ZSPM4022-06 Datasheet, PDF (25/38 Pages) List of Unclassifed Manufacturers – 12V/6A Synchronous DC/DC Buck Regulator

ZSPM4022-06
12V/6A Synchronous DC/DC Buck Regulator
3 Application Information
3.1. External Component Selection
3.1.1. Inductor Selection
Values for inductance, peak, and RMS currents are required in order to select the output inductor. The input and
output voltages and the inductance value determine the peak-to-peak inductor ripple current. Generally, higher
inductance values are used with higher input voltages. Larger peak-to-peak ripple currents will increase the power
dissipation in the inductor and MOSFETs. Larger output ripple currents will also require more output capacitance
to smooth out the larger ripple current. Smaller peak-to-peak ripple currents require a larger inductance value and
therefore a larger and more expensive inductor. A good compromise between size, loss, and cost is to set the
inductor ripple current to be equal to 20% of the maximum output current. The inductance value is calculated by
equation (3).
L
V_OUT  (V_IN(max)  V_OUT )
(3)
V_IN(max)  f_sw  20% I_OUT(max)
Where
f_SW = switching frequency, 600kHz (nominal)
20% = ratio of AC ripple current to DC output current
V_IN(max) = maximum power stage input voltage
The peak-to-peak inductor current ripple is
I_L(pp)

V_OUT  (V_IN(max)  V_OUT )
V_IN(max)  f_sw  L
(4)
The peak inductor current is equal to the average output current plus one-half of the peak-to-peak inductor current
ripple.
IL(pk) = IOUT(max) + 0.5  ΔIL(pp)
(5)
The RMS inductor current is used to calculate the I²R losses in the inductor.
I_L(RMS) 
I2
OUT(max)

ΔI_L(PP) ²
12
(6)
Maximizing efficiency requires the proper selection of core material and minimizing the winding resistance. The
high frequency operation of the ZSPM4022-06 requires the use of ferrite materials for all but the most cost-
sensitive applications. Lower cost iron powder cores can be used but the increase in core loss will reduce the
efficiency of the power supply. This is especially noticeable at low output power. The winding resistance
decreases efficiency at the higher output current levels. The winding resistance must be minimized although this
usually comes at the expense of a larger inductor. The power dissipated in the inductor is equal to the sum of the
core and copper losses. At higher output loads, the core losses are usually insignificant and can be ignored. At
lower output currents, the core losses can be a significant contributor. Core loss information is usually available
from the magnetics vendor.
Data Sheet
August 29, 2013
© 2013 Zentrum Mikroelektronik Dresden AG — Rev. 1.00
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the
prior written consent of the copyright owner. The information furnished in this publication is subject to changes without notice.
25 of 37