Boost regulator incorporating peak inductor current modulation
View Patent ↗A boost switching regulator incorporates a peak inductor current modulation circuit to modulate the peak inductor current as a function of the load current, the input voltage, the regulated output voltage, and a fixed current value. In this manner, the switching frequency of the boost regulator can be maintained above a given value or within a given frequency range over a wide range of load conditions and also over input voltage variations and output voltage settings.
1. A control circuit in a boost switching regulator, the boost switching regulator being configured to receive an input voltage on a first terminal of an inductor and to generate a regulated output voltage on an output terminal for driving a load, the boost switching regulator comprising a main power switch coupled between a second terminal of the inductor and ground, a synchronous rectifier coupled between the second terminal of the inductor and the output terminal, and an output capacitor coupled to the output terminal and ground, the control circuit being configured to control the main power switch and the synchronous rectifier using a Pulse Frequency Modulation (PFM) feedback control loop, the regulated output voltage being fed back to the boost switching regulator as a feedback voltage on a feedback node of the feedback control loop, the control circuit comprising:
a peak inductor current modulation circuit configured to receive a first current indicative of a load current flowing to the load and to generate a peak inductor current set value as a function of at least the first current, the input voltage being received on the first terminal of the inductor, the regulated output voltage and a fixed current value, wherein the load current comprises an average of a synchronous rectifier current flowing in the synchronous rectifier coupled between the second terminal of the inductor and the output terminal;
a comparator comparing the peak inductor current set value to a second current indicative of an inductor current flowing in the main power switch, the comparator generating a comparator output signal; and
a PFM control circuit configured to receive the comparator output signal and to generate a first control signal for turning on the main power switch for a given duration, wherein the PFM control circuit adjusts the duration for turning on the main power switch in response to at least the comparator output signal.
2. The control circuit of claim 1 , wherein the peak inductor current modulation circuit generates the peak inductor current set value to maintain a switching frequency of the boost switching regulator above a given value or within a given range.
3. The control circuit of claim 1 , wherein the first current comprises a function of the load current.
4. The control circuit of claim 3 , wherein the first current comprises N times the load current where N is a constant.
5. The control circuit of claim 3 , wherein the load current comprises an average of a synchronous rectifier current.
6. The control circuit of claim 3 , wherein the first current is generated as an average of the synchronous rectifier current scaled by a first scaling factor.
7. The control circuit of claim 1 , wherein the peak inductor current modulation circuit generates the peak inductor current set value as a function of the load current, the difference between regulated output voltage and the input voltage, and the fixed current value, the fixed current value being indicative of the minimum peak inductor current set value.
8. The control circuit of claim 1 , further comprising:
a current sense amplifier coupled to sense a current flowing across the synchronous rectifier and to scale the sensed current by a first scaling factor; and
a current average circuit configured to receive the scaled sensed current and to generate an output current being an average of the scaled sensed current, the first current being indicative of the output current of the current average circuit.
9. The control circuit of claim 1 , wherein the synchronous rectifier comprises a PMOS transistor.
10. A method for controlling a boost switching regulator, the boost switching regulator being configured to receive an input voltage on a first terminal of an inductor and to generate a regulated output voltage on an output terminal for driving a load, the boost switching regulator comprising a main power switch coupled between a second terminal of the inductor and ground, a synchronous rectifier coupled between the second terminal of the inductor and the output terminal, and an output capacitor coupled to the output terminal and ground, the method being configured to control the main power switch and the synchronous rectifier using a Pulse Frequency Modulation (PFM) feedback control loop, the regulated output voltage being fed back to the boost switching regulator as a feedback voltage on a feedback node of the feedback control loop, the method comprising:
measuring a synchronous rectifier current flowing in the synchronous rectifier coupled between the second terminal of the inductor and the output terminal when the synchronous rectifier is turned on;
generating a first current indicative of the synchronous rectifier current flowing in the synchronous rectifier;
generating a second current being an average of the first current, the second current being indicative of at least a load current flowing to the load;
generating a peak inductor current set value as a function of the second current, the input voltage being received on the first terminal of the inductor, the regulated output voltage and a fixed current value;
comparing the peak inductor current set value to a third current indicative of an inductor current flowing in the main power switch and generating a comparator output signal;
generating a first control signal for turning on the main power switch for a given duration determined at least by the peak inductor current set value; and
adjusting the duration for turning on the main power switch in response to the comparator output signal.
11. The method of claim 10 , wherein generating a peak inductor current set value as a function of the second current, the input voltage, the regulated output voltage and a fixed current value comprises generating the peak inductor current set value to maintain a switching frequency of the boost switching regulator above a given value or within a given range.
12. The method of claim 10 , wherein generating the first current indicative of the synchronous rectifier current flowing in the synchronous rectifier comprises:
scaling the measured synchronous rectifier current flowing in the synchronous rectifier by a first scaling factor; and
providing the scaled synchronous rectifier current as the first current.
13. The method of claim 10 , wherein generating the first current indicative of the synchronous rectifier current flowing in the synchronous rectifier comprises generating the first current as a function of the load current.
14. The method of claim 10 , wherein generating the first current as a function of the load current comprises generating the first current as N times the load current where N is a constant.
15. The method of claim 10 , wherein generating a peak inductor current set value as a function of the second current, the input voltage, the regulated output voltage and a fixed current value comprises generating the peak inductor current set value as a function of the load current, the difference between regulated output voltage and the input voltage, and the fixed current value, the fixed current value being indicative of the minimum peak inductor current set value.