MPQ4558 Datasheet, PDF (12/21 Pages) Monolithic Power Systems – 1A, 2MHz, 55V Step-Down Converter AEC-Q100 Qualified

MPQ4558 – 1A, 2MHz, 55V STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
Set the output voltage with a resistor divider
between the output voltage and the FB pin. The
voltage divider drops the output voltage down to
the feedback voltage by the ratio:
R2
V_FB =V_OUT × _R1+R2
Thus the output voltage is:
R1+R2
V_OUT =V_FB × _R2
For example, for R2 = 10kΩ, R1 can be
determined by:
R1 = 12.5 × (V_OUT − 0.8)(kΩ)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 31.6kΩ.
Inductor
The inductor supplies constant current to the
output load while being driven by the switched
input voltage. A larger value inductor will result in
less ripple current that will lower the output ripple
voltage. However, a larger-valued inductor is
physically larger, has a higher series resistance,
or lower saturation current.
Generally, determine an appropriate inductance
value by selecting the peak-to-peak inductor
ripple current equal to approximately 30% of the
maximum switch current limit. Also, make sure
that the peak inductor current is below the
maximum switch current limit. Calculate the
inductance value with:
Where:
L1= ^VOUT × (1- ^VOUT )
f_s × ΔI_L
V_IN
• V_OUT is the output voltage,
• V_IN is the input voltage,
• f_S is the switching frequency, and
• ∆I_L is the peak-to-peak inductor ripple current.
Choose an inductor that will not saturate under
the maximum inductor peak current. Calculate
the peak inductor current with:
I_LP
=
I_LOAD
+
V_OUT
2 × f_S ×
×
L1
⎜⎜⎝⎛^{1 −}
V_OUT
V_IN
⎟⎟⎠⎞
Where I_LOAD is the load current.
Table 1 lists a number of suitable inductors from
various manufacturers. The choice the inductor
style mainly depends on the price vs. size
requirements and any EMI requirement.
MPQ4558 Rev. 1.01
www.MonolithicPower.com
12
5/17/2013
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