7.1 Overview

The TPS61093 is a highly integrated boost regulator for up to 17-V output. In addition to the on-chip 1-A PWM switch and power diode, this IC also integrates an output-side isolation switch as shown in the functional block diagram. One common issue with conventional boost regulators is the conduction path from input to output even when the PWM switch is turned off. It creates three problems, which are inrush current during start-up, output leakage current during shutdown, and excessive overload current. In the TPS61093, the isolation switch turns off under shutdown-mode and overload conditions, thereby opening the current path. However, shorting the VO and OUT pins bypasses the isolation switch and enhances efficiency. Because the isolation switch is on the output side, the IC's VIN pin and power stage input power (up to 10 V) can be separated.

The TPS61093 adopts current-mode control with constant pulse-width-modulation (PWM) frequency. The switching frequency is fixed at 1.2 MHz typical. PWM operation turns on the PWM switch at the beginning of each switching cycle. The input voltage is applied across the inductor and the inductor current ramps up. In this mode, the output capacitor is discharged by the load current. When the inductor current hits the threshold set by the error amplifier output, the PWM switch is turned off, and the power diode is forward-biased. The inductor transfers its stored energy to replenish the output capacitor. This operation repeats in the next switching cycle. The error amplifier compares the FB-pin voltage with an internal reference, and its output determines the duty cycle of the PWM switching. This closed-loop system requires frequency compensation for stable operation. The device has a built-in compensation circuit that can accommodate a wide range of input and output voltages. To avoid the sub-harmonic oscillation intrinsic to current-mode control, the IC also integrates slope compensation, which adds an artificial slope to the current ramp.