max5066auit Maxim Integrated Products, Inc., max5066auit Datasheet - Page 17

• Manufacturer Part Number: max5066auit
• Description: Max5066 Configurable, Single-/dual-output, Synchronous Buck Controller For High-current Applications
• Manufacturer: Maxim Integrated Products, Inc.

prevent shoot-through currents during transition.
shows the dual-phase, single-output buck regulator.
The switching frequency per phase, peak-to-peak ripple
current in each phase, and allowable voltage ripple at
the output, determine the inductance value. Selecting
higher switching frequencies reduces the inductance
requirement, but at the cost of lower efficiency due to
the charge/discharge cycle of the gate and drain
capacitances in the switching MOSFETs. The situation
worsens at higher input voltages, since capacitive
switching losses are proportional to the square of the
input voltage. Lower switching frequencies on the other
hand will increase the peak-to-peak inductor ripple cur-
rent (∆I
tion losses (see the Power MOSFET Selection section for
a detailed description of MOSFET power loss).
When using higher inductor ripple current, the ripple
cancellation in the multiphase topology, reduces the
input and output capacitor RMS ripple current. Use the
following equation to determine the minimum induc-
tance value:
Choose ∆I
rent per channel. Since ∆I
age, the inductance value may need minor adjustment
after choosing the output capacitors for full-rated efficien-
cy. Choose inductors from the standard high-current, sur-
face-mount inductor series available from various
manufacturers. Particular applications may require cus-
tom-made inductors. Use high-frequency core material
for custom inductors. High ∆I
flux excursion increasing the core losses at higher
frequencies. The high-frequency operation coupled with
high ∆I
even makes the use of planar inductors possible. The
advantages of using planar magnetics include low-profile
design, excellent current sharing between phases due to
the tight control of parasitics, and low cost. For example,
the minimum inductance at V
= 3A, and f
The average current-mode control feature of the
MAX5066 limits the maximum inductor current, which
prevents the inductor from saturating. Choose an
Configurable, Single-/Dual-Output, Synchronous
Buck Controller for High-Current Applications
L
L
, reduces the required minimum inductance and
) and therefore increase the MOSFET conduc-
L
SW
to be equal to about 30% of the output cur-
L
= 500kHz is 0.5µH.
=
V
______________________________________________________________________________________
OUT IN MAX
V
IN
(
V
×
Design Procedures
L
(
f
SW
affects the output-ripple volt-
L
IN
causes large peak-to-peak
)
×
= 12V, V
Inductor Selection
−
∆
V
I
L
OUT
)
OUT
= 0.8V, ∆I
Figure 7
L
inductor with a saturating current greater than the
worst-case peak inductor current:
where 24.75mV is the maximum average current-limit
threshold for the current-sense amplifier and R
the sense resistor.
When choosing the MOSFETs, consider the total gate
charge, R
drain-to-source voltage, and package thermal imped-
ance. The product of the MOSFET gate charge and on-
resistance is a figure of merit, with a lower number
signifying better performance. Choose MOSFETs opti-
mized for high-frequency switching applications. The
average gate-drive current from the MAX5066’s output
is proportional to the total capacitance it drives at DH1,
DH2, DL1, and DL2. The power dissipated in the
MAX5066 is proportional to the input voltage and the
average drive current. See the Supply Voltage
Connection (V
Drives Supply (V
mum total gate charge allowed from all driver outputs
together.
The losses may be broken into four categories: conduc-
tion loss, gate drive loss, switching loss and output loss.
The following simplified power loss equation is true for
both MOSFETs in the synchronous buck-converter:
For the low-side MOSFET, the P
virtually zero because the body diode of the MOSFET is
conducting before the MOSFET is turned on.
Tables 1 and 2 describe the different losses and shows
an approximation of the losses during that period.
The discontinuous input-current waveform of the buck
converter causes large ripple currents in the input
capacitor. The switching frequency, peak inductor cur-
rent, and the allowable peak-to-peak voltage ripple
reflected back to the source, dictate the capacitance
requirement. Increasing the number of phases increas-
es the effective switching frequency and lowers the
peak-to-average current ratio, yielding lower input
capacitance requirement. It can be shown that the
P
LOSS
=
P
CONDUCTION
DS(ON)
I
L PEAK
_
IN
/V
DD
, power dissipation, the maximum
REG
) sections to determine the maxi-
=
+
Power MOSFET Selection
P
24 75
) and the Low-Side MOSFET
GATEDRIVE
.
R
SENSE
×
Input Capacitance
SWITCH
10
+
−
P
3
SWITCH
+
∆
term becomes
2
I
L
+
P
OUTPUT
SENSE
17
is