ISL88550A Datasheet, PDF (1/25 Pages) Intersil Corporation – Synchronous Step-Down Controller with Sourcing and Sinking LDO Regulator

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Data Sheet
April 23, 2008
ISL88550A
FN6168.3
Synchronous Step-Down Controller with
Sourcing and Sinking LDO Regulator
ISL88550A integrates a synchronous buck PWM controller
to generate VDDQ, a sourcing and sinking LDO linear
regulator to generate VTT, and a 10mA reference output
buffer to generate VTTR. The buck controller drives two
external N-Channel MOSFETs to generate output voltages
down to 0.7V from a 2V to 25V input with output currents up
to 15A. The LDO can source up to 2.5A and sink up to -2.0A
continuously. Both the LDO output and the 10mA reference
buffer output can be made to track the REFIN voltage via a
built-in resistive divider. These features make the
ISL88550A ideally suited for DDR memory applications in
desktops, notebooks and graphics cards.
The PWM controller in the ISL88550A uses constant-on-time
PWM architecture with a programmable switching frequency
of up to 600kHz. This control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients while maintaining
high efficiency and a relatively constant switching frequency.
The ISL88550A offers full programmable UVP/OVP and skip
mode options ideal in portable applications. Skip mode
allows for improved efficiency at lighter loads.
The VTT and VTTR outputs track to VREFIN/2. The high
bandwidth of this LDO regulator allows excellent transient
response without the need for bulk capacitors, thus reducing
the cost and size.
The buck controller and LDO regulators are provided with
independent current limits. Adjustable loss-less fold-back
current limit for the buck regulator is achieved by monitoring
the drain-to-source voltage drop of the low side synchronous
MOSFET. Once overcurrent is removed, the regulator is
allowed to enter soft-start again. This helps minimize power
dissipation during short-circuit condition. Additionally,
overvoltage and undervoltage protection mechanisms are
built in. The ISL88550A allow flexible sequencing and
standby power management using SHDNA#, and STBY#
inputs.
Features
• Pb-Free (RoHS Compliant)
Buck Controller
• Constant-On PWM with 100ns Load-Step Response
• Start-up with Pre-biased Output Voltage
• Up to 95% Efficiency
• 2V to 25V Input Voltage Range
• 2.5V Fixed or 0.7V to 3.5V Adjustable Output
• 200kHz/300kHz/450kHz/600kHz Switching Frequencies
• Programmable Current Limit with Foldback Capability
• 1.7ms Digital Soft-Start and Independent Shutdown
• Overvoltage/Undervoltage Protection Option
• Power-Good Window Comparator
LDO Section
• Fully Integrated VTT and VTTR Capability
• VTT has +2.5A/-2.0A Sourcing/Sinking Capability
• Start-Up with Pre-Biased Output Voltage
• VTT and VTTR Outputs Track VREFIN/2
• VTT and VTTR 1% of VREFIN/2
• Low All-Ceramic Output Capacitor Designs
• 1.0V to 2.8V Input REFIN Range
• Analog Soft-Start Option and Independent Shutdown
• Power-Good Window Comparator
Applications
• DDR, DDR II and DDR III Memory Power Supplies
• Desktop Computers
• Notebooks and Desknotes
• Graphics Cards
• Game Consoles
• Networking and RAID
Ordering Information
PART NUMBER (Note)
ISL88550AIRZ
ISL88550AIRZ-T*
PART MARKING
ISL88 550AIRZ
ISL88 550AIRZ
TEMP RANGE (°C)
-40 to +85
-40 to +85
PACKAGE (Pb-free)
28 Ld 5×5 TQFN
28 Ld 5×5 TQFN Tape and Reel
PKG. DWG. #
L28.5x5B
L28.5x5B
*Please refer to TB347 for details on reel specifications.
NOTE: These Intersil Pb-free plastic packaged products employ special Pb-free material sets; molding compounds/die attach materials and 100%
matte tin plate PLUS ANNEAL - e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations.
Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J
STD-020.
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CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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