MAX8550ETI+T Maxim Integrated Products, MAX8550ETI+T Datasheet - Page 15

• Manufacturer Part Number: MAX8550ETI+T
• Description: IC PWR SUP DDR INTEG 28TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8550ETI+T

• 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: 20 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
Internal power-on reset (POR) occurs when AV
above approximately 2V, resetting the fault latch and
the soft-start counter, powering up the reference, and
preparing the buck regulator for operation. Until AV
reaches 4.25V (typ), AV
(UVLO) circuitry inhibits switching. The controller
inhibits switching by pulling DH low and holding DL low
when OVP and shutdown discharge are disabled
0
Integrated DDR Power-Supply Solutions for
Desktops, Notebooks, and Graphic Cards
(SEE FIGURE 1)
CONTROLLER
______________________________________________________________________________________
TO PWM
POR, UVLO, and Soft-Start
TIME
DD
I
I
LIM(VAL) =
LOAD(MAX)
undervoltage-lockout
LX
(
1 -
LIR
2
1.0V
)
x
I
I
I
PEAK
LOAD
LIMIT
I
LOAD
DD
rises
DD
(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.
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 MAX8550/
MAX8551 divide 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
reaches 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 regu-
lator’s output.
Soft-start in the LDO section can be realized by con-
necting a capacitor between the SS pin and ground.
When SHDNB is driven low, or during thermal shut-
down of the LDOs, the SS capacitor is discharged.
When SHDNB is driven high or when the thermal limit is
removed, an internal 4µA (typ) current charges the SS
capacitor. The resulting ramp voltage on SS linearly
increases the current-limit comparator thresholds to
both the VTT and VTTR outputs, until full current limit is
MAX8550/
MAX8551
DD
or OPEN). See Table 3 for a detailed truth table
V
DD
- 1V
ILIM
REF
R
R
A
B
C
C
ILIM
REF
DD
rises
15