Circuit and method for suppressing audio noise in DC-DC converters
First Claim
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1. An audio noise suppression circuit, in a DC-DC switching converter, comprising:
- a first order gm amplifier, configured to sink excessive current from an output of the converter, and to receive a programmable voltage threshold on its inverting input and a switching converter output feedback voltage on its non-inverting input;
a low side device, connected between a node voltage and ground;
a low side scaled device, connected between the node voltage and ground; and
hysteretic Burst control logic, configured to generate bursts of on pulses to drive the low side device in a pulse-frequency mode (PFM),and dummy pulses to drive a gate of the low side scaled device, for controlling the low side scaled device at a minimum switching frequency.
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Abstract
A solution is provided for suppressing audio noise in a DC-DC switching converter. A means for limiting the minimum switching frequency of a pulse-frequency modulation (PFM) control is described. A first order gm amplifier dissipates the excess energy added to the inductor, when magnetizing at faster rate than the native PFM. A higher resistance, low-side scaled switch helps reduce wasted energy losses. The low-side scaled switch reduces the rise in the inductor current during magnetization, and hence keeps efficiency up at low loads, when the PFM minimum switching frequency is active.
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Citations
27 Claims
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1. An audio noise suppression circuit, in a DC-DC switching converter, comprising:
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a first order gm amplifier, configured to sink excessive current from an output of the converter, and to receive a programmable voltage threshold on its inverting input and a switching converter output feedback voltage on its non-inverting input; a low side device, connected between a node voltage and ground; a low side scaled device, connected between the node voltage and ground; and hysteretic Burst control logic, configured to generate bursts of on pulses to drive the low side device in a pulse-frequency mode (PFM), and dummy pulses to drive a gate of the low side scaled device, for controlling the low side scaled device at a minimum switching frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method for suppressing audio noise, in a DC-DC switching converter, comprising:
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detecting when said DC-DC switching converter is not switching, within a defined time-window; utilizing dummy pulses to insure a minimum switching frequency higher than a predefined value, wherein said dummy pulses drive a gate of a scaled pass device; and dissipating excess energy, added as a result of said dummy pulses, through a first order gm amplifier. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification