Device incorporating data communication function

A device incorporating a data communication function 15 having a power supply circuit 38 of a dispersed power supply system is provided with a terminal 51-2 for receiving power supply from another device 14 which initiates data communication and a drive circuit 53-2 for performing the data communication with the another device 14, wherein when the terminal 51-2 is supplied with power, the power supplied to the terminal 51-2 is supplied to the drive circuit 53-2 in an off state of the power supply circuit 38. It thereby reduces self-power-loss and ensures reliability of performance.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Japanese Patent Application No. 2008-19354 (filed on Jan. 30, 2008), the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a device incorporating data communication function and having a power supply circuit of a dispersed power supply system.

BACKGROUND ART

A mobile terminal such as a cellular phone, for example, is designed using a plurality of system devices. Many of such system devices included in the mobile terminal incorporate a data communication function and require a plurality of different voltages. As such, the mobile terminal uses a multiple power supply device which has a regulator and a converter for generating various voltages necessary for the plurality of system devices in one package, and supplies the voltage necessary for each system device from the multiple power supply device.

FIG. 10is a block diagram illustrating a schematic constitution of the mobile terminal using a conventional multiple power supply device. This mobile terminal is provided with a battery100, a power device101such as a power amplifier, a multiple power supply device102, and an MPU (microprocessor unit)103and a first device (device1)104to a fifth device (device5)108as the plurality of system devices. The MPU103, the first device104and the second device105are interconnected via an interface (I/F1)111to perform data communication. The MPU103, the third device106and the fourth device107are interconnected via an interface (I/F2)112to perform data communication. The MPU103and the fifth device108are interconnected via an interface (I/F3)113to perform data communication.

In the mobile terminal shown inFIG. 10, a battery voltage of the battery100is directly supplied to the power device101, whereas the battery voltage of the battery100is dropped or raised to a predetermined voltage by the multiple power supply device102before supplied to the MPU103and the first device104to the fifth device108.

Therefore, in order to supply power to respective system devices and interfaces, the multiple power supply device102is provided with a power supply circuit (MPUReg)121for an MPU core of the MPU103, a power supply circuit (1/F1Reg)122for the interface111, a power supply circuit (1/F2Reg)123for the interface112, a power supply circuit (1/F3Reg)124for the interface113, a power supply circuit (IC1Reg)125for an IC core of the first device104, a power supply circuit (IC2Reg)126for an IC core of the second device105, a power supply circuit (IC3Reg)127for an IC core of the third device106, a power supply circuit (IC4Reg)128for an IC core of the fourth device107, and a power supply circuit (IC5Reg)129for an IC core of the fifth device108. The multiple power supply device102is controlled by the MPU103via an interface (I/F0)110.

The multiple power supply device shown inFIG. 10is used not only for the mobile terminal but also for other electronic devices. The multiple power supply device is used for the electronic device because it can reduce a mounting area and therefore contribute to downsizing of the device by incorporating power supply circuits necessary to generate power for respective system devices and a power supply circuit having a regulator and a convertor common to the system devices within a single package.

In addition, when it is used for a small device such as the mobile terminal in particular, a substrate to be used can be designed to be small enough and a power supply line from the multiple power supply device to each system device can be short. Since the line impedance may thereby be reduced, it is possible to limit the voltage drop within an allowable range relatively easily.

In a case where the voltage drop cannot fall within the allowable range, a countermeasure which has been taken is, in case of a low voltage power supply, to detect a voltage for feedback from an input power supply terminal of the system device and, by using the voltage for feedback, to control a voltage at a corresponding output terminal of the multiple power supply device to be increased such that the voltage at the input power supply terminal of the system device is at a predetermined level.

However, in recent small devices, system devices which are miniaturized and perform at a high speed as well as being capable of performing large current at low voltage are used. When such a system device is used, since the voltage drop has influence even if the power supply line is short because of large current at low voltage, and a difference between the maximum operation power and the minimum operation power is large because of low power operation, it is not possible to follow the voltage drop by output setting for increasing the voltage. It may also not be able to follow to a transient response because of the high speed when output voltage is controlled by detecting a feedback voltage.

There may be a method to reduce the voltage drop by designing the power supply line (pattern) to be thick to minimize the line impedance. However, the thick pattern increases the size of substrate, thereby preventing downsizing.

