MAX15023 Maxim Integrated Products, MAX15023 Datasheet - Page 22

• Manufacturer Part Number: MAX15023
• Description: Dual-Output Synchronous Buck Controller
• Manufacturer: Maxim Integrated Products

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Wide 4.5V to 28V Input, Dual-Output
Synchronous Buck Controller
4) Place the second zero (f
5) Place the third pole (f
6) Calculate R
The MAX15023’s step-down controller drives two exter-
nal logic-level n-channel MOSFETs as the circuit switch
elements. The key selection parameters to choose
these MOSFETs include:
• On-resistance (R
• Maximum drain-to-source voltage (V
• Minimum threshold voltage (V
• Total gate charge (Qg)
• Reverse transfer capacitance (C
• Power dissipation
22
Figure 5. Type III Compensation Network
C
R
I
whichever is lower and calculate R
lowing equation:
quency and calculate C
I
______________________________________________________________________________________
R
R
C
1
2
V
CF
OUT
2
=
as:
(
R
R
2
1
2
π
DS(ON)
V
=
REF
×
=
2
0 5
V
π
.
OUT
×
×
P3
V
)
f
CF
Z
1
f
FB
SW
2
) at half the switching fre-
−
C
Z2
:
V
R
×
F
g
F
FB
M
×
C
MOSFET Selection
) at 0.2 x f
TH(MIN)
C
R
I
CF
F
×
−
RSS
R
R
×
I
1
C
)
DS(MAX)
C
F
1
)
F
)
using the fol-
−
1
O
or at f
)
COMP
PO
,
All four n-channel MOSFETs must be a logic-level type
with guaranteed on-resistance specifications at V
4.5V. For maximum efficiency, choose a high-side
MOSFET (NH_) that has conduction losses equal to the
switching losses at the typical input voltage. Ensure
that the conduction losses at minimum input voltage do
not exceed MOSFET package thermal limits, or violate
the overall thermal budget. Also, ensure that the con-
duction losses plus switching losses at the maximum
input voltage do not exceed package ratings or violate
the overall thermal budget. Ensure that the MAX15023
DL_ gate drivers can drive a low-side MOSFET (NL_).
In particular, check that the dV/dt caused by NH_ turn-
ing on does not pull up the NL_ gate through NL_’s
drain-to-gate capacitance. This is the most frequent
cause of cross-conduction problems.
Gate-charge losses are dissipated by the driver and do
not heat the MOSFET. Therefore, if the drive current is
taken from the internal LDO regulator, the power dissi-
pation due to drive losses must be checked. All
MOSFETs must be selected so that their total gate
charge is low enough; therefore, V
drivers without overheating the IC:
where Q
four MOSFETs.
Device’s maximum power dissipation depends on the
thermal resistance from the die to the ambient environ-
ment and the ambient temperature. The thermal resis-
tance depends on the device package, PCB copper
area, other thermal mass, and airflow.
The power dissipated into the package (P
the supply configuration (see the Typical Application
Circuits ). It can be calculated using the following equation:
For the circuits of Figures 7 and 8:
where V
pins, I
(I
8), I
and drivers when the internal regulator is unused for 5V
supply operation (IN = V
Typical Operating Characteristics for the typical curves
of I
quency at various load capacitance values.
IN
IN
is practically zero for the circuits of Figures 7 and
VCC
and I
IN
IN
G_TOTAL
is the current consumed by the internal core
is the current at the input of the internal LDO
and V
VCC
P
DRIVE
P
current consumption vs. operating fre-
CC
T
is the sum of the gate charges of all
= V
=
are the voltages at the respective
P
V
IN
T
CC
= V
×
x (I
CC
Q
IN
G TOTAL
). See the corresponding
IN
x I
_
+ I
Power Dissipation
IN
CC
VCC
can power all four
×
)
f
SW
T
) depends on
GS
=