Advanced fuel gauge

1. A method of operating a fuel gauge, comprising:

measuring, with a voltage analog-to-digital converter of the fuel gauge, a battery current through a battery;

measuring, with a current analog-to-digital converter of the fuel gauge, a battery voltage across the battery;

determining an equivalent resistance in an amplifier of the fuel gauge using a multiplier K and receiving resistance determined by the battery current and the battery voltage;

determining, in an engine of the fuel gauge, an open circuit voltage based, in part, on the equivalent resistance;

determining a state-of-charge in a table lookup of the fuel gauge based on the open circuit voltage; and

adjusting the multiplier K in an adaptive loop based on the battery current and the state-of-charge, wherein adjusting the multiplier K includes

integrating the battery current in an integrator of the adaptive loop to produce a charge Q;

dividing the charge Q with a full-charge value to produce an absolute state-of-charge in a divider of the adaptive loop;

producing an error value as a difference between the state-of-charge and the absolute state-of-charge in an error summer of the adaptive loop; and

producing a new multiplier K according to the error value and a loop gain in a loop amplifier of the adaptive loop,

wherein producing the new multiplier K comprises executing the following equation: K′=K−β*(error value), where K′ is the new multiplier K, K is the old multiplier K, β is the loop gain, and error_value is the error value.

2. The method of claim 1 , wherein determining the equivalent resistance includes

calculating a resistance from the measured current and the measured voltage in a divider of the fuel gauge; and

multiplying the resistance by the multiplier K in the amplifier of the fuel gauge.

3. The method of claim 1 , wherein determining the open circuit voltage includes

receiving the equivalent resistance into the engine;

receiving a difference between a prior open circuit voltage and the battery voltage from a summer of the fuel gauge;

receiving a capacitance from the table lookup based on the prior open circuit voltage; and

calculating, in the engine, the open circuit voltage from the equivalent resistance, the difference, and the capacitance.

4. The method of claim 3 , wherein the open circuit voltage OCV new is calculated from the following equation:

OCV

new

=

OCV

old

+

(

V

B

-

OCV

old

)

*

(

1

-

e

(

-

t

R

eq

*

C

)

)

where t is the time since calculation of the old open circuit voltage, OCV old .

5. The method of claim 1 , wherein determining a state of charge comprises looking up the state of charge in a look-up table based on battery characterization data and the open circuit voltage.

6. A fuel gauge, comprising:

a voltage analog-to-digital converter coupled to a battery and configured to provide a battery voltage;

a current analog-to-digital converter coupled to the battery and configured to provide a battery current;

a divider coupled to receive the battery voltage and the battery current and configured to produce a resistance;

a multiplier coupled to produce an equivalent resistance by multiplying the resistance by a multiplier value K;

an adaptive loop that produces the multiplier value K, wherein the adaptive loop includes

an integrator configured to integrate the battery current to produce a charge Q,

a divider coupled to receive the charge Q and to receive a full charge value, the divider configured to produce an absolute state-of-charge,

a summer coupled to receive a state-of-charge from the table lookup and the absolute state-of-charge and produce an error as the state-of-charge minus the absolute state-of-charge, and

an adaptive amplifier coupled to receive the error and produces the multiplier value K based on an old multiplier value K and the error,

wherein the multiplier value K is given by K′=K−β*(error) where β is a loop gain,

where error is the difference between the state-of-charge and an absolute state-of-charge;

a table lookup coupled to provide a capacitance based on an open-circuit voltage;

a summer that takes a difference between the battery voltage and the open-circuit voltage; and

an engine that produces a new open-circuit voltage based on the open-circuit voltage, the capacitance, and the difference.

7. The fuel gauge of claim 6 , wherein the table lookup receives data from a battery characterization which includes data relating open-circuit voltage, state-of-charge, and capacitance C for the battery.

8. A fuel gauge, comprising:

means for obtaining a battery voltage and a battery current from a battery;

means for producing an equivalent resistance based on the battery voltage, the battery current, and a multiplier K;

means for producing the multiplier K, wherein the means for producing the multiplier K includes

means for producing a charge from the battery current,

means for producing an absolute state-of-charge,

means for obtaining a state-of-charge based on the prior open-circuit voltage,

means for producing an error between the state-of-charge and the absolute state-of-charge, and

means for producing the multiple K from the error and a loop gain where the multiplier value K is given by K′=K−β*(error) where β is a loop gain;

means for producing a capacitance based on a prior open-circuit voltage; and

means for producing a new open-circuit voltage based on the prior open-circuit voltage, the battery voltage, the capacitance, and the equivalent resistance.