The present invention relates in general to integrated circuits, and more particularly, to a power delivery system having cascaded buck stages for use with microprocessors and other application specific integrated circuits (ASICs).
As shown in
Typically, VRM 12 operates at a very small duty cycle because of the use of a high input voltage Vin and a low output voltage Vo (duty cycle D=Vo/Vin). This results in a substantial power loss, due to significant switching losses at switch SW1, which is switched on for a short time, and large conduction losses at SW2, which is switched on for a very long time.
Microprocessors are continually being designed to operate at lower voltages, higher currents, and higher current slew rates. In order to meet the more stringent transient requirements without overly increasing output capacitance, the switching frequency of a Voltage Regulator Module (VRM) needs to be increased to the MHz range to reduce output inductance and increase control-loop bandwidth to achieve faster transient responses. The negative effect of increasing switching frequency, however, is reduced VRM efficiency (i.e., higher power losses) since switching losses are directly proportional to the switching frequency. Therefore, it has become a significant challenge to reduce the power loss of VRMs at increased switching frequencies.
The present invention provides a two-stage power delivery system that employs cascaded buck stages. For high input-to-output voltage ratios, each cascaded buck stage has a more suitable (i.e., larger) duty cycle that results in a much lower total power loss than in a single-stage buck. For applications requiring lower input-to-output voltage ratios, such as battery powered laptops, the cascaded buck arrangement of the present invention can be operated in a quasi-single-stage mode, wherein the first buck stage operates as an input filter.
In a first aspect, the present invention provides a power delivery system, comprising: a plurality of cascaded buck stages connected in series, wherein a last buck stage in the plurality of cascaded buck stages provides an output voltage Vo in response to an input voltage Vin applied to a first buck stage of the plurality of cascaded stages; and a duty cycle control for controlling a duty cycle of each buck stage to maintain the output voltage Vo, wherein the duty cycle control sets the duty cycle of the first buck stage of the plurality of cascaded buck stages to 1 if an input-to-output voltage ratio (Vin/Vo) is lower than a threshold input-to-output voltage ratio RT.
In a second aspect, the present invention provides a method for power delivery, comprising: connecting a plurality of cascaded buck stages in series, wherein a last buck stage in the plurality of cascaded buck stages provides an output voltage Vo in response to an input voltage Vin applied to a first buck stage of the plurality of cascaded stages; and controlling a duty cycle of each buck stage to maintain the output voltage Vo, wherein the duty cycle of the first buck stage of the plurality of cascaded buck stages is set to 1 if an input-to-output voltage ratio (Vin/Vo) is lower than a threshold input-to-output voltage ratio RT.
In a third aspect, the present invention provides a quasi-single-stage power delivery system, comprising: first and second cascaded buck stages connected in series, wherein the second buck stage provides an output voltage Vo in response to an input voltage Vin applied to the first buck stage; and a duty cycle control for controlling duty cycles of the first and second buck stages to maintain the output voltage Vo, wherein the duty cycle of the first buck stage is set to 1 if an input-to-output voltage ratio (Vin/Vo) is lower than a threshold input-to-output voltage ratio RT, and wherein the duty cycle of the first buck stage is set to a value less than 1 if the input-to-output voltage ratio (Vin/Vo) is higher than the threshold input-to-output voltage ratio RT.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
It should be noted that the drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.
As shown in
The opening and closing of the switches SW1, SW2, in the first and second buck stages 104, 106, is controlled by a duty cycle control 110. In particular, the duty cycle control 110 controls the switches SW1, SW2, in the first buck stage 104 via a first duty cycle signal D1, and controls the switches SW1, SW2, in the second buck stage 106 via a second duty cycle signal D2.
The first and second buck stages 104, 106, are operated at duty cycles D1 and D2, respectively, as shown in
In practice, both D1 and D2 can be varied to maintain output voltage regulation. Alternately, in some designs, either D1 or D2 can be held at a fixed value, while the other duty cycle D2 or D1 is varied to maintain output voltage regulation. Additionally, in other designs, D1 and D2 can be generated from a single source such that D1 is equal to D2. In such a case, D1=D2=(Vo/Vin)1/2. Compared to the duty cycle D of the single-stage buck (i.e., D=Vo/Vin) with the same input and output voltages, the switch duty cycle in the two-stage cascaded buck will always be larger, resulting in lower switching power losses.
A power loss comparison for the single-stage and two-stage cascaded buck power delivery systems 10, 100, of
At lower input-to-output voltage ratios (e.g., at input voltages lower than a threshold voltage VT of about 9V), it can be seen in
By setting the duty cycle D1 of the first buck stage 104 to 1 at low input-to-output voltage ratios, the switching losses due to the operation of the switches SW1, SW2, in the first buck stage 104 are eliminated. To this extent, the quasi-single-stage configuration of the present invention has a reduced power loss at low input-to-output voltage ratios.
A power loss comparison for the single-stage, two-stage cascaded buck, and quasi-single-stage power delivery systems 10, 100, 100′ of
As shown in
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. For example, in a multiple-stage cascaded buck configuration (i.e., having more than two stages), the first stage can be operated at a duty cycle D=1 to reduce power losses at lower input-to-output voltage ratios. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.
This application claims the benefit of U.S. provisional application Ser. No. 60/498,859 filed Aug. 29, 2003 which is incorporated herein in whole by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2004/051535 | 8/23/2004 | WO | 00 | 2/28/2006 |
Publishing Document | Publishing Date | Country | Kind |
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WO2005/022737 | 3/10/2005 | WO | A |
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5006782 | Pelly | Apr 1991 | A |
5886508 | Jutras | Mar 1999 | A |
6246592 | Balogh et al. | Jun 2001 | B1 |
6348781 | Midya et al. | Feb 2002 | B1 |
Number | Date | Country | |
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20070001653 A1 | Jan 2007 | US |
Number | Date | Country | |
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60498859 | Aug 2003 | US |