In addition, the multiple power supply system which supplies power using the multiple power supply device stated above needs to redesign the power supply if the system is expanded exceeding a limit for power designing because of addition of functions to the device.

On the other hand, there is known a dispersed power supply system (Point-of-Load) other than the multiple supply system described above as the power supply system for the system devices. The system arranges a power supply circuit having a regulator and a convertor close to each system device and forms shortest connection between the power supply circuit and a corresponding system device to supply power.

Since the power supply circuit is connected to each system device by the shortest connection in the dispersed power supply system, it may not cause a problem such as the voltage drop and may easily allow the device to incorporate additional functions by changing the battery capacity, for example. However, in the dispersed power supply system the power supply circuits are arranged dispersedly corresponding to the system devices, resulting in increase of the number of components and thus increase of the mounting dimension. For this reason, the dispersed power supply system has been hardly used for small devices such as the mobile terminal.

However, there is recently suggested a hybrid device, as a device for the dispersed power supply system, which is a hybrid IC mounting power supply circuits individually in a package size of a conventional device or smaller. Accordingly, such hybrid device of the dispersed power supply system can solve both issues of downsizing and low voltage performance.

Nonetheless, in the dispersed power supply system, as shown inFIG. 10for example, the voltage of the interface111which interconnects the MPU103, the first device104and the second device105for data communication is generated at each device of the MPU103, the first device104and the second device105. Therefore, in comparison to the multiple power supply system which supplies power by generating the voltage of the interface111with a single power supply circuit (I/F1Reg)122commonly provided to the multiple power supply device102, power supply circuits are overlapped and, the more overlapped they are, the more self-power-loss is generated at voltage conversion.

In addition, when the voltage for the interface is generated at each device connected via the interface, it is difficult to generate the same voltage, because of difference in individual power supply circuits. Therefore, it is concerned that some interfaces would not operate because of voltage difference between the devices and that malfunction may be caused because of detecting a false value, reducing reliability of performance.

As a power supply circuit which reduces self-power-loss, there is known a power supply circuit to be turned on/off based on an output voltage of a main battery (for example, see Patent Document 1).

However, the power supply circuit disclosed in Patent Document 1, if the output voltage of the main battery is equal to or higher than a predetermined value when a system is off, performs backup of a memory device by turning the power supply circuit off and directly supplying the output voltage of the main battery to the memory device of the system. While the system is on by external power supply (from another power supply circuit), the power supply circuit is never turned off. Therefore, it cannot reduce self-power-loss.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

It is an object of the present invention to provide a device incorporating a data communication function capable of reducing self-power-loss and ensuring reliability of performance.

SUMMARY OF THE INVENTION

In order to achieve the above object, a device incorporating a data communication function and having a power supply circuit of a dispersed power supply system according to a first aspect of the present invention, includes:

a terminal for receiving power supply from another device which initiates data communication; and

a drive circuit for performing data communication with the another device,

wherein if the power is supplied to the terminal, the power supplied to the terminal is supplied to the drive circuit in an off state of the power supply circuit.

A second aspect of the present invention is that the device incorporating the data communication function according to the first aspect includes:

a comparator for comparing voltage applied to the terminal and a standard voltage; and

a reverse current preventing circuit for preventing reverse current from flowing to the power supply circuit,

wherein if the comparator detects that the voltage applied to the terminal is lower than the standard voltage, the power supply circuit is turned on such that power is supplied to the drive circuit from the power supply circuit via the reverse current preventing circuit, and

wherein if the comparator detects that the voltage applied to the terminal is equal or higher than the standard voltage while the power is supplied to the terminal, the power supply circuit is turned off such that the power being supplied to the terminal is supplied to the drive circuit.

A third aspect of the present invention is that the device incorporating the data communication function according to the first aspect includes:

a comparator for comparing voltage applied to the terminal and a standard voltage; and

a reverse current preventing circuit for preventing reverse current from flowing to the power supply circuit,

wherein if the comparator detects that the voltage applied to the terminal is lower than the standard voltage, the power supply circuit is turned on such that power is supplied to the drive circuit from the power supply circuit via the reverse current preventing circuit, and

wherein if the comparator detects that the voltage applied to the terminal is reduced while the power is supplied to the terminal, the power is supplied to the drive circuit from the power supply circuit without the reverse current preventing circuit.

