Lossless current sensing in buck converters working with low duty cycles and high clock frequencies
First Claim
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1. A valley current control buck converter for stepping down an input voltage to a lower output voltage, said buck converter comprising:
- a high-side switch and a low-side switch coupled in series between an input voltage and ground;
a current-sense amplifier coupled across said low-side switch and configured to measure a voltage drop across said low-side switch; and
a comparator coupled to said current-sense amplifier and configured to compare said voltage drop across said low-side switch to an error voltage,wherein said comparator switches from a discharging phase to a charging phase when said voltage drop across said low-side switch becomes less than said error voltage.
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Abstract
A buck converter having a synchronous rectifier topology that performs current sensing at the low-side switch and employs "valley current control" to terminate a discharging phase and commence a charging phase of the converter. The buck converter is able to withstand high operating frequencies and low duty cycles to produce a low output voltage from a given high input voltage.
131 Citations
28 Claims
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1. A valley current control buck converter for stepping down an input voltage to a lower output voltage, said buck converter comprising:
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a high-side switch and a low-side switch coupled in series between an input voltage and ground; a current-sense amplifier coupled across said low-side switch and configured to measure a voltage drop across said low-side switch; and a comparator coupled to said current-sense amplifier and configured to compare said voltage drop across said low-side switch to an error voltage, wherein said comparator switches from a discharging phase to a charging phase when said voltage drop across said low-side switch becomes less than said error voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A buck converter, comprising:
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a high-side switch having a first end coupled to an input voltage; a low-side switch having a first end coupled to a second end of said high-side switch and a second end coupled to ground; an inductor having a first end coupled to said second end of said high-side switch and a second end defining an output of said converter; a filter capacitor having a first end coupled to said output of said converter and a second end coupled to ground; a current-sense amplifier having an inverting input coupled to said second end of said high-side switch and a noninverting input coupled to said second end of said low-side switch; an error amplifier having an inverting input coupled to said output of said converter and a noninverting input coupled to a reference voltage; a comparator having an inverting input coupled to an output of said current-sense amplifier and a noninverting input coupled to an error voltage output of said error amplifier; and a flip-flop having a set input coupled to an output of said comparator, a reset input coupled to an external clock, an output coupled to a control input of said high-side switch and a complementary output coupled to a control input of said low-side switch. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A valley current control buck converter, wherein an inductor current of said buck converter is monitored by measuring a voltage drop across a low-side switch of said buck converter, and wherein said voltage drop is compared to an error voltage to cause said converter to switch from a discharging phase to a charging phase when said voltage drop becomes less than said error voltage.
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20. A method for converting an input voltage to a stepped-down lower voltage, comprising the steps of:
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closing a first switch, to initiate a discharging step through an inductor and an output load; comparing a signal across said first switch to an error signal during said discharging step, the signal being characteristic of the current through said inductor; and opening said first switch, when said signal characteristic of the current through said inductor becomes less than said error signal, and closing a second switch, to couple said input voltage to said inductor and output load to initiate a charging step. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28)
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Specification