SC1406G View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC1406G
Semtech Corporation
'SC1406G' PDF : 28 Pages View PDF
SC1406G
POWER MANAGEMENT
RCS; V(RCS) = IOUT * RCS.
· In order to keep the voltage between CMP and
in having a larger transient response band to work with, thereby
providing a solution with the fewest output capacitors. On the
·
CMPREF = 0V, V(RCS) appears across RCORE.
V(RCS) + V(RCORE) = 0, so V(RCORE) = -V(RCS); therefore, a
current flows through RCORE from VOUT to CMPREF.
other hand, this also means that at low currents, the processor
will burn more power than without the offset, since CV2F still
applies, so battery life will be reduced.
·
·
·
I(RCORE) = IOUT * RCS / RCORE
An equal, but opposite current must flow in RDAC, so the
voltage at CMPREF is reduced by I(RCORE) l RDAC, so
VCMPREF = VDAC - I(RCORE) * RDAC
Substituting the equations from above: VCMPREF = VDAC
IOUT * RCS * RDAC / RCORE
The numbers in the sample calculations are taken from the Intel
Mobile Pentium III Processor in
BGA2 and Micro-PGA2 Packages Datasheet, Revision 1.0,
Document Number: 245302-002. Please consult the data for
your specific processor.
· Since VOUT = VCMPREF V(RCS), with a little algebra:
· VOUT = VDAC - IOUT * RCS (1 + RDAC / RCORE)
Hysteretic Converter Design Equations:
So, with the SC1406G, you get an accurate, linear droop greater
than the drop across the current sense resistor, without the
efficiency penalty of a large RCS, with a gain that is set by 1%
resistors! Adding ROFFSET shifts the position at zero current, as
described later.
For further information on IMVP, consult the Intel yellow-cover
document Intel® Mobile Voltage Positioning Voltage Regulation
Controller Application Note, Reference Number OR-2101.
The SC1405, a smart MOSFET driver, provides industry-leading
performance, driving a 3000pF load in under 15nS, typically.
Not only does the SC1405 offer built-in shoot-through protec-
tion, but also has externally programmable dead time. In
addition, it provides other protection and performance features,
such as under-voltage lock-out (UVLO), programmable adaptive
over-voltage protection (OVP), and the SMOD pin, which may be
used to force the low-side gate drive LO during very light load
conditions to prevent negative circulating current in the inductor.
It comes in the small TSSOP-14 package.
DESIGN PROCEDURE:
Requirements:
The first step in designing any converter is in defining the
requirements, which can come from many sources. For the
SC1406G, you need to determine the minimum and maximum
input voltages, which are determined by the battery and AC
adapter characteristics, unless you plan to use an existing
regulated voltage, such as +5V. The processor determines other
requirements; they are:
· Maximum output voltage
· Minimum output voltage
· Maximum output current
· Minimum output current
· Maximum transient current
· Transient voltage requirements
One decision you need to make is whether a positive offset
voltage at zero current is desirable. Providing this offset results
The Typical Application Schematic on Page 12 is a schematic of
the sample converter. Note that several of the resistors have
annotations along with reference designators and values.
These resistors set the basic functions and IMVP.
Referring to Figure 1, the basic equations for a hysteretic
converter are:
( ) ( ) 1)
VHYS := d⋅
VIN − VOUT ⋅ ESR + RCS
FS ⋅ L
where,
( ) 2) d :=
TON
TON + TOFF
VOUT
d :=
VIN
IIn equation 2), d is commonly referred to as the duty cycle.
The output voltage of the SC1406G is set digitally by the VID
(0:4) inputs, producing a voltage at the DAC output (pin 21)
accurate to better than 0.85%. The DAC voltage requirements
are given in the referenced Intel document and the SC1406G
datasheet. A similarly accurate fixed voltage internal bandgap
reference, Vref, has a nominal value of 1.70V, and is used for
setting voltage hysteresis and current limiting levels. In addition,
these references are used to provide active voltage positioning
adjusting the output voltage as a function of load current
scaled by external resistors.
The output voltage of an IMVP converter has three
components:
· The programmed DAC voltage, VDAC
· The load dependent droop VIMVP
· An optional positive offset, VOFFSET
In equation form,
3) VOUT := VDAC − VIMVP + VOFFSET
The full equations for the IMVP converter are:
4) ( ) ( ) VDAC⋅ ROFFSET + ROH ⋅RCORE − IOUT⋅RCS ⋅ROFFSET⋅ RCORE + RDAC
VOUT :=
RCORE ⋅ROFFSET + RDAC⋅ROH
ã 2000 Semtech Corp.
13
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