U.S. patent application number 15/479162 was filed with the patent office on 2017-10-19 for multiphase switching power supply with robust current sensing and shared amplifier.
The applicant listed for this patent is Linear Technology Corporation. Invention is credited to Yi Ding Gu, Yingyi Yan.
Application Number | 20170302174 15/479162 |
Document ID | / |
Family ID | 60021674 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170302174 |
Kind Code |
A1 |
Yan; Yingyi ; et
al. |
October 19, 2017 |
MULTIPHASE SWITCHING POWER SUPPLY WITH ROBUST CURRENT SENSING AND
SHARED AMPLIFIER
Abstract
In a multiphase, current mode controlled switching power supply,
current through the inductors in the various phases is sensed to
determine when to turn off the switching transistors. An AC current
feedback path, sensing the ramping ripple current, is separate from
the DC current path, sensing the lower frequency average current. A
shared differential amplifier has its inputs multiplexed to receive
only the DC component signals from all the phases. The gain of the
amplifier is set so that the DC sense signal has the proper
proportion to the AC sense signal. The output of the amplifier is
sampled and held for each phase using a second multiplexer. The AC
sense signal and the amplified DC sense signal, for each phase, are
combined by a summing circuit. The composite sense signal is
applied to a comparator for each phase to control the duty cycle of
the associated switch.
Inventors: |
Yan; Yingyi; (Fremont,
CA) ; Gu; Yi Ding; (Pleasanton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Linear Technology Corporation |
Milpitas |
CA |
US |
|
|
Family ID: |
60021674 |
Appl. No.: |
15/479162 |
Filed: |
April 4, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62323490 |
Apr 15, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 3/157 20130101;
H02M 1/14 20130101; H02M 1/084 20130101; H02M 2001/0009 20130101;
H02M 3/1584 20130101; H02M 1/12 20130101 |
International
Class: |
H02M 3/157 20060101
H02M003/157; H02M 1/12 20060101 H02M001/12; H02M 1/14 20060101
H02M001/14; H02M 1/084 20060101 H02M001/084 |
Claims
1. A multiphase switching power supply comprising: a first power
supply portion switching at a first phase, wherein the first power
supply portion comprises a first inductor and a first current
detection circuit for generating a first voltage signal
corresponding to a first AC component of current through the first
inductor and for generating a second voltage signal corresponding
to a first DC component of current through the first inductor,
wherein the first power supply portion further comprises a first
summing circuit for summing the first voltage signal and the second
voltage signal to create a composite first current sense signal
corresponding to a current through the first inductor; a second
power supply portion, substantially identical to the first power
supply portion, switching at a second phase, different from the
first phase, wherein the second power supply portion comprises a
second inductor and a second current detection circuit for
generating a third voltage signal corresponding to a second AC
component of current through the second inductor and generating a
fourth voltage signal corresponding to a second DC component of
current through the second inductor, wherein the second power
supply portion further comprises a second summing circuit for
summing the third voltage signal and the fourth voltage signal to
create a composite second current sense signal corresponding to a
current through the second inductor; a differential amplifier,
wherein the first current detection circuit and the second current
detection circuit share the differential amplifier, wherein the
differential amplifier has a gain for amplifying a fifth voltage
signal in the first current detection circuit, to generate the
second voltage signal corresponding to the first DC component of
current through the first inductor, and for similarly amplifying a
sixth voltage signal in the second current detection circuit, to
generate the fourth voltage signal corresponding to the second DC
component of current through the second inductor; a first
multiplexer having inputs coupled to the first power supply portion
and the second power supply portion to receive the fifth voltage
signal and the sixth voltage signal and having an output coupled to
inputs of the differential amplifier, the first multiplexer
coupling the fifth voltage signal to the inputs of the differential
amplifier during a switching cycle of the first power supply
portion, and the first multiplexer coupling the sixth voltage
signal to the inputs of the differential amplifier during a
switching cycle of the second power supply portion; a first sample
and hold circuit sampling and holding the second voltage signal
output from the differential amplifier, corresponding to the first
DC component of current through the first inductor, during the
switching cycle of the first power supply portion, an output of the
first sample and hold circuit being connected to an input of the
first summing circuit; a second sample and hold circuit sampling
and holding the fourth voltage signal output from the differential
amplifier corresponding to the second DC component of current
through the second inductor, during the switching cycle of the
second power supply portion, an output of the second sample and
hold circuit being connected to an input of the second summing
circuit; and a second multiplexer having an input coupled to the
output of the differential amplifier, the second multiplexer
connecting the output of the differential amplifier to the first
sample and hold circuit during the switching cycle of the first
power supply portion and connecting the output of the differential
amplifier to the second sample and hold circuit during the
switching cycle of second power supply portion.
