MAX8554EEE+ Maxim Integrated Products, MAX8554EEE+ Datasheet - Page 20

• Manufacturer Part Number: MAX8554EEE+
• Description: IC CNTRLR BUCK PWM 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX8554EEE+

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 550kHz
• Duty Cycle: 95%
• Voltage - Supply: 4.5 V ~ 28 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: Yes
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-QSOP
• Frequency-max: 550kHz
• Output Voltage: 0.6 V to 3.5 V
• Output Current: 25000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 550 KHz
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Synchronous Pin: No
• Topology: Buck
• Dc: 0649
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The adjustable current limit accommodates MOSFETs
with a wide range of on-resistance values. The current-
limit threshold is adjusted with an external resistor con-
nected from ILIM to GND (R
range is 50mV to 200mV measured across the low-side
MOSFET. The value of R
lowing formula:
where I
the on-resistance of the low-side MOSFET. To avoid
reaching the current at a lower current than expected,
use the maximum value for R
tion temperature. Refer to the MOSFET manufacturer’s
data sheet for maximum values.
Foldback current limit is used to reduce power dissipa-
tion during overload and short-circuit conditions. This is
accomplished by lowering the current-limit threshold as
the output voltage drops due to the overload.
To use foldback current limit, connect a resistor
(R
(R
and R
First, select the percentage of foldback, P
cent corresponds to the current limit when V
zero divided by the current limit when V
nominal voltage. Typical values range from 15% to
30%. To solve for the resistor values, use the following
equations:
If R
side MOSFET with lower R
combination of both for the best compromise of cost,
efficiency, and lower short-circuit power dissipation.
4.5V to 28V Input, Synchronous PWM Buck Controllers
for DDR Termination and Point-of-Load Applications
20
R
FOBK
ILIM
ILIM
ILIM
______________________________________________________________________________________
FOBK
) from ILIM to GND
=
VALLEY
) from ILIM to the output, and connect a resistor
results in a negative number, select another low-
10
V
R
are calculated as follows:
OUT
ILIM
×
is the valley current limit and R
R
R
-
=
FOBK
DS ON
(
10
10
(
×
×
)
=
Setting the Current Limit
R
×
ILIM
DS ON
I
(Figure
VALLEY
P
I
5
VALLEY
FB
DS(ON)
5µ
(
µ
is calculated using the fol-
A
A
DS(ON)
(
)
×
Foldback Current Limit
Constant Current Limit
1
ILIM_
×
-
5). The values of R
V
×
×
or increase P
OUT
I
P
VALLEY
(
FB
). The adjustment
1
R
-
DS ON
at elevated junc-
P
)
FB
(
OUT
)
FB
×
×
)
OUT
. This per-
(
equals its
R
1
DS(ON)
-
FOBK
FB
P
equals
FB
or a
ILIM
)
)
is
Figure
Resistors, R ILIM and R FOBK
The switching frequency of the MAX8553/MAX8554 can
be lowered from the value set by FSEL by adding a
resistor voltage-divider to EN/HSD (HSD) as shown in
Figure
measures on EN/HSD (HSD), which increases the on-
time. The switching frequency with the added resistor-
divider is calculated as follows:
where K = 1.7µs and N is given in Tables 1 and 2. To set
the frequency, select a value for R2 between 10kΩ and
100kΩ, then calculate R1 from the following equation:
With the minimum input voltage, make sure that the
voltage present at EN/HSD (HSD) is greater than 1.5V
when the resistor-divider is used:
R
ILIM
R
5. Setting the Foldback Current Limit with Two
FOBK
6. This voltage-divider lowers the voltage the IC
Adjusting the Switching Frequency
ILIM
f
S
R
V
MAX8553
1
IN MIN
≅
=
R
(
1
K
K N
+
×
1
)
1
×
PGND
R
×
DH
N
DL
LX
2
R
×
×
2
R
f
S
2
>
R
-
1
1 5
R
R
.
+
2
2
V
R
2
V
OUT