Integrated switched-mode power supplies with digital control enabling fast transient responses and parameter identification

Abstract

Integrated switched-mode power supplies benefit from innovative digital control loop designs and implementations, fast and goal-oriented parameter identifications, and from robust and fast transient controls of this work. A digital control loop comprises an ADC, a digital controller, and a digital pulse-width modulator / DAC. The ADC and the DPWM / DAC are required to operate with high sample rates, minimum conversion delay, monotonic transfer characteristics, and high resolution. The control loop components of this work extend the application range to SMPS with output voltages higher than 3.3V of prior publications. A presented delay line ADC (6 bit, 9.5 MSps, 90 ns latency, 1.2V dynamic operation range) enriches the standard window concept with a live-tracking functionality, which is firstly proposed in this work. This functionality increases the resolution and enlarges the dynamic operation range. A charge pump DAC design offers 40x higher resolution compared to prior art. It guarantees monotonicity and low conversion time, enabling high-bandwidth digital control, along with low steady-state current consumption (20 μA). Large output voltages (>3.3 V) are supported with a high resolution in the order of 15 bits. A comparison of digital control to analog control demonstrates that digital control can be fully integrated. In contrast, this is not guaranteed for analog control and, if possible, chip area is significantly larger. Operating parameters in an SMPS may change significantly, together with its transfer behavior. SMPS passives face production tolerances, temperature dependencies, and aging. An adaption to varying operating conditions and actual values of the passives improves the SMPS behavior, ensures reliability, and saves cost. However, it requires an identification of the present operating conditions and parameters. A parameter identification concept yields results within less than 85 μs in startup and 2 μs in operation, which is 12x and 7000x shorter than prior art. It concentrates on and accurately identifies the most influential parameters of the SMPS, the inductor and the capacitor. A lossless load current identification runs without interruption of ongoing operation with only 3% maximum identification inaccuracy. A controller adapts to a right half plane zero, that limits the converters’control bandwidths. With the proposed adaption, maximum bandwidth is achieved. Output voltage deviations are reduced by a factor of 2.4 and recovery times by a factor of 1.5 in case of load transients. For the first time, this work introduces a DV/Dt-intervention control concept, which is applicable, as add-on, to any standard controller. The voltage deviations are reduced by a factor of 2.8, which allows for downscaling the output capacitor by the same factor. The proposed innovative digital control loop designs, fast and goal-oriented parameter identifications, and robust fast transient controls, meet the needs of small cost, high reliability and flexibility in electronics, that are driven by a rising number of functionalities and features.