# US 11,896,838 B2 · Recharge algorithm for accurate heat control estimation in presence of ferrite and electronics > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,896,838 B2 - Document ID: US11896838B2 - Status: Granted - Kind: B2 - Application number: 17/078,479 - Filed: 2020-10-23 - Published: 2021-04-29 - Granted: 2024-02-13 - Earliest claimed: 2019-10-25 - Assignees: Medtronic, Inc. - Applicants: Medtronic, Inc. - Inventors: Andrew Fried; Brett Otteson; Douglas Brown; Venkat Gaddam - Web page: https://patentgrep.com/patent/US11896838B2 ## CPC - A61N 1/3787: {from an external energy source} - A61N 1/37252: {Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data} - H02J 50/10: using inductive coupling - H02J 50/80: involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices - A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY ## Abstract A method for controlling charging a power source of an implantable medical device (IMD) in a patient including determining a power being delivered to a primary coil of an external charging device for recharging, determining an estimated power delivered to the IMD power source an estimated heat generated by the primary coil based on a resistance of the primary coil determined as function of at least one of a recharge frequency, a temperature of the primary coil, and a current supplied to the primary coil, calculating an estimated heat generated by the IMD by subtracting the estimated heat generated by the primary coil and the estimated power delivered stored by the rechargeable power source from the power being delivered to a primary coil; and controlling based on the heat generated by the IMD, the power being delivered by the primary coil of the external charging device. ## Claims ### Claim 1 A method for controlling charging of a rechargeable power source of an implantable medical device (IMD) in a patient, the method comprising: determining, by processing circuitry of an external charging device, a power being delivered to a primary coil of the external charging device for recharging the IMD, wherein the external charging device comprises the primary coil and a ferrite material adjacent to the primary coil and spanning an aperture defined by the primary coil; determining, by the processing circuitry, an estimated power delivered to the rechargeable power source during charging of the IMD; calculating, by the processing circuitry, an estimated heat generated by the primary coil based on a resistance of the primary coil, wherein the resistance of the primary coil is determined as a function of at least one of a recharge frequency, a temperature of the primary coil, and a current supplied to the primary coil, the resistance of the primary coil determined as a variable so as to account for the presence of the ferrite material in the external charging device; calculating, by the processing circuitry, an estimated heat generated by the IMD by subtracting the estimated heat generated by the primary coil and the estimated power delivered stored by the rechargeable power source from the power being delivered to a primary coil; and controlling, by the processing circuitry and based on the heat generated by the IMD, the power being delivered by the primary coil of the external charging device, wherein the estimated heat generated by the primary coil is determined at least in part by empirically derived values for a given recharge frequency based on a regression analysis fitting a curve to a measured coil resistance for the primary coil as a function of frequency for a given temperature of the primary coil. ### Claim 2 (depends on 1) The method of claim 1, wherein the estimated heat generated by the primary coil is determined based on below Equation 2: QCHARGER=RPRIM*(ICHARGER)2 (2) wherein QCHARGER is the estimated heat generated by the primary coil; RPRIM is the resistance through a recharge circuit including the primary coil; and ICHARGER is the current passed through the primary coil. ### Claim 3 (depends on 2) The method of claim 2, wherein RPRIM is variable dependent on the recharge frequency, the temperature of the primary coil (TPRIM), and ICHARGER. ### Claim 4 (depends on 3) The method of claim 3, wherein RPRIM is calculated based on below Equation (3): RPRIM−A0+A1*ICHARGER+A2*TPRIM (3) wherein TPRIM is a temperature of the primary coil; and A0, A1, and A2 are empirically derived values for a given recharge frequency based on a regression analysis fitting a curve to a measured coil resistance for the primary coil as a function of frequency for a given TPRIM. ### Claim 5 (depends on 1) The method of claim 1, wherein the IMD does not include a temperature sensor. ### Claim 6 (depends on 1) The method of claim 1, wherein the resistance of the primary coil is determined as a function the recharge frequency, the temperature of the primary coil, and the current supplied to the primary coil. ### Claim 7 (depends on 1) The method of claim 1, wherein the external charger is configured to deliver recharge power at a recharge frequency of greater than 40 kHz. ### Claim 8 (depends on 1) The method of claim 1, wherein the external charger is configured to deliver recharge power at a recharge frequency of about 100 kHz and 120 kHz. ### Claim 9 (depends on 1) The method of claim 1, wherein controlling the power being delivered by the primary coil of the external charging device comprises: calculating, by the processing circuitry, the estimated heat generated by the IMD reaches or exceeds a predetermined threshold, reducing or ceasing the power being delivered to a primary coil. ### Claim 10 An external charging device comprising: a primary coil configured to provide recharge power to a rechargeable power source of an implantable medical device (IMD) through transcutaneous charging; a ferrite material adjacent to the primary coil and spanning an aperture defined by