2. The power supply of claim 1, wherein the first power supply
portion comprises: a first switch switching at the first phase, the
first switch having a first input terminal for coupling to an input
voltage; the first inductor having a first terminal coupled to the
first switch so as to conduct current during an on-time of the
first switch, current through the first inductor ramping up during
an on-time of the first switch, current through the first inductor
having the low frequency first DC component and the higher
frequency first AC component; a first comparator comparing the
composite first current sense signal, corresponding to the current
through the first inductor, to a control voltage corresponding to
an output voltage of the power supply, an output of the first
comparator controlling a duty-cycle of the first switch to generate
a regulated output voltage of the power supply; and a first
flip-flop receiving the output of the first comparator and a first
clock signal, an output of the first flip-flop controlling when to
turn on and turn off the first switch, the first clock signal
determining when to turn on the first switch, and the output of the
first comparator determining when to turn off the first switch;
wherein the second power supply portion comprises: a second switch
switching at the second phase, the second switch having a second
input terminal for coupling to the input voltage; the second
inductor having a second terminal coupled to the second switch so
as to conduct current during an on-time of the second switch,
current through the second inductor ramping up during an on-time of
the second switch, current through the second inductor having the
low frequency second DC component and the higher frequency second
AC component; a second comparator comparing the composite second
current sense signal, corresponding to the current through the
second inductor, to the control voltage corresponding to the output
voltage of the power supply, an output of the second comparator
controlling a duty-cycle of the second switch to generate the
regulated output voltage of the power supply; and a second
flip-flop receiving the output of the second comparator and a
second clock signal, wherein a phase of the second clock signal is
different from a phase of the first clock signal, an output of the
second flip-flop controlling when to turn on and turn off the
second switch, the second clock signal determining when to turn on
the second switch, and the output of the second comparator
determining when to turn off the second switch.
3. The power supply of claim 1 wherein the first inductor has a
first winding having a first DC resistance (DCR1) and an inductance
of L1, wherein L1/DCR1 is a first time constant, wherein the first
current detection circuit comprises: a first resistor, having a
resistance of R1, in series with a first capacitor, having a
capacitance of C1, connected at least across the first inductor,
wherein R1*C1 is a second time constant less than the first time
constant; and a second resistor in series with a second capacitor
connected across the first capacitor, wherein the second resistor
and the second capacitor form a low pass filter for passing only a
DC component for application to the first multiplexer.
4. The power supply of claim 1 further comprising a sense resistor,
with resistance R1, connected in series with the first inductor,
wherein the first inductor has a first winding having a first DC
resistance (DCR1) and an inductance of L1, wherein L1/(DCR1+R1) is
a first time constant, wherein the first current detection circuit
comprises: a first resistor, having a resistance of R1, in series
with a first capacitor, having a capacitance of C1, connected at
least across the first inductor and sense resistor, wherein R1*C1
is a second time constant less than the first time constant; and a
second resistor in series with a second capacitor connected across
the sense resistor, wherein the second resistor and the second
capacitor form a low pass filter for passing only a DC component
for application to the first multiplexer.
