MAX17004ETJ+ Maxim Integrated Products, MAX17004ETJ+ Datasheet - Page 31

• Manufacturer Part Number: MAX17004ETJ+
• Description: IC PS CTRLR FOR NOTEBOOKS 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX17004ETJ+

• Applications: Controller, Notebook Computers
• Voltage - Input: 6 ~ 26 V
• Number Of Outputs: 4
• Voltage - Output: 3.3V, 5V, 2 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

lower losses in between. If the losses at V
significantly higher, consider increasing the size of N
Conversely, if the losses at V
higher, consider reducing the size of N
vary over a wide range, maximum efficiency is achieved
by selecting a high-side MOSFET (N
tion losses equal to the switching losses.
Choose a low-side MOSFET (N
sible on-resistance (R
package (i.e., 8-pin SO, DPAK, or D
ably priced. Ensure that the MAX17003/MAX17004 DL_
gate driver can supply sufficient current to support the
gate charge and the current injected into the parasitic
drain-to-gate capacitor caused by the high-side MOSFET
turning on; otherwise, cross-conduction problems may
occur. Switching losses are not an issue for the low-side
MOSFET since it is a zero-voltage switched device when
used in the step-down topology.
Worst-case conduction losses occur at the duty-factor
extremes. For the high-side MOSFET (N
case power dissipation due to resistance occurs at mini-
mum input voltage:
Generally, use a small high-side MOSFET to reduce
switching losses at high input voltages. However, the
R
tion limits often limits how small the MOSFET can be. The
optimum occurs when the switching losses equal the
conduction (R
do not become an issue until the input is greater than
approximately 15V.
Calculating the power dissipation in high-side MOSFETs
(N
allow for difficult-to-quantify factors that influence the turn-
on and turn-off times. These factors include the internal
gate resistance, gate charge, threshold voltage, source
inductance, and PC board layout characteristics. The fol-
lowing switching-loss calculation provides only a very
rough estimate and is no substitute for breadboard evalu-
ation, preferably including verification using a thermocou-
ple mounted on N
DS(ON)
H
) due to switching losses is difficult, since it must
PD N
PD N
⎛
⎜
⎝
I
LOAD G SW
(
required to stay within package power-dissipa-
(
Supply Controllers for Notebook Computers
H
I
GATE
H
Re
Q
High-Efficiency, Quad-Output, Main Power-
Re
DS(ON)
sistive
(
sistive
H
______________________________________________________________________________________
:
)
) losses. High-side switching losses
DS(ON)
)
+
=
)
C
=
⎛
⎜
⎝
OSS IN MAX
V
Power-MOSFET Dissipation
V
OUT
), comes in a moderate-sized
IN
V
L
2
IN(MAX)
) that has the lowest pos-
⎞
⎟
⎠
(
(
I
LOAD
2
PAK), and is reason-
H
)
) that has conduc-
⎞
⎟
⎠
H
)
are significantly
V
. If V
2
IN MAX SW
R
H
(
DS ON
), the worst-
IN
IN(MIN)
(
)
does not
f
)
are
H
.
where C
the charge needed to turn on the N
is the peak gate-drive source/sink current (1A typ).
Switching losses in the high-side MOSFET can become
a heat problem when maximum AC adapter voltages
are applied, due to the squared term in the switching-
loss equation (C x V
chosen for adequate R
becomes extraordinarily hot when subjected to
V
lower parasitic capacitance.
For the low-side MOSFET (N
dissipation always occurs at maximum battery voltage:
The absolute worst case for MOSFET power dissipation
occurs under heavy overload conditions that are
greater than I
exceed the current limit and cause the fault latch to trip.
To protect against this possibility, “overdesign” the cir-
cuit to tolerate:
where I
limit circuit, including threshold tolerance and sense-
resistance variation. The MOSFETs must have a
relatively large heatsink to handle the overload power
dissipation.
Choose a Schottky diode (D
drop low enough to prevent the low-side MOSFET’s
body diode from turning on during the dead time. As a
general rule, select a diode with a DC current rating
equal to 1/3rd the load current. This diode is optional
and can be removed if efficiency is not critical.
The boost capacitors (C
enough to handle the gate-charging requirements of
the high-side MOSFETs. Typically, 0.1µF ceramic
capacitors work well for low-power applications driving
medium-sized MOSFETs. However, high-current appli-
cations driving large, high-side MOSFETs require boost
capacitors larger than 0.1µF. For these applications,
select the boost capacitors to avoid discharging the
capacitor more than 200mV while charging the high-
side MOSFETs’ gates:
IN(MAX)
LIMIT
OSS
, consider choosing another MOSFET with
PD N
⎡
⎢
⎢
⎣
I
1
LOAD
is the output capacitance of N
is the peak current allowed by the current-
−
(
LOAD(MAX)
⎛
⎜
⎝
L
V
IN MAX
Re
=
V
OUT
(
I
IN
LIMIT
sistive
2 x f
DS(ON)
)
⎞
⎟
⎠
BST
−
SW
⎤
⎥
⎥
⎦
but are not high enough to
)
(
⎛
⎜
⎝
I
=
LOAD
). If the high-side MOSFET
Δ
) must be selected large
L
L
I
INDUCTOR
) with a forward-voltage
), the worst-case power
at low battery voltages
Boost Capacitors
H
)
2
2
MOSFET, and I
R
DS ON
(
⎞
⎟
⎠
H
)
, Q
G(SW)
GATE
31
is