SC1406G View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC1406G
Semtech Corporation
'SC1406G' PDF : 28 Pages View PDF
POWER MANAGEMENT
SC1406G
Figure 1 - Hysteretic Converter Basics
The major advantages of this approach are simplicity, inherent
stability (there are no reactive elements in the control circuit to
provide the phase shift required for classical stability problems),
and the fastest possible transient response. Any transient
which takes the voltage out of the hysteretic range forces the
converter immediately into the proper response. There are no
error voltages to slew, and no maximum or minimum duty cycle
limits to slow the transient response as in most other control
schemes. A significant benefit of the controller/driver architec-
ture is that low-level analog control functions do not have to
coexist in an environment of thousands of volts and amps per
microsecond, reducing noise problems.
The SC1406G also supports the Intel Mobile Voltage Positioning
(IMVP) functions. In short, IMVP allows notebook designers to
reduce the output voltage with increasing load current. This has
two potential benefits:
· IMVP minimizes power by reducing the voltage under
heavy loads; processor power is proportional to V2, so
a 5% reduction in voltage results in a nearly 10%
reduction in power drawn by the processor.
· IMVP can reduce the number of capacitors required to
respond to transients by producing a larger allowable
transient; briefly, the no-load voltage is positioned
above nominal, so when a transient occurs, the load
has farther to drop before hitting the regulation limit.
The loaded voltage is allowed to remain below the
nominal so that when the load returns to zero, the
voltage can rise farther without reaching the transient
specification. Since the allowable transient voltages
are larger, less capacitance and higher ESR can
provide the required performance.
The SC1406G provides the precise voltage positioning required
by IMVP because it employs a current-sense resistor, multiplied
by a gain set by external resistors to very accurately set the
voltage as a function of load current.
R23 (RCS)
+
-
+
R6
(ROH)
CMP
-
(pin 25)
+ CMPREF
(pin 26)
-
+
R22
(ROFFSET)
-
IOUT
VOUT
+
R5
(RCORE)
-
-
R21
(RDAC)
+
DAC
DAC
(pin 21)
Figure 2IMVP Example Illustration
The SC1406G implements IMVP, previously named DSPS
(dynamic set-point switching) in the following manner: Please
see Figure 2 above, and assume, for simplicity:
· ROFFSET is open
· The current into the CMP and CMPREF pins is zero.
Then, please note:
· The SC1406G regulates to the + side of the current
sense resistor, because that is where the CMP pin is
tied, and,
· No current flows through ROH, since the input current of
the comparator is ~0; V(ROH) = 0.
· The difference in voltage between CMP and CMPREF
is ~0V in order for the controller to be in regulation
In these conditions:
· At zero load, VOUT = VDAC and the voltage across the
current sense resistor is also zero;
· As the load increases, a voltage is developed across
ã 2000 Semtech Corp.
12
www.semtech.com
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