JP3362027B2 - USB device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a US equipped with a USB (Universal Serial Bus) as an interface bus.
The present invention relates to a B-compatible device, and more particularly, to a device having a high-side switch circuit for limiting the magnitude of a power supply current supplied from the outside of the device via the USB and sending it to the inside of the device.

[0002]

2. Description of the Related Art In recent years, a USB has come into the market as an interface bus for connecting a host computer such as a personal computer and peripheral devices (a floppy (registered trademark) disk drive device, a printer, a scanner, etc.) to the spotlight.
In the peripheral device equipped with the USB (hereinafter, referred to as a USB device), interfaces that have been separately provided in the related art can be shared.

FIG. 3 is a block diagram showing a schematic configuration of a computer system including a conventional USB device. As shown in the figure, the USB device 100 ′ has a USB cable 15
It is connected to the host computer 200 such as a personal computer through the 0. This USB cable 150 has a USB device 1
00 'and the signal line 151 for transmitting signals between the host computer 200 and the host computer 200 to the USB
Power supply line 152 for supplying power to the device 100 '
And are assigned.

The signal line 1 introduced into the USB device 100 '
The USB device 1 is connected to the internal circuit 110.
Signals are exchanged between 00 'and the host computer 200. On the other hand, the power supply line 152 is connected to the internal circuit 1
10 is not directly connected to the internal circuit 110, but is connected to the internal circuit 110 via the high side switch circuit 130.

The high side switch circuit 130 is a current limiter that limits the magnitude of the power supply current supplied from the host computer 200 to a predetermined level. FIG. 4 is a block diagram showing a schematic configuration of the high side switch circuit 130. As shown in the figure, the high-side switch circuit 130 includes a reference voltage circuit unit 131, a current limit circuit unit 132, a thermal shutdown circuit unit 133, a gate control circuit unit 134, an oscillation circuit unit 135, and a charge pump circuit unit 136. is doing.

Further, one end of a resistor R2 is connected to an input terminal T _in which receives power supply from the power supply line 152. The other end of the resistor R2 is connected to the drain (D) of the power transistor Q2 which is an N-channel MOS transistor. The source (S) of the power transistor Q2 is connected to the output terminal T _out that supplies power to the internal circuit 110, and is also connected to the ground via the bypass capacitor C2 for removing a noise component (AC component). . The gate (G) of the power transistor Q2 is connected to the gate control circuit section 134.

The high side switch circuit 130 having the above configuration
The operation of will be described. The reference voltage circuit unit 131 is connected to the input terminal T _in, and is connected to the host computer 200.
Based on the power supply voltage (for example, 5 V) supplied from the above, a reference voltage (for example, 1.2 V) that is a drive voltage for each circuit unit included in the high side switch circuit 130 is generated. The thermal shutdown circuit section 133 and the gate control circuit section 134 operate with this reference voltage. Further, the reference voltage circuit unit 131 also generates a reference voltage (for example, 0.1 V) used in the current limit circuit unit 132 by dividing the reference voltage.

The current limit circuit section 132 compares the reference voltage with the voltage across the resistor R2 and sends the comparison result to the gate control circuit section 134. The gate control circuit unit 134 is the current limit circuit unit 13.
The gate voltage of the power transistor Q2 is controlled based on the comparison result obtained from No. 2. By controlling the magnitude of the voltage across the resistor R2 by such feedback control, the power supply current flowing through the output terminal _Tout can be limited.

The thermal shutdown circuit section 13
_{Reference numeral} 3 denotes an analog circuit section having a function of detecting abnormal heat generation that occurs when the input terminal T _in and the output terminal T _out are short-circuited and controlling the gate control circuit 134 to cut off the power supply to the internal circuit 110. is there. By providing such a safety mechanism, it is possible to prevent the internal circuit 110 from being destroyed or ignited.

The charge pump circuit section 136 has a function of boosting the gate voltage applied to the gate (G) of the power transistor Q2 by using the oscillation circuit section 135. By providing such a boosting mechanism, the on resistance of the power transistor Q2 can be reduced. Therefore, it is possible to suppress the power consumed by the power transistor Q2 and contribute to the power saving of the high side switch circuit 130.

The high side switch circuit 130 having the above configuration
Then, by limiting the power supply current flowing to the output terminal T _out , the USB device 100 ′ and the host computer 2
It is possible to soften the rising of the current that occurs when 00 and 0 are plug-connected, and it is possible to suppress the generation of noise due to the inrush current. In addition, since noise is removed by the bypass capacitor C2, even if noise is superimposed on the power supply current supplied to the USB device 100 ′, the adverse effect of the noise does not reach the internal circuit 110. be able to.

