KR20080042271A - A usb device sensing usb connection - Google Patents

Abstract

A USB(Universal Serial Bus) device for sensing USB connection is provided to sense USB connection correctly regardless of influence of a USB cable and an operation state of a USB device. A tri-state buffer(211) receives an input signal corresponding to USB power provided from a pc(101). A first pull-down resistor(212) sets an initial value of the tri-state buffer by connecting to the tri-state buffer. A bi-state buffer(210) is connected to an edge of the tri-state buffer and removes oscillation caused by an undefined area of the tri-state buffer. A USB connection sensing module senses the USB connection from rising and falling edges output from the tri-state buffer. A ripple and discharge processing module removes and discharges ripple from the USB power. An enable pin of the tri-state is connected to a USB pull-up enable port for controlling pull-up operation of a data line transmitting USB data. An SOC(System On Chip)(120) includes an USBPUEN(105) port for performing a pull-up operation and a DM/DP port(113) for transmitting real data.

Description

A USB device sensing a USB connection {A USB device sensing USB connection}

1 is a USB device according to the prior art.

2 is a block diagram illustrating an example of a USB device according to the present invention.

3 shows the waveform at the time of rising edge due to USB cable attachment.

Figure 4 shows the waveform when there is no Schmitt trigger buffer according to the present invention when the USB cable is disconnected.

5 is a diagram illustrating hysteresis of the Schmitt trigger buffer according to the present invention.

6 shows waveforms when the Schmitt trigger buffer according to the present invention is present when the USB cable is disconnected.

The present invention relates to a USB device, and more particularly, to a USB device for accurately detecting a connection state with an external device.

USB (Universal Serial Bus) refers to a bus standard for connection between various electronic devices including a PC. Devices conforming to the USB standard can exchange data by connecting cables conforming to the USB standard.

In general, the USB interface is implemented as a host such as a PC and a slave such as a USB memory, and a USB controller connecting the host and the slave. In addition, the USB controller is a structure including a CPU and an external interface, and thus, in real circuit implementation, all signals related to addresses and data and signals for control must be connected. However, recently, it is simply implemented as a system on chip (SOC) as a USB IP type inside a single chip. Accordingly, the SOC device, that is, the USB controller is directly connected to the USB connector.

1 is a USB device according to the prior art. In FIG. 1, the host role is performed by the PC 101, and the PC 101 and the slave 130 device are connected through a USB cable. The slave device includes the above-described SOC 120, the USB connector 102, and other interface devices.

More specifically, the SOC 120 is a USBSENSE 107 port for determining whether there is a physical connection between a powered VDDUSB 108 port and an external device and a USB cable, and a pull-up according to a conventionally proposed standard. There is a USBPUEN 105 port for performing a pull-up operation, and a DM and DP 113 ports for actual data transmission. The signals output from the DM and DP ports are USB differential signals, and the outputs of the DM and DP have different values.

The slave 130 device also includes other interface devices as follows.

First, a regulator 104 for supplying a voltage to the SOC 120 and a voltage distribution circuit 114 for connecting and disconnecting a USB cable and a DP line output from the DP 113 port. There is a pull-up control unit 106 that controls the pull-up operation. As shown, the voltage applied to the regulator 104 and the voltage applied to the USBSENSE 107 port are different, which is due to the voltage divider circuit 114.

Hereinafter, the operation of connecting the USB cable to the USB connector 102 via the USB cable will be referred to as attaching the USB cable, and the operation of removing the USB cable from the USB connector 102 will be referred to as USB cable detachment.

The USBSENSE 107 port of FIG. 1 detects USB cable attach and detach. More specifically, the USB device signals whether the USB cable is connected to the SOC 120 by generating a signal rising / falling edge using VBUS. In addition, the pull-up control unit 106 that controls the pull-up on the DP line serves to inform the USB host device of a conventional USB standard (eg, full speed, high speed). The USB standard is also called USB 2.0 / USB 1.1. The pull-up control unit 106 performs an operation according to a conventional standard.

Of course, USB speed is not only full speed and high speed but also low speed, which is not considered below since it is a pull-up operation on the DM line rather than the DP line.

The operation of the conventional apparatus will be described below.

In FIG. 1, when the USB cable is connected to the USB connector 102 and the USB connector of the PC 101, the DP / DM line is directly connected to the SOC 120 device from the host PC. In addition, the USB power source VBUS output from the host PC is input to a regulator 104 that converts 5V into 3.3V.

The VBUS converted by the regulator 104 is fed to the VDDUSB 108 of the SOC 120. The output of the regulator 104 is applied to the USBSENSE 107 via the voltage distribution circuit 114. The input and output signals used by the USBSENSE 107 to determine whether the USB is connected are generally interrupt input / output (I / O). For this reason, there may be a case where the VDDUSB 108 and the USBSENSE 107 need to be powered by separate power sources. For this case, the voltage distribution circuit 114 supplies suitable power to the USBSENSE 107.

