Figure 3: Quad-phase configuration - controller and target waveforms. (Source: Analog Devices)
two devices for triple-phase or quad-phase operation. It has an internal high-voltage FB level shifter for differentially sensing the output voltage when configured as an inverting-buck-boost converter. Through a dedicated reference input pin or via an I2C digital interface, the output voltage can be set dynamically. An external resistor can be used to adjust the internal oscillator, or the regulator can be synchronized with an external clock to maintain a constant switching frequency. Switching frequencies from 120 kHz to 1 MHz are supported. The controller is also protected against overcurrent, output overvoltage, input undervoltage, and thermal shutdown.
The resistor at the OVP pin designates the number of phases to the controller. This identification is used to determine how the controller responds to the primary phase's multiphase clock signal. In a quad-phase converter, the two phases of the MAX15258 controller or the target are interleaved by 180°, whereas the phase shift between the controller and target is 90° (Figure 3). In multiphase operations, the MAX15258 monitors the low-side MOSFET current for active phase current balancing. As feedback, the current imbalance is applied to the cycle-by-cycle current sensing circuitry to help regulate the load current. Doing so ensures equitable distribution between the two phases. Unlike forward
converter designs, designers do not need to account for a possible 15% to 20% phase imbalance during the design calculation stages when using this IC. In triple-phase or quad-phase operation, the average per-chip current is transmitted between the controller and target via dedicated differential connections. The current-mode controller and target devices regulate their respective currents so that all phases equitably share the load current. The quad-phase interleaved inverting buck-boost power supply shown in Figure 4 is suitable for applications requiring large amounts of power. The CSIO+ and CSIO– signals connect the
we get technical
59
Powered by FlippingBook