[0012]

However, in the conventional high-side switch circuit 130 having the above-mentioned configuration,
Only the reference voltage circuit unit 131 is provided with the means for generating the driving reference voltage for each of the circuit units 131 to 136 that configures itself. As described above, the reference voltage circuit unit 131 is connected to the input terminal T _in and generates the reference voltage based on the power supply from the host computer 200. But,
The USB cable 150, which is the supply path of the supply power, is used by being routed around, and noise removal by a capacitor is not performed. Therefore, the power supply is supplied to the USB device 100 ′ in a state of including the noise component. Therefore, the reference voltage generated from the power supply also becomes a voltage including a noise component.

Even if the reference voltage contains a little noise, the feedback control in the current limit circuit section 132 and the gate control circuit section 134 can be performed without any problem. However, in a circuit section that requires analog characteristics such as the thermal shutdown circuit section 133, there is a problem that the operation characteristics deteriorate when a noise component is added to the reference voltage.

Further, for example, when the input terminal T _in is short-circuited to the ground to cause an abnormality in the power supply, the thermal shutdown circuit section 133 and the like cannot function normally in the conventional high side switch circuit 130, and U
There is a possibility that the SB device 100 'may develop into a fatal trouble.

In view of the above problems, it is an object of the present invention to provide a USB device having a high side switch circuit having stable analog characteristics against noise of the power supply. Another object of the present invention is to provide a USB device capable of performing fail-safe control for an abnormality in power supply obtained from outside the device.

[0016]

To achieve the above object, in a USB device according to the present invention, a USB (Universal Serial Bus) is provided as an interface bus and is supplied from outside the device via the USB. In a USB device equipped with a high-side switch circuit for limiting the magnitude of a power supply current and sending it to the inside of the device, the USB device is connected to an input side of the high-side switch circuit,
A first reference voltage circuit unit for generating a predetermined reference voltage from an input voltage to the high side switch circuit and an output side of the high side switch circuit, and a predetermined reference voltage from the output voltage of the high side switch circuit. And a second reference voltage circuit section for generating the reference voltage, and the respective reference voltages generated by the first and second reference voltage circuit sections are separately used for each circuit section constituting the USB device and supplied. .

In the USB device, the reference voltage generated by the first reference voltage circuit unit is supplied to the circuit unit that must operate when power is supplied from the outside of the device, and analog characteristics are required. It is preferable to supply the reference voltage generated by the second reference voltage circuit section to the circuit section that operates.

Further, the USB device is provided with output voltage detecting means for detecting the magnitude of the output voltage output from the high side switch circuit, and the reference voltage generated by the second reference voltage circuit section is supplied. A part or all of the circuit section may be controlled by the output signal of the output voltage detecting means.

Further, in the USB device, it is preferable that a part or all of an internal circuit constituting the USB device is incorporated as a circuit part to which the reference voltage generated by the second reference voltage circuit part is supplied. .

[0020]

1 is a block diagram showing a schematic configuration of a computer system including a USB device according to the present invention. As shown in the figure, the USB device 1 according to the present invention
00 has a configuration similar to that of the conventional USB device 100 ′ shown in FIG.
It is characterized by the internal configuration of 20. Therefore, regarding each circuit other than the high side switch 120, FIG.
The description of the configuration and the operation is omitted by giving the same reference numerals to the following, and the internal configuration of the high-side switch 120 will be mainly described below.

The high side switch circuit 120 is a current limiter which limits the magnitude of the power supply current supplied from the host computer 200 to a predetermined level. FIG. 2 is a block diagram showing an embodiment of the high side switch circuit 120. The high side switch circuit 120 according to this embodiment includes a first reference voltage circuit unit 121, a current limit circuit unit 122, a thermal shutdown circuit unit 123,
A gate control circuit section 124, an oscillation circuit section 125,
In addition to the charge pump circuit unit 126, it has a second reference voltage circuit unit 127 and an output voltage detection circuit unit 128.

The high-side switch circuit 120 of this embodiment uses a part or all of an analog circuit (for example, the internal circuit 110) conventionally provided outside the high-side switch circuit as the other circuit section 129. It has a built-in configuration.

Further, one end of the resistor R1 is connected to the input terminal T _in which receives power supply from the power supply line 152. The other end of the resistor R1 is connected to the drain (D) of the power transistor Q1 which is an N-channel MOS transistor. The source (S) of the power transistor Q1 is an output terminal T _{out for} supplying power to the internal circuit 110, and a second terminal
Reference voltage circuit unit 127 and output voltage detection circuit unit 128
To the ground via a bypass capacitor C1 for removing a noise component (AC component). Power transistor Q1
(G) is connected to the gate control circuit section 124.