Moreover, in order to achieve the above object, a device incorporating a data communication function and having a power supply circuit of a dispersed power supply system according to a fourth aspect of the present invention, includes:

a drive circuit for performing data communication with another device;

a terminal for supplying power to the another device or for receiving power supply from the another device;

a comparator for comparing voltage applied to the terminal and a standard voltage; and

a reverse current preventing circuit for preventing reverse current from flowing to the power supply circuit,

wherein in order to initiate data communication the power supply circuit is turned on and power is supplied from the power supply circuit to the drive circuit as well as to the terminal, and

wherein if the comparator detects that the voltage applied to the terminal is equal to or higher than the standard voltage while the power is supplied to the terminal, power is supplied to the drive circuit and the terminal from the power supply circuit via the reverse current preventing circuit, and then, if the comparator detects that the voltage applied to the terminal is equal to or higher than the standard voltage in a state where power supply from the power supply circuit is blocked, the power supply circuit is turned off and the power supplied to the terminal is supplied to the drive circuit.

EFFECT OF THE INVENTION

The device incorporating the data communication function according to the present invention, when receiving power supply from another device which initiates the data communication, turns off the power supply circuit of itself and drives the drive circuit by using power supplied from the another device. It is thus possible to reduce self-power-loss. Moreover, the device incorporating the data communication function according to the present invention, when receiving power supply with a voltage equal to or higher than a standard voltage from a reception-side device of the data communication, turns off the power supply circuit of itself and drives the drive circuit by using power supplied from the reception-side device. Thereby, it is possible to reduce self-power-loss. Furthermore, no voltage difference is generated in relation to the counterpart device of the communication since the power supply circuit of itself is turned off. Therefore, the data communication is performed without fail and reliability of performance is ensured.

REFERENCE SIGNS LIST

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be described as follows, with reference to the accompanying drawings.

First Embodiment

FIG. 1is a block diagram illustrating an exemplified schematic configuration of a mobile terminal using a device incorporating a data communication function according to a first embodiment of the present invention. The mobile terminal is provided with a battery10, a power device11such as a power amplifier, an MPU13, and a first device (device1)14to a fifth device (device5)18. The power device11is directly driven by the battery voltage VDD of the battery10.

Each of the MPU13and the first device14to the fifth device18is comprised of the device incorporating the data communication function according to the first embodiment of the present invention. The device means a machine, an apparatus, an electronic component and the likes having a particular function and includes also a module to achieve a particular function by combining components. The MPU13, the first device14and the second device15are interconnected via an interface (I/F1)21to perform data communication. The MPU13, the third device16and the fourth device17are interconnected via an interface (I/F2)22to perform data communication. The MPU13and the fifth device18are interconnected via an interface (I/F3)23to perform data communication.

Therefore, the MPU13has a power supply circuit (MPUReg)31for an MPU core, a power supply circuit (I/F1Reg1)32for the interface21, a power supply circuit (I/F2Reg1)33for the interface22, and a power supply circuit (I/F3Reg1)34for the interface23which are mounted thereon, and connects them to the battery10.

The first device14has a power supply circuit (IC1Reg)35for an IC core and a power supply circuit (I/F1Reg2)36for the interface21, which are mounted thereon, and connects each of them to the battery10. Likewise, the second device15has a power supply circuit (IC2Reg)37for the IC core and a power supply circuit (I/F1Reg3)38for the interface21, which are mounted thereon, and connects them to the battery10.

The third device16has a power supply circuit (IC3Reg)39for the IC core and a power supply circuit (I/F2Reg2)40for the interface22, which are mounted thereon, and connects them to the battery10. Likewise, the fourth device17has a power supply circuit (IC4Reg)41for the IC core and a power supply circuit (I/F2Reg3)42for the interface22, which are mounted thereon, and connects them to the battery10.

In addition, the fifth device18has a power supply circuit (IC5Reg)43for the IC core and a power supply circuit (I/F3Reg2)44for the interface23, which are mounted thereon, and connects them to the battery10. It is to be noted that only the power supply circuits mounted on the MPU13and the first device14to the fifth device18are shown inFIG. 1and a configuration of interface units corresponding to the power supply circuits for respective interfaces are not shown.

FIG. 2is a block diagram illustrating a configuration of a main section of the interface unit of the device incorporating the data communication function according to the first embodiment of the present invention shown inFIG. 1. Configurations of the interface unit45of the first device14and the interface unit46of the second device15, which are interconnected via the interface21, are exemplified inFIG. 2. Other devices have the same configuration of the interface unit for each interface.

