Buck-boost converter with small disturbance at mode transitions
The disclosure describes decreasing the overshoot and undershoots during the mode transitions of a Buck-Boost switching converter, without causing mode bounces. This is achieved by a main compensation capacitor of an error amplifier being charged or discharged, so that the output voltage level is shifted close to the target value. The expected behavior of the disclosure is contributed to two items, one is a mode transition detector, configured to detect mode transition among buck, buck-boost, boost, and ½f buck/boost modes, and the other is charge/discharge circuitry configured within one-clock cycle of a mode transition being detected.
1. A Buck-Boost switching power converter, comprising:
a mode transition detector, configured to monitor Buck and Boost pulse-width modulation (PWM) input signals, and to detect skipping or regeneration of said input signals;
an error amplifier;
a main compensation capacitor, at an output of said error amplifier; and charge and discharge circuitry, comprising a PMOS current source, and a NMOS current source, configured to charge or discharge said main compensation capacitor during a mode transition, based on detection of said mode transition by said mode transition detector,
wherein for a mode transition from Buck to ½frequency Buck, from Buck to Buck-Boost, from Buck-Boost to Boost, and from ½frequency Boost to Boost, said PMOS current source is configured to be on, and
wherein for a mode transition from Boost to ½frequency Boost, from Boost to Buck-Boost, from Buck-Boost to Buck, and from ½frequency Buck to Buck, said NMOS current source is configured to be on.
2. The Buck-Boost switching power converter of claim 1 , wherein said mode transition detector further comprises digital logic gates, configured to detect a mode transition between said PWM input signals.
3. The Buck-Boost switching power converter of claim 1 , further comprising a pulse signal generator connected between said mode transition detector and said charge and discharge circuitry.
4. The Buck-Boost switching power converter of claim 3 , wherein said pulse signal generator is configured to skip or regenerate said PWM input signals, during said mode transition.
5. The Buck-Boost switching power converter of claim 3 , wherein said pulse signal generator is configured to output a pulse having a signal width of one clock cycle.
6. The Buck-Boost switching power converter of claim 1 , wherein said main compensation capacitor is charged or discharged, such that said output of said error amplifier is shifted close to a target value.
7. The Buck-Boost switching power converter of claim 1 , wherein said error amplifier comprises an operational transconductance amplifier.
8. The Buck-Boost switching power converter of claim 7 , wherein said error amplifier is configured to receive inputs comprising a reference voltage and a feedback output voltage.
9. The Buck-Boost switching power converter of claim 8 , further comprising a feed-forward gain path connected across said error amplifier inputs and having a feed-forward capacitor at its output.
10. The Buck-Boost switching power converter of claim 9 , wherein a feed-forward resistor is connected across said main compensation capacitor and said feed-forward capacitor.
11. The Buck-Boost switching power converter of claim 10 , wherein said main compensation capacitor is charged or discharged, such that said output of said error amplifier is shifted close to a target value across said feed-forward resistor.
12. The Buck-Boost switching power converter of claim 1 , wherein said charge and discharge circuitry comprises control switches for said current sources.
13. The Buck-Boost switching power converter of claim 12 , wherein said charge and discharge circuitry is configured such that one of said control switches for said PMOS or NMOS current sources is turned on.
14. A method for operating a Buck-Boost switching converter comprising the steps of:
monitoring Buck and Boost pulse-width modulation (PWM) input signals to detect a mode transition, and skippinq or regenerating said input signals;
providing an error amplifier, and a main compensation capacitor at an output of said error amplifier; and
charging said main compensation capacitor with a PMOS current source for said mode transition from Buck to ½frequency Buck, from Buck to Buck-Boost, from Buck-Boost to Boost, and from ½frequency Boost to Boost or discharging said main compensation capacitor with a NMOS current source for said mode transition from Boost to ½frequency Boost, from Boost to Buck-Boost, from Buck-Boost to Buck, and from ½frequency Buck to Buck, based on detection of said mode transition.
15. The method of claim 14 , further comprising a pulse signal generator that skips or regenerates said PWM input signals, during said mode transition.
16. The method of claim 15 , wherein said pulse signal generator outputs a pulse having a signal width of one clock cycle.
17. The method of claim 14 , wherein said main compensation capacitor charges or discharges, such that said output of said error amplifier shifts close to a target value.
18. The method claim 14 , wherein said error amplifier receives inputs comprising a reference voltage and a feedback output voltage.
19. The method of claim 18 , further comprising a feed-forward gain path connected across said error amplifier inputs and a feed-forward capacitor.
20. The method of claim 19 , wherein a feed-forward resistor connects across said main compensation capacitor and said feed-forward capacitor.
21. The method of claim 20 , wherein said main compensation capacitor charges or discharges, such that said output of said error amplifier shifts close to a target value across said feed-forward resistor.