5. The power supply of claim 1 wherein the first power supply
portion switches a first switch, and wherein the second power
supply portion switches a second switch, the multiphase switching
power supply further comprising a clock generator for switching the
first switch and the second switch at the same frequency.
6. The power supply of claim 1 wherein the first power supply
portion and the second power supply portion are coupled to receive
the same input voltage.
7. The power supply of claim 1 wherein the first power supply
portion and the second power supply portion are coupled to output
the same output voltage.
8. The power supply of claim 1 wherein the first power supply
portion and the second power supply portion are coupled to the same
load.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. provisional
application Ser. No. 62/323,490, filed Apr. 15, 2016.
FIELD OF THE INVENTION
[0002] This invention relates to DC/DC converters and, in
particular, to multiphase current mode switching converters.
BACKGROUND
[0003] Multiphase switching power supplies are well known and
frequently used for high power applications. FIG. 1 illustrates a
two-phase power supply. In such a multiphase power supply, a
plurality of independently controlled switching power supplies are
connected in parallel to drive a load, represented as a resistor
RL, coupled to the regulated output voltage Vo. Typically, the
controller 10 is implemented as an integrated circuit, and the
inductors L1 and L2 and output capacitor Co are external. The
switching transistors Q1-Q4 may be internal or external depending
on the power requirements.
[0004] A clock sets each power supply during a different phase of a
cycle by turning the top transistor Q1 or Q3 on at the beginning of
its associated phase. In this way, the current conducted by each
phase is only a fraction of the load current, and the output
voltage ripple is reduced. This reduces the filtering requirements,
reduces RMS power dissipation in the switches, reduces hot spots,
enables more rapid response to load changes, and eases the
requirements for traces on printed circuit boards and in integrated
circuits. Ideally, the currents provided by the phases are the same
under steady state conditions.
[0005] Current mode switching power supplies are commonly used in
multiphase switching power supplies and require a very accurate
current sensor to feed back the instantaneous inductor current to
regulate the peak currents through the various inductors in the
phases. Basically, when the ramping inductor current crosses a
threshold voltage, the switching transistor is turned off for the
remainder of the clock cycle. The current sensing should be
identical for each phase to ensure the load current is balanced
evenly across all the phases. FIG. 1 shows the current feedback
signals Ifb1 and Ifb2 for each of the phases, and shows the output
voltage feedback signal Vfb. The output voltage feedback signal Vfb
may be a divided voltage.
[0006] One technique for detecting the inductor current in each
phase is to insert a low value sense resistor (e.g., less than 0.1
ohm) in series with the inductor and measure the voltage drop
across the resistor. The voltage drop includes a relatively large
drop due to the DC component of the ramping inductor current and a
much smaller drop due to the AC-ripple component of the ramping
inductor current. Since the resistor in each phase has a very low
value, there is a poor signal to noise ratio. The signal to noise
problem is due to the relatively small ripple voltage (AC) drops
across the sense resistor while the resistor is simultaneously
conducting a high DC current and switching noise. Further, losses
in the resistors waste power.
[0007] Instead of using a separate series resistor, current can be
measured "losslessly" by sensing the voltage across the inductor
(since the inductor has a DC winding resistance called DCR) or
sensing the voltage across the synchronous rectifier switch (when
it is turned on). This technique is considered lossless because it
relies on resistive losses inherent in the converter topology.
[0008] Another way to effectively sense the current is to emulate
the inductor current using a resistor-capacitor network across the
inductor, where the time constant of the RC network is the same as
the inductor-DCR time constant so that RC=L/DCR. Accordingly, the
ramping voltage across the capacitor will track the ramping current
through the inductor. However, if DCR is very low, there will be a
switching noise problem and a signal to noise ratio problem. This
will lead to pulse width modulation (PWM) phase jittering, current
imbalances, and other issues.
