Patent Publication Number: US-2016239070-A1

Title: Semiconductor device and wireless power feeding system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2015-29904 filed on Feb. 18, 2015; the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present invention herein relates generally to a semiconductor device and a wireless power feeding system. 
     BACKGROUND 
     A rechargeable battery has been mounted on a portable terminal such as a cellular phone or a smart phone. When charging the battery of the portable terminal, a user needs to connect one end of a charging device to a commercial power supply and connect a terminal provided at the other end of the charging device to the portable terminal. Such operation is annoying. 
     Therefore, in recent years, a wireless power feeding technique has started to be used. For example, it is possible to feed electric power to a portable terminal incorporating a wireless power feeding and receiving function simply by placing the portable terminal on a wireless power feeding transmitter. 
     In such wireless power feeding, after the power feeding is started, a host or a charging control circuit provided in the portable terminal determines whether a battery of a charging target device (the portable terminal) is fully charged. Thereafter, when the host or the charging control circuit determines that the battery is fully charged, the portable terminal transmits a signal indicating the full charge to a power transmitter and stops the power feeding. However, when the signal indicating the full charge is not transmitted from the host or the charging control circuit, the power transmitter cannot determine whether the battery of the charging target device is fully charged. 
     In this way, there has been a problem that, when the signal indicating the full charge cannot be transmitted, the portable terminal cannot request the power transmitter to stop the power feeding, the power feeding is continued even in a full charge state, and useless electric power is consumed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a wireless power feeding system including a semiconductor device according to an embodiment; 
         FIG. 2  is a diagram showing a detailed circuit configuration of the wireless power feeding system including the semiconductor device according to the embodiment; 
         FIG. 3  is a diagram for explaining an example of a charging characteristic of a charging control circuit  11 ; and 
         FIG. 4  is a flowchart for explaining an example of a flow of detection processing for full charge of a power receiving IC  5 . 
     
    
    
     DETAILED DESCRIPTION 
     A semiconductor device in an embodiment includes an arithmetic unit and a determining unit. The arithmetic unit detects an output current outputted to a charging target device or calculates output power outputted to the charging target device. The determining unit determines, according to the output current or the output power, whether a battery of the charging target device is fully charged. 
     The embodiment is explained in detail with reference to the drawings. 
     First, a configuration concerning a wireless power feeding system according to the embodiment is explained with reference to  FIGS. 1 and 2 . Note that, concerning the configuration in the embodiment, a part of functions related to the wireless power feeding system is extracted and explained. 
       FIG. 1  is a diagram showing the configuration of the wireless power feeding system including the semiconductor device according to the embodiment.  FIG. 2  is a diagram showing a detailed circuit configuration of the wireless power feeding system including the semiconductor device according to the embodiment. 
     A wireless power feeding system  1  in the embodiment includes a portable terminal  2  such as a cellular phone or a smart phone, a portable cover accessory  3  having a wireless power receiving function attachable to the portable terminal  2 , and a power transmitter  4  having a wireless power transmitting function and capable of transmitting electric power to the portable cover accessory  3 . When the portable cover accessory  3  is attached to the portable terminal  2  and power transmission (power feeding) from the power transmitter  4  is started, electric power received by the portable cover accessory  3  is supplied to the portable terminal  2 , which is a charging target device. Wireless power feeding can be performed. That is, even a portable terminal not mounted with the wireless power feeding function can receive wireless power feeding if the portable cover accessory having the wireless power receiving function is attached to the portable terminal. In particular, in general, a power receiving device such as a portable cover accessory is developed without taking into account communication with a host or a charging control circuit of a portable terminal. Therefore, it is likely that the power receiving device cannot determine whether a battery of the portable terminal is fully charged. Therefore, even after the battery of the portable terminal is fully charged, the power receiving device cannot notify the power transmitter to stop power transmission and always receives wireless power feeding. 
     As shown in  FIG. 2 , the portable terminal  2  includes a lithium ion secondary battery (hereinafter referred to as battery)  10  and a charging control circuit  11  that performs charging control of the battery  10 . Note that the battery  10  of the portable terminal  2  is not limited to the lithium ion secondary battery and may be secondary batteries of other types. 
