MAX1965TEEP Maxim Integrated, MAX1965TEEP Datasheet - Page 18

• Manufacturer Part Number: MAX1965TEEP
• Description: Current & Power Monitors & Regulators
• Manufacturer: Maxim Integrated

current-sense range. For a good compromise between
efficiency and cost, choose a high-side MOSFET (N
that has conduction losses equal to the switching loss-
es at the optimum input voltage. Check to ensure that
the conduction losses at minimum input voltage don’t
exceed the package thermal limits or violate the overall
thermal budget. Check to ensure that the conduction
losses plus switching losses at the maximum input volt-
age don’t exceed package ratings or violate the overall
thermal budget.
The low-side MOSFET (N
signal, so choose a MOSFET with an R
enough to provide adequate circuit protection (see the
Setting the Current-Limit section):
Use the worst-case maximum value for R
the MOSFET NL data sheet, and add some margin for
the rise in R
rule is to allow 0.5% additional resistance for each °C of
the MOSFET junction temperature rise. Ensure that the
MAX1964/MAX1965 DL gate drivers can drive N
other words, check that the dv/dt caused by N
on does not pull up the N
capacitance, causing cross-conduction problems.
MOSFET package power dissipation often becomes a
dominant design factor. I
est heat contributor for both high-side and low-side
MOSFETs. I
N
below. Generally, switching losses affect only the high-
side MOSFET, since the low-side MOSFET is a zero-
voltage switched device when used in the buck
topology.
Gate-charge losses are dissipated by the driver and do
not heat the MOSFET. Calculate the temperature rise
according to package thermal-resistance specifications
to ensure that both MOSFETs are within their maximum
junction temperature at high ambient temperature. The
worst-case dissipation for the high-side MOSFET (P
occurs at both extremes of input voltage, and the worst-
case dissipation for the low-side MOSFET (P
at maximum input voltage.
I
determined by:
Tracking/Sequencing Triple/Quintuple
Power-Supply Controllers
18
GATE
L
according to duty factor as shown in the equations
P
______________________________________________________________________________________
NH SWITCHING
is the average DH driver output current capability
(
2
DS(ON)
R losses are distributed between N
R
DS ON
)
over temperature. A good general
=
(
V I
IN LOAD OSC
)
2
R power losses are the great-
=
L
L
) provides the current-limit
V
I
VALLEY
gate due to drain-to-gate
VALLEY
ƒ



Q
GS
I
GATE
DS(ON)
DS(ON)
+
NL
Q
H
GD
) occurs
turning
H



large
from
L
and
NH
; in
H
)
)
where R
resistance (4Ω max), and R
placed between DH and the high-side MOSFET’s gate
(Figure 5).
To reduce EMI caused by switching noise, add a 0.1µF
ceramic capacitor from the high-side switch drain to the
low-side switch source or add resistors (max 47Ω) in
series with DL and DH to increase the switches’ turn-on
and turn-off times (Figure 5).
The minimum load current should exceed the high-side
MOSFET’s maximum leakage current over temperature
if fault conditions are expected.
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor must meet the ripple current
requirement (I
defined by the following equation:
Figure 5. Reducing the Switching EMI
P
P
P
NH CONDUCTION
NH TOTAL
NL
(
(
=
DS(ON)DH
MAX1964
MAX1965
I
LOAD
TO VL
I
GATE
)
RMS
2
=
R
P
DS ON NL
NH SWITCHING
) imposed by the switching currents
=
is the high-side MOSFET driver’s on-
(
GND
BST
(
2
)
DH
DH
LX
(
=
R
)
I
DS ON DH
LOAD
(



(OPTIONAL)
(OPTIONAL)
1-
C
R
BST
R
2
GATE
GATE
)



R
VL
GATE
V
DS ON NH
)
OUT
V
+
IN
+
(
P
R
NH CONDUCTION
GATE



is any resistance
)



(
N
N
Input Capacitor
H
L



)
V
V
L
OUT
IN



)