MAX8744AETJ+ Maxim Integrated Products, MAX8744AETJ+ Datasheet - Page 19

• Manufacturer Part Number: MAX8744AETJ+
• Description: IC CNTRLR PWR SUP QUAD 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8744AETJ+

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The LDO5 input undervoltage-lockout (UVLO) circuitry
inhibits switching if the 5V bias supply (LDO5) is below
its 4V UVLO threshold. Once the 5V bias supply
(LDO5) rises above this input UVLO threshold and the
SMPS controllers are enabled (ON_ driven high), the
SMPS controllers start switching, and the output volt-
ages begin to ramp up using soft-start. If the LDO5
voltage drops below the UVLO threshold, the controller
stops switching and pulls the low-side gate drivers low
until the LDO5 voltage recovers or drops below the
POR threshold.
The internal soft-start gradually increases the feedback
voltage with a 1V/ms slew rate. Therefore, the outputs
reach their nominal regulation voltage 2ms after the
SMPS controllers are enabled (see the Soft-Start
Waveform in the Typical Operating Characteristics ).
This gradual slew rate effectively reduces the input
surge current by minimizing the current required to
charge the output capacitors (I
V
ON3 and ON5 control SMPS power-up sequencing.
ON3 or ON5 rising above 2.4V enables the respective
outputs. ON3 or ON5 falling below 1.6V disables the
respective outputs. Driving ON_ below 0.8V clears the
overvoltage, undervoltage, and thermal fault latches.
Table 3. Operating Mode Truth Table
* SHDN is an accurate, low-voltage logic input with 1V falling-edge threshold voltage and 1.6V rising-edge threshold voltage. ON3
and ON5 are tri-level CMOS logic inputs, a logic-low voltage is less than 0.8V, a logic-high voltage is greater than 2.4V, and the mid-
dle-logic level is between 1.7V and 2.3V (see the Electrical Characteristics table).
Shutdown Mode
Standby Mode
Normal Operation
3.3V SMPS Active
5V SMPS Active
Normal Operation
(Delayed 5V SMPS
Startup)
Normal Operation
(Delayed 3.3V SMPS
Startup)
OUT(NOM)
MODE
Supply Controllers for Notebook Computers
/t
SMPS Enable Controls (ON3, ON5)
SLEW
High-Efficiency, Quad-Output, Main Power-
).
______________________________________________________________________________________
SHDN
High
High
High
High
High
High
Low
OUT
INPUTS*
High
High
High
ON5
Low
Low
Ref
X
= I
LOAD
High
High
High
ON3
Low
Low
Ref
+ C
X
OUT
OFF
ON
ON
ON
OFF
LDO5 to CSL5 bypass
switch enabled
OFF
LDO5 to CSL5 bypass
switch enabled
OFF
LDO5 to CSL5 bypass
switch enabled
x
LDO5
Connecting ON3 or ON5 to REF forces the respective
outputs off while the other output is below regulation
and starts after that output regulates. The second
SMPS remains on until the first SMPS turns off, the
device shuts down, a fault occurs, or LDO5 goes into
UVLO. Both supplies begin their power-down
sequence immediately when the first supply turns off.
When the switching regulators are disabled—when ON_
or SHDN is pulled low, or when an output undervoltage
fault occurs—the internal soft-shutdown gradually
decreases the feedback voltage with a 0.5V/ms slew rate.
Therefore, the regulation voltage drops to 0V within 4ms
after the SMPS controllers are disabled (see the SMPS
Shutdown Waveform in the Typical Operating
Characteristics ). This slowly discharges the output
capacitance, eliminating the negative output voltages
caused by quickly discharging the output through the
inductor and low-side MOSFET. When an SMPS target
voltage discharges to 0.1V, its low-side driver (DL_) is
forced high, clamping the respective SMPS output to
GND. The reference remains active to provide an accu-
rate threshold and to provide overvoltage protection. Both
SMPS controllers contain separate soft-shutdown circuits.
ON
OFF
OFF
ON
OFF
ON
ON
Power-up after 3.3V
SMPS is in regulation
Output Discharge (Soft-Shutdown)
OUTPUTS
5V SMPS
SMPS Power-Up Sequencing
OFF
OFF
ON
ON
OFF
ON
ON
Power-up after 5V
SMPS is in regulation
3V SMPS
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