Charger External Power Device Gain Sampling

Abstract

A power management unit accurately measures and controls charging current. The power management unit may be implemented more efficiently than prior designs, leading to cost savings in the implementation of the power management unit as well as in the implementation of the device that incorporates the power management unit. The power management unit incorporates a model of an external charge control device (e.g., a transistor) and uses that model in a way that allows the power management unit to eliminate external device pins and other circuitry.

What is claimed is: 
     
         1 . A method comprising:
 measuring charging current flowing from a charging power source by instead measuring battery current flowing through a rechargeable battery connected to the charging power source, the charging current comprising rechargeable battery current and supplemental current;   controlling the charging current using a model parameter of a device model for a switching device through which the charging current flows.   
     
     
         2 . The method of  claim 1 , where:
 the supplemental current comprises digital logic current, power amplifier current, or both.   
     
     
         3 . The method of  claim 1 , where the model parameter comprises gain of the switching device. 
     
     
         4 . The method of  claim 1 , where controlling comprises:
 increasing the charging current over time.   
     
     
         5 . The method of  claim 1 , where controlling comprises:
 increasing the charging current over time after measuring the charging current to ensure it is within predetermined boundaries.   
     
     
         6 . The method of  claim 1 , where measuring charging current comprises:
 taking a first measurement of the battery current while the charging current is flowing to the rechargeable battery;   taking a second measurement of the battery current while the charging current has stopped flowing to the rechargeable battery; and   determining the difference between the first measurement and the second measurement.   
     
     
         7 . A charging system comprising:
 charging circuitry comprising:
 a switching device; and 
 a battery current sensor in communication with the switching device; 
   a power management unit comprising:
 a switching model for the switching device; 
 a switch driver for the switching device; and 
 charging current measurement logic operable to:
 drive the switching device with the switch driver to provide charging current, including battery current that flows through the battery current sensor, and obtain a first measurement of the battery current; 
 deactivate the switching device with the switch driver to stop the charging current, and obtain a second measurement of the battery current; 
 determine the charging current from the first measurement and the second measurement; and 
 control the charging current by driving the switching device according to the switching model. 
 
   
     
     
         8 . The charging system of  claim 7 , where the switching model comprises a gain parameter for the switching device. 
     
     
         9 . The charging system of  claim 7 , where the power management unit is operable to control the charging current by increasing the charging current over time. 
     
     
         10 . The charging system of  claim 7 , where the power management unit is operable to control the charging current by increasing the charging current over time starting when a charging operation begins. 
     
     
         11 . The charging system of  claim 10 , where the power management unit is operable to incrementally increase the charging current. 
     
     
         12 . The charging system of  claim 10 , where the power management unit is operable to incrementally increase the charging current after obtaining a charging current measurement and determining that the charging current measurement meets a charging current criteria.