Current mode pulse frequency modulation switching regulator
View Patent ↗A method of providing current mode pulse frequency modulation (PFM) for a switching regulator can include resetting a driver input for a fixed duration when a first current in the driver reaches a first value set by an error amplifier output. The first current can be associated with PMOS switching transistors in the driver. The method can also include setting the driver input signal for the same fixed duration when a second current in the driver reaches a second value. This second current can be associated with NMOS switching transistors in the driver. In one embodiment, the driver can be tristated to ignore both the resetting and the setting. Using this method, perturbations of the inductor current can be substantially corrected and have limited impact on the current waveform beyond the cycle in which they occur.
1. A switching regulator comprising:
a driver circuit for receiving a pulse frequency modulation (PFM) signal and responding by turning on a set of first type switching transistors and turning off a set of second type switching transistors;
an error amplifier for receiving a first reference voltage and a voltage control loop signal on its input terminals as well as a voltage limit signal on a control terminal, the voltage limit signal setting a maximum output voltage of the error amplifier, the voltage limit signal being a first current control loop signal generated by the driver circuit;
a PFM comparator for receiving an output of the error amplifier and a second current control loop signal generated by the driver circuit;
a timer circuit for receiving a reset signal generated by the PFM comparator and other current control loop signals generated by the driver circuit, the timer circuit generating the PFM signal based on a steady state mode and at least one of a positive over-current condition and a negative over-current condition; and
an LC filter for receiving an output of the driver circuit and generating the voltage control loop signal.
2. The switching regulator of claim 1 , wherein the error amplifier and the PFM comparator determine the positive over-current condition.
3. The switching regulator of claim 2 , wherein the timer circuit includes:
a first timer for receiving the reset signal;
a negative current limit comparator for receiving the other current control loop signals, which are used to determine the negative over-current condition;
a second timer for receiving a set signal generated by the negative current limit comparator; and
a set of logic gates for receiving outputs of the first and second timers and generating the PFM signal.
4. The switching regulator of claim 3 , wherein the first and second timers generate one-shot signals when triggered.
5. A method of providing current mode pulse frequency modulation for a switching regulator, the method comprising:
resetting a driver input signal for a fixed duration when a first current in a driver reaches a first value set by one of:
an error amplifier output; and
at least one of a positive over-current condition and a negative over-current condition,
the first current being associated with a set of first type switching transistors in the driver,
wherein resetting the driver input includes comparing the error amplifier output with a first-type current signal associated with the set of first type switching transistors in the driver, a maximum value of the error amplifier output being set by a voltage limit signal, the voltage limit signal being a first current control loop signal generated by the driver.
6. The method of claim 5 , further including setting the driver input signal for the fixed duration when a second current in the driver reaches a second value, the second current being associated with a set of second type switching transistors in the driver.
7. The method of claim 6 , wherein the driver generates the second value.
8. The method of claim 6 , further including tristating the driver to ignore both resetting and setting.
9. A switching regulator comprising:
a driver circuit for receiving a pulse frequency modulation (PFM) signal and responding by turning on a set of first type switching transistors and turning off a set of second type switching transistors;
an error amplifier for receiving a first reference voltage and a voltage control loop signal on its input terminals as well as a voltage limit signal on a control terminal, the voltage limit signal setting a maximum output voltage of the error amplifier, the voltage limit signal being a first current control loop signal generated by the driver circuit;
a PFM comparator for receiving an output of the error amplifier and a second current control loop signal generated by the driver circuit;
a timer circuit for receiving a reset signal generated by the PFM comparator and other current control loop signals generated by the driver circuit; and
an LC filter for receiving an output of the driver circuit and generating the voltage control loop signal, wherein a measured voltage drop associated with the set of first type switching transistors when turned on provides current sensing of an inductor of the LC filter.
10. The switching regulator of claim 9 , wherein the driver circuit includes a replica device formed with substantially the same semiconductor process as and having a scaled area compared to the set of first type switching transistors, and wherein the measured voltage drop associated with the set of first type switching transistors when turned on is a voltage drop across the replica device when conducting.