     The portable cover accessory  3  includes a power receiving IC  5  and a reception coil  20 . The power receiving IC  5 , which is the semiconductor device in the embodiment, includes a rectifier  21 , a regulator  22 , a voltage detection circuit  23 , a current detection circuit  24 , a modulation circuit  25 , an arithmetic/control circuit  26 , and a memory  27 . 
     The power transmitter  4  is connected to, for example, a household commercial power supply via an AC adapter  30 . The power transmitter  4  includes a control circuit  31 , a PWM circuit  32 , a pre-driver circuit  33 , a detector  34 , a filter circuit  35 , a full bridge circuit  36 , and a transmission coil  37 . 
     Alternating-current power from the commercial power supply is converted into direct-current power by the AC adapter  30  and supplied to the power transmitter  4 . After being subjected to PWM control by the PWM circuit  32 , the converted direct-current power is driven by the pre-driver circuit  33  and supplied to the full bridge circuit  36 . 
     The control circuit  31  controls the PWM circuit  32  on the basis of information transmitted from the portable cover accessory  3  on a power reception side to control transmission power. More specifically, data modulated by the modulation circuit  25  of the portable cover accessory  3  is transmitted from the reception coil  20  to the transmission coil  37 . The data transmitted to the power transmitter  4  is, for example, information concerning received power currently being received, information for instructing an increase or a reduction of the received power, or information for instructing a power transmission stop. 
     The control circuit  31  controls the PWM circuit  32  on the basis of the information concerning the received power currently being received and the information for instructing an increase or a reduction of the received power and controls the transmission power (amount) transmitted to the portable cover accessory  3 . The control circuit  31  performs control for a stop of power transmission to the portable cover accessory  3  on the basis of the information for instructing the power transmission stop. 
     The full bridge circuit  36  converts the direct-current power into alternating-current power and supplies the alternating-current power to the transmission coil  37 . Consequently, since an alternating current flows to the transmission coil  37 , a magnetic flux is generated. As a result, the alternating current flows to the reception coil  20  as well. Wireless power feeding is performed. 
     In this way, as a system of the wireless power feeding in the wireless power feeding system  1  in the embodiment, an electromagnetic induction system, which is currently a most major system, is explained. However, the system is not limited to the electromagnetic induction system. The system may be another system such as a magnetic resonance system, an electric field coupling system, or a microwave system. 
     The rectifier  21  rectifies the alternating current received by the reception coil  20  and supplies the alternating current to the regulator  22 . The regulator  22  includes an LDO (low drop out) regulator or a DCDC converter. The regulator  22  is a circuit that regulates electric power rectified by the rectifier  21 . The regulator  22  supplies the regulated electric power to the charging control circuit  11  of the portable terminal  2 . Note that the electric power rectified by the rectifier  21  may be directly supplied to the charging control circuit  11  without providing the regulator  22 . 
     The voltage detection circuit  23  monitors and measures an output voltage from the regulator  22  and outputs a measurement result to the arithmetic/control circuit  26 . The current detection circuit  24  monitors and measures an output current from the regulator  22  and outputs a measurement result to the arithmetic/control circuit  26 . Note that the current detection circuit  24  may monitor and measure an electric current equivalent to the output current from the regulator  22 , that is, an electric current rectified by the rectifier  21  as indicated by a broken line in  FIG. 2 . 
     The arithmetic/control circuit  26  calculates, on the basis of the measurement result of the voltage detection circuit  23  and the measurement result of the current detection circuit  24 , output power outputted to the portable terminal  2  and stores the output power in the memory  27 . Note that the arithmetic/control circuit  26  may also store the measurement result of the voltage detection circuit  23  and the measurement result of the current detection circuit  24  in the memory  27 . 
     The arithmetic/control circuit  26  monitors a change in the output power or the output current outputted to the portable terminal  2  and determines whether the battery  10  of the portable terminal  2  is fully charged. When determining that the battery  10  is fully charged, the arithmetic/control circuit  26  transmits a request for a power transmission stop to the power transmitter  4 . Alternatively, the arithmetic/control circuit  26  can monitor a change in the output power or the output current outputted to the portable terminal  2 , calculate a charging state of the battery  10  of the portable terminal  2 , and transmit the charging state of the battery  10  to the power transmitter  4 . Note that a determination method for full charge is explained in detail with reference to  FIGS. 3 and 4  below. 
