MPQ4560 – 2A, 2MHz, 55V, STEP-DOWN CONVERTER
APPLICATION INFORMATION
To determine the inductance, allow the inductor’s
peak-to-peak ripple current to approximately
equal 30% of the maximum switch current limit.
Make sure that the peak inductor current is less
than the maximum switch current limit. The
inductance value can be calculated by:
COMPONENT SELECTION
Setting the Output Voltage
A resistive voltage divider from the output voltage
to FB pin sets the output voltage. The voltage
divider divides the output voltage down to the
feedback voltage by the ratio:
VOUT
VOUT
R2
L1=
(1-
)
VFB=VOUT
fs ΔIL
V
IN
R1+R2
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ∆IL is
the peak-to-peak inductor ripple current.
Thus the output voltage is:
R1+R2
R2
VOUT =VFB
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
For example, the value for R2 can be 10kΩ. With
this value, R1 is:
VOUT
VOUT
R1=12.5(VOUT -0.8)(KΩ)
ILP ILOAD
1
2 fS L1
V
IN
So for a 3.3V output voltage, R2 is 10kΩ, and R1
is 31.6kΩ.
Where ILOAD is the load current.
Table 1 lists several suitable inductors from
various manufacturers. The different inductor
choices include price vs. size requirements and
any EMI requirements.
Inductor
The inductor provides constant current to the
output load while being driven by the switched
input voltage. A larger-value inductor will result in
lower ripple current that will lower the output
ripple voltage. However, a larger inductor value
will be physically larger, have higher series
resistance, or lower saturation current.
MPQ4560 Rev. 1.1
3/29/2013
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