Cycle-by-cycle peak current limiting in current mode buck/boost converters
An SMPS current mode control loop with an adjusted cycle-by-cycle peak current limit for buck and boost (and bidirectional buck/boost) regulators. An SMPS regulator can include a PWM driver to drive switching control signals with a PWM duty cycle to an output terminal OUT, and a PWM controller to control the PWM duty cycle based on a current mode control loop that includes slope compensation to provide a signal VPK corresponding to a current sense signal from a current sense terminal CS, based on sensed peak current through the energy storage element, superimposed with an injected slope compensation current corresponding to a predefined slope compensation based on PWM duty cycle. Adjusted peak limit circuitry generates a signal VLMT corresponding to an adjusted peak current limit based on a pre-defined peak current limit threshold for the energy storage element, including generating a peak limit adjustment current corresponding to the injected slope compensation current, and combining the peak limit adjustment current with the pre-defined peak current limit threshold so that VLMT is substantially constant.
1. A circuit for use in a switched mode power supply (SMPS) for generating a regulated output voltage, the SMPS including at least one power switching transistor, and an energy storage element, the circuit comprising:
a PWM driver to drive switching control signals with a PWM (pulse-width modulated) duty cycle to an output terminal (OUT);
PWM control circuitry to control the PWM duty cycle, including a current mode control loop that includes:
slope compensation circuitry to provide a signal (VPK) corresponding to
a current sense signal from a current sense terminal (CS), based on sensed peak current through the energy storage element, superimposed with
an injected slope compensation signal corresponding to a predefined slope compensation based on the PWM duty cycle; and
adjusted peak limit circuitry to generate a peak current limit signal (VLMT) corresponding to an adjusted peak current limit threshold based on a pre-defined peak current limit for the energy storage element, and including circuitry
to generate a peak current limit threshold adjustment signal corresponding to the injected slope compensation signal, and
to combine the peak current limit threshold adjustment signal with the pre-defined peak current limit threshold so that VLMT is substantially constant.
2. The circuit of claim 1 , wherein the SMPS is one of: a buck regulator, a boost regulator, a bi-directional regulator.
3. The circuit of claim 1 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is an injected slope compensation current;
the peak current limit threshold adjustment signal is a peak current limit threshold adjustment current based on the injected slope compensation current multiplied by the PWM duty cycle.
4. The circuit of claim 1 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on an output voltage for the SMPS.
5. The circuit of claim 1 , wherein the SMPS is a boost regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on a difference between an output voltage and an input voltage for the SMPS.
6. The circuit of claim 1 , wherein the SMPS is a bi-directional buck/boost regulator with high and low voltage rails, in which, for buck mode, the high voltage rail is an input rail, and the low voltage rail is an output rail, and for boost mode, the low voltage rail is the input rail and the high voltage rail is the output rail, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated for the high and low voltage rails using a high voltage VCCS driven by a difference between the high voltage rail and the low voltage rail, and a low voltage VCCS driven by the low voltage rail.
7. The circuit of claim 1 , wherein the PWM control circuitry further includes a voltage mode regulation.
8. The method of claim 1 , wherein controlling the PWM duty cycle is further based on a voltage mode regulation loop.
9. A circuit for use in a switched mode power supply (SMPS) for generating a regulated output voltage, including an energy storage element, the circuit comprising:
at least one power switching transistor, and
a PWM driver to drive switching control signals with a PWM (pulse-width modulated) duty cycle to the at least one power switching transistor;
PWM control circuitry to control the PWM duty cycle, including:
a voltage mode control loop; and
a current mode control loop that includes:
slope compensation circuitry to provide a signal (VPK) corresponding to
a current sense signal from a current sense terminal (CS), based on sensed peak current through the energy storage element, superimposed with
an injected slope compensation signal corresponding to a predefined slope compensation based on the PWM duty cycle; and
adjusted peak limit circuitry to generate a peak current limit signal (VLMT) corresponding to an adjusted peak current limit threshold based on a pre-defined peak current limit for the energy storage element, and including circuitry
to generate a peak current limit threshold adjustment signal corresponding to the injected slope compensation signal, and
to combine the peak current limit threshold adjustment signal with the pre-defined peak current limit threshold so that VLMT is substantially constant.
10. The circuit of claim 9 , wherein the SMPS is one of: a buck regulator, a boost regulator, a bi-directional regulator.
11. The circuit of claim 9 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is an injected slope compensation current;
the peak current limit threshold adjustment signal is a peak current limit threshold adjustment current based on the injected slope compensation current multiplied by the PWM duty cycle.
12. The circuit of claim 9 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on an output voltage for the SMPS.
13. The circuit of claim 9 , wherein the SMPS is a boost regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on a difference between an output voltage and an input voltage for the SMPS.
14. The circuit of claim 9 , wherein the SMPS is a bi-directional buck/boost regulator with high and low voltage rails, in which, for buck mode, the high voltage rail is an input rail, and the low voltage rail is an output rail, and for boost mode, the low voltage rail is the input rail and the high voltage rail is the output rail, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated for the high and low voltage rails using a high voltage VCCS driven by a difference between the high voltage rail and the low voltage rail, and a low voltage VCCS driven by the low voltage rail.
15. A method for controlling a switched mode power supply (SMPS) that generates a regulated output voltage, the SMPS including at least one power switching transistor, and an energy storage element, the method comprising:
driving switching control signals with a PWM (pulse-width modulated) duty cycle to the at least one power switching transistor;
controlling the PWM duty cycle based on a current mode control loop that includes:
providing slope compensation based on a signal (VPK) corresponding to
a current sense signal based on sensed peak current through the energy storage element, superimposed with
an injected slope compensation signal corresponding to a predefined slope compensation based on the PWM duty cycle; and
providing a peak current limit signal (VLMT) corresponding to an adjusted peak current limit threshold based on a pre-defined peak current limit for the energy storage element, including
generating a peak current limit threshold adjustment signal corresponding to the injected slope compensation signal, and
combining the peak current limit threshold adjustment signal with the pre-defined peak current limit threshold so that VLMT is substantially constant.
16. The method of claim 15 , wherein the SMPS is one of: a buck regulator, a boost regulator, a bi-directional regulator.
17. The method of claim 15 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is an injected slope compensation current;
the peak current limit threshold adjustment signal is a peak current limit threshold adjustment current based on the injected slope compensation current multiplied by the PWM duty cycle.
18. The method of claim 15 , wherein the SMPS is a buck regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on an output voltage for the SMPS.
19. The method of claim 15 , wherein the SMPS is a boost regulator, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated by a VCCS with a substantially identical pre-defined conductance; and
the peak current limit threshold adjustment signal is based on a difference between an output voltage and an input voltage for the SMPS.
20. The method of claim 15 , wherein the SMPS is a bi-directional buck/boost regulator with high and low voltage rails, in which, for buck mode, the high voltage rail is an input rail, and the low voltage rail is an output rail, and for boost mode, the low voltage rail is the input rail and the high voltage rail is the output rail, and wherein:
the injected slope compensation signal is generated by a voltage controlled current source (VCCS) with a pre-defined conductance;
the peak current limit threshold adjustment signal is generated for the high and low voltage rails using a high voltage VCCS driven by a difference between the high voltage rail and the low voltage rail, and a low voltage VCCS driven by the low voltage rail.