the primary coil; and processing circuitry configured to: determine a power being delivered to the primary coil of the external charging device for recharging the IMD; determine an estimated power delivered stored by the rechargeable power source during charging of the IMD; calculate an estimated heat generated by the primary coil based on a resistance of the primary coil, wherein the resistance of the primary coil is determined as a function of at least one of a recharge frequency, a temperature of the primary coil, and a current supplied to the primary coil, the resistance of the primary coil determined as a variable to account for the presence of the ferrite material in the external charging device; calculate an estimated heat generated by the IMD by subtracting the estimated heat generated by the primary coil and the estimated power delivered stored by the rechargeable power source from the power being delivered to the primary coil; and control, based on the heat generated by the IMD, the power being delivered by the primary coil of the external charging device, wherein the estimated heat generated by the primary coil is determined at least in part by empirically derived values for a given recharge frequency based on a regression analysis fitting a curve to a measured coil resistance for the primary coil as a function of frequency for a given temperature of the primary coil. ### Claim 11 (depends on 10) The external charging device of claim 10, wherein the estimated heat generated by the primary coil is determined based on below Equation 2: QCHARGER=RPRIM*(ICHARGER)2 (2) wherein QCHARGER is the estimated heat generated by the primary coil; RPRIM is the resistance through a recharge circuit including the primary coil; and ICHARGER is the current passed through the primary coil. ### Claim 12 (depends on 11) The external charging device of claim 11, wherein RPRIM is variable dependent on the recharge frequency, the temperature of the primary coil, and ICHARGER. ### Claim 13 (depends on 12) The external charging device of claim 12, wherein RPRIM is calculated based on below Equation (3): RPRIM=A0+A1*ICHARGER+A2*TPRIM (3) wherein TPRIM is a temperature of the primary coil; and A0, A1, and A2 are empirically derived values for a given recharge frequency based on a regression analysis fitting a curve to a measured coil resistance for the primary coil as a function of frequency for a given TPRIM. ### Claim 14 (depends on 10) The external charging device of claim 10, wherein the processing circuitry does not rely on a measured temperature of the IMD to calculate the estimated heat generated by the IMD. ### Claim 15 (depends on 10) The external charging device of claim 10, wherein the external charging device is configured to deliver recharge power at a recharge frequency of greater than 40 kHz. ### Claim 16 (depends on 10) The external charging device of claim 10, wherein the external charging device is configured to deliver recharge power at a recharge frequency about 100 kHz and about 120 kHz. ### Claim 17 (depends on 10) The external charging device of claim 10, wherein to control the power being delivered by the primary coil of the external charging device, the processing circuitry calculates the estimated heat generated by the IMD reaches or exceeds a predetermined threshold and then reduces or ceases the power being delivered to a primary coil. ### Claim 18 A system comprising: an implantable neurostimulator device comprising a housing containing a rechargeable power source; and an external charging device comprising: a primary coil configured to provide recharge power to the rechargeable power source of the implantable neurostimulator device through transcutaneous charging; a ferrite material adjacent to the primary coil and spanning an aperture defined by the primary coil; and processing circuitry configured to: determine a power being delivered to the primary coil of the external charging device for recharging the implantable neurostimulator device; determine an estimated power delivered stored by the rechargeable power source during charging of the implantable neurostimulator device; calculate an estimated heat generated by the primary coil based on a resistance of the primary coil, wherein the resistance of the primary coil is determined as a function of at least one of a recharge frequency, a temperature of the primary coil, and a current supplied to the primary coil, the resistance of the primary coil determined as a variable to account for the presence of the ferrite material in the external charging device; calculate an estimated heat generated by the implantable neurostimulator device by subtracting the estimated heat generated by the primary coil and the estimated power delivered stored by the rechargeable power source from the power being delivered to the primary coil; and control, based on the heat generated by the implantable neurostimulator device, the power being delivered by the primary coil of the external charging device, wherein the estimated heat generated by the primary coil is determined at least in part by empirically derived values for a given recharge frequency based on a regression analysis fitting a curve to a measured coil resistance for the primary coil as a function of frequency for a given temperature of the primary coil. ### Claim 19 (depends on 18) The system of claim 18, wherein the estimated heat generated by the primary coil is determined based on below Equation 2: QCHARGER=RPRIM*(ICHARGER)2 (2) wherein QCHARGER is the estimated heat generated by the primary coil; RPRIM is the resistance through a recharge circuit including the primary coil; and ICHARGER is the current passed through the primary coil. ### Claim 20 (depends on 19) The system of claim 19, wherein RPRIM is variable dependent on the recharge frequency, the temperature of the primary coil, and ICHARGER.