Switched Input Buck Converter Reference Design for Critical Power Rails
The TIDA-070001 switched input buck converter design from Texas Instruments includes the TPS7H2201-SP and the TPS50601A-SP in a design that highlights how redundancy can be implemented to the input voltage in order to increase the reliability of a design. The two load switches allow for a primary and redundant voltage to be supplied to the point of load converter which allows robustness for critical power lines.
Examples of targeted applications include: satellite power distribution for FPGAs, microcontrollers, data converters and ASICs; radiation hardened applications; and space satellite payloads.
The current limit of the load switch along with a current sense pin allows for monitoring and protection of the point of load converter. The load switch is also able to provide overvoltage protection for the point of load converter device. The point of load converter current limit adds additional protection to shorts at the output of the point of load converter.
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The design consists of two TPS7H2201-SP load switches supplying input power for a TPS50601A-SP point of load converter in a redundancy configuration. The redundancy of the input voltage to the point of load converter is critical in keeping important power lines to high priority parts of a satellite such as an FPGA or microcontroller functioning.
Switched input buck converter reference design board
When using the TPS7H2201-SP as a current limiting load switch, the current limit must be calculated based on the duty cycle and efficiency of the TPS50601A-SP. Since the load switch is limiting the input and not the output current for the load switch, the input current will heavily depend on the duty cycle and efficiency of the converter.
The output voltage of the TPS7H2201-SP will degrade slowly after the TPS50601A-SP turns off. The TPS50601A-SP has a minimum input voltage of 3 V. When the output voltage of the TPS7H2201-SP is below 3 V and disabled, the TPS50601A-SP will stop lowering the voltage and the charge stored on those capacitors will very slowly decrease. Enabling the TPS7H2201-SP during this time may result in the TPS50601A-SP turning on faster than anticipated.
Switched input buck converter reference design (click on schematic to enlarge)
- Overcurrent limit
- Overvoltage limit
- Input voltage redundancy
- Soft start
- Enable/disable functionality