN step on the input, can induce ringing at the VIN pin. The ringing can couple to the output and be mistaken as loop instability, or could even damage the part by exceeding the maximum ratings.

Table 4. List of Capacitors

CAPACITANCE (µF) DIMENSIONS (mm) PART NUMBER MANUFACTURER
4.7 0603: 1.6 × 0.8 × 0.8 GRM188R60J475K Murata
10 0603: 1.6 × 0.8 × 0.8 GRM188R60J106M69D Murata

9.2.3 Application Curves

TPS62242-Q1 eff_12v_gnd_lvs762.gif Figure 8. Efficiency vs Output Current
TPS62242-Q1 top_pwm1_lvsb38.png Figure 10. Typical Operation vs PWM Mode
TPS62242-Q1 pfmripp_18_lvsb38.png Figure 12. PFM Mode Ripple
TPS62242-Q1 litr_pfm_5_lvsb38.png Figure 14. PFM Line Transient
TPS62242-Q1 st_vo_18_lvsb38.png Figure 9. Start-Up Timing
TPS62242-Q1 top_pfm1_lvsb38.png Figure 11. Typical Operation vs PFM Mode
TPS62242-Q1 pfm_ltr20_lvsb38.png Figure 13. PFM Load Transient
TPS62242-Q1 litr_pfm_25_lvsb38.png Figure 15. PFM Line Transient