A single-inductor multiple-output converter with peak current state-machine control

An integrated single-inductor multiple positive/negative output dual-loop DC-DC converter with multiplexed rectifiers for TFT LCD display supply will be presented. The converter operates with a tiny chip-size inductor. Based on the physical behavior of the inductor a very robust power stage will be shown, which can service an unlimited number of positive and negative output channels with a single inductor. All the different voltage levels (positive and negative) will be regulated independently on a cycle by cycle base. There are two different types of regulation loops running in the converter. The control of the individual channels is managed by a state machine (first loop) which takes care of the power stage switching pattern and allows the hysteretic converter to run in a pseudo continuous current mode to guarantee a high power conversion capability. The second loop works as a variable peak current control to minimize the inductor current. It will be demonstrated why running with a controlled peak current also yields in a small output voltage ripple and how the state-machine can help to further control the amount of energy delivered into one output channel. To achieve even lower ripple voltages below 10mV and high accuracy the main output is post-regulated by a tracking current-mode LDO. Finally the whole TPS6512X architecture with the multi-output converter, LDO´s and control circuitry will be shown. The converter with 4.5ksqmil chip-size fits in a 16-pin 3×3 QFN package. Due to the high maximum switching frequency of the device a single, inexpensive and ultra-thin 10μH inductor can be used, which offers a very compact and small power supply solution to provide all voltage levels required by small form-factor TFT-LCD panels.