Feature: Power


Figure 4: A single-phase LT8627SP 6-12A load transient optimised for minimum recovery time


High-current wireless applications Te multiphase operation of the Silent Switcher 3 architecture has already been used in many power supply designs; see Figure 5 for an example of how the LT8627SP powers a fast, high-current transient SoC with 0.8VOUT


and 22-60A 1µs load transient. To


prevent the SoC performance from degrading due to the transient, a VPP


of below 5% (40mV) is needed. Te four-phase interleaving the LT8627SP enables a high


control bandwidth, of around 300kHz. In the time domain we can roughly model the relationship between the voltage deviation during the load transient and control bandwidth as:


Tis determines the minimum output capacitance at 1583µF,


giving a 10mV ripple voltage. Te design needs capacitance higher than this value, in this case requiring polymer capacitors, to provide enough damping during the transient. Te final output capacitance is decided by trial and error, since the output capacitance also affects the loop bandwidth and stability. Te four-phase LT8627SPs are interleaved at a switching frequency of 1MHz to a combined ripple frequency of 4MHz.


Figure 5: A four- phase interleaving the LT8627SP solution achieving a < 5% VPP


for a


0.8V, 22-50A 1 µs transient


www.electronicsworld.co.uk November 2023 23


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