A 1V buck converter IC with hybrid current-mode control and a charge-pump DAC

This paper presents an integrated dc-dc converter with an output voltage of 1 V for portable applications. A hybrid peak current-mode control-scheme is demonstrated, where the voltage-loop compensation is achieved in the digital domain, while the current-regulation loop has a more traditional analog implementation. The main contribution of this work is the novel DAC architecture, which was developed specifically to achieve fast transient-response without needing clock frequencies beyond f_s, or expensive signal processing. Unlike the previous approach, based on an adaptive DeltaSigma DAC, the charge-pump (CP) DAC is capable of rapidly increasing the current-command in a single-cycle during load-steps. In addition to a low steady-state current-consumption of 3 muA, the CP-DAC has a guaranteed monotonic transfer characteristic and simplifies the overall system architecture. The resulting system solution achieves dynamic response comparable to state-of-the-art analog current-mode solutions, without using a power-hungry controller, or quantizing the inductor current. A custom IC, which was fabricated in a 0.18 mum CMOS process with 5 V compatible transistors, achieves a response-time of 4 mus at f_s = 3 MHz and V_out = 1 V, for a 200 mA load-step. The active area of the controller is only 0.077 mm², and the total controller current-draw, which is heavily dominated by the on-chip senseFET current-sensor, is below 0.5 % of the load current at I_out= 50 mA.