MAX15046EVKIT+ Maxim Integrated Products, MAX15046EVKIT+ Datasheet - Page 14

• Manufacturer Part Number: MAX15046EVKIT+
• Description: EVAL KIT FOR MAX15046
• Manufacturer: Maxim Integrated Products

Specifications of MAX15046EVKIT+

• Silicon Manufacturer: Maxim
• Silicon Core Number: MAX15046
• Kit Application Type: Power Management
• Application Sub Type: Synchronous Buck Converter
• Kit Contents: Board
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

40V, High-Performance, Synchronous
Buck Controller
An external resistor connecting RT to GND sets the
switching frequency (f
and R
where f
300kHz switching frequency is set with R
Higher frequencies allow designs with lower inductor
values and less output capacitance. Peak currents and
I
core losses, gate-charge currents, and switching losses
increase.
Three key inductor parameters must be specified for
operation with the MAX15046: inductance value (L),
inductor saturation current (I
(R
inductor peak-to-peak AC current to DC average cur-
rent (LIR) first. For LIR values that are too high, the RMS
currents are high, and therefore I
Use high-valued inductors to achieve low LIR values.
Typically, inductor resistance is proportional to induc-
tance for a given package type, which again makes I
losses high for very low LIR values. A good compromise
between size and loss is a 30% peak-to-peak ripple cur-
rent to average-current ratio (LIR = 0.3). The switching
frequency, input voltage, output voltage, and selected
LIR determine the inductor value as follows:
where V
switching frequency is set by R
Switching Frequency section). The exact inductor value
is not critical and can be adjusted to make trade-offs
among size, cost, and efficiency. Lower inductor val-
ues minimize size and cost, but also improve transient
response and reduce efficiency due to higher peak cur-
rents. On the other hand, higher inductance increases
efficiency by reducing the RMS current.
Find a low-loss inductor with the lowest possible DC
resistance that fits in the allotted dimensions. The
14
2
R losses are lower at higher switching frequencies, but
DC
_____________________________________________________________________________________
). To determine the inductance, select the ratio of
RT
SW
IN
is:
, V
is in Hz and R
R
OUT
Setting the Switching Frequency
RT
L
=
=
, and I
V
IN
f
SW
V
SW
OUT
×
f
+
SW
). The relationship between f
(1x10 ) x (f
OUT
17.3 10
(V - V
RT
×
IN
I
SAT
OUT
×
is in I. For example, a
-7
are typical values. The
Inductor Selection
OUT
), and DC resistance
9
×
2
T
R losses are high.
SW
LIR
)
(see Setting the
2
)
RT
= 49.9kI.
SW
2
R
saturation current rating (I
ensure that saturation cannot occur below the maximum
current-limit value (I
on-resistance of the low-side MOSFET and of the LIM
reference current (I
select an inductor with a saturation current (I
where I
factor 1.35 includes R
for the LIM reference current error. A variety of inductors
from different manufacturers are available to meet this
requirement (for example, Vishay IHLP-4040DZ-1-5 and
other inductors from the same series).
The minimum current-limit threshold must be high enough
to support the maximum expected load current with the
worst-case low-side MOSFET on-resistance value as the
R
sense element. The inductor’s valley current occurs at
I
minimum value of the current-limit threshold voltage
(V
MOSFET during the ripple-current valley,
where R
of the low-side MOSFET at maximum load current
I
where R
side MOSFET at ambient temperature T
Celsius), TC
the low-side MOSFET in ppm/NC, and T
Celsius) is the temperature at maximum load current
I
MOSFET data sheet.
LOAD(MAX)
LOAD(MAX)
LOAD(MAX) .
R
DS(ON)
ITH
DS(ON,MAX)
) must be higher than the voltage on the low-side
V
CL(TYP)
ITH
DS(ON,MAX)
DS(ON)
of the low-side MOSFET is used as the current-
>
and is calculated from the following equation:
minus one half of the ripple current. The
Obtain the R
MOSFET
R
=
DS(ON,MAX)
R
Setting the Valley Current Limit
is the typical current-limit set point. The
(in I is the on-resistance of the low-
DS(ON)
I
SAT
CL(MAX)
LIM
in I is the maximum on-resistance
is the temperature coefficient of
DS(ON)
≥
). Combining these conditions,
× +
1.35 I
DS(ON)
[1 TC
SAT
×
I
), given the tolerance of the
LOAD(MAX)
×
variation of 25% and 10%
) must be high enough to
CL(TYP)
MOSFET
and TC
×
AMB
MAX
MOSFET
× 
(T


1
MAX
−
(in degrees
SAT
(in degrees
LIR
2
- T
from the
) of:



AMB
)]