SLVSC68A June   2015  – June 2015 TPS62745 , TPS627451

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Typical Application Schematic
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Characteristics
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 DCS-Control™
      2. 8.3.2 Enable / Shutdown
      3. 8.3.3 Power Good Output (PG)
      4. 8.3.4 Output Voltage Selection (VSEL1 - 4)
      5. 8.3.5 Input Voltage Switch
    4. 8.4 Device Functional Modes
      1. 8.4.1 Soft Start
    5. 8.5 VOUT Discharge
    6. 8.6 Internal Current Limit
  9. 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 Voltage Selection (VSEL1 - 4)
        2. 9.2.2.2 Output Filter Design (Inductor and Output Capacitor)
        3. 9.2.2.3 Inductor Selection
        4. 9.2.2.4 DC/DC Output Capacitor Selection
        5. 9.2.2.5 Input Capacitor Selection
      3. 9.2.3 Application Curves
    3. 9.3 System Examples
      1. 9.3.1 TPS62745 Set to a Fixed Voltage of 3.3 V
        1. 9.3.1.1 Design Requirements
        2. 9.3.1.2 Detailed Design Procedure
        3. 9.3.1.3 Application Curves
      2. 9.3.2 Dynamic Voltage Change on TPS62745
        1. 9.3.2.1 Design Requirements
        2. 9.3.2.2 Detailed Design Procedure
        3. 9.3.2.3 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 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Related Links
    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

9.1 Application Information

The TPS62745 devices are a step down converter family featuring typical 400-nA quiescent current and operating with a tiny 4.7-μH inductor and a 10-μF output capacitor. These DCS-Control™ based devices extend the light load efficiency range below 10-μA load currents. TPS62745 supports output currents up to 300 mA,

9.2 Typical Application

TPS62745 TPS627451 TPS627450_1V8.gifFigure 5. TPS62745 Typical Application

9.2.1 Design Requirements

The TPS62745 is a highly integrated DC/DC converter. The output voltage is set via the VSEL pin interface without any additional external components. For proper operation only an input and output capacitor and an inductor is required. When the input voltage switch is not used, its enable input should be tied to GND. The output VIN_SW can either be left open or tied to GND. Table 3 shows the components used for the application characteristic curves.

Table 3. List of Components

REFERENCE DESCRIPTION Value MANUFACTURER(1)
IC TPS62745 Texas Instruments
L DFE252010 4.7 µH Toko
CIN TMK212BBJ106MG 10 µF / 25 V / X5R / 0805 Taiyo Yuden
COUT LMK212ABJ106KG-T 10 µF / 10 V / X5R / 0805 Taiyo Yuden

9.2.2 Detailed Design Procedure

9.2.2.1 Output Voltage Selection (VSEL1 - 4)

The VSEL pins select the output voltage of the converters. See the Output Voltage Selection (VSEL1 - 4) of the Feature Descriptions. The output voltage can be changed during operation by changing the logic level of these pins. The output voltage of the TPS62745 ramps to the new target with a slew rate as defined in the electrical characteristics. Typically these pins are driven by an applications processor with an I/O voltage of either 1.8 V or 3.3 V or hard wired to a logic high or logic low signal. In case the pins are not driven from an applications processor and the supply voltage is higher than the voltage rating of the VSEL pins, a logic high level can be taken from the output voltage at pin VOUT. During start-up, when the output is rising from 0 V to its target, the VSEL pins connected to VOUT will change their logic level from low to high. TPS62745 is designed such that such a configuration ensures a steadily rising output voltage.

9.2.2.2 Output Filter Design (Inductor and Output Capacitor)

The external components have to fulfill the needs of the application, but also the stability criteria of the devices control loop. The TPS62745 is optimized to work within a range of L and C combinations. The LC output filter inductance and capacitance have to be considered together, creating a double pole, responsible for the corner frequency of the converter. Table 4 can be used to simplify the output filter component selection.

Table 4. Recommended LC Output Filter Combinations

Inductor Value [µH](2) Output Capacitor Value [µF](1)
10 µF 22 µF
4.7 √(3) √
3.3 √ √
(1) Capacitance tolerance and bias voltage derating is anticipated. The effective capacitance can vary by 20% and -50%.
(2) Inductor tolerance and current derating is anticipated. The effective inductance can vary by 20% and -30%.
(3) This LC combination is the standard value and recommended for most applications.

9.2.2.3 Inductor Selection

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 VIN or VOUT and can be estimated according to Equation 1.

Equation 2 calculates the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 2. This is recommended because during heavy load transient the inductor current will rise above the calculated value. A more conservative way is to select the inductor saturation current according to the high-side MOSFET switch current limit ILIMF.

