SLVS952G April   2010  – January 2017 TPS62671 , TPS62672 , TPS62674 , TPS62675 , TPS626751 , TPS626765 , TPS62679

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Simplified Schematic
  5. Revision History
  6. Device Comparison Table
  7. Pin Configuration and Functions
  8. Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 Handling Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Typical Characteristics
  9. Parameter Measurement Information
  10. 10Detailed Description
    1. 10.1 Overview
    2. 10.2 Functional Block Diagram
    3. 10.3 Feature Description
      1. 10.3.1 Switching Frequency
      2. 10.3.2 Power Save Mode
      3. 10.3.3 Mode Selection
      4. 10.3.4 Spread Spectrum, PWM Frequency Dithering
      5. 10.3.5 Short-Circuit Protection
      6. 10.3.6 Thermal Shutdown
    4. 10.4 Device Functional Modes
      1. 10.4.1 Soft Start
      2. 10.4.2 Enable
      3. 10.4.3 Active Output Discharge
      4. 10.4.4 Undervoltage Lockout
  11. 11Application and Implementation
    1. 11.1 Application Information
    2. 11.2 Typical Applications
      1. 11.2.1 TPS6267x Point-Of-Load Supply
        1. 11.2.1.1 Design Requirements
        2. 11.2.1.2 Detailed Design Procedure
          1. 11.2.1.2.1 Inductor Selection
          2. 11.2.1.2.2 Output Capacitor Selection
          3. 11.2.1.2.3 Input Capacitor Selection
          4. 11.2.1.2.4 Checking Loop Stability
        3. 11.2.1.3 Application Curves
      2. 11.2.2 1.26V CMOS Sensor Embedded Power Solution — Featuring Sub 0.4mm Profile
        1. 11.2.2.1 Design Requirements
        2. 11.2.2.2 Detailed Design Procedure
        3. 11.2.2.3 Application Curves
  12. 12Power Supply Recommendations
  13. 13Layout
    1. 13.1 Layout Guidelines
    2. 13.2 Layout Example
  14. 14Device and Documentation Support
    1. 14.1 Device Support
      1. 14.1.1 Third-Party Products Disclaimer
    2. 14.2 Documentation Support
      1. 14.2.1 Related Documentation
        1. 14.2.1.1 References
    3. 14.3 Related Links
    4. 14.4 Trademarks
    5. 14.5 Electrostatic Discharge Caution
    6. 14.6 Glossary
  15. 15Mechanical, Packaging, and Orderable Information

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Application and Implementation

Application Information

TPS6267x are high frequency step-down converters. They can convert from a 2.3V to 4.8V input source to various fixed output voltages, providing up to 500mA. Needing a minimum amount of external components, the design procedure is easy to do and usually done by choosing input and output capacitor as well as an appropriate inductor which is described in the sections below.

Typical Applications

TPS6267x Point-Of-Load Supply

TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 fxd3_lvs952.gif Figure 28. 1.8V/0.5A Power Supply Using TPS62671

Design Requirements

The TPS6267x devices are optimized to work with the external components as shown in Figure 28, providing stable operation for the input voltage and load current range up to 500mA. Connecting the MODE pin to GND provides PWM/PFM operation.

Detailed Design Procedure

Inductor Selection

The TPS6267x series of step-down converters have been optimized to operate with an effective inductance value in the range of 0.3μH to 1.8μH and with output capacitors in the range of 2.2μF to 4.7μF. The internal compensation is optimized to operate with an output filter of L = 0.47μH and CO = 2.2μF. Larger or smaller inductor values can be used to optimize the performance of the device for specific operation conditions. For more details, see the CHECKING LOOP STABILITY section.

The inductor value affects its peak-to-peak ripple current, the PWM-to-PFM transition point, the output voltage ripple and the efficiency. The selected inductor has to be rated for its dc resistance and saturation current. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VI or VO.

Equation 4. TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 q3_il_lvs528.gif

With:

fSW = switching frequency (6 MHz typical)

L = inductor value

ΔIL = peak-to-peak inductor ripple current

IL(MAX) = maximum inductor current

In high-frequency converter applications, the efficiency is essentially affected by the inductor AC resistance (i.e. quality factor) and to a smaller extent by the inductor DCR value. To achieve high efficiency operation, care should be taken in selecting inductors featuring a quality factor above 25 at the switching frequency. Increasing the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor size, increased inductance usually results in an inductor with lower saturation current.

The total losses of the coil 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

The following inductor series from different suppliers have been used with the TPS6267x converters.

Table 1. List of Inductors(1)

MANUFACTURER SERIES DIMENSIONS (in mm)
MURATA LQM21PN1R0NGR 2.0 x 1.2 x 1.0 max. height
LQM21PNR47MC0 2.0 x 1.2 x 0.55 max. height
LQM21PN1R0MC0 2.0 x 1.2 x 0.55 max. height
LQM18PN1R5-B35 1.6 x 0.8 x 0.4 max. height
LQM18PN1R5-A62 1.6 x 0.8 x 0.33 max. height
PANASONIC ELGTEAR82NA 2.0 x 1.2 x 1.0 max. height
SEMCO CIG21L1R0MNE 2.0 x 1.2 x 1.0 max. height
TAIYO YUDEN BRC1608T1R0M6, BRC1608TR50M6 1.6 x 0.8 x 1.0 max. height
CKP1608L1R5M 1.6 x 0.8 x 0.55 max. height
CKP1608U1R5M 1.6 x 0.8 x 0.4 max. height
CKP1608S1R0M, CKP1608S1R5M 1.6 x 0.8 x 0.33 max. height
NM2012NR82, NM2012N1R0 2.0 x 1.2 x 1.0 max. height
TDK MLP2012SR82T 2.0 x 1.2 x 0.6 max. height
TOKO MDT2012-CR1R0A 2.0 x 1.2 x 1.0 max. height

Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the TPS6267x allows the use of tiny ceramic capacitors. Ceramic capacitors with low ESR values have the lowest output voltage ripple and are recommended. For best performance, the device should be operated with a minimum effective output capacitance of 0.8μF. 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 overall output voltage ripple is the sum of the voltage step caused by the output capacitor ESL and the ripple current flowing through the output capacitor impedance.