In the device incorporating the data communication function according to the present embodiment, an initiator device of the data communication supplies power for an interface to a reception-side device of the data communication. Thereby, the reception-side device turns off its own power supply circuit for the interface and enables the data communication.

The interface unit45of the first device14is provided with a power terminal51-1for supplying power to another device or receiving power supply from another device, a data terminal52-1for sending and receiving data, a drive circuit53-1for performing data communication via the data terminal52-1, a control unit54-1for controlling the drive circuit53-1, a switch55-1, a reverse current preventing circuit56-1comprising a diode and the likes, and a switch57-1. The first device14is configured such that the power supply circuit36for the interface21is capable of supplying power to the power terminal51-1and the drive circuit53-1via the switch55-1and also supplying power to the power terminal51-1and the drive circuit53-1via the reverse current preventing circuit56-1and the switch57-1.

The interface unit45is provided with a comparator58-1for comparing the battery voltage VDD, which is an input voltage of the power supply circuit36, an output voltage of the power supply circuit36, and a voltage applied to the power terminal51-1. The comparator58-1determines whether there is an applied voltage to the power terminal51-1, compares the output voltage of the power supply circuit36to the voltage of the power terminal51-1, and compares a predetermined standard voltage to the voltage of the power terminal51-1. The predetermined standard voltage referred to by the comparator58-1is a voltage necessary to drive the drive circuit53-1and generated from the battery voltage VDD by the comparator58-1.

Output of the comparator58-1is supplied to the control unit54-1. Thereby, the power supply circuit36is controlled to be on/off, and the switches55-1and57-1are also controlled to be on/off. In an initial state, the power supply circuit36and the switches55-1and57-1are off.

The interface unit46corresponding to the interface21of the second device15is configured in the same manner as the interface unit45of the first device14. InFIG. 2, the elements of the second device15which are the same as those of the first device14are provided with the same reference signs but have a hyphen and a number2thereafter.

In the first device14shown inFIG. 2, in addition, the power supply circuit36for the interface is referred to as “Reg1”, the power terminal51-1as “Terminal1-1”, the data terminal52-1as “Terminal2-1”, the drive circuit53-1as “Drive circuit1”, the control unit54-1as “Control unit1”, the switch55-1as “SW1-1”, the reverse current preventing circuit56-1as “Reverse current blocking1”, and the switch57-1as “SW2-1”, which are expressed in corresponding blocks.

Likewise, in the second device15, the power supply circuit38for the interface is referred to as “Reg2”, the power terminal51-2as “Terminal1-2”, the data terminal52-2as “Terminal2-2”, the drive circuit53-2as “Drive circuit2”, the control unit54-2as “Control unit2”, the switch55-2as “SW1-2”, the reverse current preventing circuit56-2as “Reverse current blocking2”, and the switch57-2as “SW2-2”, which are expressed in corresponding blocks.

The following is a description of an operation of data communication by the device incorporating the data communication function according to the present embodiment shown inFIG. 2, by using an exemplified case where the data communication is initiated by the first device14to the second device15, with reference to the flow charts inFIG. 3andFIG. 4. It is to be noted that terms expressed in the blocks inFIG. 2are used in the following description.

Until communication is initiated, the device1maintains an initial state in which all of the Reg1, SW1-1and SW2-1are off. Likewise, the device2maintains the initial state in which all of the Reg2, SW1-2and SW2-2are off (step S11). In order for the device1to initiate a communication to the device2in the initial state, the control unit1first checks whether voltage is applied to the terminal1-1from the output of the comparator1(step S12). If the voltage is applied to the terminal1-1, the Reg1is controlled to be on/off by the control unit1. In this case, since the Reg1is off in the initial state, power is supplied from an external device (device2inFIG. 2). Here, it is assumed that voltage is not applied to the terminal1-1.

When it is confirmed that voltage is not applied to the terminal1-1at step S12, power supply of the Reg1is turned on (step S13) and then the SW1-1is turned on as well, thereby supplying power from the Reg1to the terminal1-1via the SW1-1and also supplying power to the Drive circuit1so as to drive the Drive circuit1(step S14).

