Method and apparatus for sensing inductor input/output current in a DC-DC converter circuit
A switching regulator circuit has a switching transistor actuated during a switching on phase of a duty cycle. The current flowing through an inductor of the switching regulator circuit is determined from sensing a transistor current flowing through the switching transistor during switching on phase and selectively charging a capacitor of a switched capacitor circuit dependent on a current sense signal during the switching on phase.
1. A switching regulator circuit, comprising:
a high side (HS) transistor coupled between a first node and a switching node;
a low side (LS) transistor coupled between the switching node and a second node;
driver circuitry for controlling actuation of the HS transistor and LS transistor in accordance with a duty cycle including a switching on phase and a switching off phase with a first dead time delimiting the switching off phase;
an inductor having a first terminal coupled to the switching node and a second terminal coupled to a third node, wherein a coil current flows through the inductor; and
a coil current detection circuit comprising:
a current sensing circuit configured to sense a transistor current flowing through only one of the HS transistor and LS transistor during the switching on phase and generate a current sense signal;
a first capacitor;
a first switch configured to selectively charge the first capacitor in response to the current sense signal only during the switching on phase.
2. The circuit of claim 1 , wherein the switching regulator circuit is a buck-type regulator circuit, wherein the first node is configured to receive an input voltage, the second node is configured to receive a reference voltage and the third node is an output voltage node, and wherein the coil current is output current from the buck-type regulator circuit.
3. The circuit of claim 1 , wherein the switching regulator circuit is a boost-type regulator circuit, wherein the first node is an output voltage node, the second node is configured to receive a reference voltage and the third node is configured to receive an input voltage, and wherein the coil current is input current to the boost-type regulator circuit.
4. The circuit of claim 1 , wherein the driver circuitry controls operation in continuous conduction mode (CCM), further comprising:
a low pass filter circuit; and
switching circuitry that passes a voltage at the first capacitor to an input of the low pass filter circuit.
5. The circuit of claim 1 , wherein the driver circuitry controls operation in discontinuous conduction mode (DCM) where the HS transistor and LS transistor are further controlled to switch off and provide a high impedance state at the switching node, the coil current detection circuit further comprising:
a filter circuit comprising a first resistor and a second capacitor;
a second switch configured to selectively pass a voltage at the first capacitor to an input of the filter circuit when the switching node is not in the high impedance state; and
a third switch configured to couple the input of the filter circuit to ground when the switching node is in the high impedance state.
6. The circuit of claim 5 , wherein the coil current detection circuit further comprises a buffer circuit connected between the first capacitor and the second switch.
7. The circuit of claim 1 , wherein said current sensing circuit comprises:
a differential amplifier having a first input, a second input and an output;
a first input transistor coupled between a first terminal of said one of the HS transistor and LS transistor and the first input of the differential amplifier;
a second input transistor coupled between a second terminal of said one of the HS transistor and LS transistor and the second input of the differential amplifier;
wherein said first and second input transistors are actuated during switching on phase for the duty cycle;
an output transistor coupled between the first input of the differential amplifier and a first intermediate node; and
a resistor coupled between the first intermediate node and the second node;
wherein said current sense signal is sourced by the output transistor.
8. The circuit of claim 1 , wherein said current sensing circuit comprises:
a differential amplifier having a first input, a second input and an output;
a first input transistor coupled between a first terminal of said one of the HS transistor and LS transistor and the first input of the differential amplifier;
a second input transistor coupled between a second terminal of said one of the HS transistor and LS transistor and the second input of the differential amplifier;
wherein said first and second input transistors are actuated during switching on phase for the duty cycle;
an output transistor coupled between the first input of the differential amplifier and a first intermediate node;
a current mirror having an input leg coupled to the first intermediate node and an output leg coupled to a second intermediate node; and
a resistor coupled between the second intermediate node and the second node;
wherein said current sense signal is sourced by the output leg of the current mirror.
9. A circuit for detecting a coil current flowing through an inductor of a switching regulator circuit having a switching transistor coupled to the inductor and driver circuitry for controlling actuation of the switching transistor in accordance with a duty cycle including a switching on phase and a switching off phase delimited by dead time, comprising:
a current sensing circuit configured to sense a transistor current flowing through the switching transistor during switching on phase of the duty cycle to generate a current sense signal indicative of the sensed transistor current; and
a switched capacitor circuit actuated in response to the switching on phase to charge a capacitor dependent on the current sense signal.
10. The circuit of claim 9 , wherein the switching regulator circuit is a buck-type regulator circuit, wherein the switching transistor is a high-side transistor, and wherein the coil current is output current from the buck-type regulator circuit.
11. The circuit of claim 9 , wherein the switching regulator circuit is a boost-type regulator circuit, wherein the switching transistor is a low-side transistor, and wherein the coil current is input current to the boost-type regulator circuit.
12. The circuit of claim 9 , wherein the driver circuitry controls operation in continuous conduction mode (CCM), further comprising:
a low pass filter circuit; and
switching circuitry that passes a voltage at the capacitor to an input of the low pass filter.
13. The circuit of claim 9 , wherein the driver circuitry controls operation in discontinuous conduction mode (DCM) where the HS transistor and LS transistor are further controlled to switch off and provide a high impedance state at the switching node, further comprising:
a low pass filter circuit;
a switch configured to selectively pass a voltage at the capacitor to an input of the low pass filter when the switching node is not in the high impedance state; and
a further switch configured to couple the input of the low pass filter to ground when the switching node is in the high impedance state.
14. The circuit of claim 13 , further comprising a buffer circuit connected between the switched capacitor circuit and the switch.
15. A method for detecting a coil current flowing through an inductor of a switching regulator circuit having a switching transistor coupled to the inductor and driver circuitry for controlling actuation of the switching transistor in accordance with a duty cycle including a switching on phase and a switching off phase delimited by dead time, comprising:
sensing a transistor current flowing through the switching transistor during switching on phase to generate a current sense signal indicative of the sensed transistor current; and
selectively charging a capacitor of a switched capacitor circuit dependent on the current sense signal during the switching on phase.
16. The method of claim 15 , wherein the switching regulator circuit is a buck-type regulator circuit, wherein the switching transistor is a high-side transistor, and wherein the coil current is output current from the buck-type regulator circuit.
17. The method of claim 15 , wherein the switching regulator circuit is a boost-type regulator circuit, wherein the switching transistor is a low-side transistor, and wherein the coil current is input current to the boost-type regulator circuit.
18. The method of claim 15 , wherein the driver circuitry controls operation in continuous conduction mode (CCM), further comprising:
passing a voltage at the capacitor to an input of a low pass filter.
19. The method of claim 15 , wherein the driver circuitry controls operation in discontinuous conduction mode (DCM) where the HS transistor and LS transistor are further controlled to switch off and provide a high impedance state at the switching node, further comprising:
selectively passing a voltage at the capacitor to an input of a low pass filter when the switching node is not in the high impedance state; and
coupling the input the low pass filter to ground when the switching node is in the high impedance state.