Feature: Power


Figure 1: A four-phase interleaving the LT8627SP solution powering 1.8VOUT


RF digital load


, 5A


ripple frequency so that the control bandwidth can be increased. Te compensation network is adjusted, to achieve at least a


45° phase margin and a gain margin over 8dB, whilst pushing the bandwidth as wide as possible. As a result, its control loop was tuned to its widest bandwidth of 280kHz with 45° phase margin and 9dB gain margin; see Figure 2. As a comparison, a single-phase LT8627SP with equivalent output capacitance per phase (2 × 100µF + 1 × 1µF + 1 × 0.1µF) was tested at 1.8V, 12A output. Te Bode plot is also shown in Figure 2 with the same stability criterion. To comparatively test the recovery time, a 50% load transient


Figure 2: A bode plot comparison between a four-phase LT8627SP at 50A and a one-phase LT8627SP at 12A


was performed for both four-phase and one-phase LT8627SP, with a slew rate of 6A/µs per phase. Te results are shown in Figure 3, where the recovery time is around 2.5μs at the rising edge of the transient. Figure 4 shows almost a ten-fold reduction in recovery time for the one-phase LT8627SP.


Figure 3: A four- phase LT8627SP 25-50A load transient optimised for minimum recovery time


22 November 2023 www.electronicsworld.co.uk


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