On the other hand, when power is supplied from the terminal1-1of the device1to the terminal1-2of the device2via the interface21, the voltage applied to the terminal1-2is input to the comparator2and the power supplied to the terminal1-2is supplied to the Drive circuit2so as to drive the Drive circuit2(step S15), and thereby a high-level signal is output from the terminal2-2to the interface21(step S16).

The device1detects the high level signal from the device2with the Drive circuit1via the terminal2-1, and starts the data communication with the device2(step S17).

In this state, accordingly, since the Reg2of the device2is off and the data communication is performed between the device1and the device2via the interface21by using power of the Reg1of the device1, it reduces power consumption.

In an actual configuration of the apparatus, however, there may be a case where the power only from Reg1is not sufficient during the data communication. The device incorporating the data communication function according to the present embodiment enables the data communication even in such a case. In the device2, the voltage at the terminal1-2and the standard voltage generated from the battery voltage VDD are compared by the comparator2, so as to monitor the voltage applied to the terminal1-2(step S18).

If the voltage at the terminal1-2is equal to or higher than the standard voltage as a result, the control unit2determines that power from the device1is sufficient to operate (step S19) and returns to step S18to maintain the monitoring state of the voltage.

In contrast, if the voltage at the terminal1-2is lower than the standard voltage, the control unit2turns the Reg2and the SW2-2on so as to supply power from the Reg2to the Drive circuit2via the reverse current blocking2and the SW2-2, thereby ensures normal data communication (step S20).

In such a state, however, both of the Reg1and the Reg2are turned on and thus increasing power consumption. Therefore, the device incorporating the data communication function according to the present embodiment turns the Reg2off wherever possible. For this reason, the device2monitors the load of the terminal1-2by comparing the output voltage of the Reg2and the voltage at the terminal1-2by the comparator2(step S21).

As a result, if there is no change in a difference between the output voltage of the Reg2and the voltage at the terminal1-2after the Reg2is turned on, that is, if there is no change in load or if the difference in the voltages is increased, namely, the load is increased, the control unit2determines to maintain the on state of the Reg2and the SW2-2(step S22) and returns to step S21to maintain the monitoring state of the load.

In contrast, if the difference between the output voltage of the Reg2and the voltage at the terminal1-2is decreased, that is, if the load is reduced, the control unit2turns the SW2-2off (step S23) and controls the comparator2to compare the voltage at the terminal1-2and the standard voltage (step S24).

As a result, if the voltage at the terminal1-2is lower than the standard voltage, which means that the voltage is still not sufficient, thus the control unit2turns the SW2-2on (step S25) again and returns to step S24to monitor the load of the terminal1-2.

In contrast, if the voltage at the terminal1-2is equal to or higher than the standard voltage, which means that sufficient power is supplied by the Reg1, thus the control unit2turns the Reg2off (step S26) and shifts to a process at step S18.

As described above, since the device incorporating the data communication function according to the present embodiment turns off the Reg2of itself and drives the Drive circuit2to perform a communication by using power supplied to the terminal1-2from the Reg1of the device1, which initiates the communication, and also maintains the Reg2off while the voltage applied to the terminal1-2is equal to or higher than the standard voltage, it is thus possible to reduce self-power-loss. Moreover, if the comparator2detects that the voltage applied to the terminal1-2is lower than the standard voltage, the device incorporating the data communication function according to the present embodiment turns the Reg2and the SW2-2on so as to drive the Drive circuit2by using power from the Reg1and power from the Reg2of itself, which is supplied via the reverse current blocking2and the SW2-2. It is thus possible to perform highly reliable communication in a stable manner.

Second Embodiment

FIG. 5is a block diagram illustrating a configuration of a main section of an interface unit of the device incorporating the data communication function according to a second embodiment of the present invention. According to the device incorporating the data communication function of the present embodiment, if the Reg2of the device2of the reception side is turned on after the Reg1of the device1which initiates the data communication is turned on in the first embodiment, the Reg1of the device1may be turned off under a predetermined condition.

Therefore, the device incorporating the data communication function according to the present embodiment further includes, in the configuration shown inFIG. 2, a switch (SW3-1)62-1between a connection point61-1of the switch55-1, the switch57-1and the drive circuit53-1and the power terminal51-1in the interface unit45of the first device14. In addition, a comparator58-1monitors voltage applied to the power terminal51-1, as well as comparing the voltage and the standard voltage generated from the battery voltage VDD to provide a result of the comparison to the control unit54-1. Thereby, the control unit54-1controls the power supply circuit36to be turned on/off, as well as controlling the switches55-1,57-1and62-1to be turned on/off. In an initial state, the power supply circuit36and the switches55-1,57-1and62-1are off. Other constitutions are the same as those of the device1shown inFIG. 2.

