A tri-loop low-dropout regulator with fast transient response based on
flipped voltage follower
Abstract
This paper introduces a low-dropout regulator (LDO) with a quick
transient response to the load and no off-chip capacitance. The LDO in
this work powers digital modules in system-on-chip (SoC). It has low
output voltage variation and fast recovery time during load changes.
This paper proposed a novel tri-loop regulation method. The basic loop
is a conventional feedback loop for LDO to ensure output voltage
accuracy. The transient-enhanced loop is an improved design based on the
flipped voltage follower (FVF) that compensates for the effect of
removing off-chip capacitance on circuit stability. The introduced
Miller capacitor is used to form the AC-coupled loop, further ensuring
pole separation. It is worth mentioning that this paper introduces 2
FVFs for building basic loop and transient-enhanced loop. In addition, a
bandgap reference (BGR) with a self-starting circuit is designed in this
paper. The LDO described in this paper operates at 5V. The LDO is based
on a 0.18 um CMOS process. The dropping and rising voltages are merely
24.5 mV and 25 mV when the load current (I load)
fluctuates between 1 and 50 mA. And the corresponding settling times are
2.5 us and 1.9 us respectively. The LDO described in this paper has an
output of 1.8 V and the load regulation (LDR) is as low as 6.68 uV/mA.