TIDUFE2 October   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Fault Detection and Protection
      2. 2.2.2 Theory of Operation - Parallel LDOs Using Op Amps
      3. 2.2.3 Theory of Operation - Parallel LDOs Using Ballast Resistors
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS7B7702-Q1, Automotive, Dual-Channel Antenna Low Dropout (LDO) Regulator With Current Sense
      2. 2.3.2 OPAx388 Automotive, Precision, Zero-Drift, Zero-Crossover, True Rail-to-Rail, Input/Output Operational Amplifiers
      3. 2.3.3 LMV321A-Q1 Automotive Low-Voltage Rail-to-Rail Output Operational Amplifier
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results - Parallel LDOs Using Op Amps
      1. 3.3.1 Short to Battery
      2. 3.3.2 Load Transient Response
      3. 3.3.3 Current Limit
      4. 3.3.4 Start-Up
      5. 3.3.5 Shutdown
      6. 3.3.6 Line Transient
      7. 3.3.7 PSRR
      8. 3.3.8 Thermal Performance
      9. 3.3.9 Thermal Limit Protection
    4. 3.4 Test Results - Parallel LDOs Using Ballast Resistors
      1. 3.4.1 Short to Battery
      2. 3.4.2 Load Transient Response
      3. 3.4.3 Current Limit
      4. 3.4.4 Start-Up
      5. 3.4.5 Line Transient
      6. 3.4.6 Thermal Performance
      7. 3.4.7 Thermal Limit Protection
    5. 3.5 Comparison of Results Between Parallel LDO Techniques
      1. 3.5.1 VLOAD vs ILOAD
      2. 3.5.2 PSRR
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 Layout Prints
    2. 4.2 Tools
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

1 System Description

Low-noise low-dropout regulators (LDO) are required in many applications to make sure that power supply noise does not couple into the signal chain. The requirements for LDO output current continue to increase as new sensors require additional current or different loads are combined to save space. Using a single LDO for the supply is not always possible due to power dissipation limitations or output current capability. The TIDA-050096 reference design solves this issue by using multiple LDOs configured to share current in parallel. There are two methods for paralleling the TPS7B7702-Q1 in this reference design:

  1. Operational Amplifiers: The first method uses op amps to parallel multiple TPS7B7702-Q1 channels. A wide range of op amps can be used to parallel the TPS7B7702-Q1, including the OPA388-Q1 and LMV321A-Q1. Up to four TPS7B7702-Q1 channels are paralleled in this reference design, using op amps, to deliver up to 1.2A to the load while maintaining all of the key features of a single TPS7B7702-Q1 channel. This approach can be scaled above four LDO channels; however, there is no limit to the number of channels that can be placed in parallel using this technique.
  2. Ballast Resistors: The second method uses ballast resistors, which can be designed either as discrete resistors or as copper traces on the printed-circuit board (PCB). In some applications, the harness resistance inherent in the system can also be used as part as all of the ballast resistance. Although there is no theoretical limit to the number of TPS7B7702-Q1 LDO channels that can be paralleled using this technique, Texas Instruments recommends limiting the number to two channels. This is recommended because the error voltage, or difference between the output of each individual LDO[1], increases with output voltage as a result of the gain set by the feedback resistors. At higher voltages, the increased gain amplifies the error voltage, leading to larger ballast resistance values - potentially exceeding 1Ω for the TPS7B7702-Q1. Increasing ballast resistance can lead to an impractical approach given the adverse impact on load regulation.