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.
35 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