[0009] U.S. Pat. No. 8,823,352 discloses various current sense
techniques for a single-phase power supply, but does not address
current sensing for a multiphase power supply. The '352 patent
discloses a technique to separate out the AC and DC components of
the inductor current, to effectively independently amplify the AC
component, and then suitable amplify the DC component to have the
proper proportion to the AC component. However, this technique has
issues when applied to a multiphase power supply, since each phase
would need a separate amplifier having exactly the same gain to
similarly amplify its associated DC component, and it is difficult
to form identical amplifiers for each of the phases. Providing the
separate amplifiers also adds cost and size to the system.
[0010] What is needed is a multiphase switching power supply that
uses current mode converter phases, where the current sensing for
each phase can be made more accurate and identical for each
phase.
SUMMARY
[0011] A multiphase switching power supply is disclosed having
phased current mode converters (also referred to as phases). An RC
network emulates the inductor current for each phase. The RC
network separates out the DC and AC components of the emulated
inductor current so the two paths can be separately processed, then
later combined. The AC component can be made to have a high peak to
peak voltage, since it is separated from the DC component, which
improves the signal to noise ratio. The DC component is separately
amplified. Accurate processing of the emulated inductor current for
the phased current mode converters requires precisely the same
amplification of the DC component for each phase.
[0012] Only a single differential amplifier for the DC component is
used for all the phases since its inputs and output are
multiplexed, and the output of the amplifier is applied to a sample
and hold circuit for each phase. The output of the sample and hold
circuit (containing the amplified DC component of the inductor
current) is then summed with the AC component. The "input"
multiplexer clock may be the same clock that sets the phases of the
current mode converters, and the "output" multiplexer clock may be
slightly delayed to avoid sampling switching noise in the amplifier
output.
[0013] Therefore, the amplification is exactly the same for each
phase, there is less switching noise due to the sample and hold of
the DC component, and there is better current balancing by all the
phases. Additionally, since there is only one amplifier, the cost
and size of the system is reduced.
[0014] The sum of the AC component and the sample and held output
of the amplifier, for each phase, is then compared to a control
voltage for regulating the peak current through each of the
inductors. All the phases will have the same control voltage, so
the currents supplied by the phases should be the same.
[0015] The resistors in each of the current sensing circuits can be
made to match and can be customized for the inductors in the
different phases.
[0016] As a result, the current sensing for the various phased
current mode converters will be more accurate and identical, with
little added space since the same amplifier is used for all
phases.
[0017] The current sensing and shared DC sense signal amplifier can
be applied to any type of multiphase current mode converter
including, buck, boost, buck-boost, valley current control,
constant on-time control, constant off-time control, etc. All
aspects of the converters may be conventional except for the
current sensing and shared amplifier, enabling the invention to be
easily incorporated in existing multiphase converter designs.
[0018] The various phases may use the same input voltage or
different input voltages, and the phases may drive the same load or
different loads. In all cases, the DC component of the inductor
current will change slowly, enabling an average DC component in
each phase to be sampled and used for the entire switching
cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a prior art generic multiphase switching
power supply using current mode converters.
[0020] FIG. 2 illustrates an embodiment of the invention for a
two-phase power supply, where the phased current mode converters
each emulate their respective inductor current, separately process
the AC and DC components of the emulated signal to improve the
signal to noise ratio, use the same DC amplifier to process the DC
component (by multiplexing), and use a sample and hold circuit to
hold the DC amplified value throughout the clock cycle while the DC
amplifier is intermittently coupled to each phase.
[0021] FIG. 3 illustrates another embodiment of the invention where
a low value sense resistor is used in the inductor current path,
rather than only using the inductor's DCR, to drop a voltage. This
may provide more consistent current readings across all phases.
[0022] Elements that are the same or equivalent are labeled with
the same numeral.
DETAILED DESCRIPTION
[0023] FIG. 2 illustrates a first embodiment of the invention,
which is a multiphase switching power supply. Although only two
phases are shown for simplicity, any number of phases may be used,
depending on the required power and desired ripple. The operation
of the conventional portion of the power supply will first be
described. Many other types of power supplies may be used instead,
and the invention is primarily related to the current sensing
portion that generates separate AC and DC sense signals and the
sharing of the DC sense amplifier by all the phases.
[0024] A clock (Clk) signal is applied to the set input of an RS
flip flop 20. Each phase has its own clock signal, and the phases
are equally divided over a single clock cycle. In the example of
two phases, there is a half cycle difference between the phases.
Generating phased clock signals is well known. The clock frequency
will typically be between tens of kHz to a couple of MHz. Other
types of multiphase current mode converters are not necessarily
switched at a constant frequency, but inductor current detection is
still required for controlling the switch.
[0025] The setting of the RS flip flop 20 generates a high signal
at its Q output. A logic circuit 24, in response, turns transistor
switch 26 on and turns the synchronous rectifier switch 28 off.
Both switches may be MOSFETs or other transistors. A diode may
replace the synchronous rectifier switch 28. The logic circuit 24
ensures that there is no cross-conduction of switches 26 and 28.
The input voltage Vin applied to an inductor L1 through the switch
26 causes a ramping current to flow through the inductor L1. The
ramping current is filtered by an output capacitor 36 and supplies
current to a load connected to the output voltage Vo. The output
capacitor 36 is relatively large to smooth out ripple.
[0026] The output voltage Vo is applied to a voltage divider 42,
and the divided voltage is applied to the negative input of a
transconductance error amplifier 44. A reference voltage Vref is
applied to the positive input of the amplifier 44. The output
current of the amplifier 44 corresponds to the difference between
the actual output voltage Vo and the desired output voltage. The
voltage (a control voltage Vc) across a capacitor 46 at the output
of the amplifier 44 is adjusted up or down based on the positive or
negative current output of the amplifier 44. The control voltage Vc
at the capacitor 46, among other things, sets the duty cycle of the
switch 26, and the level of the control voltage Vc is that needed
to equalize the inputs into the amplifier 44. A resistor and
capacitor may be connected in parallel with the capacitor 46 for
controlling and optimizing the phase and loop stability, as is well
known.
[0027] FIG. 2 also illustrates a conventional slope compensation
circuit 48, as is well known for current mode power converters. A
sawtooth output of the slope compensation circuit 48 is subtracted
from the control voltage Vc by a subtractor 50. At high duty cycles
(typically greater than 50%), the effect of the slope compensation
circuit 48 is to reduce sub-harmonic oscillations that may occur in
the current loop at the high duty cycles. The slope compensation
circuit 48 is unrelated to the present invention. Slope
compensation is not needed for certain types of multiphase current
mode converters.
[0028] The compensated control voltage Vc is applied to one input
of a comparator 52.
[0029] As will be described in more detail later, an emulated
signal representing the instantaneous ramping inductor current is
applied to the other input of the comparator 52. When the ramping
signal crosses the compensated control voltage Vc, the RS flip flop
20 is reset, which turns off the switch 26 and turns on the switch
28 for discharging the inductor, until the start of the next clock
cycle. In this way, the peak current through the inductor L1 for
each cycle is regulated to generate a desired output voltage Vo.
Other types of suitable current mode converters do not regulate
peak current but still switch the transistor based on the detected
inductor current.
[0030] The other phase is identical to the phase just described and
uses its own comparator (not shown), RS flip flop, and logic to
independently switch its switches 56 and 58. All phases use the
same compensated control voltage Vc for setting the peak current
through their inductor. Ideally, each phase has the same duty cycle
and supplies one-half the total current to the load. Although each
phase is shown driving a separate output capacitor 36, they are the
same common capacitor 36.
[0031] The current through the inductor L1 includes a DC component
(the lower frequency, average current) and an AC component (the
higher frequency, ripple current).
[0032] In prior art designs, switching noise (e.g., high frequency
spikes and oscillations) in the inductor current, by the turning on
or off of the various switches, is a problem and, if high enough,
can cause false triggering of the comparator, resulting in jitter
and an increase of ripple on the output voltage Vo.