     The arithmetic/control circuit  26  controls the modulation circuit  25 , executes control of communication with the power transmitter  4 , and executes error processing when an error occurs. 
     The modulation circuit  25  is a circuit that modulates data transmitted to the power transmitter  4 . The modulation circuit  25  performs, for example, ASK (amplitude-shift keying) modulation. The ASK-modulated data is transmitted from the reception coil  20  to the transmission coil  37 . As explained above, the data transmitted to the power transmitter  4  is, for example, the information concerning the received power currently received, the information for instructing an increase or a reduction of the received power, or the information for instructing a power transmission stop. 
     The information from the power receiving IC  5  is detected by the detector  34  of the power transmitter  4  and supplied to the control circuit  31  via the filter circuit  35 . Consequently, the control circuit  31  performs control of the transmission power (amount) or control of a stop of the transmission power on the basis of the information transmitted from the portable cover accessory  3  on a power reception side. 
     A determination method for full charge of the battery  10  is explained with reference to  FIG. 3 .  FIG. 3  is a diagram for explaining an example of a charging characteristic of the charging control circuit  11 . 
     As shown in  FIG. 3 , in normal charging control, a voltage is raised by constant current charging and, when the battery  10  approaches a full charge state, the constant current charging is switched to constant voltage charging. That is, as shown in FIG.  3 , the charging control circuit  11  charges the battery  10  with a constant current until time t 1  and charges the battery  10  with a constant voltage after time t 1 . 
     On the other hand, as an output from the power receiving IC  5 , an output current and output power change according to the charging characteristic of the charging control circuit  11  shown in  FIG. 3 . Note that a product of a charging current and a charging voltage shown in  FIG. 3  is equivalent to the output power (power consumption and the like in a charging circuit is neglected). In the embodiment, the arithmetic/control circuit  26  calculates output power (or calculates an output current) from the regulator  22  to determine a switching point (time t 2 ) when the constant current charging is switched from the constant current charging to the constant voltage charging. The arithmetic/control circuit  26  determines whether a change in the output power (or the output current) from the switching point (time t 1 ) coincides with a parameter range set in advance. When the change in the output power (or the output current) coincides with the parameter range set in advance, the arithmetic/control circuit  26  determines that the battery  10  is fully charged and requests the power transmitter  4  to stop the power feeding. 
     As an example, more specifically, when the output power (or the output current) decreases at a predetermined decrease ratio from maximum output power (or a maximum output current), the arithmetic/control circuit  26  determines that the battery  10  is fully charged. Alternatively, when the output power (or the output current) decreases to be equal to or smaller than a predetermined threshold, the arithmetic/control circuit  26  determines that the battery  10  is fully charged. Note that, when the output power (or the output current) decreases at the predetermined decrease ratio from the maximum output power (or the maximum output current) and the output power (or the output current) decreases to be equal to or smaller than the predetermined threshold, the arithmetic/control circuit  26  may determine that the battery  10  is fully charged. 
     In this way, when the output power of the regulator  22  reaches a maximum, the arithmetic/control circuit  26  determines that the constant current charging is switched to the constant voltage charging. In order to determine the maximum output power with which the output power of the regulator  22  reaches a maximum, the arithmetic/control circuit  26  always calculates output power and stores data of the calculated output power in the memory  27 . The arithmetic/control circuit  26  compares data of output power calculated anew and the data of the output power stored in the memory  27  to determine the maximum output current. 
     The arithmetic/control circuit  26  continuously stores and compares data of output power to prevent erroneous detection of the maximum output power. After a difference of compared data becomes substantially equal, when detecting that data of output power calculated anew gradually decreases, the arithmetic/control circuit  26  determines that data at a point in time when before the data of the output power calculated anew decreases is the maximum output power. 
     Detection processing for full charge of the power receiving IC  5  configured as explained above is explained  FIG. 4  is a flowchart for explaining an example of a flow of the detection processing for the full charge of the power receiving IC  5 . 
     First, the arithmetic/control circuit  26  acquires output power (n) outputted from the power receiving IC  5  (step S 1 ) and stores the acquired output power (n) in the memory  27  (step S 2 ). In this processing in step S 1 , the arithmetic/control circuit  26  calculates output power on the basis of an output voltage and an output current of the regulator  22  detected by the voltage detection circuit  23  and the current detection circuit  24 . 