An interface unit46corresponding to the interface unit21of the second device15is configured in the same manner as the interface unit of the first device14. InFIG. 5, the same elements as those in the first device14are provided with the same reference signs but have a hyphen and a number2thereafter.

The following is a description of an operation of data communication by the device incorporating the data communication function according to the present embodiment shown inFIG. 5, by using an exemplified case where the data communication is initiated by the first device14to the second device15, with reference to the flow charts inFIG. 6toFIG. 8. It is to be noted that terms expressed in blocks inFIG. 5are used in the following description.

Until communication is initiated, the device1maintains the initial state in which all of the Reg1, the SW1-1, the SW2-1and the SW3-1are off. Likewise, the device2maintains the initial state in which all of the Reg2, the SW1-2, the SW2-2and the SW3-2are off (step S31). In order for the device1to initiate communication with the device2in the initial state, the control unit1first checks whether voltage is applied to the terminal1-1from the output of the comparator1(step S32). Here, it is assumed that the voltage is not applied to the terminal1-1.

When it is confirmed that voltage is not applied to the terminal1-1at step S32, the control unit1turns the power supply of the Reg1on (step S33) and also turns SW1-1and SW3-1on, thereby supplying power from the Reg1to the terminal1-1via the SW1-1and the SW3-1and also supplying power to the Drive circuit1via the SW1-1so as to drive the Drive circuit1(step S34).

When the Reg1, the SW1-1and the SW3-1are turned on, the terminal1-2of the device2is supplied with power from the terminal1-1of the Reg1via the interface21(step S35).

In the device2, when the comparator2detects that voltage is applied to the terminal1-2(step S36), the control unit2turns the SW3-2on so as to drive the Drive circuit2by providing the Drive circuit2with the power supplied to the terminal1-2(step S37) and also controls the Drive circuit2such that a high level signal is output from the terminal2-2to the interface21(step S38).

The device1detects the high level signal from the device2with the Drive circuit1via the terminal2-1, and starts the data communication with the device2by detecting.

Accordingly, in this state the Reg2of the device2is turned off and the data communication is performed between the device1and the device2via the interface21by using power of the Reg1of the device1, thereby reducing power consumption.

In the same manner as the first embodiment, the present embodiment considers a case where the Reg1cannot supply sufficient power during the data communication and enables the data communication even in such a case. In the device2, the voltage at the terminal1-2and the standard voltage generated from the battery voltage VDD are compared by the comparator2, so as to monitor the voltage applied to the terminal1-2(step S40).

If the voltage at the terminal1-2is equal to or higher than the standard voltage as a result, the control unit2determines that power from the device1is sufficient to operate (step S41) and returns to step S40to maintain the monitoring state of the voltage.

In contrast, if the voltage at the terminal1-2is lower than the standard voltage, the control unit2determines that the power from the device1is insufficient and performs a power supply process of the device2(step S42). Therefore, the Reg2and the SW2-2are turned on (step S43) and thereby the Drive circuit2is supplied with not only power from the device1but also power from the Reg2via the reverse current blocking2and the SW2-2, so as to ensure the normal data communication (step S44).

In such a state, however, both of the Reg1and the Reg2are turned on and thus increasing power consumption. Therefore, the device incorporating the data communication function according to the present embodiment turns off the Reg1whenever possible.

In the device1, therefore, the control unit1detects increase in the voltage at the terminal1-1to be higher than the standard voltage from the output of the comparator1(step S45), turns the SW2-1on and then turns the SW1-1off so as to insert the reverse current blocking1to a power supply path (step S46). That is, since the voltage applied to the terminal1-1of the device1becomes higher when the Reg2of the device2is turned on, it is detected that the Reg2is turned on by detecting a change in the voltage by the comparator1.

When the reverse current blocking1is inserted at step S46, the voltage at the terminal1-1detected by the comparator1is decreased as much as power loss by the reverse current blocking1(step S47). Likewise, the voltage at the terminal1-2detected by the comparator2is also decreased in the device2(step S48).

