Power Supply Reference Design Selection Guide
In modern electronic systems, the stability and reliability of power supply design are crucial, especially in applications requiring negative voltage, such as optical module biasing, operational amplifier supplies, and line drivers for low-power devices. This guide introduces a reference design based on the TPS62933 chip, which supports an input voltage range of 8V to 16V, providing a -12V output with a maximum current of 1.2A. This design offers engineers a simple and efficient solution for meeting various negative voltage requirements.
Introduction
In modern electronic systems, the stability and reliability of power supply design are crucial, especially in applications requiring negative voltage, such as optical module biasing, operational amplifier supplies, and line drivers for low-power devices. This guide introduces a reference design based on the TPS62933 chip, which supports an input voltage range of 8V to 16V, providing a -12V output with a maximum current of 1.2A. This design offers engineers a simple and efficient solution for meeting various negative voltage requirements.
System Description
This reference design utilizes the TPS62933, a high-efficiency, low-IQ synchronous buck converter, configured in an inverting buck-boost topology to achieve a -12V output voltage with a current capacity of up to 1.2A. The design accommodates an input voltage range of 8V to 16V, making it suitable for a variety of applications that require negative voltage. The TPS62933 features optimized internal loop compensation, which eliminates the need for external compensation components, simplifying the circuit design.
In this design, the TPS62933's ground pin is connected to the negative output voltage rather than the system ground. This inverting topology increases the voltage differential between the input and ground, so careful attention must be paid to ensure the input voltage remains within the device's operating limits.
Design Considerations
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Input and Output Voltage Relationship: The unique inverting buck-boost topology requires that the input voltage range be carefully managed. The input voltage must be within 3.8V to 30V minus the output voltage (-12V in this case) to ensure the TPS62933 operates reliably.
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Inductor Selection: The choice of inductor is critical in this topology, as it affects the system's stability and transient response. A 12µH inductor is recommended to ensure stable operation with a 1.2A output current.
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Start-Up and Shutdown Circuit Design: Since the TPS62933's ground is tied to the negative output voltage, additional level-shifting circuitry may be required to properly enable and disable the device during start-up and shutdown.
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Output Capacitor Selection: To maintain continuous load current, it is essential to select an appropriate output capacitor. A total capacitance of 66µF is recommended to meet the system's transient response and stability requirements.
System Design Theory
The TPS62933-based inverting buck-boost power supply design operates similarly to a traditional buck converter, but with an inverted output. The design ensures stable -12V output with low ripple (less than 1%), even under varying load conditions. The system's operation relies on the careful management of the on and off times of the MOSFETs, ensuring the inductor effectively stores and releases energy to maintain a steady output voltage.
This design is well-suited for applications requiring negative voltage, offering a robust solution that meets stringent performance requirements.
Testing and Performance
The performance of this reference design was validated through comprehensive testing:
- Start-Up Performance: The system demonstrated rapid start-up with stable -12V output at a 12V input.
- Load Transient Response: The output voltage deviation remained within 5% during load changes from 0.4A to 1.2A, indicating strong transient response capabilities.
- Output Ripple: At full load (1.2A), the output voltage ripple was maintained below 1%, ensuring stable operation.
- Thermal Performance: The system exhibited minimal temperature rise under full load at 27°C ambient temperature, indicating effective thermal management and reliable operation.
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