Programmable Soft Start for Buck-Boost Converters
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Solution Overview
Problem
Current USB Type-C controllers face challenges in efficiently performing a soft start of buck-boost converters due to the need for additional pins and large external capacitors, which increase design complexity and cost, while also lacking control over in-rush current profiles and startup speed.
Innovation Solution
A programmable soft start solution is implemented using firmware in an IC controller, which stores pulse width and frequency values in a register and controls the buck-boost converter switches through multiplexers, allowing dynamic adjustment of these parameters to manage output voltage ramping and in-rush current without relying on the error amplifier control loop bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional soft start method using external capacitors is used, then soft start function is achieved, but device complexity and cost increase due to additional pins and large external capacitors
Solution Approach 1:
The soft start function is extracted from the external hardware domain and implemented within the IC controller's firmware. The patent removes the need for external soft start capacitors and pins by implementing the soft start control logic in the controller's internal register and firmware, thereby reducing device complexity while maintaining the soft start function.
Solution Approach 2:
A register is introduced as an intermediary between the firmware and the PWM generator. This register stores the pulse width and frequency values that control the soft start process, allowing the firmware to programmatically control the converter's startup behavior without requiring external hardware components.
2Stability of the object's composition
If traditional soft start method is used, then output voltage ramping is controlled, but startup speed is limited by error amplifier control loop bandwidth
Solution Approach 1:
The control process is segmented into two distinct phases: soft start phase and normal operation phase. During soft start, a dedicated PWM generator with programmable parameters takes control, independent of the error amplifier loop. This segmentation allows the system to achieve fast startup initially, then transition to stable regulated operation, resolving the contradiction between startup speed and voltage ramping control.
Solution Approach 2:
The system dynamically switches between different control modes. The firmware programmatically controls the PWM generator during soft start to achieve rapid voltage ramping, then transitions to error amplifier control for steady-state regulation. This dynamic approach allows the system to optimize for speed during startup while maintaining stability during normal operation.
3Reliability
If traditional soft start method is used, then basic soft start is achieved, but control over in-rush current profiles is lacking
Solution Approach 1:
The patent enables dynamic control of PWM parameters (pulse width and frequency) through firmware-programmable registers. This allows the system to adjust the in-rush current profile by modifying the PWM duty cycle and frequency during soft start, providing adaptability for different load conditions and converter configurations while maintaining reliable soft start operation.
Data Source
AI summary
An IC controller for a USB Type-C device includes a register that is programmable to store a pulse width and a frequency. A buck-boost converter of the controller includes a first high-side switch and a second high-side switch. Control logic is coupled to the register and gates of the first/second high-side switches. To perform a soft start in one of buck mode or boost mode, the control logic: causes the second high-side switch to operate in diode mode; retrieves values of the pulse width and the frequency from the register; causes the first high-side switch to turn on using pulses having the pulse width and at the frequency; detects an output voltage at the output terminal of the buck-boost converter that exceeds a threshold value; and in response to the detection, transfers control of the buck-boost converter to an error amplifier loop coupled to the control logic.