PLL-based charge control scheme for SIMO buck DC-DC converter

Abstract

This paper presents a phase-locking-loop-based (PLL-based) charge control scheme to enhance the cross regulation (CR) performance of charge-controlled SIMO Buck DC-DC without freewheel period. By combining PLL structure with the traditional charge control scheme, each channel could be regulated by an independent charge control loop. Moreover, a gain-adapted charge pump (GACP) technique is applied for the stability in multi-load condition. The multi-loop stability and CR expressions are derivated to improve their relative performance. Experimental results show that the proposed scheme can achieve worstcase CR of 0.052mV/mA in 384mA load transient, and 0.038mV/mA CR in 150mA load transient with at least 43.2% improvement above the existing charge control schemes.

An optimization method for PLL‐based charge control SIMO Buck DC‐DC

“…The rising of DC-output V o<1:4> during the start process is smoothly slowed by the softstart cell. And the OPDC time sequence as in literature [1][2][3][4][5][6][7] is achieved by the logic cell through identifying S <1:4> as the off timing of D <1:4> , respectively.…”

“…It contains PFD, optimized GACP, Z lpf , PD, and CLOT control. According to the experimental results in Liu et al, 4 the bandwidth of PLL loop is Therefore in this paper, the F comp in the Z lpf and the PD are replaced with BW lpf and BW pd , respectively. The Z lpf is a passive low-pass filter (LPF) composed of R zlpf , C zlpf and C plpf , which is written as:…”

“…The optimized GACP is shown in Figure 4A, which is based on the traditional charge pump by charging the V lpf node with the switched current mirrored from current-mirror-pair P CP < 4:5> and N CP < 3:4> . The switched charging current is the sum of the continued I c<1:4> as in Liu et al 4 and the interrupted I plus for optimization. The I c<1:4> are equal to V c < 1: In order to figure out the on-timing of SW n5 and the value of α, the PLL-based structure in Figure 3 is simplified as model in Figure 5, where T cr (s), T cl (s), and T vl (s) represent the closed loop gain of charge control loop, current loop, and PLL loop, respectively.…”

“…The time sequence waveforms of inductor current I L and DC-outputs V o<1:4> during ΔI o1 = 616 mA load transient are simulated on Matlab/Simulink platform, and compared in Figure 9. When the current loop in literature 1,2,4 and the traditional GACP are applied, the I L and V o<1:4> during load transient is obviously unregulated, and the I L response time would be 64.5 μs. By the optimized GACP, the regulation of I L is speeded up, and the I L response time is decreased to 39 μs, but there is still large load regulation and CR.…”

“…[1][2][3] But in the traditional charge-controlled SIMO without additional freewheel period, 1,3 the charge control loop cannot be used in the last DC-output, where large CR would happen. A novel scheme called PLL-based charge control is introduced to apply the charge control loop to every DC-output in the literature 4 to decrease CR during heavy load transient. And the PLL-based structure [5][6][7] is designed to be compatible with charge control to eliminate freewheel period of these references 2,7 for better trade-off among chip area, load range, and efficiency performance.…”