MAX5037 MAXIM [Maxim Integrated Products], MAX5037 Datasheet - Page 25

• Manufacturer Part Number: MAX5037
• Description: VRM 9.0, Dual-Phase, Parallelable, Average Current-Mode Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

Although lower switching frequencies per phase increase
the peak-to-peak inductor ripple current (∆I
cancellation in the multiphase topology reduces the input
and output capacitor RMS ripple current.
Use the following equation to determine the minimum
inductance value:
Choose ∆I
per phase. Since ∆I
the inductance value may need minor adjustment after
choosing the output capacitors for full-rated efficiency.
Choose inductors from the standard high-current, sur-
face-mount inductor series available from various manu-
facturers. Particular applications may require
custom-made inductors. Use high-frequency core mate-
rial for custom inductors. High ∆I
peak flux excursion increasing the core losses at higher
frequencies. The high-frequency operation coupled with
high ∆I
making possible even the use of planar inductors. The
advantages of using planar magnetics include low-pro-
file design, excellent current-sharing between phases
due to the tight control of parasitics, and low cost.
For example, calculate the minimum inductance at
V
250kHz:
The MAX5037 average current-mode control feature lim-
its the maximum peak-inductor current which prevents
the inductor from saturating. Choose an inductor with a
saturating current greater than the worst-case peak
inductor current. Use the following equation to determine
the worst-case inductor current for each phase:
where R
IN(MAX)
L
= +13.2V, V
SENSE
, reduces the required minimum inductance
L
L
L
MIN
MIN
equal to about 40% of the output current
is the sense resistor in each phase.
I
L PEAK
=
=
_
______________________________________________________________________________________
(
(
13 2 1 75
V
13 2 250
OUT
L
INMAX
.
.
affects the output ripple voltage,
−
=
= +1.75V, ∆I
×
V
IN
R
.
0 051
SENSE
−
×
.
)
k
f
SW
V
×
×
OUT
1 75
L
10
VRM 9.0, Dual-Phase, Parallelable,
.
× ∆
causes large peak-to-
+
)
∆
Average Current-Mode Controller
I
L
×
L
=
2
I
L
= 10A, and f
V
0 6
OUT
.
µ
H
L
), the ripple
(8)
SW
(9)
(10)
=
When choosing a MOSFET for voltage regulators, con-
sider the total gate charge, R
and package thermal impedance. The product of the
gate charge and on-resistance of the MOSFET is a figure
of merit, with a lower number signifying better perfor-
mance. Choose MOSFETs optimized for high-frequency
switching applications.
The average gate-drive current from the MAX5037 out-
put is proportional to the total capacitance it drives
from DH1, DH2, DL1, and DL2. The power dissipated in
the MAX5037 is proportional to the input voltage and
the average drive current. See the V
section to determine the maximum total gate charge
allowed from all the driver outputs together.
The gate charge and drain capacitance (CV
cross-conduction loss in the upper MOSFET due to finite
rise/fall time, and the I
MOSFET R
MOSFET. Estimate the power loss (PD
side and low-side MOSFETs using following equations:
where Q
MOSFET’s total gate charge, on-resistance at +25°C,
rise time, and fall time, respectively.
where D = V
(I
PD



OUT
V
PD
IN



MOS HI
2
+ ∆I
×
I
I
MOS LO
×
RMS LO
RMS HI
I
OUT
C
−
G
L
OSS
, R
)/2
−
−
−
=
DS(ON)
×
(
DS(ON)
(
×
Q
4
=
OUT
3
=
t
=
R
V
G
(
IN
Q
+
(
×
(
I
/V
2
I
2
t
G
account for the total losses in the
2
, t
V
F
DC
DC
×
IN
DD
)
×
R
f
×
2
, I
SW
, and t
V
+
R loss due to RMS current in the
+
f
DD
×
SW
I
DC
2
I
2
f

 +

SW
PK
PK
×

 +

= (I
1 4
f
+
SW
)
F
+
Switching MOSFETs
.
DS(ON)
+
1 4
I
DC
I
are the upper-switching
R
DC
.
OUT
)
DS ON
R
+
×
DS ON
×
(
I
, power dissipation,
PK
I
- ∆I
PK
(
MOS
IN
)
)
)
×
×
, V
×
L
)
)/2 and I
I
D
_) in the high-
×
3
2
(
1
RMS LO
CC,
I
2
−
3
2
RMS HI
D
) loss, the
and V
)
−
−
(11)
(12)
(13)
(14)
PK
25
DD
=