Battery Management for an Implantable Medical Device

Abstract

Battery management circuitry for an implantable medical device such as an implantable neurostimulator is described. The circuitry has a T-shape with respect to the battery terminal, with charging circuitry coupled between rectifier circuitry and the battery terminal on one side of the T, and load isolation circuitry coupled between the load and the battery terminal on the other side. The load isolation circuitry can comprise two switches wired in parallel. An undervoltage fault condition opens both switches to isolate the battery terminal from the load to prevent further dissipation of the battery. Other fault conditions will open only one the switches leaving the other closed to allow for reduced power to the load to continue implant operations albeit at safer low-power levels. The battery management circuitry can be fixed in a particular location on an integrated circuit which also includes for example the stimulation circuitry for the electrodes.

What is claimed is: 
     
         1 . An implantable medical device, comprising:
 a plurality of electrodes configured to contact a patient's tissue;   a battery comprising a battery voltage; and   an integrated circuit formed in a substrate, the integrated circuit comprising:
 a plurality of integrated circuit outputs each coupled to one of the plurality of electrodes; 
 stimulation circuitry configured to provide stimulation to the plurality of integrated circuit outputs; 
 a battery integrated circuit input/output, wherein the battery voltage is connected to the battery integrated circuit input/output; 
 a DC voltage integrated circuit input; 
 battery management circuitry configured to (i) receive a DC voltage at the DC voltage integrated circuit input, wherein the DC voltage is configured to provide power to charge the battery via a charging path comprising the battery integrated circuit input/output, and (ii) regulate coupling of the battery voltage to a power supply voltage; and 
 a first load powered by the power supply voltage, wherein the load comprises the stimulation circuitry. 
   
     
     
         2 . The implantable medical device of  claim 1 , wherein the load first comprises other circuitry on the integrated circuit. 
     
     
         3 . The implantable medical device of  claim 1 , further comprising a second load outside of the integrated circuit, wherein the integrated circuit comprises a load integrated circuit output configured to receive the power supply voltage, wherein the second load is powered by the power supply voltage. 
     
     
         4 . The implantable medical device of  claim 3 , wherein the second load comprises a microcontroller. 
     
     
         5 . The implantable medical device of  claim 1 , wherein the charging path comprises a passive trickle charging path, wherein the DC voltage is configured to provide the power to charge the battery through the trickle charging path. 
     
     
         6 . The implantable medical device of  claim 1 , wherein the battery management circuitry comprises a current source, wherein the DC voltage is configured to provide power to the current source, wherein the current source is configured to charge the battery via the charging path. 
     
     
         7 . The implantable medical device of  claim 1 , further comprising rectifier circuitry configured to produce the DC voltage from an AC input of the rectifier circuitry. 
     
     
         8 . The implantable medical device of  claim 7 , further comprising a charging coil, wherein the charging coil is configured to receive a magnetic charging field and produce the AC input of the rectifier circuitry. 
     
     
         9 . The implantable medical device of  claim 1 , further comprising means for isolating the battery management circuitry from other circuitry on the integrated circuit. 
     
     
         10 . The implantable medical device of  claim 1 , further comprising a bus outside of the integrated circuit, wherein the integrated circuit further comprises bus integrated circuit inputs/outputs coupled to the bus. 
     
     
         11 . The implantable medical device of  claim 10 , further comprising a microcontroller coupled to the bus. 
     
     
         12 . The implantable medical device of  claim 1 , wherein the integrated circuit further comprises a microcontroller. 
     
     
         13 . The implantable medical device of  claim 1 , wherein the charging path comprises an overvoltage switch configured to open if the battery voltage exceeds a threshold. 
     
     
         14 . The implantable medical device of  claim 1 , wherein the battery management circuitry further comprises at least one load switch configured to couple the battery voltage to the power supply voltage. 
     
     
         15 . The implantable medical device of  claim 14 , wherein the at least one load switch is configured to open at least if the battery voltage is lower than a threshold. 
     
     
         16 . The implantable medical device of  claim 14 , wherein the at least one load switch comprises first and second load switches in parallel. 
     
     
         17 . The implantable medical device of  claim 16 , wherein the first load switch has a first resistance, and the second load switch has a second resistance smaller than the first resistance. 
     
     
         18 . The implantable medical device of  claim 16 , wherein the first load switch is configured to open if the battery voltage is lower than a threshold, and wherein the second load switch is configured to open if (i) the battery voltage is lower than a threshold, or (ii) if at least one other fault condition is asserted. 
     
     
         19 . The implantable medical device of  claim 18 , wherein the at least one other fault condition comprises an overcurrent between the battery voltage and the power supply voltage. 
     
     
         20 . The implantable medical device of  claim 18 , wherein the at least one other fault condition comprises an emergency shutdown condition. 
     
     
         21 . The implantable medical device of  claim 20 , wherein the emergency shutdown condition comprises a magnetic field generated external to the implantable medical device.