SC1406G 데이터 시트보기 (PDF) - Semtech Corporation
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SC1406G
Semtech Corporation
SC1406G Datasheet PDF : 28 Pages
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SC1406G
POWER MANAGEMENT
( ) RCORE ⋅ ROFFSET + ROH
ESR
5) ( ) VRIPPLE := 2⋅ VHYS⋅ RCORE ⋅ROFFSET + RDAC⋅ROH ⋅
RCORE ⋅ ROFFSET + ROH
ESR + RCORE ⋅ROFFSET + RDAC⋅ROH ⋅RCS
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, RBAL, 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.
8)
VNL ⋅RDAC
ROH + VDAC
ROFF :=
VNL
−1
VDAC
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, RCS (R23), RDAC resistor (R21), and
RCORE (R5) set the IMVP gain. VIMVP is a function of current, and is
subtracted from the zero current output voltage.
Intel Nomenclature
Schematic Reference
Designator
RHSY
R1
RCLSET
R2
RCORE
R5
ROH
R6
RCLOH
R3
RDAC
R21
ROFFSET
R22
RCS
R23
Without IMVP, the ROH (R6) and RHYS (R1) resistors set the
hysteresis voltage via the following equation:
9)
RDAC
VIMVP:= IOUT⋅RCS⋅ 1
+
RCORE
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, RCLOH (R3), and RCLSET (R2). Current limiting will cycle
from ICLMAX to ICLMIN until the load becomes less than ICLMAX:
10)
RCLOH
ICLMIN := 2⋅ VREF⋅ RCLSET ⋅RCS
ROH
6) VHYS := 2⋅ VREF⋅ RHYS
RCLOH
11) ICLMAX:= 3⋅ VREF⋅ RCLSET ⋅RCS
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:
7)
ROH
VNL := VDAC⋅ 1 +
ROFFSET
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 IOUT = 0A.
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.
ã 2000 Semtech Corp.
14
www.semtech.com
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