Equation 1. TPS62745 TPS627451 eq4_dil_lvs941.gif
Equation 2. TPS62745 TPS627451 eq5_ilmax_lvs941.gif

where

  • f = Switching frequency
  • L = Inductor value
  • ΔIL= Peak-to-peak inductor ripple current
  • ILmax = Maximum inductor current

In DC/DC converter applications, the efficiency is essentially affected by the inductor AC resistance (i.e. quality factor) and 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 RDC) 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:

Table 5. List of Inductors

INDUCTANCE [µH] DCR [Ω], typical DIMENSIONS [mm3] INDUCTOR TYPE SUPPLIER(1)
4.7 0.250 2.5 x 2.0 x 1.0 DFE252010 TOKO
3.3 0.190 2.5 x 2.0 x 1.0 DFE252010 TOKO
4.7 0.336 2.0 x 1.9 x 1.0 XPL2010 Coilcraft
3.3 0.207 2.0 x 1.9 x 1.0 XPL2010 Coilcraft
4.7 0.217 3.0 x 3.0 x 1.1 XFL3010 Coilcraft
4.7 0.270 4.5 x 3.2 x 3.2 CC453232 Bourns

9.2.2.4 DC/DC Output Capacitor Selection

The DCS-Control™ scheme of the TPS62745 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 light load currents, the converter operates in power save mode and the output voltage ripple is dependent on the output capacitor value and the PFM peak inductor current. A larger output capacitor can be used, but it should be considered that larger output capacitors lead to an increased leakage current in the capacitor and may reduce overall conversion efficiency. Furthermore, larger output capacitors impact the start up behavior of the DC/DC converter. Furthermore, the contol loop of the TPS62745 requires a certain voltage ripple across the output capacitor. Super-capacitors can be used in parallel to the ceramic capacitors when it is made sure that the super-capacitors series resistance is large enough to provide a valid feedback signal to the error amplifier which is in phase with the inductor current. Applications using an output capacitance above of what is stated under Recommended Operating Conditions should be checked for stability over the desired operating conditions range.

9.2.2.5 Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is required for best input voltage filtering to ensure proper function of the device and to minimize input voltage spikes. For most applications a 10 µF or 4.7 µF ceramic capacitor is recommended. The input capacitor can be increased without any limit for better input voltage filtering.

Table 6 shows a list of tested input/output capacitors.

Table 6. List of Input and Output Capacitors

CAPACITANCE [μF] SIZE CAPACITOR TYPE SUPPLIER(1)
10 0603 GRM188R61C106MA73 Murata
10 0603 EMK107BBJ106MA Taiyo Yuden
4.7 0805 EMK212ABJ475KG Taiyo Yuden
10 0805 TMK212BBJ106MG Taiyo Yuden
10 0805 LMK212ABJ106KG-T Taiyo Yuden

9.2.3 Application Curves

TPS62745 TPS627451 A01_TPS62745_Efficiency_vs_ Iout_3V3.gif
Figure 6. VOUT = 3.3 V
TPS62745 TPS627451 A03_TPS62745_Efficiency_vs_ Iout_1V8.gif
Figure 8. VOUT = 1.8 V
TPS62745 TPS627451 A05_TPS62745_Vo_vs_ Iout_3V3.gif
Figure 10. VOUT = 3.3 V
TPS62745 TPS627451 A07_TPS62745_Vo_vs_ Iout_1V8.gif
Figure 12. VOUT = 1.8 V
TPS62745 TPS627451 A09_SW_Frequency_Vout_3V3.gif
Figure 14. VOUT = 3.3 V
TPS62745 TPS627451 A11_SW_Frequency_Vout_1V8.gif
Figure 16. VOUT = 1.8 V
TPS62745 TPS627451 A14_TPS62745_Voripple_vs_ Iout_3V3.gif
Figure 18. VOUT = 3.3 V
TPS62745 TPS627451 A16_TPS62745_Voripple_vs_ Iout_1V8.gif
Figure 20. VOUT = 1.8 V
TPS62745 TPS627451 A18_TPS62745_Line_transient_response_3V3.pngFigure 22. Line Transient Response; VOUT = 3.3 V
TPS62745 TPS627451 A20_TPS62745_Line_transient_response_1V8.pngFigure 24. Line Transient Response; VOUT = 1.8 V
TPS62745 TPS627451 A22_TPS62745_Load_transient_response_3V3.pngFigure 26. Load Transient Response; VOUT = 3.3 V
TPS62745 TPS627451 A24_TPS62745_Load_transient_response_1V8.pngFigure 28. Load Transient Response; VOUT = 1.8 V
TPS62745 TPS627451 A26_TPS62745_Startup_3V3.pngFigure 30. Startup with VOUT = 3.3 V
TPS62745 TPS627451 A28_TPS62745_Startup_1V8.pngFigure 32. Startup with VOUT = 1.8 V
TPS62745 TPS627451 A02_TPS62745_Efficiency_vs_ Iout_2V5.gif
Figure 7. VOUT = 2.5 V
TPS62745 TPS627451 A04_TPS62745_Efficiency_vs_ Iout_1V5.gif
Figure 9. VOUT = 1.5 V
TPS62745 TPS627451 A06_TPS62745_Vo_vs_ Iout_2V5.gif
Figure 11. VOUT = 2.5 V
TPS62745 TPS627451 A08_TPS62745_Vo_vs_ Iout_1V5.gif
Figure 13. VOUT = 1.5 V
TPS62745 TPS627451 A10_SW_Frequency_Vout_2V5.gif
Figure 15. VOUT = 2.5 V
TPS62745 TPS627451 A12_SW_Frequency_Vout_1V5.gif
Figure 17. VOUT = 1.5 V
TPS62745 TPS627451 A15_TPS62745_Voripple_vs_ Iout_2V5.gif
Figure 19. VOUT= 2.5 V
TPS62745 TPS627451 A17_TPS62745_Voripple_vs_ Iout_1V5.gif
Figure 21. VOUT= 1.5 V
TPS62745 TPS627451 A19_TPS62745_Line_transient_response_2V5.pngFigure 23. Line Transient Response; VOUT = 2.5 V
TPS62745 TPS627451 A21_TPS62745_Line_transient_response_1V5.pngFigure 25. Line Transient Response; VOUT = 1.5 V
TPS62745 TPS627451 A23_TPS62745_Load_transient_response_2V5.pngFigure 27. Load Transient Response; VOUT = 2.5 V
TPS62745 TPS627451 A25_TPS62745_Load_transient_response_1V5.pngFigure 29. Load Transient Response; VOUT = 1.5 V
TPS62745 TPS627451 A27_TPS62745_Startup_2V5.pngFigure 31. Startup with VOUT = 2.5 V
TPS62745 TPS627451 A29_TPS62745_Startup_1V5.pngFigure 33. Startup with VOUT = 1.5 V