The high side switch circuit 120 having the above structure
The operation of will be described. The first reference voltage circuit unit 121 is connected to the input terminal T _in, and is connected to the host computer 2
Based on the power supply voltage (for example, 5V) supplied from 00, a first reference voltage (for example, 1.2V) that is a drive voltage for each circuit unit included in the high side switch circuit 120 is generated. The first reference voltage is supplied to a circuit unit, such as the gate control circuit unit 124, which must operate when power is supplied from the outside of the device. Also, the first
The reference voltage circuit unit 121 also generates a reference voltage (for example, 0.1 V) used in the current limit circuit unit 122 by dividing the first reference voltage.

The current limit circuit section 122 compares the reference voltage with the voltage across the resistor R1 and sends the comparison result to the gate control circuit section 124. The gate control circuit unit 124 is the current limit circuit unit 12.
The gate voltage of the power transistor Q1 is controlled based on the comparison result obtained from No. 2. By controlling the magnitude of the voltage across the resistor R1 by such feedback control, the power supply current flowing to the output terminal T _out can be limited.

The thermal shutdown circuit section 12
_{Reference numeral} 3 denotes an analog circuit unit having a function of detecting abnormal heat generation that occurs when the input terminal T _in and the output terminal T _out are short-circuited and controlling the gate control circuit 124 to cut off the power supply to the internal circuit 110. is there. By providing such a safety mechanism, it is possible to prevent the internal circuit 110 from being destroyed or ignited.

Further, the charge pump circuit section 126 has a function of boosting the gate voltage applied to the gate (G) of the power transistor Q1 by using the oscillation circuit section 125. By providing such a boosting mechanism, the on resistance of the power transistor Q1 can be reduced. Therefore, it is possible to suppress the power consumed by the power transistor Q1 and contribute to the power saving of the high side switch circuit 120.

The high side switch circuit 120 having the above structure
Then, by limiting the power supply current flowing to the output terminal T _out , the USB device 100 and the host computer 20
It is possible to soften the rise of the current that occurs when 0 and 0 are plug-connected, and it is possible to suppress the generation of noise due to the inrush current. In addition, the bypass capacitor C
Since the noise is removed by 1, even if noise is superimposed on the power supply current supplied to the USB device 100, it is possible to prevent the adverse effect of the noise from reaching the internal circuit 110.

Here, in the high side switch circuit 120 of this embodiment, the second reference voltage circuit section 121 is connected to the output terminal T _out , and based on the output voltage of the high side switch circuit 120, it becomes high. The configuration is such that a second reference voltage that is a drive voltage for each circuit unit that constitutes the side switch circuit 120 is generated. This second reference voltage is supplied to a circuit section requiring analog characteristics, for example, the thermal shutdown circuit section 123 or other circuit section 129.

As described above, the output voltage of the high side switch circuit 120 is subjected to feedback control by the current limit circuit section 122 and the gate control circuit section 124 and noise removal by the bypass capacitor C1, and the input terminal T _in It is a voltage with much less noise than the power supply applied to the. Therefore, it can be said that the second reference voltage generated based on the output voltage is a voltage less susceptible to the power supply noise than the first reference voltage.

With such a structure, even if the power supply from the outside of the apparatus contains a noise component,
It is possible to supply the second reference voltage, which is not easily affected by the power supply noise, to a circuit section that requires analog characteristics, such as the thermal shutdown circuit section 133. Therefore,
Even when a noise component is added to the power supply, deterioration of the operating characteristics of the thermal shutdown circuit unit 133 and the like is suppressed, and the high-side switch circuit 120 having stable analog characteristics with respect to the noise of the power supply can be provided. .

Further, in the high side switch circuit 120 of the present embodiment, the output voltage detection circuit section 128 is connected to the output terminal T _out , the output voltage value of the high side switch circuit 120 is detected, and the detection result is obtained. Is a configuration for controlling the operation of part or all of the circuit section to which the second reference voltage is supplied.

For example, at the time of transition immediately after turning on the power supply from the outside of the apparatus or when the wiring pattern is short-circuited,
When the output voltage value of the high side switch circuit 120 is detected to be equal to or lower than the predetermined voltage value, the output voltage detection circuit unit 1
28 determines that power supply to the high side switch circuit 120 is not normally performed. Then, in such a reduced voltage state, a circuit portion (the thermal shutdown circuit portion 123 or the other circuit portion 129) that may cause a fatal trouble that destroys the IC itself or data.
Etc.) for fail-safe operation control.
For example, a signal for detecting a temperature abnormality is continuously output to the thermal shutdown circuit unit 123 to shut off (protect) the high side switch circuit 120,
Prohibits writing to the recording device.

