SLUSBN5B August   2013  – July 2015 TPS53515

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  5-V LDO and VREG Start-Up
      2. 7.3.2  Enable, Soft Start, and Mode Selection
      3. 7.3.3  Frequency Selection
      4. 7.3.4  D-CAP3 Control and Mode Selection
        1. 7.3.4.1 D-CAP3 Mode
        2. 7.3.4.2 Sample and Hold Circuitry
        3. 7.3.4.3 Adaptive Zero-Crossing
      5. 7.3.5  Power-Good
      6. 7.3.6  Current Sense and Overcurrent Protection
      7. 7.3.7  Overvoltage and Undervoltage Protection
      8. 7.3.8  Out-of-Bounds Operation
      9. 7.3.9  UVLO Protection
      10. 7.3.10 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Auto-Skip Eco-mode Light Load Operation
      2. 7.4.2 Forced Continuous-Conduction Mode
  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 Choose the Switching Frequency
        2. 8.2.2.2 Choose the Operation Mode
        3. 8.2.2.3 Choose the Inductor
        4. 8.2.2.4 Choose the Output Capacitor
        5. 8.2.2.5 Determine the Value of R1 and R2
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Performance
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8 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.

8.1 Application Information

The TPS53515 device is a high-efficiency, single-channel, synchronous-buck converter. The device suits low-output voltage point-of-load applications with 12-A or lower output current in computing and similar digital consumer applications.

8.2 Typical Application

This design example describes a D-CAP3-mode, 8-A synchronous buck converter with integrated MOSFETs. The device provides a fixed 1.2-V output at up to 8 A from a 12-V input bus.

TPS53515 typ_app_slusbn5.gifFigure 43. Application Circuit Diagram

8.2.1 Design Requirements

This design uses the parameters listed in Table 5.

Table 5. Design Example Specifications

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
INPUT CHARACTERISTIC
VIN Voltage range 5 12 18 V
IMAX Maximum input current VIN = 5 V, IOUT = 8 A 2.5 A
No load input current VIN = 12 V, IOUT = 0 A with auto skip mode 1 mA
OUTPUT CHARACTERISTICS
VOUT Output voltage 1.2 V
Output voltage regulation Line regulation,
5 V ≤ VIN ≤ –14 V with FCCM		 0.2%
Load regulation,
VIN = 12 V, 0 A ≤ IOUT ≤ 8 A with FCCM		 0.5%
VRIPPLE Output voltage ripple VIN = 12 V, IOUT = 8 A with FCCM 10 mVPP
ILOAD Output load current 0 12 A
IOVER Output over current 11
tSS Soft-start time 1 ms
SYSTEMS CHARACTERISTICS
fSW Switching frequency 1 MHz
η Peak efficiency VIN = 12 V, VOUT = 1.2 V, IOUT = 4 A 88.5%
η Full load efficiency VIN = 12 V, VOUT = 1.2 V, IOUT = 8 A 86.9%
TA Operating temperature 25 ºC

8.2.2 Detailed Design Procedure

The external components selection is a simple process using D-CAP3 mode. Select the external components using the following steps

8.2.2.1 Choose the Switching Frequency

The switching frequency is configured by the resistor divider on the RF pin. Select one of eight switching frequencies from 250 kHz to 1 MHz. Refer to Table 1 for the relationship between the switching frequency and resistor-divider configuration.

8.2.2.2 Choose the Operation Mode

Select the operation mode using Table 4.

8.2.2.3 Choose the Inductor

Determine the inductance value to set the ripple current at approximately ¼ to ½ of the maximum output current. Larger ripple current increases output ripple voltage, improves signal-to-noise ratio, and helps to stabilize operation.

Equation 7. TPS53515 q_de_l_slusbq8.gif

The inductor requires a low DCR to achieve good efficiency. The inductor also requires enough room above peak inductor current before saturation. The peak inductor current is estimated using Equation 8.

Equation 8. TPS53515 q_de_iindpeak_slusbq8.gif

8.2.2.4 Choose the Output Capacitor

The output capacitor selection is determined by output ripple and transient requirement. When operating in CCM, the output ripple has two components as shown in Equation 9. Equation 10 and Equation 11 define these components.

Equation 9. TPS53515 q_vripple_slusbn5.gif
Equation 10. TPS53515 q_vripplec_slusbn5.gif
Equation 11. TPS53515 q_vrippleesr_slusbn5.gif

8.2.2.5 Determine the Value of R1 and R2

The output voltage is programmed by the voltage-divider resistors, R1 and R2, shown in Equation 12. Connect R1 between the VFB pin and the output, and connect R2 between the VFB pin and GND. The recommended R2 value is from 1 kΩ to 20 kΩ. Determine R1 using Equation 12.

Equation 12. TPS53515 q_de_r1_slusbq8.gif

8.2.3 Application Curves

TPS53515 C004_SLUSBN5.pngFigure 44. Efficiency vs. Output Current
TPS53515 C009_SLUSBN5.pngFigure 46. Output Voltage vs. Output Current
TPS53515 startup_6a_slusbq8.gif
ILOAD = 6 A
Figure 48. Start-Up Sequence
TPS53515 transient_0a6a_slusbq8.gif
ILOAD from 0 A to 6 A
Figure 50. Load Transient
TPS53515 transient_0a6a0a_slusbq8.gif
ILOAD from 0 A to 6A to 0 A
Figure 52. Full Cycle Load Transient
TPS53515 transient_vripple_6a_slusbq8.gif
ILOAD = 6 A
Figure 54. Output Voltage Ripple
TPS53515 C008_SLUSBN5.pngFigure 45. Output Voltage vs. Output Current
TPS53515 C012_SLUSBN5.pngFigure 47. Switching Frequency vs. Output Current
TPS53515 shutdown_6a_slusbq8.gif
ILOAD = 6 A
Figure 49. Shutdown Sequence
TPS53515 transient_6a0a_slusbq8.gif
ILOAD from 6A to 0 A
Figure 51. Load Transient
TPS53515 transient_vripple_0a_slusbq8.gif
ILOAD = 0 A
Figure 53. Output Voltage Ripple
TPS53515 transient_prebias_slusbq8.gif
Preset VOUT = 0.5 V
Figure 55. Prebias Start-Up