JAJU299A June   2017  – January 2023

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 TPS82130
    3. 2.3 Design Considerations
      1. 2.3.1 Inverting Buck-Boost Topology Concept
      2. 2.3.2 VIN and VOUT Range
      3. 2.3.3 Maximum Output Current
        1. 2.3.3.1 Thermal Limits
        2. 2.3.3.2 Stability Limits and Output Capacitor Selection
      4. 2.3.4 Design Precautions
      5. 2.3.5 Enable Pin Configuration
      6. 2.3.6 Power Good Pin Configuration
      7. 2.3.7 Discharging Output Voltage
      8. 2.3.8 Adjustable Soft-Start Time
      9. 2.3.9 Input Capacitor Selection
  8. 3Getting Started Hardware
  9. 4Testing and Results
  10. 5Design Files
    1. 5.1 Schematics
    2. 5.2 Bill of Materials
    3. 5.3 PCB Layout Recommendations
      1. 5.3.1 Layout Prints
    4. 5.4 Gerber Files
    5. 5.5 Assembly Drawings
  11. 6Related Documentation
  12. 7Trademarks
  13. 8Revision History

2.3.4 Design Precautions

When using TPS82130 module for an inverting buck-boost application, there is a risk if VIN and EN pins are connected together directly.

The inverting buck-boost is commonly used to power the negative side of a differential rail. If the positive rail is applied to this differential rail first, the downstream devices activate and their Iq charges a positive prebias voltage on the negative rail. Input brownout and quick power cycles are other scenarios that can prebias the negative rail and cause startup issues. With VIN and EN tied together and having a positive prebias on the output of inverting buck-boost, the device might enable before it has time to initialize internal circuitry which can cause unexpected startup behavior or cause the device to get stuck. Ensuring that the EN pin is asserted after VIN is powered on can eliminate this issue robustly.

There are three proposed workarounds to avoid this issue:

  1. The first suggestion is to adjust the system power up sequence to prevent the unintended voltage buildup on the negative rail. This means enabling the negative rail first so that it is able to start up correctly, then enabling the positive rail. Adjusting the power on sequence this way can ensure that the TPS82130 as inverting buck-boost converter has a correct startup.
  2. If the application relies on the device enabling with VIN, then an RC filter is required to add a delay between VIN and EN pin. This ensures that the device has enough time to initialize the internal circuitry before the device is enabled to start regulating the output. The 100 kΩ and 1 μF RC filter provides the necessary delay between the VIN and EN pins for the device's initialization. An example of this schematic modification is shown in two different options. One using a series resistors to limit the current into the EN pin Figure 2-5 and another using a schottky diode to clamp the EN pin Figure 2-6. When using the schottky diode option, the forward voltage drop needs to be selected less than 0.3 V so that the device does not exceed the absolute maximum rating on EN pin.
    GUID-20230106-SS0I-NCJM-5JWN-LZTCBDKPLZJL-low.svg Figure 2-5 EN Pin Delay Using an RC Filter and Series Resistor
    GUID-20230106-SS0I-P8ZS-Q72G-QFH7GM95TNC1-low.svg Figure 2-6 EN Pin Delay Using an RC Filter and Schottky Diode
  3. Lastly, if the application requires enabling and disabling of the device from an external control signal, like a microcontroller or PG pin from an upstream device, then the order of power sequence is important. During power up, VIN must be applied before the EN signal and during power down, the EN pin needs to go low before VIN is removed. This ensures that EN pin does not exceed the maximum rating of VIN + 0.3 V, which can damage the device. See Section 2.3.5 for more information on level shifting the digital inputs.