The LP8764-Q1 includes four synchronous buck converters, that can be combined in a multi-phase configuration. All of the buck converters support the following features:

• Automatic mode control based on the loading (PFM or PWM mode) or Forced-PWM mode operation
• External clock synchronization option to minimize crosstalk
• Optional spread spectrum technique to reduce EMI
• Soft start
• AVS support with configurable slew-rate
• Windowed undervoltage and overvoltage monitors with configurable threshold
• Windowed voltage monitor for external supply when the buck converter is disabled
• Output Current Limit
• Short-to-Ground Detection on SW_Bx pins at start-up of the buck regulator

When the outputs of these buck converters are combined in multi-phase configuration, it also supports the following features:

• Current balancing between the phases of the converter
• Differential voltage sensing from point of the load
• Phase shifted outputs for EMI reduction
• Optional dynamic phase shedding or adding

There are two modes of operation for the buck converter, depending on the required output current: pulse-width modulation (PWM) and pulse-frequency modulation (PFM). The converter operates in PWM mode at high load currents of approximately 600 mA or higher. Lighter output current loads cause the converter to automatically switch into PFM mode for reduced current consumption. The device avoids pulse skipping and allows easy filtering of the switch noise by external filter components when forced-PWM mode is selected (BUCKn_FPWM = 1). The forced-PWM mode is the recommended mode of operation for the buck converter to achieve better ripple and transient performance. The drawback of this forced-PWM mode is the higher quiescent current at low output current levels.

When operating in PWM mode the phases of a multi-phase regulator are automatically added or shed based on the load current level. The forced multi-phase mode can be enabled for lower ripple at the output.

A multi-phase synchronous BUCK converter offers several advantages over a single power stage converter. Lower ripple on the input and output currents and faster transient response to load steps are the most significant advantages for application processor power delivery. The heat generated is greatly reduced for each channel due to the fact that power loss is proportional to the square of current with the even distribution of the load current in a multi-phase output configuration. The physical size of the output inductor shrinks significantly due to this heat reduction.

Figure 8-9 shows a block diagram of a single core.

Figure 8-10 shows the interleaving switching action of the multi-phase converters.

Figure 8-9 BUCK Core Block Diagram

Figure 8-10 Example of PWM Timings, Inductor Current Waveforms, and Total Output Current in 4-Phase Configuration. ⁽¹⁾