At light loads, the output capacitor limits the output ripple voltage and provides holdup during large load transitions. A 2.2μF or 4.7μF ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions. The typical output voltage ripple is 1% of the nominal output voltage VO.

For best operation (i.e. optimum efficiency over the entire load current range, proper PFM/PWM auto transition), the TPS6267x requires a minimum output ripple voltage in PFM mode. The typical output voltage ripple is ca. 1% of the nominal output voltage VO. The PFM pulses are time controlled resulting in a PFM output voltage ripple and PFM frequency that depends (first order) on the capacitance seen at the converter's output.

Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is required to prevent large voltage transients that can cause misbehavior of the device or interferences with other circuits in the system. For most applications, a 1 or 2.2-μF capacitor is sufficient. If the application exhibits a noisy or erratic switching frequency, the remedy will probably be found by experimenting with the value of the input capacitor.

Take care when using only 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 can induce ringing at the VIN pin. This ringing can couple to the output and be mistaken as loop instability or could even damage the part. Additional "bulk" capacitance (electrolytic or tantalum) should in this circumstance be placed between CI and the power source lead to reduce ringing than can occur between the inductance of the power source leads and CI.

Checking Loop Stability

The first step of circuit and stability evaluation is to look from a steady-state perspective at the following signals:

  • Switching node, SW
  • Inductor current, IL
  • Output ripple voltage, VO(AC)

These are the basic signals that need to be measured when evaluating a switching converter. When the switching waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the regulation loop may be unstable. This is often a result of board layout and/or L-C combination.

As a next step in the evaluation of the regulation loop, the load transient response is tested. The time between the application of the load transient and the turn on of the P-channel MOSFET, the output capacitor must supply all of the current required by the load. VO immediately shifts by an amount equal to ΔI(LOAD)  x  ESR, where ESR is the effective series resistance of CO. ΔI(LOAD) begins to charge or discharge CO generating a feedback error signal used by the regulator to return VO to its steady-state value. The results are most easily interpreted when the device operates in PWM mode.

During this recovery time, VO can be monitored for settling time, overshoot or ringing that helps judge the converter’s stability. Without any ringing, the loop has usually more than 45° of phase margin.

Because the damping factor of the circuitry is directly related to several resistive parameters (e.g., MOSFET rDS(on)) that are temperature dependant, the loop stability analysis has to be done over the input voltage range, load current range, and temperature range.

Application Curves

TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 line2_trns_lvs952.gif Figure 29. Combined Line/Load Transient Response
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_tr_lvs952.gif Figure 31. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm2_lvs952.gif Figure 33. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm4_lvs952.gif Figure 35. Load Transient Response in PWM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm6_lvs952.gif Figure 37. Load Transient Response in PWM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_tr2_1v8_lvs952.gif Figure 39. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 ac_load_lvs952.gif Figure 41. AC Load Transient Response
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 pwm_op_lvs952.gif Figure 43. Typical PWM Mode Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 pwsrr_lvs952.gif Figure 45. Typical Power Save Mode Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 start_up_lvs952.gif Figure 47. Start-Up
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 shutdown_RF_lvs952.gif Figure 49. Shut-Down (RF Clock)
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 line3_trns_lvs952.gif Figure 30. Combined Line/Load Transient Response
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm_lvs952.gif Figure 32. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm3_lvs952.gif Figure 34. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_pwm5_lvs952.gif Figure 36. Load Transient Response in PWM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_tr1_1v8_lvs952.gif Figure 38. Load Transient Response in PFM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 load_tr3_1v8_lvs952.gif Figure 40. Load Transient Response in PWM/PWM Operation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 ac_load_1v8_lvs952.gif Figure 42. AC Load Transient Response
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 PWM_ssfm_lvs952.gif Figure 44. PWM Mode Operation - SSFM Modulation
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 start_up_1v8_lvs952.gif Figure 46. Start-Up
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 start_up_RF_lvs952.gif Figure 48. Start-Up (RF Clock)

1.26V CMOS Sensor Embedded Power Solution — Featuring Sub 0.4mm Profile

TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 app1_cir_lvs952.gif Figure 50. 1.26V CMOS Sensor Embedded Power Solution — Featuring Sub 0.4mm Profile

Design Requirements

A CMOS sensor power supply providing a voltage of 1.26V is needed. The profile height mustn't exceed 0.4mm and the device is enabled/switched off by external clock signal.

Detailed Design Procedure

See previous Detailed Design Procedure. To provide 1.26V, the TPS62674 or TPS62679 can be used. The inductor can be chosen from Table 1, selecting low profile device. Startup and shut down sequence with external clock are shown below.

Application Curves

TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 start2_up_RF_lvs952.gif Figure 51. Start-Up (RF Clock)
TPS62671 TPS62672 TPS62674 TPS62675 TPS626751 TPS626765 TPS62679 shutdown2_RF_lvs952.gif Figure 52. Shut-Down (RF Clock)