SLUSC78A November   2015  – December 2015 TPS548A20

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 Electrical Characteristics
    5. 6.5 Thermal Information
    6. 6.6 Typical Characteristics
    7. 6.7 Thermal Performance
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1  Powergood
      2. 7.3.2  D-CAP3 Control and Mode Selection
      3. 7.3.3  D-CAP3 Mode
      4. 7.3.4  Sample and Hold Circuitry
      5. 7.3.5  Adaptive Zero-Crossing
      6. 7.3.6  Forced Continuous-Conduction Mode
      7. 7.3.7  Current Sense and Overcurrent Protection
      8. 7.3.8  Overvoltage and Undervoltage Protection
      9. 7.3.9  Out-of-Bounds Operation (OOB)
      10. 7.3.10 UVLO Protection
      11. 7.3.11 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
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 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 TPS548A20 device is a high-efficiency, single-channel, synchronous-buck converter. The device suits low-output voltage point-of-load applications with 15-A or lower output current in computing and similar digital consumer applications.

8.2 Typical Application

TPS548A20 typ_app_slusc78.gif Figure 40. Typical Application Circuit Diagram

8.2.1 Design Requirements

This design uses the parameters listed in Table 4.

Table 4. 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 91.2%
η Full load efficiency VIN = 12 V, VOUT = 1.2 V, IOUT = 8 A 90.3%
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 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 3.

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 6. TPS548A20 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 7.

Equation 7. TPS548A20 q_de_iindpeak_slusc78.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 8. Equation 9 and Equation 10 define these components.

Equation 8. TPS548A20 q_vripple_slusbn5.gif
Equation 9. TPS548A20 q_vripplec_slusbn5.gif
Equation 10. TPS548A20 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 11. 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 11.

Equation 11. TPS548A20 q_de_r1_slusbq8.gif

8.2.3 Application Curves

TA = 25°C (unless otherwise noted)
TPS548A20 D031_SLUSC78.gif
fSW = 500 kHz FCCM
VIN = 12 V
Figure 41. Efficiency vs. Output Current
TPS548A20 D007_SLUSC78.gif
fSW = 500 kHz VOUT = 1.2 V
Figure 43. DC Load Regulation
TPS548A20 waveform_02_slusc78.png
ILOAD = 0 A
Figure 45. FCCM Steady-State Operation
TPS548A20 waveform_06_slusc78.png
ILOAD = 8 A
Figure 47. Steady-State Operation
TPS548A20 waveform_08_slusc78.png
ILOAD from 0 A to 8 A Div = 2 A/µs
Figure 49. Load Transient
TPS548A20 D005_SLUSC78.gif
fSW = 500 kHz VOUT = 1.2 V
Figure 42. DC Load Regulation
TPS548A20 waveform_01_slusc78.png
IOUT = 0 A
Figure 44. Auto-skip Mode Steady-State Operation
TPS548A20 waveform_05_slusc78.png
ILOAD = 8 A
Figure 46. Auto-skip Mode Steady-State Operation
TPS548A20 waveform_07_slusc78.png
ILOAD from 0 A to 8 A Div = 2 A/µs
Figure 48. Auto-skip Mode Load Transient