MAX8744ETJ+ Maxim Integrated Products, MAX8744ETJ+ Datasheet - Page 28

• Manufacturer Part Number: MAX8744ETJ+
• Description: IC CNTRLR PWR SUP QUAD 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8744ETJ+

• Applications: Controller, Notebook Computers
• Voltage - Input: 6 ~ 26 V
• Number Of Outputs: 4
• Voltage - Output: 3.3V, 5V, 1 ~ 26 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Duty Cycle (max): 99 %
• Output Voltage: 3.315 V, 5.015 V, 2 V to 5.5 V
• Mounting Style: SMD/SMT
• Switching Frequency: 200 KHz, 300 KHz, 500 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• Topology: Boost, Flyback, Forward
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The total output voltage sag is the sum of the voltage
sag while the inductor is ramping up, and the voltage
sag before the next pulse can occur:
where D
Characteristics ), T is the switching period (1/f
ΔT equals V
I
overshoot during a full-load to no-load transient due to
stored inductor energy can be calculated as:
The minimum current-limit threshold must be great
enough to support the maximum load current when the
current limit is at the minimum tolerance value. The
peak inductor current occurs at I
the ripple current; therefore:
where I
old voltage divided by the current-sense resistance
(R
limit threshold is 45mV.
Connect ILIM to LDO5 for a default 50mV current-limit
threshold. In adjustable mode, the current-limit thresh-
old is precisely 1/10 the voltage seen at ILIM. For an
adjustable threshold, connect a resistive divider from
REF to analog ground (GND) with ILIM connected to
the center tap. The external 0.5V to 2V adjustment
range corresponds to a 50mV to 200mV current-limit
threshold. When adjusting the current limit, use 1% tol-
erance resistors and a divider current of approximately
10mA to prevent significant inaccuracy in the current-
limit tolerance.
The current-sense method (Figure 7) and magnitude
determines the achievable current-limit accuracy and
power loss. Typically, higher current-sense limits provide
High-Efficiency, Quad-Output, Main Power-
Supply Controllers for Notebook Computers
28
MAX
SENSE_
/(V
______________________________________________________________________________________
IN
LIMIT_
V
MAX
SAG
). For the default setting, the minimum current-
I
- V
LIMIT
OUT
is maximum duty factor (see the Electrical
OUT
=
V
equals the minimum current-limit thresh-
SOAR
/V
2
>
Δ
C
IN
) when in skip mode. The amount of
I
I
LOAD MAX
LOAD MAX
OUT IN
x T when in PWM mode, or L x 0.2 x
≈
L I
(
(
(
Setting the Current Limit
(
Δ
V
(
Δ
C
I
2
LOAD MAX
LOAD MAX
OUT
C
x D
OUT OUT
)
)
+
(
T
(
(
⎛
⎜
⎝
MAX
−
V
Δ
I
INDUCTOR
Δ
LOAD(MAX)
T
)
)
−
)
)
)
2
2
2
V
L
OUT
⎞
⎟
⎠
)
+
OSC
plus half
), and
tighter accuracy, but also dissipate more power. Most
applications employ a current-limit threshold (V
50mV to 100mV, so the sense resistor may be deter-
mined by:
For the best current-sense accuracy and overcurrent
protection, use a 1% tolerance current-sense resistor
between the inductor and output as shown in Figure
7A. This configuration constantly monitors the inductor
current, allowing accurate current-limit protection.
However, the parasitic inductance of the current-sense
resistor can cause current-limit inaccuracies, especially
when using low-value inductors and current-sense
resistors. This parasitic inductance (L
canceled by adding an RC circuit across the sense
resistor with an equivalent time constant:
Alternatively, high-power applications that do not
require highly accurate current-limit protection may
reduce the overall power dissipation by connecting a
series RC circuit across the inductor (Figure 7B) with
an equivalent time constant:
and:
where R
and R
the worst-case inductance and R
by the inductor manufacturer, adding some margin for
the inductance drop over temperature and load.
The output filter capacitor must have low enough equiv-
alent series resistance (ESR) to meet output ripple and
load-transient requirements, yet have high enough ESR
to satisfy stability requirements. The output capaci-
tance must be high enough to absorb the inductor
energy while transitioning from full-load to no-load con-
ditions without tripping the overvoltage fault protection.
When using high capacitance, low-ESR capacitors
DCR
CS
is the inductor’s series DC resistance. Use
is the required current-sense resistance,
R
CS
R
R
DCR
CS
C
=
EQ
Output Capacitor Selection
V
I
=
LIMIT
=
LIMIT
R
⎛
⎜
⎝
1 =
C
R
1
L
EQ
R
+
L
R
2
=
R
SENSE
SENSE
⎡
⎢
⎣
10
R
2
1
1
⎞
⎟
⎠
R
V
x I
+
ILIM
DCR
DCR
LIMIT
R
1
2
⎤
⎥
⎦
values provided
SENSE
) can be
LIMIT
) of