An integrated five-output single-inductor multiple-output dc-dc converter with ordered power-distributive control (OPDC) in a 0.5 m Bi-CMOS process is presented. The converter has four main positive boost outputs programmable from +5 V to +12 V and one dependent negative output ranged from 12 V to 5 V. A maximum efficiency of 80.8% is achieved at a total output power of 450 mW, with a switching frequency of 700 kHz. The performance of the converter as a commercial product is successfully verified with a new control method and proposed circuits, including a full-waveform inductor-current sensing circuit, a variation-free frequency generator, and an in-rush-current-free soft-start method. With simplicity, flexibility, and reliability, the design enables shorter time-to-market in future extensions with more outputs and different operation requirements.

Of the different flat panel displays that can meet the increasing requirements of customers, the active matrix OLED (AMOLED) display is a strong candidate for mobile applications owing to its high resolution, low power consumption and low cost. AMOLED panels, however, usually require multiple power supplies with different regulated voltages. Therefore, step-up switching converters that can supply multiple outputs for this application are important.A single inductor bipolar output (SIBO) converter, shown in Fig. 7.4.1, is presented in this paper to power an AMOLED display for TDMA (GSM) mobile sets, which requires both positive and negative voltages with a gap of 10 to 12V. This converter reduces the overall size and cost of a mobile set. The most critical specification for this application is the line transient response of the positive supply, V OP , which can seriously affect the display by changing V gs of M p4 if it is not fast enough, thus changing the current I OP through the AMOLED. Based on experimentally verified data, the average variation of V OP should be strictly less than 4mV within 51.2µs of a 0.5V fluctuation in the battery voltage, V g , to avoid visible flicker on the display as illustrated in Fig. 7.4.1. Its switching ripple should also be under 30mV for a clean image. However, for the negative output V ON , its variation only affects V ds of M p4 , and hence, its line transient and ripple specifications are not as severe. Because of the stringent requirements for V OP , some chipmakers have attempted to obtain the V OP with an LDO [1] regulator, which creates a trade-off between reduced efficiency and increased cost and area.The converter in Fig. 7.4.1 is a combination of two converters: V OP is obtained from a boost operation employing modified comparator control (MCC) and V ON from a charge-pump circuit with PIcontrol. The control of the power switches is simplified compared to the topologies reported in [2] by delivering charge to all outputs at every switching cycle with priority given to V OP . The charge remaining after transferring charge to V OP is used to control the PWM signal for M n1 . Therefore, the effect of battery voltage fluctuations can be seen on V ON but is very small on V OP since V OP is controlled by a comparator while V ON is controlled by a PI loop. An additional high voltage output V H (= |V ON | + V D1 ) is intentionally generated to supply all gate drivers and to bias the bodies of the power PMOS transistors to reduce the sizes of the switches. The freewheeling switch M p3 is active in the discontinuous-conduction mode (DCM) with the zero-inductor-current detection technique reported in [3]. Consequently, the size and the conduction loss of M p3 are smaller than those of the one in the converter of [4]. .4.3 shows the peak current sensing method used in this converter. The circuit can accurately sense the peak inductor current I peak both in DCM and CCM. Normally, I peak is obtained from the on-voltage across M n1 (in Fig. 7.4.1). However, in this SIBO, the curren...

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