Intersil ISL6553EVAL1 Application Note Download Page 1

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Introduction

Power supply designers are
continually faced with next
generation microprocessors which

draw higher peak currents while demanding faster slew
rates. Intersil’s Endura™ multiphase product family provides
a wide variety of controllers and drivers to address these
changing requirements.

Intersil ISL6553 and HIP6601A

The ISL6553 controller coupled with two HIP6601A single
channel drivers form a highly integrated solution for high
current, high slew rate applications. This controller is
recommended specifically for VRM8.5-compliant Pentium

processor core-voltage regulation.

The ISL6553 regulates the output voltage and balances load
currents for two synchronous rectified buck converter
channels. A five-bit DAC provides a digital interface to
program the 1% accurate reference over a range of 1.050V
to 1.825V. Overvoltage and overcurrent protection monitors
ensure a microprocessor safe environment. For a more
detailed description of the ISL6553 functionality, refer to the
ISL6553 Data Sheet [1].

The HIP6601A is a dual MOSFET driver specifically
designed to drive two N-Channel Power MOSFETs in a
synchronous-rectified bridge configuration. A single logic
signal input controls both the upper and lower MOSFETs.
Shoot-through protection is provided on both switching
edges to provide optimal dead time. Internal bootstrap
circuitry only requires an external capacitor and provides
better enhancement of the upper MOSFET. For a more
detailed description of the HIP6601A, refer to the HIP6601A
data sheet [2]. The HIP6602A dual-channel driver provides
equivalent functionality with some space savings [3].

ISL6553EVAL1 Reference Design

The ISL6553EVAL1 evaluation board is designed to meet the
high end requirements of Intel Celeron processors covered by
the VRM8.5 specification. The entire circuit fits within the
slightly less than 5 in

white outline rectangle on the top side

of the board. The components outside the box simplify the
evaluation process. These include input and output power
connectors, VID selection jumpers, critical probe points,
power-good indicator and a load transient generator. The
evaluation board is implemented on a two-ounce, four-layer,
printed circuit board. See pp. 7–9 for layout plots.

With the VID jumpers set to 10110 (1.5V), the evaluation
board meets the design specifications indicated in Table 1.

Quick Start Evaluation

Output Voltage Selection

The ISL6553EVAL1 will arrive with the VID jumper
combination (JP1) set to 1.5V (10110). This can easily be
changed to the desired output voltage by changing the VID
jumpers per the DAC table in the ISL6553 data sheet [1].
VID0 and VID4 on the board correspond to VID25mV and
VID3 respectively. The output voltage of the ISL6553 can be
set from 1.05V to 1.825V in steps of 25mV.

Input Power Connections

The ISL6553EVAL1 provides two options for powering the
evaluation board. A 20-pin header, J1, is provided to mate
with a standard ATX supply main power connector. If an
ATX is not available, bench supplies can be connected to
female banana jacks. Connect 12V and 5V supplies to J2
and J3 respectively. Connect the grounds from both supplies
to J4. Using bench-top supplies allows easy evaluation of
power-on levels and power sequencing issues.

Power Supply Considerations

When using bench-top supplies the sequencing of the
supplies is important. Applying the 5V supply prior to the 12V
supply is not desirable. This sequencing could result in the
ISL6553 starting before the HIP6601A drivers are initialized.
The ISL6553 could complete its soft-start interval and produce
maximum duty cycle PWM drive signals before the drivers are
capable of switching power to the output. This can result in an
overcurrent trip due to the lack of soft-start, followed by a new
soft-start interval. This abnormal start-up sequence can be
avoided by applying the 5V supply after or at the same time as
the 12V supply. Power supply sequencing is not an issue
when using an ATX power supply.

The power-on reset function of the ISL6553 can be
inadvertently activated when operating the transient load
generator. Not all bench-top and ATX power supplies are
capable of responding to load transients, and they may
cause a momentary dip of VCC5. If low enough, this dip can

TABLE 1. ISL6553EVAL1 DESIGN PARAMETERS

PARAMETER

MAX

MIN

Static Regulation

1.565V

1.435V

Transient Regulation

1.590V

1.410V

Overvoltage Protection

1.800V