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US 8,803,495 B2Granted
Pre-bias control for switched mode power supplies
AssigneeTexas Instruments Incorporated
InventorsBaoson Nguyen, Rex M. Teggatz, Li Li
Life of this patent
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Abstract
An embodiment of the invention provides a method of reducing a drop in voltage on a pre-biased output of a DC-DC step-down switching converter. A high side switch is activated to conduct a first current to the pre-biased output. After the high side switch is activated, a low side switch is activated to draw a second current from the pre-biased output such that the magnitude of the first current is greater than the magnitude of the second current for at least a portion of a time period T1. After the time period T1 ends, the magnitudes of the first and second currents are changed to maintain a predetermined voltage on the pre-biased output.
Claims15
A method of reducing a drop in voltage on a pre-biased output of a DC-DC step-down switching converter comprising:
- applying a pre—bias voltage to the output of the DC—DC step—down converter before activating the converter;
- activating a HS switch, the HS switch conducting a first current to the pre-biased output;
- activating a LS switch after the HS switch is activated, the LS switch drawing a second current from the pre-biased output wherein the second current is smaller in magnitude than the first current for at least a portion of a time period T1,
- changing the magnitudes of the first and second currents to maintain the predetermined voltage on the pre-biased output of the DC-DC step-down switching converter after the time period T1, wherein the second current drawn through the LS switch is controlled by the clock signal, a variable voltage reference and the feedback signal from the pre-biased output of the DC-DC step-down switching converter;
- delaying activating the LS switch until after the feedback signal exceeds the variable voltage reference whereby droop in output voltage is reduced, wherein the first current conducted through the HS switch is controlled by a clock signal, a fixed voltage reference, and a feedback signal from the pre-biased output of the DC-DC step-down switching converter.
2 more elements
A DC-DC step-down switching converter comprising:
- a HS switch having a control node, an input connected to a first terminal of a current source and an output connected to a first terminal of an inductor,
- a second terminal of the inductor being connected to an output of the DC-DC step-down converter and a first terminal of a capacitor,
- a second terminal of the capacitor being grounded;
- wherein a DC voltage is connectable to a second terminal of the current source;
- wherein a cathode of a diode is connected to the first terminal of the inductor and an anode of the diode is connected to ground;
- wherein the HS switch conducts a first current to the output, the first current being controlled by a first signal on the control node of the HS switch;
- a LS switch having a control node, an input connected to the first terminal of a variable current source and an output connected to the first terminal of the inductor, wherein the LS switch conducts a second current from the output after the HS switch stops conducting the first current;
- wherein the second current is controlled by a second signal on the control node of the LS switch by a soft start circuit for allowing the DC—DC converter to start up with a pre—bias voltage applied to the output, activation of the low side switch being delayed until a feedback signal from an output voltage of the converter exceeds a voltage of the soft start circuit whereby droop in the output voltage is reduced, and
- wherein a magnitude of the first current is larger than a magnitude of the second current for at least a portion of the time period T1;
- wherein the magnitudes of the first and second currents are changed to maintain a predetermined voltage on the pre-biased output of the DC-DC step-down switching converter after the time period T1;
- wherein the first current conducted through the HS switch is controlled by a clock signal, a fixed voltage reference, and a feedback signal from the pre-biased output of the DC-DC step-down switching converter.
8 more elements
In a DC-DC step-down switching converter, a start up circuit comprising:
- a first control circuit for a HS switch wherein the HS switch conducts a first current to an output couplable to a source of pre-bias voltage;
- a second control circuit for a LS switch wherein the LS switch conducts a second current from the output for a period T1 after the HS switch begins conducting the first current;
- a soft start circuit coupled to the second control circuit for controlling the LS switch for delaying activation of the LS switch until a feedback signal exceeds a variable voltage reference whereby droop in an output voltage is reduced;
- wherein the magnitudes of the first and second currents are changed to maintain a predetermined voltage on the pre-biased output of the DC-DC step-down switching converter after the time period T1;
- wherein the first current conducted through the HS switch is controlled by a clock signal, a fixed voltage reference, and a feedback signal from the pre-biased output;
- wherein the second current conducted through the LS switch is controlled by the clock signal, a variable voltage reference and the feedback signal from the pre-biased output.
3 more elements
Dependencies are inferred from the claim text.