[0033] The present invention mitigates the problem with switching
noise and helps all phases to have identical characteristics so
that each phase will supply the same proportion of current to the
load. This avoids one phase from conducting more current, causing
it to get hotter than other phases, lower its efficiency, and limit
the maximum operation ambient temperature. Keeping the phases
identical also reduces output voltage ripple. The present invention
uses a multiplexed differential amplifier that is shared by all
phases, which reduces the size of the phased converter and causes
all phases to have more similar operating characteristics.
[0034] FIG. 2 illustrates the current sense circuit having
different RC circuits for an AC sense path and a DC sense path. The
resistance DCR1 represents the inductor winding DC resistance. An
inductor winding may have a DC resistance on the order of a few
mohms to less than 1 mohm. An RC network, comprising the series
connection of a resistor R3 and capacitor C3, Kelvin connected
across the inductor L1 is selected to have a time constant much
less than that of the inductor and DCR so that R3*C3<L1/DCR. The
AC ripple voltage is sensed across the capacitor C3 terminals. The
R3*C3 time constant may be any time constant below L1/DCR for
proper operation, since the gain of the DC path will be suitably
adjusted to avoid distortion. By lowering the time constant of
R3*C3, the AC ripple voltage magnitude across capacitor C3 can be
greatly increased as the current through the inductor L1 ramps up.
This increased voltage signal increases the signal to noise ratio
of the AC sense signal, making triggering of the comparator 52 more
accurately timed.
[0035] Since any switching noise contains frequencies much greater
than the switching frequency, much of the switching noise will be
filtered out by the capacitor C3, so the reduction of the time
constant of R3*C3 does not adversely impact the effect of switching
noise in the AC path.
[0036] A second RC network is formed by the series connection of
resistor R4 and capacitor C4 across the capacitor C3. Resistor R4
and capacitor C4 act as a low pass filter, to filter out the
switching noise and AC ripple, where the filtered signal across the
capacitor C4 is proportional to the DC component of the inductor
current. The voltage across capacitor C4 is the average voltage
across the capacitor C3.
[0037] The voltage across the sense terminals SNSP1 and
SNS.sub.AVG1 represents the DC component V.sub.DC1 of the inductor
current, and the voltage across the sense terminals SNSP1 and SNSN1
represents the AC ripple voltage V.sub.AC1 of the inductor
current.
[0038] The AC ripple voltage is buffered by a unity gain buffer 60
for each phase, and the output of the buffer 60 is applied to a
summer 62 for each phase.
[0039] The DC component of the inductor current is relatively
constant during steady state operation, so its instantaneous value
during a switching cycle is not important. Therefore, the DC
component for a phase can be amplified by a shared differential
amplifier 66 and sampled by a sample and hold circuit 68 only once
per cycle at a time after switching noise has subsided. The amount
of amplification is set to cause the DC sense signal to have the
proper proportion to the AC sense signal for no distortion. The
required amplification gain K can be determined by simulation.
[0040] The summer 62 adds the AC and DC sense signals to generate a
signal that emulates the actual inductor current. The output of the
summer 62 will be (K+1)*V.sub.DCR1.
[0041] Since the same amplifier 66 is used by each phase, the DC
component for each phase is amplified by exactly the same gain.
This is accomplished by multiplexing the DC sense inputs from all
the phases so that they are applied in sequence to the amplifier
66. This also reduces the size of the controller by only requiring
one amplifier 66.
[0042] A first multiplexer 70 is controlled by the various clock
phases to sequentially connect each phase to the amplifier 66 for a
brief moment.
[0043] A second multiplexer 72 is controlled by the clock phases to
sample and hold the output of the amplifier 66 at a time shortly
after the first multiplexer 70 has connected the amplifier 66 to
the associated phase to eliminate any switching noise. A hold
capacitor 74 for each phase holds the amplified DC sense signal for
the remainder of the clock cycle for that phase. The sampled and
held signals are applied to the phase's associated summer 62 for
virtually the entire clock cycle for that phase so that the output
of the summer 62 for that phase accurately represents the inductor
current over the clock cycle.
