Charge measurement in a system using a pulse frequency modulated DC-DC converter

• US 10,270,272 B2
• Filed: 12/28/2016
• Issued: 04/23/2019
• Est. Priority Date: 12/28/2016
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Sonntag, Jeffrey L., Dupuis, Timothy J., Xiao, Jinwen
• Primary Examiner(s): Astacio-Oquendo, Giovanni
• Application Number:
  US15/392,487
• Publication Number:
  US 20180180699A1
• Time in Patent Office: 846 Days
• Field of Search: 324431, 324426, 324425
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3833 using analog integrators, e.g. coulomb-meters
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]

Abstract

The charge drawn from a battery during each switching event (pulse) of a pulse frequency modulated DC-DC converter is determined during a calibration period. based on differences in pulse rate with different current loading. Another approach calibration approach determines charge drawn from the battery by measuring voltage across a sense resistor while measuring the total pulse rate and while adding sufficient load current to ensure that the voltage is much larger than the residual offset of the measurement system. During operation, the system counts number of pulses are counted and the total charge drawn from the battery is determined based, at least in part, on the charge transferred per pulse during calibration, the operational mode, the battery voltage during calibration and operationally and the output voltage. Based on the total charge drawn and temperature (for temperature dependent battery types), the battery state of charge is estimated.

Claims

1. A method comprising:

providing a calibration current load on an output of a pulse frequency modulated (PFM) DC-DC converter during at least a part of a calibration operation;

determining, based on the calibration operation, a calibration charge drawn per pulse from a battery supplying an input voltage to a pulse frequency modulated (PFM) DC-DC converter;

determining an operational battery voltage;

during operation, counting a number of pulses corresponding to switching events that occur in the PFM DC-DC converter associated with the operational battery voltage; and

determining charge drawn from the battery during the number of pulses, based at least in part on, the operational battery voltage, the calibration charge drawn per pulse, and the number of pulses.

2. The method as recited in claim 1 further comprising determining battery state of charge based, at least in part, on the charge drawn from the battery during the number of pulses.

3. The method as recited in claim 2 further comprising:

sensing temperature and providing a sensed temperature; and

determining the battery state of charge, based at least in part, on the sensed temperature.

4. The method as recited in claim 1 further comprising determining the charge drawn from the battery during the number of pulses, based at least in part, on a current output voltage of the DC-DC converter and a calibration output voltage of the DC-DC converter determined during the calibration operation.

5. The method as recited in claim 1 further comprising determining the charge drawn from the battery during the number of pulses, based in part, on a current operating mode of the PFM DC-DC converter.

6. The method as recited in claim 5 further comprising:

performing the calibration operation in a first operating mode; and

determining the charge drawn from the battery during the number of pulses while operating in the current operating mode that is different than the first operating mode.

7. The method as recited in claim 1 further comprising storing a battery voltage value corresponding to a maximum battery voltage, a minimum battery voltage, and an average battery voltage.

8. The method as recited in claim 7 further comprising using the average battery voltage for determining the operational battery voltage.

9. The method as recited in claim 1 wherein determining the calibration charge drawn per pulse further comprises:

determining a first PFM frequency with a first current load on the output of the PFM DC-DC converter during the calibration operation;

determining a second PFM frequency with the calibration current load configured to provide a second current load on the output of the PFM DC-DC converter during the calibration operation, the second current load being higher than the first current load and the first PFM frequency being lower than the second PFM frequency; and

determining the calibration charge drawn per pulse based in part on the first PFM frequency and the second PFM frequency.

10. The method as recited in claim 1 wherein determining the calibration charge drawn per pulse further comprises:

enabling the calibration current load;

counting a calibration number of pulses in a measurement interval;

sensing a voltage across a resistor in series with the battery during the measurement interval; and

integrating the voltage across the resistor over the measurement interval and providing an integrated voltage; and

determining the calibration charge drawn per pulse from the battery, using the number of pulses, the integrated voltage, and a resistance value of the resistor.

11. An apparatus comprising:

a pulse frequency modulated (PFM) DC-DC converter;

logic to determine, based on a calibration operation, a calibration charge drawn per pulse from a battery supplying an input voltage to the PFM DC-DC converter;

a calibration current load controlled to be added to a system current load during at least a part of the calibration operation to provide an increased current load seen by the PFM DC-DC converter;

a counter to count a number of pulses corresponding to switching events that occur in the PFM DC-DC converter during operation associated with an operational battery voltage; and

wherein the logic is configured to determine charge drawn from the battery during the number of pulses, based at least in part on, the operational battery voltage, the calibration charge drawn per pulse, and the number of pulses.

12. The apparatus as recited in claim 11 wherein the apparatus is configured to determine battery state of charge based, at least in part, on the charge drawn from the battery during the number of pulses.

13. The apparatus as recited in claim 11 further comprising:

a temperature sensor to provide a sensed temperature; and

wherein the logic is further configured to determine state of charge of the battery, based at least in part, on the sensed temperature.

14. The apparatus as recited in claim 11 wherein the logic is further configured to determine the charge drawn from the battery during the number of pulses, based at least in part, on a current output voltage of the DC-DC converter and a calibration output voltage of the DC-DC converter determined during the calibration operation.

15. The apparatus as recited in claim 11 wherein the logic is configured to determine the charge drawn from the battery during the number of pulses, based in part, on a current operating mode of the PFM DC-DC converter.

16. The apparatus as recited in claim 15:

wherein the calibration operation is performed in a first operating mode; and

wherein the charge drawn from the battery during the number of pulses is determined while operating in the current operating mode, which is different than the first operating mode.

17. The apparatus as recited in claim 11 further comprising:

first storage to store a maximum battery voltage,

second storage to store a minimum battery voltage, and

a third storage to store an average battery voltage.

18. The apparatus as recited in claim 17 wherein the average battery voltage is used to determine the operational battery voltage.

19. The apparatus as recited in claim 11 further comprising:

a variable current load including a variable resistance set to a first resistance corresponding to a low current load to determine a first PFM frequency with the low current load and wherein the variable current load is set to a second resistance, lower than the first resistance, and corresponding to the increased current load provided by the calibration current load, to determine a second PFM frequency with the increased current load,

wherein the calibration charge drawn per pulse from the battery is determined based in part on the first PFM frequency and the second PFM frequency.

20. The apparatus as recited in claim 11 further comprising:

control logic to enable the increased current load;

a counter to count a calibration number of pulses in a measurement interval;

a resistor in series with the battery; and

an integrator to integrate a voltage across the resistor over the measurement interval and provide an integrated voltage; and

wherein the calibration charge drawn per pulse from the battery is determined using the number of pulses, the integrated voltage, and a resistance value of the resistor.