DC-DC converter with digital current sensing
A regulated DC-DC switching converter includes a bypass mode in which ends of an output inductor are coupled together. Circuitry determines output capacitor current and load current components of output inductor current during operation of the switching converter, for use in controlling switching operations.
1. A method of determining output inductor current for a DC-DC switching regulator including a bypass switch coupling ends of the output inductor and an output capacitor, the output inductor having one end coupled to a node between a high side switch and a low side switch coupled in series and another end coupled to the output capacitor, comprising:
digitizing a first voltage of a node between the output inductor and the output capacitor at a first time to obtain a first digital output capacitor voltage;
storing an indication of the first digital output capacitor voltage;
digitizing a second voltage of the node between the output inductor and the output capacitor at a second time to obtain a second digital output capacitor voltage;
determining a first value indicative of output capacitor current based on the indication of the first digital output capacitor voltage and the second digital output capacitor voltage;
digitizing a third voltage of the node between the output inductor and the output capacitor at a third time to obtain a third digital output capacitor voltage;
storing an indication of the third digital output capacitor voltage;
digitizing a fourth voltage of the node between the output inductor and the output capacitor at a fourth time to obtain a fourth digital output capacitor voltage;
determining a second value indicative of output capacitor current based on the indication of the third digital output capacitor voltage and the fourth digital output capacitor voltage; and
determining an indication of output inductor current based on the first value indicative of output capacitor current and the second value indicative of output capacitor current to obtain an indication of output inductor current;
wherein the bypass switch is open at the first time and the second time and the bypass switch is closed at the third time and the fourth time.
2. The method of claim 1 , wherein a difference between the first time and the second time is equal to a difference between the third time and the fourth time.
3. The method of claim 1 , wherein the indication of the first digital output capacitor current and the indication of the second digital output capacitor current are stored as digital values in a memory.
4. The method of claim 1 , further comprising determining if the bypass switch has been closed within a first predetermined period of time, and closing the bypass switch for a second predetermined period of time if the bypass switch has not been closed within the first predetermined period of time.
5. The method of claim 1 , wherein digitization of the first, second, third, and fourth voltages of the node between the output indicator and the output capacitor are performed using an analog to digital converter.
6. The method of claim 1 , wherein the indication of output inductor current is determined by summing the first value indicative of output capacitor current and the second value indicative of output capacitor current.
7. The method of claim 6 , wherein the summing the first value indicative of output capacitor current and the second value indicative of output capacitor current is performed by adder circuitry.
8. The method of claim 5 , wherein the analog to digital converter provides greater than eight bits of meaningful output across a range within two percent of expected voltages of the node between the output inductor and the output capacitor during voltage regulation of power.
9. The method of claim 5 , wherein the analog to digital converter comprises at least ten comparators.