Comparator for synchronous rectification and method of operation
AssigneeFreescale Semiconductor, Inc.
InventorMichael T. Berens
Life of this patent
Estimating the term…
Abstract
A buck converter includes a comparator having first and second gain stages that operate in compare and auto-zero modes. The comparator measures voltage drop across an N-channel transistor to determine when current through an inductor reaches zero. When the inductor current reaches zero, the N-channel transistor becomes inactive to prevent a reduction in efficiency caused by allowing negative inductor current to draw current from a load. The comparator is then placed in a low power state. When the comparator is not in a compare mode, the comparator can operate in an auto-zero mode to cancel offset when measuring the input of the comparator.
Claims20
A buck converter, comprising:
- a comparator having:
- a first and second diode connected P-channel transistors, a source of the first and second P-channel transistors coupled to an output voltage of the converter, a drain of the first and second P-channel transistors coupled to a respective control gate of the first and second P-channel transistors;
- a switch connected between the drain and the control gate of the second P-channel transistor and operated by a complementary P-gate signal;,
- a first N-channel transistor having a drain coupled to the drain of the first P-channel transistor and a source coupled to a drain of a second N-channel transistor and a drain of a third N-channel transistor;
- the second N-channel transistor includes a control gate coupled to the complementary P-gate signal, and a source coupled to ground;
- the third N-channel transistor includes a control gate coupled to an N-gate signal, and a source coupled to a coil voltage;
- a fourth N-channel transistor having a drain coupled to the drain of the second P-channel transistor and a source coupled to a drain of a fifth N-channel transistor and a drain of a sixth N-channel transistor;
- the fifth N-channel transistor includes a control gate coupled to the N-gate signal, and a source coupled to ground;
- and
- the sixth N-channel transistor includes a control gate coupled to the complementary P-gate signal, and a source coupled to ground.
A DC-DC buck converter comprising:
- an inductor having a first terminal coupled to a coil voltage;
- a capacitor having a first terminal coupled to a second terminal of the inductor and a second terminal coupled to ground;
- a comparator having a first input coupled to the coil voltage and a second input coupled to ground, the comparator including:
- a first diode-connected P-channel transistor;
- a second diode-connected P-channel transistor having a switch coupled between a drain and a control gate;
- a capacitor having a first terminal coupled to a control gate of the first diode-connected P-channel transistor and a second terminal coupled to the control gate of the second diode-connected P-channel transistor;
- a first N-channel transistor having a drain coupled to a drain of the first diode-connected P-channel transistor;
- a second N-channel transistor having a drain coupled to a source of the first N-channel transistor, a control gate coupled to a complementary P-gate signal and a source coupled to ground;
- a third N-channel transistor having a control gate coupled to an N-gate signal, a drain coupled to the source of the first N-channel transistor and a source coupled to the coil voltage;
- a fourth N-channel transistor having a drain coupled to the source of the second diode-connected P-channel transistor and a control gate coupled to a control gate of the first N-channel transistor and a current source;
- a fifth N-channel transistor having a control gate coupled to the N-gate signal, a drain coupled to a source of the fourth N-channel transistor and a source coupled to ground;
- a sixth N-channel transistor having a drain coupled to the source of the fourth N-channel transistor, a control gate coupled to a complementary P-gate signal and a source coupled to ground.
Dependencies are inferred from the claim text.