With such a configuration, it is possible to perform a fail-safe control for an abnormality in the power supply obtained from the outside of the apparatus. Therefore, even if an abnormality occurs in the power supply. It is possible to prevent a fatal trouble of the USB device 100.

The high-side switch circuit 120 of this embodiment uses a part or all of an analog circuit (for example, the internal circuit 110) conventionally provided outside the high-side switch circuit as the other circuit section 129. It has a built-in configuration. Conventionally, in the USB device 100, it is general that the internal circuit 110 and the high side switch circuit 120 are configured by separate ICs, but by adopting this embodiment, both ICs are integrated into one chip. It becomes possible. With such a configuration, U
Reduction of the board area mounted on the SB device 100, and
This can contribute to downsizing and weight reduction of the B device 100 itself.

[0036]

As described above, in the USB device according to the present invention, the first reference voltage circuit section for generating the first reference voltage from the input voltage to the high side switch circuit and the output voltage of the high side switch circuit. A second reference voltage circuit unit for generating a second reference voltage from the device, and the first and second reference voltages are separately used for each circuit unit constituting the USB device and supplied, particularly from the outside of the device. The first reference voltage is supplied to the circuit section that must operate when power is supplied, and the second reference voltage is supplied to the circuit section that requires analog characteristics.

With such a structure, even if the power source supplied from the outside of the apparatus contains a noise component,
It is possible to supply the second reference voltage, which is not easily affected by the power supply noise, to the circuit unit requiring the analog characteristic. Therefore, even when a noise component is added to the power supply, deterioration of the operating characteristics of the circuit unit that requires analog characteristics is suppressed, and a high-side switch circuit having stable analog characteristics against the noise of the power supply is provided. US
A B device can be provided.

Further, in the USB device having the above configuration,
An output voltage detection unit that detects the magnitude of the output voltage output from the high-side switch circuit is provided, and a part or all of the circuit unit to which the second reference voltage is supplied is output by the output signal of the output voltage detection unit. It is recommended that the configuration be controlled.

With such a configuration, it is possible to perform a fail-safe control for an abnormality in the power supply obtained from the outside of the apparatus. Therefore, even if an abnormality occurs in the power supply. It is possible to prevent a fatal trouble of the USB device.

Further, in the USB device having the above configuration, the circuit unit to which the second reference voltage is supplied is the US unit.
It is preferable that a part or all of the internal circuits that configure the device B are built-in. With such a configuration, the internal circuit and the high side switch circuit, which are conventionally provided as separate ICs, can be integrated into one chip IC. Therefore, it is possible to contribute to the reduction in the area of the board mounted on the USB device and the reduction in size and weight of the USB device itself.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a computer system including a USB device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a high side switch circuit 120.

FIG. 3 is a block diagram showing a schematic configuration of a computer system including a conventional USB device.

FIG. 4 is a block diagram showing a schematic configuration of a high side switch circuit 130.

[Explanation of symbols]

100 USB device 110 Internal circuit 120 high side switch circuit 121 First Reference Voltage Circuit Unit 122 Current limit circuit 123 Thermal shutdown circuit section 124 Gate control circuit section 125 oscillator circuit 126 Charge pump circuit 127 Second reference voltage circuit section 128 Output voltage detection circuit 129 Other circuits 150 USB cable 151 signal line 152 power supply line 200 host computer

Claims (4)

(57) [Claims] 1. A USB (Univ
and a high-side switch circuit for limiting the magnitude of the power supply current supplied from the outside of the device via the USB and sending the power current to the inside of the device. A first reference voltage circuit unit connected to an input side of the circuit and generating a predetermined reference voltage from an input voltage to the high side switch circuit; and a high side switch circuit connected to an output side of the high side switch circuit. And a second reference voltage circuit section for generating a predetermined reference voltage from the output voltage of each of the reference voltages generated by the first and second reference voltage circuit sections.
A USB device, wherein the USB device is selectively used and supplied for each circuit unit constituting the USB device. 2. A circuit section that must operate when power is supplied from the outside of the device is supplied with a reference voltage generated by a first reference voltage circuit section, and a circuit section that requires analog characteristics is supplied with a second reference voltage. 2. The USB device according to claim 1, wherein the reference voltage generated by the two-reference voltage circuit unit is supplied. 3. A part of a circuit portion to which the reference voltage generated by the second reference voltage circuit portion is supplied, or an output voltage detecting means for detecting the magnitude of the output voltage output from the high side switch circuit is provided. All are controlled by an output signal of the output voltage detecting means.
Alternatively, the USB device according to claim 2. 4. A circuit part to which a reference voltage generated by a second reference voltage circuit part is supplied, wherein a part or all of an internal circuit constituting the USB device is built in. Item 4. The USB device according to any one of Items 3.