Therefore, when the comparator2detects that the voltage at the terminal1-2is reduced in the device2, the control unit2turns the SW1-2on and then turns the SW2-2off so as to cancel the reverse current blocking2. The power from Reg2is thereby supplied to the Drive circuit2and the terminal1-2without the reverse current blocking2(step S49).

When the reverse current blocking2in the device2is cancelled as stated above, power of Reg2is not lost by the reverse current blocking2, and thus the voltage at the terminal1-2increases and also the voltage applied to the terminal1-1of the device1increases to be equal to or higher than the standard voltage.

When increase in the voltage at the terminal1-1of the device1is detected by the comparator1(step S50), the control unit1turns the SW2-1off (step S51) and compares the voltage at the terminal1-1and the standard voltage by the comparator1(step S52), so as to check whether it is possible to drive only with the Reg2of the device2.

If the voltage at the terminal1-1is equal to or higher than the standard voltage as a result, the control unit1turns the Reg1Off (step S53). In this case, accordingly, the data communication is performed between the device1and the device2via the interface21by the power of Reg2of the device2, and it is thus possible to reduce power consumption.

In contrast, if the voltage at the terminal1-1is lower than the standard voltage, the control unit1turns the SW2-1on again (step S54). Since both of the Reg1of the device1and the Reg2of the device2are on in this state, it is preferred to eliminate power loss by the reverse current blocking1and the reverse current blocking2and to supply power to the Drive circuit1and the Drive circuit2individually.

In this case, therefore, the control unit1of the device1turns the SW3-1off, and then turns the SW1-1on and the SW2-1off so as to cancel the reverse current blocking1(step S55). In this state, the reverse current blocking2of the device2has been already cancelled at step S49.

As stated above, with regard to the device incorporating the data communication function according to the present embodiment, the device2of a reception side of the data communication turns the Reg2of itself off in the same manner as the first embodiment and performs the communication by driving the Drive circuit2by using power supplied to the terminal1-2from Reg1of the device1which initiates the communication and, if the voltage applied to the terminal1-2is equal to or higher than the standard voltage, maintains the Reg2off. It is thus possible to reduce self-power-loss.

In addition, if the Reg2of the device2is turned on and the voltage applied to the terminal1-1is equal to or higher than the standard voltage after Reg1of the device1as the initiator of the data communication is turned on to start the data communication, the reverse current blocking1is inserted. And then, if the voltage applied to the terminal1-1is higher than the standard voltage in a state where the power supply from the Reg1is blocked, the Reg1is turned off and Drive circuit1is driven by the Reg2to perform the communication. Therefore, it is possible to reduce self-power-loss of the device1.

As described in the above embodiments, since each of the device incorporating the data communication function according to the present invention has power supply circuit, even if power supply is insufficient when a system is constituted by connecting a plurality of devices via the same interface such as a bus connection or a daisy chain, for example, it is possible to address by turning on the power supply circuits of the plurality of devices, and thus there is no need to redesign the power supply circuit, unlike the multiple power supply device. Thus, since there is no restriction by the power supply circuit, it is possible to easily achieve expansion of functions for the mobile terminal and the likes. That is, expansion of functions can be achieved without changing an operating time by changing a battery capacity for supplying power to the entire system in accordance with expanded configuration.

Moreover, when the system is constituted by using the multiple power supply device as shown inFIG. 9, a power supply of the interface (I/F) is turned on/off according to a state transition of the system such as a sleep mode or a suspend mode. However, if the system is constituted by using the device incorporating the data communication function according to the present invention, it enables to turn on/off a corresponding power supply circuit only when respective interface I/F exchanges signals. Accordingly, since it is possible to reduce power consumption of the power supply circuit in a normal operation state as well, power consumption can be reduced much more than the system constituted by using the multiple power supply device. In addition, since power consumption by each power supply circuit is thereby reduced, it is possible to reduce the area of the power supply circuit of the hybrid IC and achieve downsizing of the device.

It is to be understood that the present invention is not limited to the embodiment set forth above but may be varied or altered in a multiple of manners. For example, the device incorporating the data communication function according to the present invention is not only applicable to the mobile terminal used in the above embodiments but also may be used as a component of a variety of electronic devices. In addition, since the device itself has a power supply circuit capable of being turned on/off, the device incorporating the data communication function according to the present invention can be mounted in a system using the conventional multiple power supply device and can be incorporated when shifting the conventional multiple power supply system to the dispersed power supply system.