The TPS40090 is a two-, three-, or four-phase programmable synchronous buck controller that is optimized for low-voltage, high-current applications powered by a 5-V to 15-V distributed supply. A multi-phase converter offers several advantages over a single power stage including lower current ripple on the input and output capacitors, faster transient response to load steps, improved power handling capabilities, and higher system efficiency.
Each phase can be operated at a switching frequency up to 1-MHz, resulting in an effective ripple frequency of up to 4-MHz at the input and the output in a four-phase application. A two-phase design operates 180° out of phase, a three-phase design operates 120° out of phase, and a four-phase design operates 90° out of phase, as shown in Figure 1.
The number of phases is programmed by connecting the deactivated phase PWM output to the output of the
internal 5-V LDO. In two-phase operation the even phase outputs should be deactivated.
The TPS40090 uses fixed frequency, peak current mode control with forced phase current balancing. When
compared to voltage mode control, current mode results in a simplified feedback network and reduced input line
sensitivity. Phase current is sensed by using either current sense resistors installed in series with output
inductors or, for improved efficiency, by using the DCR (direct current resistance) of the filter inductors. The latter method involves generation of a current proportional signal with an R-C circuit (shown in Figure 11).
The R-C values are selected by matching the time constants of the R-C circuit and the inductor; R-C = L/DCR. With either current sense method, the current signal is amplified and superimposed on the amplified voltage error signal to provide current mode PWM control.
An output voltage droop can be programmed to improve the transient window and reduce size of the output filter. Other features include a single voltage operation, a true differential sense amplifier, a programmable current limit, soft-start, and a power good indicator.
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