Method and apparatus for improved current mode control for large conversion ratio synchronous buck converter with lossless current sense
View Patent ↗Methods and apparatuses are provided for monitoring an inductor output current delivered to a load by a power converter. For example, there is provided an apparatus comprising: at least one power switch operatively coupled to an input voltage source; an output inductor operatively coupled to the at least one power switch and to the load; and a current sensor operatively coupled to the output inductor, the current sensor providing a current sense signal corresponding to the inductor output current delivered to the load. In one embodiment, the current sensor comprises: a filter comprising a first resistor coupled in series with a first capacitor; and a second capacitor coupled in parallel with the first resistor, the first and second capacitors forming an AC voltage divider to increase the signal-to-noise ratio of the current sense signal.
1. A DC-to-DC power converter with improved monitoring of output inductor current delivered to a load, comprising:
at least one power switch connected to an input voltage source;
an output inductor connected to the at least one power switch and to the load; and
a current sensor circuitry coupled to the output inductor, the current sensor circuitry providing a current sense signal corresponding to current passing through an internal DC resistance of the output inductor, the current sensor circuitry comprising:
a filter comprising a first resistor connected in series with a first capacitor; and
a second capacitor connected in parallel with the first resistor, the first and second capacitors forming an AC voltage divider;
wherein the second capacitor is characterized by a second capacitance value that is at least one order of magnitude smaller than a first capacitance value of the first capacitor, thereby increasing signal-to-noise ratio of the current sense signal for improved monitoring of the output inductor current delivered to the load.
2. The DC-to-DC power converter of claim 1 , further comprising at least one phase sensing switch connected to the input voltage source in parallel with the at least one power switch.
3. The DC-to-DC power converter of claim 2 , further comprising a pulse width modulation circuit for generating common control pulses for the at least one power switch and the at least one phase sensing switch responsive to a current sense signal.
4. The DC-to-DC power converter of claim 3 , wherein the at least one phase sensing switch and the pulse width modulation circuit are included in a common integrated circuit.
5. The DC-to-DC power converter of claim 2 , wherein:
the at least one power switch comprises a high-side power switch connected to the input voltage source and a low-side power switch connected to ground; and
the high-side power switch and the low-side power switch are connected together to define a power phase node therebetween, the output inductor being connected to the power phase node.
6. The DC-to-DC power converter of claim 5 , wherein:
the at least one phase sensing switch comprises a high-side phase sensing switch connected to the input voltage source and a low-side phase sensing switch connected to ground; and
the high-side phase sensing switch and the low-side phase sensing switch are connected together to define a signal phase node therebetween, the filter being connected to the signal phase node.
7. The DC-to-DC power converter of claim 6 , wherein the filter further comprises:
a first on-state resistance of the high-side power switch and the high-side phase sensing switch during a first conductive state of the high-side switches; and
a second on-state resistance of the low-side power switch and the low-side phase sensing switch during a second conductive state of the low-side switches.
8. The DC-to-DC power converter of claim 1 , wherein the at least one power switch comprises a MOSFET device.
9. An apparatus for monitoring an inductor output current delivered to a load, comprising:
at least one power switch operatively coupled to an input voltage source;
an output inductor operatively coupled to the at least one power switch and to the load; and
a current sensor operatively coupled to the output inductor, the current sensor providing a current sense signal corresponding to the inductor output current delivered to the load, the current sensor comprising:
a filter comprising a first resistor coupled in series with a first capacitor; and
a second capacitor coupled in parallel with the first resistor, the first and second capacitors forming an AC voltage divider;
wherein the second capacitor is characterized by a second capacitance value that is smaller than a first capacitance value of the first capacitor, thereby increasing signal-to-noise ratio of the current sense signal for improved monitoring of the output inductor current delivered to the load.
10. The apparatus of claim 9 , wherein the second capacitance value is at least one order of magnitude smaller than the first capacitance value.
11. The apparatus of claim 9 , further comprising at least one phase sensing switch connected to the input voltage source in parallel with the at least one power switch.
12. The apparatus of claim 11 , further comprising a pulse width modulation circuit for generating common control pulses for the at least one power switch and the at least one phase sensing switch responsive to a current sense signal.
13. The apparatus of claim 12 , wherein the at least one phase sensing switch and the pulse width modulation circuit are included in a common integrated circuit.
14. The apparatus of claim 11 , wherein:
the at least one power switch comprises a high-side power switch connected to the input voltage source and a low-side power switch connected to ground; and
the high-side power switch and the low-side power switch are connected together to define a power phase node therebetween, the output inductor being connected to the power phase node.
15. The apparatus of claim 14 , wherein:
the at least one phase sensing switch comprises a high-side phase sensing switch connected to the input voltage source and a low-side phase sensing switch connected to ground; and
the high-side phase sensing switch and the low-side phase sensing switch are connected together to define a signal phase node therebetween, the filter being connected to the signal phase node.
16. The apparatus of claim 15 , wherein the filter further comprises:
a first on-state resistance of the high-side power switch and the high-side phase sensing switch during a first conductive state of the high-side switches; and
a second on-state resistance of the low-side power switch and the low-side phase sensing switch during a second conductive state of the low-side switches.
17. The apparatus of claim 9 , wherein the at least one power switch comprises a MOSFET device.
18. A method for monitoring output current in a DC-to-DC power converter, the power converter comprising at least one power switch, an output inductor operatively coupled to the at least one power switch, and a current sensor operatively coupled to the output inductor, the method comprising:
(a) measuring the output current passing through the output inductor using the current sensor, the current sensor comprising:
a filter comprising a first resistor coupled in series and a first capacitor; and
a second capacitor coupled in parallel with the first resistor, the first and second capacitors forming an AC voltage divider, wherein the second capacitor is characterized by a second capacitance value that is at least one order of magnitude smaller than a first capacitance value of the first capacitor; and
(b) generating a current sense signal corresponding to the output current, wherein the AC voltage divider increases signal-to-noise ratio of the current sense signal for improved monitoring of the output current.
19. The method of claim 18 , further comprising operating a pulse width modulation circuit to control the at least one power switch in response to the current sense signal.
20. The method of claim 18 , wherein the step of generating a current sense signal comprises measuring a voltage differential across at least one of the first capacitor and the second capacitor.
21. The method of claim 18 , further comprising filtering noise from the current sense signal when the at least one power switch changes state.