Automotive & motorsport Inductor NCL0804-4 DL = 32 nH
Height: mm/ Relative
4.0 max/1×
4.4 max/1.1× larger
DL = 100 nH 6.4 max/1.6× larger
Efficiency, Relative Current Ripple, Relative
OK Low OK 1× 2.35× larger 1.33× smaller
Transient, Relative Relative Transient/ Ripple Benefit (Equation 9)
1× 1.9× slower 5.9× slower TABLE 1. COMPARISON OF THE DIFFERENT MAGNETICS OPTIONS FOR THE FOUR-PHASE BUILDING BLOCK
Substituting the DL = 32 H inductors with NCL0804-4 resulted in enhanced efficiency, as shown in Figure 6. This improvement is mainly attributed to the significant reduction in current ripple (Figure 4), leading to lower rms currents in windings, power stages, and traces. Additionally, it contributes to lower AC losses, as depicted in Figure 6.
Figure 4. Current ripple for the developed NCL=4× 17 nH and theoretical NCL = 8× 17 nH compared to DL = 32 nH and DL = 100 nH as a function of the output voltage VOUT.
enhance the trade-off between transient and ripple (effectively transient efficiency). However, it’s crucial to note that implementing such a change would be a significant departure from the existing design and layout. Whether this proposed approach is considered in the future will depend on customer preferences.
EXPERIMENTAL RESULTS Figure 5. The voltage regulator four-phase building block with inductor footprint that accepts (a) DL = 100 nH (h = 6.4 mm max) and (b) NCL0804-4 (h = 4.0 mm max).
At the same time, the 17 nH/phase NCL (Figure 5b) offers ~1.9× faster current slew rate in transient and generally improves the phase margin in the feedback loop. Stepping down on ripple with DL = 100 nH (Figure 5a) recovers the efficiency, Figure 6, but such DL is significantly taller than the allowed h = 4 mm height, while also being ~5.9× slower than developed NCL. The latter would cause extreme implications for the amount of needed output capacitors. The results confirm the fundamental performance advantage of NCL as expected from the FOM estimates, against the different trade-off options of the discrete inductor approach.
CONCLUSION
In summary, a new coupled inductor with the NCL structure was developed to optimise performance for an application with very low output voltage and aggressive load transient specifications. This CL was also done to fit the specified low profile for the automotive design. The NCL structure was chosen to minimise
4.4× 1× 1×
Figure 6. Efficiency comparison of the DL = 32 nH (h = 4.4 mm), DL = 100 nH (h = 6.4 mm), and NCL = 4× 17 nH (h = 4.0 mm): 5 V to 0.8 V, four phases.
leakage, achieving a formal benefit of over 4× in transient/ripple performance compared to the conventional discrete inductor option. To match the efficiency of the developed NCL, a discrete inductor (DL) with 1.6× the height (DL = 100 nH) would be needed. However, this alternative would fall 5.9× behind in transient speed, significantly impacting the size and cost of the output capacitance. The comparison in Table 1 highlights the advantages of the NCL0804-4 in terms of height, efficiency, current ripple, and transient speed.
Analog Devices
www.analog.com
Figure 5. The voltage regulator four-phase building block with inductor footprint that accepts (a) DL = 100 nH (h = 6.4 mm max) and (b) NCL0804-4 (h = 4.0 mm max).
Instrumentation Monthly February 2025 59
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