Nexperia NEX40400 - A High Efficiency, Low Quiescent Current Buck Regulator
Switch-mode power converters are the most efficient way to improve a system's power efficiency. Unfortunately, their quiescent current can be an interesting challenge. With the NEX40400, Nexperia is able to reduce the quiescent current to approximately 60 Microampere.
The buck converter's superiority is obvious: while a linear regulator transforms excessive voltage/energy into heat, the buck regulator uses an inductor to achieve effective transformation.
Fully Adjustable Buck Regulator
The NEX40400's application schematic presents itself as shown in the figure.
The NEX40400 covers the range of 4.5 V to 40 V DC in terms of input voltage. As for output current, the part can handle up to 600 mA. All this is accomplished at very high efficiency.
The part is available with 1.05 and 2.1 MHz switching frequencies, which allows for the use of extremely small inductors. The table below provides a few values for the passive components.
Two criteria can be used to select the actual inductor: first, the regulator's operating frequency must not exceed the maximum specified for the magnetic core. Second, the inductor must withstand the peak current the regulator will produce---a formula for determining this is provided in the data sheet.
The two resistors Rfbb and Rfbt determine the actual output voltage. Nexperia always recommends using a 20-kiloohm resistor for the lower resistor. The value of the top resistor can then be determined via another formula found in the component's data sheet.
Six SKUs for Maximum Efficiency
Even though the NEX40400's high performance and low quiescent current make it a high-quality part, in practice, a variety of different SKUs are required to allow the power electronics designer to select the integrated circuit best suited to the task at hand.
Most importantly, the SKUs NEX40400ADAZ, NEX40400BDAZ, and NEX40400CDAZ provide a 2.1 MHz switching frequency, while the NEX40400DDAZ, NEX40400EDAZ and NEX40400FDAZ variants operate with a frequency of 1.05 MHz. This selection permits the clearing of sensitive bands - if the rest of the analog electronics found on the printed circuit board reside in one of the bands, move the switching regulator to minimize parasitic EMI.
Furthermore, the SKUs NEX40400CDAZ and NEX40400FDAZ use spread spectrum modulation. This means that the switching frequency of the buck regulator is varied, thereby limiting the amount of EMI seen in each band. This trick can greatly simplify passing EMI certification, should this be required for the product.
Conclusion
If an application can make do with 600 mA output current, the NEX40400 most definitely deserves a chance. Its low quiescent current and simple external circuit design make it a viable replacement for linear regulators in almost all applications. This leads to significantly improved power efficiency, reduces waste heat, and positively affects product longevity. In short, a highly recommended marvel of modern semiconductor engineering.