SC1406GCTSTR datasheet(14/28 Pages) SEMTECH

14 / 28 page

ã 2000 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC1406G

For customers familiar with the Intel IMVP application notes, the

above schematic has the IMVP resistors denoted using bold

lettering. To these resistors, Semtech has added one additional

resistor, R

BAL, which is used to balance the impedance at the

current limit comparator for improved noise performance. A

cross-reference between the IMVP nomenclature and the

reference designator in the schematic above is provided in the

table below.

Without IMVP, the R

OH (R6) and RHYS (R1) resistors set the

hysteresis voltage via the following equation:

The factor of 2 is due to the fact that half of the total hysteresis

occurs above the DC set point, half below, per Figure 1. Be-

cause output ripple is fed back to CMPREF via the R5/R21

divider, the uncorrected output ripple is increased. We correct

for this later when selecting R1.

The no load offset in a non-IMVP converter is set by R6 and R22.

The zero load voltage is:

As in the case of the hysteresis resistor, IMVP requires an

adjustment of the offset resistor value because at zero current,

the current drawn by the offset resistor divider is mirrored into

the R5/R21 divider, and increases the offset just as it increases

the ripple. R22 is calculated by solving equation 4) for I

OUT = 0A.

To disable the no-load positive offset, leave R22 unpopulated.

Negative offsets are also possible contact Semtech Applica-

tions Engineering for details.

The current sense resistor, R

CS (R23), RDAC resistor (R21), and

CORE (R5) set the IMVP gain. VIMVP is a function of current, and is

subtracted from the zero current output voltage.

Note that the SC1406G regulates to the + side of R23; as a

result, the minimum load dependent drop is Iout x R23. In

addition, the ripple voltage across R23 provides a minimum

input to the hysteretic comparator, so the SC1406G works well

with very low ESR capacitors.

The constant-current type of over current protection is provided

via R23, R

CLOH (R3), and RCLSET (R2). Current limiting will cycle

from I

CLMAX to ICLMIN until the load becomes less than ICLMAX:

10)

11)

Design Example SC1406G:

We can use the above equations to design a mobile voltage

regulator circuit to meet the requirements of the Intel® 650/

500MHz SpeedStep processor using values from the proces-

sor datasheet. This example is for reference only; your require-

ments, parts availability, and newer processors may require

different component values. Contact Intel for the latest

processor requirements. Note that in the calculations, results

have been rounded to the nearest commonly available compo-

nent value.

VRIPPLE

2VHYS

⋅

RCORE ROFFSET

ROH

()

⋅

RCORE ROFFSET

⋅

RDAC ROH

⋅

ESR

RCORE ROFFSET

ROH

()

⋅

RCORE ROFFSET

⋅

RDAC ROH

⋅

RCS

⋅

VHYS

2VREF

⋅

ROH

RHYS

⋅

VNL

VDAC 1

ROH

ROFFSET











⋅

ROFF

ROH

VNL RDAC

⋅

VDAC

VNL

VDAC

−

VIMVP IOUT RCS

⋅

RDAC

RCORE











⋅

ICLMIN

2VREF

⋅

RCLOH

RCLSET RCS

⋅

ICLMAX 3VREF

⋅

RCLOH

RCLSET RCS

⋅

SC1406GCTSTR Datasheet(PDF) 14 Page - Semtech Corporation

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