Current sensing circuit for switching power converters
A current sensing circuit for a switched mode power converter employs a passive current sensing network coupled in parallel with the switched inductor. The passive current sensing network is impedance matched to the inductance its inherent resistance, and provides a current sensing node for single wire current sensing by a current sensing circuit. The passive current sensing network can be employed in each of a plurality of phased switching circuits that each contribute to an output of the power converter.
1. A current sensing circuit for a power converter, comprising:
a first current sense resistance and a second current sense resistance coupled in series at a current sense node to form a series current sense resistance;
the series current sense resistance coupled in parallel with an inductor having an inductance and an inherent resistance, and a first end connected to a switching network;
the first current sense resistance coupled to the first end of the inductor, and the second current sense resistance coupled to a second end of the inductor, wherein the first end of the inductor is coupled to a first end of a switching transistor, the switching transistor having a second end coupled to an input power source, the current sensing circuit further comprises:
a field effect transistor having a first end coupled to the current sense node; and
an amplifier circuit having a first input coupled to a second end of the field effect transistor and a second input coupled to an offset voltage reference;
wherein the switching transistor has a control terminal, and
the field effect transistor has a control terminal coupled to the control terminal of the switching transistor; and
a capacitance coupled in parallel with the first current sense resistance.
2. The current sensing circuit of claim 1 , wherein a current sense voltage is provided between the current sense node and the ground.
3. The current sensing circuit of claim 1 , wherein a current sense voltage is provided between the current sense node and a second end of the switching transistor.
4. The current sensing circuit of claim 1 , wherein the input power source is a ground.
5. The current sensing circuit of claim 1 , wherein the second end of the inductor is coupled to an output network.
6. The current sensing circuit of claim 1 , further comprising a leakage compensation resistance coupled between the current sense node and the ground.
7. The current sensing circuit of claim 1 , wherein the power converter is a multi-phase power converter, the current sensing circuit is duplicated for each phase of the multi-phase power converter.
8. A current sensing circuit for a switched mode power supply, comprising:
an inductor having an inductance and an inherent resistance and a first end connected to a switching transistor;
a passive current sensing network coupled in parallel with the inductor and forming a current sense node, wherein the passive current sensing network is impedance matched to the inductor, wherein the first end of the inductor is coupled to a first end of the switching transistor, the switching transistor having a second end coupled to a ground, the current sensing circuit further comprises:
a field effect transistor having a first end coupled to the current sense node; and
an amplifier circuit having a first input coupled to a second end of the field effect transistor and a second input coupled to an offset voltage reference;
wherein the switching transistor has a control terminal and
the field effect transistor has a control terminal coupled to the control terminal of the switching transistor; and
a current sense circuit that provides a current sense signal to a switching controller that drives the switching transistor, wherein the current sense signal is based on voltage produced at the current sense node relative to a reference to which the current sense circuit is connected.
9. The current sensing circuit of claim 8 , wherein the passive current sensing network comprises: a first current sense resistance and a second current sense resistance coupled in series at the current sense node to form a series current sense resistance; the series current sense resistance coupled in parallel with the inductor and a first end connected to the switching transistor; the first current sense resistance coupled to the first end of the inductor, and the second current sense resistance coupled to a second end of the inductor; and a capacitance coupled in parallel with the first current sense resistance.
10. The current sensing circuit of claim 9 , wherein the passive current sensing network is impedance matched by keeping a ratio of values of the inductance to the inherent resistance of the inductor equal to a product of values of a resistance ratio and the capacitance, where the resistance ratio is a ratio of the product of resistance values of the first and second current sense resistances to the sum of the resistance values of the first and second current sense resistances.
11. The current sensing circuit of claim 8 further comprising a leakage compensation resistance coupled between the current sense node and the ground.
12. The current sensing circuit of claim 8 , wherein a second end of the inductor is coupled to an output network.
13. The current sensing circuit of claim 8 , wherein a second end of the inductor is coupled to an input power source.
14. The current sensing circuit of claim 8 , wherein the switched mode power supply is a multi-phase switched mode power supply, and wherein the current sensing circuit is duplicated for each of a plurality of phases, where each phase contributes to an output of the switched mode power supply.
15. A multi-phase switched mode power supply, comprising:
a plurality of phased switching circuits which each contribute to an output of the multi-phase switched mode power supply;
each of the plurality of phased switching circuits having an inductor having an inductance value and an inherent resistance and a first end connected to a switching transistor, and a passive current sensing network coupled in parallel with the inductor and forming a current sense node, wherein the passive current sensing network is impedance matched to the inductor; wherein, for each of the respective plurality of phased switching circuits, the first end of the inductor is coupled to a first end of a switching transistor, the switching transistor having a second end coupled to a source of potential, the current sensing circuit further comprises:
a field effect transistor having a first end coupled to the current sense node; and
amplifier circuit having a first input coupled to a second end of the field effect transistor and a second input coupled to an offset voltage reference;
wherein the switching transistor has a control terminal, the field effect transistor has a control terminal coupled to the control terminal of the switching transistor; and
a current sense circuit that provides a respective current sense signal for each of the plurality of phase circuits to a switching controller that drives the respective switching transistor for each of the plurality of phase circuits, wherein each respective current sense signal is based on a respective voltage produced at the respective current sense node of each of the plurality of phased switching circuits relative to a common reference to which the current sense circuit is connected.
16. The multi-phase switched mode power supply of claim 15 , wherein the passive current sensing network of each of the plurality of phased switching circuits is impedance matched by keeping a ratio of values of the inductance to the inherent resistance of the inductor equal to a product of values of a resistance ratio and the capacitance, where the resistance ratio is a ratio of the product of resistance values of the first and second current sense resistances to the sum of the resistance values of the first and second current sense resistances.