ISL88550AEVAL1【PDF 1/7 页】EVALUATION BOARD 1 ISL88550A

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ISL88550AEVAL1Z Kit: Synchronous Step Down

Controller with Sourcing and Sinking LDO Regulator

Application Note

July 23, 2008

AN1200.3

General Description

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 sink or source up to1.5A continuous

and 2.5A peak current with fast response. 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 graphic

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 within 1% of 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.

Features

Buck Controller

? Constant-On PWM with 100ns Load-Step Response

? Up to 95% Efficiency

? 2V to 25V Input Voltage Range

? 1.8V/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 Sourcing/Sinking Capability

? VTT and VTTR Outputs Track VREFIN/2

? VTT and VTTR within 1% of VREFIN/2

? All Ceramic Output Capacitor Designs

? 1.0V to 2.8V Input REFIN Range

? Analog Soft-Start Option and Independent Shutdown

? Power-Good Window Comparator

Pinout

ISL88550A

(28 LD TQFN)

TOP VIEW

Applications

? DDR I and DDR II Memory Power Supplies

? Desktop Computers

? Notebooks and Desknotes

? Graphics Cards

? Game Consoles

TON

OVP/UVP

LGATE

BOOT

? Networking and RAID

Ordering Information

REF

ILIM

POK1

POK2

STBY#

PHASE

UGATE

VIN

OUT

PART

ISL88550AEVAL1Z Evaluation Board

PACKAGE

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.

All other trademarks mentioned are the property of their respective owners.

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