     Subsequently, the arithmetic/control circuit  26  acquires output power (n+1) outputted from the power receiving IC  5  (step S 3 ) and determines whether the output power (n+1) acquired anew is larger than the output power (n) stored in the memory  27  (step S 4 ). When determining that the output power (n+1) acquired anew is larger than the stored output power (n) (YES in step S 4 ), the arithmetic/control circuit  26  stores the output power (n+1) acquired anew in the memory  27  as the maximum output power (step S 5 ). The arithmetic/control circuit  26  executes n=n+1 (step S 6 ) and returns to step S 3 . 
     On the other hand, when determining that the output power (n+1) acquired anew is not larger than the stored output power (n) (NO in step S 4 ), the arithmetic/control circuit  26  stores the output power (n) in the memory  27  as the maximum output power (step S 7 ), stores subsequent output power in the memory  27 , and monitors a change in the output power (step S 8 ). 
     Subsequently, the arithmetic/control circuit  26  determines whether the monitored change in the output power coincides with a parameter range set in advance (step S 9 ). That is, the arithmetic/control circuit  26  determines whether the change in the output power is a set change. More specifically, the arithmetic/control circuit  26  determines whether a transition of the output power is a decrease ratio set in advance or the output power is equal to or smaller than a threshold set in advance. 
     Note that the charging characteristic is sometimes different depending on a type of the portable terminal  2 , a type of the battery  10 , or the like. Therefore, a plurality of kinds of parameters are stored in the memory  27  such that various sequences can be assumed. 
     When the monitored change of the output power does not coincide with the parameter range set in advance (NO in step S 9 ), the arithmetic/control circuit  26  executes n=1 (step S 10 ), returns to step S 1 , and acquires output power. For example, the output power from the power receiving IC  5  sometimes temporarily increases or decreases because of an influence of noise or the like. In such a case, since the monitored change of the output power does not coincide with the parameter range set in advance, the arithmetic/control circuit  26  returns to step S 1  and continues the acquisition of output power from the power receiving IC  5 . 
     On the other hand, when the monitored change of the output power coincides with the parameter range set in advance (YES in step S 9 ), the arithmetic/control circuit  26  determines that the battery  10  of the portable terminal  2 , which is the charging target device, is fully charged (a wireless power supply stop condition) (step S 11 ) and ends the processing. 
     When determining that the battery  10  is fully charged, the arithmetic/control circuit  26  controls the modulation circuit  25  and transmits a command for instructing a power transmission stop or a command representing a charging state to the power transmitter  4 . Note that the power receiving IC  5  may transmit the charging state of the battery  10  to the power transmitter  4  without transmitting the command for instructing the power transmission stop to the power transmitter  4 . The power transmitter  4  may determine the power transmission stop. 
     Note that means for calculating the maximum output power compares the magnitude of an average value (or an addition value) of a continuous predetermined number of output powers (or output currents). Therefore, the maximum output power is not erroneously detected even if fluctuation of output power due to noise occurs. For example, when output power (n+1)+output power (n+2)+output power (n+3) is larger than output power (n)+output power (n+1)+output power (n+2), the determination in step S 4  is YES. 
     As explained above, the power receiving IC  5  monitors the output power (or the output current) outputted from the regulator  22 , which changes according to the charging state of the battery  10 , to determine the full charge of the battery  10 . 
     A conventional power receiving IC cannot issue a request for a power transmission stop to the power transmitter  4  unless the power receiving IC receives a signal indicating that the battery  10  is fully charged from the charging control circuit  11 , that is, from the portable terminal  2 , which is the charging target device. 
     On the other hand, the power receiving IC  5  in the embodiment monitors a change in output power (or output current) outputted from the power receiving IC  5  to the charging target device to determine the full charge of the battery  10 . Therefore, the power receiving IC  5  alone can determine the full charge of the battery  10  and issue a request for a power transmission stop to the power transmitter  4 . 
     Therefore, with the power receiving IC, which is the semiconductor device in the embodiment, it is possible to control transmission power from the power transmitter on the basis of information due to a charging state of the charging target device. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel apparatuses, methods and circuits described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatuses, methods and circuits described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.