System and method for measuring battery current

A medical device, comprising:

• a battery;
• a pulse generator, wherein the pulse generator draws a pulse generator current from the battery;
• an electrode system in electrical communication with the pulse generator, wherein the electrode system applies electrical therapy to a patient;
• and
• a current measuring device for determining the pulse generator current, the current measurement device including:
• an oscillator for producing an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• a counter for providing an oscillator count from which the pulse generator current is determined;
• and
• a current source for providing an oscillator input current to the oscillator that is dependent on the pulse generator current, wherein the current source includes a current divider for dividing current drawn from the battery into both the pulse generator current and an attenuated current.

A device for determining a pulse generator current drawn from a battery of an implantable medical device, comprising:

• a current source that provides an input current that is dependent on the pulse generator current, wherein the current source is adapted for providing the input current while being calibrated;
• an oscillator for receiving the input current and producing an oscillating output, wherein the oscillating output has a frequency of oscillation dependent on the pulse generator current;
• and
• a counter for providing an oscillation count for the oscillating output, wherein the pulse generator current is determined from the oscillation count.

A medical device, comprising:

• a battery;
• a pulse generator, wherein the pulse generator draws a pulse generator current from the battery;
• an electrode system in electrical communication with the pulse generator, wherein the electrode system applies electrical therapy to a patient;
• and
• a current measuring device for determining the pulse generator current, the current measurement device including:
• an oscillator for producing an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• a counter for providing an oscillator count from which the pulse generator current is determined;
• and
• a first and second current source for providing an oscillator input current to the oscillator that is dependent on the pulse generator current, wherein each current source includes a current divider for dividing current drawn from the battery into both the pulse generator current and an attenuated current, wherein the current divider includes:
• a sense resistor through which the pulse generator current flows;
• an attenuation resistor through which the attenuated current flows;
• and
• an operational amplifier for providing substantially equal voltage drops across the sense resistor and across the attenuation resistor, wherein:
• the operational amplifier further provides negative feedback;
• and
• each operational amplifier has a feature for autozeroing an offset voltage such that the current measuring device continuously measures current as one current source is autozeroed while the other current source continues to operate.

A method for determining current drain for a battery-operated medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time,
• wherein providing an oscillating output with a frequency of oscillation that is dependent on a pulse generator current comprises:
• charging a capacitor;
• comparing a voltage formed across the capacitor with a reference voltage;
• and
• discharging the capacitor when the voltage across the capacitor increases to a level equal to the reference voltage.

A method for determining current drain for a battery-operated medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time,
• wherein providing an oscillator input current to the oscillator that is dependent on the pulse generator current comprises:
• dividing current drawn from a battery into the pulse generator current and into an attenuated current that is dependent on the pulse generator current;
• and
• reducing the attenuated current to the oscillating input current.

A method for determining current drain for a battery-operated medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time,
• wherein:
• providing an input current to an oscillator includes providing at least two current sources;
• each of the at least two current sources operate in a current measurement state in which the current source is providing the input current that allows the pulse generator current to be determined, and further operate in a calibration state in which the current source is being calibrated;
• and
• one of the at least two current sources is operating in the current measurement state while the other of the at least two current sources is operating in the calibration state.

A method for tracking charge depletion of a battery in an implantable medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current drawn by the implantable medical device;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the charge depletion of a battery by continuously summing the oscillation count over successive periods of time,
• wherein providing an oscillating output with a frequency of oscillation that is dependent on a pulse generator current comprises:
• charging a capacitor;
• comparing a voltage formed across the capacitor with a reference voltage;
• and
• discharging the capacitor when the voltage across the capacitor increases to a level equal to the reference voltage.

A method for tracking charge depletion of a battery in an implantable medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current drawn by the implantable medical device;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the charge depletion of a battery by continuously summing the oscillation count over successive periods of time,
• wherein providing an oscillator input current to the oscillator that is dependent on the pulse generator current comprises:
• dividing current drawn from a battery into the pulse generator current and into an attenuated current that is dependent on the pulse generator current;
• and
• reducing the attenuated current to the oscillating input current.

A method for tracking charge depletion of a battery in an implantable medical device, comprising:

• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current drawn by the implantable medical device;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the charge depletion of a battery by continuously summing the oscillation count over successive periods of time,
• wherein:
• providing an input current to an oscillator includes providing at least two current sources;
• each of the at least two current sources operate in a current measurement state in which the current source is generating the input current that allows the pulse generator current to be determined, and further operate in a calibration state in which the current source is being calibrated;
• and
• one of the at least two current sources is operating in the current measurement state while the other of the at least two current sources is operating in the calibration state.

A method of determining battery status of an implantable medical device, comprising:

• determining a total charge capacity for a battery of an implantable medical device;
• determining a degree of precision for tracking charge depleted from the battery;
• determining a replacement percentage;
• tracking the charge depleted from the battery, including:
• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time;
• and
• providing an indication when remaining charge in the battery equals the replacement percentage.

A method of detecting potential faults within an implantable medical device, comprising:

• determining an upper limit for current from a battery of the implantable medical device;
• and
• determining current drain from the battery, including:
• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time.

A method of reporting drain current in an implantable medical device, comprising:

• determining current drain from the battery using a current measurement circuit, including:
• providing an input current to an oscillator, wherein:
• the input current is dependent on a pulse generator current;
• and
• the oscillator responds to the input current by generating an oscillating output with a frequency of oscillation that is dependent on the pulse generator current;
• providing an oscillation count for the oscillating output over a period of time;
• and
• determining the pulse generator current based on the oscillation count over the period of time;
• disconnecting a telemetry circuit from the current measuring circuit in preparation for a telemetry session;
• interrogating the implantable medical device via telemetry;
• and
• upon completing the telemetry session, connecting the telemetry circuit to the current measuring circuit.