9.3 System Examples

9.3.1 TPS62745 Set to a Fixed Voltage of 3.3 V

TPS62745 TPS627451 TPS627450_3V3.gifFigure 34. TPS62745 Typical Application for Vout = 3.3 V

9.3.1.1 Design Requirements

The minimum input voltage needs to be at least 700 mV above the desired output voltage for full output current.

Table 7. List of Components

REFERENCE DESCRIPTION Value MANUFACTURER(1)
IC TPS62745 Texas Instruments
L DFE252010 4.7 µH Toko
CIN TMK212BBJ106MG 10 µF / 25 V / X5R / 0805 Taiyo Yuden
COUT LMK212ABJ106KG-T 10 µF / 10 V / X5R / 0805 Taiyo Yuden

9.3.1.2 Detailed Design Procedure

The logic level of the VSEL pins sets the output voltage. The maximum high level does not allow a direct connection to the supply voltage if it is above 6 V. The output voltage can be used instead to provide a logic high level.

9.3.1.3 Application Curves

TPS62745 TPS627451 A26_TPS62745_Startup_3V3.pngFigure 35. TPS62745 with VOUT = 3.3 V Startup
TPS62745 TPS627451 A30_TPS62745_Voripple_3V3.pngFigure 36. TPS62745 with VOUT = 3.3 V; Output Voltage Ripple for IOUT = 1 mA

9.3.2 Dynamic Voltage Change on TPS62745

TPS62745 allows to change its output voltage during operation by changing the logic level of the VSEL pins.

TPS62745 TPS627451 TPS627450_vochange.gifFigure 37. TPS62745 Typical Application for Switching Between Two Output Voltages

9.3.2.1 Design Requirements

The minimum input voltage needs to be at least 700 mV above the maximum output voltage for full output current. For an input voltage above 6V, the VSELx pins have to be tied to the output for a logic high level as their voltage rating is 6V.

Table 8. List of Components

REFERENCE DESCRIPTION Value MANUFACTURER(1)
IC TPS62745 Texas Instruments
L DFE252010 4.7 µH Toko
CIN TMK212BBJ106MG 10 µF / 25 V / X5R / 0805 Taiyo Yuden
COUT LMK212ABJ106KG-T 10 µF / 10 V / X5R / 0805 Taiyo Yuden

9.3.2.2 Detailed Design Procedure

Toggle the logic level at VSEL1, VSEL3 and VSEL4 to change the output voltage from 2.0 V to 3.3 V and vice versa. The slope from higher output voltage to the lower output voltage is determined by the load current and output capacitance because the discharge of the output capacitor is through the load current only.

9.3.2.3 Application Curves

TPS62745 TPS627451 A35_TPS62745_Vout_scaling_rising.pngFigure 38. TPS62745 Output Voltage Change from 2.0 V to 3.3 V for IOUT = 10 mA
TPS62745 TPS627451 A36_TPS62745_Vout_scaling_falling.pngFigure 39. TPS62745 Output Voltage Change from 3.3 V to 2.0 V for IOUT = 10 mA