MAX8543EEE+ Maxim Integrated Products, MAX8543EEE+ Datasheet - Page 19

• Manufacturer Part Number: MAX8543EEE+
• Description: IC CNTRLR STEP DOWN 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX8543EEE+

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 11 V
• Current - Output: 25A
• Frequency - Switching: 200kHz ~ 1MHz
• Voltage - Input: 3 ~ 13.2 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 667mW
• Output Voltage: 0.8 V to 11.88 V
• Output Current: 25000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 200 KHz to 1000 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: Yes
• Topology: Buck
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A good compromise between size and efficiency is an
LIR of 0.3. Once all the parameters are chosen, the
inductor value is determined as follows:
where f
value inductor close to the calculated value. The exact
inductor value is not critical and can be adjusted to
make trade-offs among size, cost, and efficiency. Lower
inductor values minimize size and cost, but they also
increase the output ripple and reduce the efficiency due
to higher peak currents. On the other hand, higher induc-
tor values increase efficiency, but eventually resistive
losses due to extra turns of wire exceed the benefit
gained from lower AC current levels. This is especially
true if the inductance is increased without also increas-
ing the physical size of the inductor. Find a low-loss
inductor with the lowest possible DC resistance that fits
the allotted dimensions. Ferrite cores are often the best
choice, although powdered iron is inexpensive and can
work well at 300kHz. The chosen inductor’s saturation
current rating must exceed the peak inductor current
determined as:
The valley current limit employs a current foldback
scheme. The MAX8543 has a fixed valley current-limit
threshold of 130mV, and a fixed foldback ratio (P
23%. The foldback ratio is the current-limit threshold
when the output is at 0V (output shorted to ground),
divided by the threshold when the output is at its nominal
regulated value. Thus, the minimum output current limit
(I
ed as:
where R
low-side MOSFET at the highest expected operating
junction temperature, and I
rent, calculated as:
LIM
) and maximum short-circuit current (I
S
I
Lossless Sensing, Synchronization, and OVP
Step-Down Controllers with Prebias Startup,
PEAK
DS(ON)
is the switching frequency. Choose a standard-
L
I
=
P P
=
−
I
I
V
LIM
is the maximum on-resistance of the
LOAD MAX
IN
______________________________________________________________________________________
=
V
×
OUT
=
(
f
V
Setting the Current Limits
S
(
IN
R
×
0 11
DS ON
−
×
I
.
f
LOAD MAX
S
)
P-P
(
(
V
V
× ×
+
OUT
V
IN
L V
LIR
)
is the inductor ripple cur-
2
(
−
+
)
V
×
I
IN
OUT
Valley Current Limit
P P
×
V
2
−
)
OUT
I
×
LOAD MAX
)
LIR
SC
(
) is calculat-
)
FB
) of
Ensure that I
mum load current at peak current limit (see the Peak
Current Limit section):
where 40mV is the maximum current-limit threshold
when the output is shorted (V
The MAX8544 has an adjustable valley current limit and
can be selected for foldback with automatic recovery,
or constant current with latch-up. To set the current limit
for foldback mode, connect a resistor from ILIM2 to the
output (R
GND (R
R
1) First, select the percentage of foldback (P
Figure 6. ILIM2 Resistor Connections
ILIM
R
percentage corresponds to the current limit when
V
V
P
P
equations are used to calculate R
where I
current at maximum load (I
and R
low-side MOSFET at the highest operating junction
temperature.
ILIM
OUT
OUT
FB
FB
are calculated as follows:
ILIM
is in the range of 15% to 40%. A lower value of
yields lower short-circuit current. The following
=
equals zero, divided by the current limit when
FOBK
equals a nominal voltage. A typical value of
DS(ON)
5
V
MAX8544
VALLEY
). See Figure 6. The values of R
OUT
×
LIM
R
R
), and another resistor from ILIM2 to
DS ON
I
FOBK
SC
−
is equal to or greater than the maxi-
is the maximum on-resistance of the
(
[
5
is the value of the inductor valley
=
ILIM2
×
)
R
R
LX
=
×
0 04
DS ON
DS ON
I
.
5
VALLEY
μ
P
(
(
FB
A
V
OUT
× −
)
)
×
(
×
+
1
V
LOAD(MAX)
× −
I
I
OUT
VALLEY
= 0V).
P P
P
(
2
1
−
FB
FOBK
P
)
FB
× −
)
(
×
and R
1
- 1/2 I
R
R
R
FOBK
OUT
FOBK
ILIM
FOBK
P
FB
FB
). This
ILIM:
)
]
P-P
and
19
),