[0044] The emulated inductor current signals for the various phases
are then applied to the associated comparators 52 for the phases
and compared to the common compensated control voltage Vc to
determine when to turn of the power switch (e.g., switch 26 or 56)
for the associated phase.
[0045] As a result of the circuitry in FIG. 2, switching noise is
virtually eliminated from the feedback path, the phases are made
more similar due to the shared amplifier 66, and signal to noise
ratio is greatly increased. This results in more precise current
balancing, smaller duty cycler jittering, a lower cost control IC,
and a more accurate and constant output voltage Vo.
[0046] Further, the comparator 52 and the buffer 60 of each phase
both have inevitable offset as a result of fabrication variances.
The offsets of each phase are inevitably different in practice. The
mismatch offset contributes to the current imbalance between
phases. Now, with the inventive improvement, as the DC and AC sense
signals are both effectively amplified by K times, the imbalance
due to these mismatch offsets is reduced by a factor of 1/K.
[0047] If the controller IC used the prior art technique of N
different amplifiers for N phases, the inevitable mismatch between
these amplifiers' gains K would contribute to the current
imbalance. Now, with the inventive method, every phase uses the
same amplifier, so the gains K are exactly the same. This
contributing factor of current imbalance is eliminated.
[0048] The corner of the low pass filter, comprising the resistor
R4 and capacitor C4, is ideally designed so that the summed signal
is proportional to the voltage signal across the DCR1 at any
frequency without phase shift. Also, it is preferred that the
resistors R3 and R4 have values that cause the voltages across
these two resistors to be equal.
[0049] The circuit only has one Kelvin connection to the inductor,
simplifying implementation.
[0050] The other phase of the power supply is identical to the
first phase and includes resistors R1 and R2, capacitors C1 and C2,
inductor L2, and the AC and DC component processing circuitry. The
AC ripple voltage and DC sense voltage are applied to the terminals
SNSP2, SNSN2 and SNS.sub.AVG2. The DC sense voltage is labeled
V.sub.DC2. Any additional phases would also be identical.
[0051] FIG. 3 is similar to FIG. 2 but a low value sense resistor
Rsense is used to detect the DC component of the inductor current
rather than the average voltage across the capacitor C3. The
voltage drop across the resistor Rsense is filtered by the low pass
filter, comprising the resistor R4 and capacitor C4, and the
voltage across the capacitor C4 is the DC component of the inductor
current to be applied to the amplifier 66. The RC time constant of
resistor R3 and capacitor C3 is lower than the L1/(DCR1+Rsense)
time constant. The remainder of the circuitry and operation is the
same as in FIG. 2.
[0052] The current sensing and shared DC sense signal amplifier can
be applied to any type of multiphase current mode converter
including, buck, boost, buck-boost, valley current control,
constant on-time control, constant off-time control, etc.
[0053] Some multiphase converters do not use a common phased clock
to set the switching transistor, but use frequency modulation,
where the switching frequency for all the phases is independent and
controlled to cause the converter to output the regulated voltage.
Such types of converters are still referred to as multiphase
converters since the switches do not all switch at the same
time.
[0054] All aspects of the converters may be conventional except for
the current sensing and shared amplifier, enabling the invention to
be easily incorporated in existing multiphase converter
designs.
[0055] The various phases may use the same input voltage or
different input voltages, and the phases may drive the same load or
different loads. In all cases, the DC component of the inductor
current will change slowly, enabling an average DC component in
each phase to be sampled and used for the entire switching
cycle.
[0056] All phases may be controlled by the same controller IC
incorporating the present invention.
[0057] While particular embodiments of the present invention have
been shown and described, it will be obvious to those skilled in
the art that changes and modifications may be made without
departing from this invention in its broader aspects and,
therefore, the appended claims are to encompass within their scope
all such changes and modifications that are within the true spirit
and scope of this invention.
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