SLVSDF2A May   2017  – July 2017 TPS22970

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 Switching Characteristics
    7. 6.7 Typical DC Characteristics
    8. 6.8 Typical AC Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 On and Off Control
      2. 8.3.2 Quick Output Discharge (QOD)
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Thermal Consideration
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Maximum Voltage Drop and On-Resistance
        2. 9.2.2.2 Managing Inrush Current
      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 Documentation Support
      1. 12.1.1 Related Documentation
    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

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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

9.1.1 Thermal Consideration

It is recommended to limit the junction temperature (TJ) to below 125°C. To calculate the maximum allowable dissipation, PD(max) for a given output current and ambient temperature, use Equation 1 as a guideline.

Equation 1. TPS22970 eq2_lvsbh4.gif

where

  • PD(max) is maximum allowable power dissipation
  • TJ(max) is maximum allowable junction temperature
  • TA is ambient temperature of the device
  • ΘJA is junction to air thermal impedance. See the Thermal Information section. This parameter is highly dependent upon board layout

9.2 Typical Application

TPS22970 typ_app_lvsbt9.gif Figure 20. Typical Application Circuit

9.2.1 Design Requirements

For this design example, below, use the input parameters shown in Table 2.

Table 2. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
VIN 0.65 V to 3.6 V
ILOAD 10 mA
Load Capacitance (CL) 800 µF
Maximum voltage drop 1%
Maximum Inrush Current 2.5 A

9.2.2 Detailed Design Procedure

9.2.2.1 Maximum Voltage Drop and On-Resistance

At 3.6-V input voltage, with a maximum voltage drop tolerance of 1%, the TPS22970 has a typical RON of 4.7 mΩ. The rail is supplying 10 mA of current; the voltage drop for a rail is calculated based on Equation 2 and Equation 3.

Equation 2. VDROP = RON × ILOAD
Equation 3. VDROP = 0.047 mV

The maximum voltage drop is 1% which is 36 mV. The voltage drop caused by the load current across the on resistance is 0.047 mV.

9.2.2.2 Managing Inrush Current

When the switch is enabled, the output capacitors must be charged up from 0 V to VIN. This charge arrives in the form of inrush current. Inrush current may be calculated using Equation 4.

Equation 4. TPS22970 Inrush_equation.gif

where

  • IINRUSH is the Inrush current
  • CL is the Load capacitance
  • SR is the Output Slew Rate
  • VIN is the Input voltage
  • tR is the Rise time

The typical rise time is 985 μs at VIN = 3.6 V. When CL = 800 µF, the expected inrush current limit at the typical rise time is 2.34 A.

The typical rise time is 320 μs at VIN = 0.65 V. When CL = 800 µF, the expected inrush current limit at the typical rise time is 1.3 A.

9.2.3 Application Curves

TPS22970 3p6_cout800.png
VIN = 3.6 V VON = 3.6 V CIN = 1 µF
RL = OPEN TA = 25°C CL = 800 µF
Figure 21. TPS22970 Inrush Current at 3.6 VIN With CL = 800 µF
TPS22970 0p65_cout800.png
VIN = 0.65 V VON = 3.6 V CIN = 1 µF
RL = OPEN TA = 25°C CL = 800 µF
Figure 22. TPS22970 Inrush Current at 0.65 VIN With CL = 800 µF