MAX8550AETI+ Maxim Integrated Products, MAX8550AETI+ Datasheet - Page 15

• Manufacturer Part Number: MAX8550AETI+
• Description: IC PWR SUP DDR INTEG 28TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8550AETI+

• Applications: Controller, DDR
• Voltage - Input: 2 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: 1.8V, 2.5V, 0.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Output Voltage: 0.7 V to 5.5 V, 1.8 V, 2.5 V
• Output Current: 1.5 A
• Input Voltage: 2 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 3. Adjustable Current-Limit Threshold
Figure 4. Valley Current-Limit Threshold
(UVLO) circuitry inhibits switching. The controller
inhibits switching by pulling DH low and holding DL low
when OVP and shutdown discharge are disabled
(OVP/UVP = REF or GND) or forcing DL high when OVP
and shutdown discharge are enabled (OVP/UVP =
AV
for OVP/UVP and shutdown settings. When AV
above 4.25V, the controller activates the buck regulator
and initializes the internal soft-start.
DD
or OPEN). See Table 3 for a detailed truth table
0
Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
______________________________________________________________________________________
(SEE FIGURE 1)
CONTROLLER
TO PWM
TIME
I
I
LIM(VAL) =
LOAD(MAX)
LX
(
1 -
LIR
2
)
1.0V
x
I
I
I
PEAK
LOAD
LIMIT
I
LOAD
DD
rises
The buck regulator’s internal soft-start allows a gradual
increase of the current-limit level during startup to
reduce the input surge currents. The MAX8550A
divides the soft-start period into five phases. During the
first phase, the controller limits the current limit to only
20% of the full current limit. If the output does not reach
regulation within 425µs, soft-start enters the second
phase, and the current limit is increased by another
20%. This process repeats until the maximum current
limit is reached, after 1.7ms, or when the output reach-
es the nominal regulation voltage, whichever occurs
first. Adding a capacitor in parallel with the external
ILIM resistors creates a continuously adjustable analog
soft-start function for the buck regulator’s output.
Soft-start in the LDO section can be realized by con-
necting a capacitor between the SS pin and ground.
When VTT is turned off or placed in standby mode, or
during thermal shutdown of the LDOs, the SS capacitor
is discharged. When VTT is turned on or when the ther-
mal limit is removed, an internal 4µA (typ) current
charges the SS capacitor. The resulting ramp voltage
on SS linearly increases the current-limit comparator
threshold to the VTT output, until full current limit is
attained when SS reaches approximately 1.6V. This
lowering of the current limit during startup limits the ini-
tial inrush current peaks, particularly when driving
capacitors. Choose the value of the SS cap appropri-
ately to set the soft-start time window. Leave SS floating
to disable the soft-start feature.
MAX8550A
V
DD
- 1V
ILIM
REF
R
R
A
B
C
C
ILIM
REF
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