The USBSENSE 107 provided in the SOC 120 detects whether a USB cable is connected in the following manner.

The detection method is to detect a rising edge / falling edge. That is, when the USB cable is connected or removed, a rising edge or a falling edge is generated. At this time, the signal applied to the USBSENSE 107 is checked to be high or low to attach. Or detect separation.

Conventional USB devices have a predetermined capacitor C1 103 as shown in FIG.

As shown, capacitor C1 103 attached to VBUS is intended to remove ripples that occur when the USB cable is attached or detached.

The USBPUEN 105 port of the SOC 120 determines whether to enable USB pull-up operation for the DP line. According to the conventional standard, when a USB connection is detected, the SOC 120 enables a pull-up operation, and when the connection is released, the SOC 120 disables the pull-up.

The problem of the prior art will be described below.

When attaching / detaching the USB cable to the connector 102 When the connector side provided in the host 101 is connected to the USB cable and attached / detached from the slave 130 side (hereinafter, 'A 'Case') and the slave 130 may be connected and attached / detached from the host 101 (hereinafter, referred to as 'case B').

In general, 'A case' is no problem. However, 'B' causes the following problem.

If the USB cable is removed, it may be perceived as high for a considerable time by the capacitor 103 to remove the line charging effect and VBUS ripple caused by the length of the cable. Voltage is maintained. In particular, the larger the capacitance value of the ripple removing capacitor 103, the better the ripple is removed. On the other hand, the discharge of the USB cable is rather poor.

As a result, for this reason, the USB cable is actually disconnected but the output of regulator 104 may remain abnormally high. In this situation, if the USB cable is directly connected, the rising edge does not occur and there may be a problem in detecting the USB connection.

This problem may occur in cases other than A / 'B'. Hereinafter, another case where a problem occurs in detecting whether or not a USB connection is described will be described.

If the power of the slave 130 device is switched from off to on, it may take a certain time. In addition, a regular booting operation must also be performed for the normal operation of the slave 130 device, and this booting takes a certain time. If the USB cable is attached (hereinafter, referred to as 'C') after the power supply and booting are completed, the rising edge is input at the moment when the device of the slave 130 is normally operated. Can be detected accurately.

But. If the physical connection of the USB cable is already completed (hereinafter referred to as 'D') before the power supply or booting operation is completed normally, a problem occurs. That is, since the rising edge has already been input at the time when the slave 130 device cannot detect anything, the slave 130 after the booting is not able to detect the rising edge.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to propose a USB device capable of accurately detecting a USB connection.

Another object of the present invention is to propose a USB device capable of accurately detecting a USB connection irrespective of the effect of the USB cable.

Another object of the present invention is to propose a USB device capable of accurately detecting a USB connection regardless of the operating state of the USB device.

Summary of the Invention

According to an aspect of the present invention, a USB device includes: a tri-state buffer configured to receive an input signal corresponding to an externally provided USB power source to achieve the above object; A first pull-down resistor connected to the output of the three-phase buffer to set an initial value of the three-phase buffer; A bi-stable buffer connected to an input of the three-phase buffer to remove oscillation by an undefined region of the three-phase buffer; A USB connection sensing module configured to detect a USB connection through a rising edge or a falling edge output from the three-phase buffer; And a ripple and discharge processing module for removing and discharging a ripple in the USB power source.

Preferably, the enable pin of the three-phase buffer is connected to a USB pull-up enable port for controlling a pull-up operation of a data line transmitting USB data.

Preferably, the bistable buffer is a Schmitt trigger buffer.

Work of invention Example

The present invention provides a stable connection and disconnection when connecting through a USB cable in a system board including a SOC with a built-in USB controller, and correctly connects the USB cable even when the power is turned on while the cable is connected in advance. It relates to a device that can be recognized.

The construction, operation and specific features of the present invention will be further embodied by one embodiment of the present invention described below. Hereinafter, an example according to the present invention will be described with reference to the accompanying drawings.

2 is a block diagram illustrating an example of a USB device according to the present invention.

The USB device of FIG. 2 includes a SOC 120, a USB control unit, a USB connector 102, and other interface devices.

More specifically, the SOC 120 includes a VDDUSB 108 port for receiving power and a USBSENSE 107 port for determining whether a USB cable is connected to an external device. In general, the detection of the USB connection, there is a method to determine based on the level (level) of the input signal, there is a method of determining based on the edge (edge) of the input signal. The SOC 120 depends on a method of determining based on an edge of an input signal.

In addition, the SOC 120 includes a USBPUEN 105 port for performing a pull-up operation, and a DM and DP 113 ports for actual data transmission.

The slave 130 device also includes other interface devices as follows.

First, a Schmitt trigger buffer 210 and a high enable tri-state buffer 211 are included instead of the regulator 104 of FIG. 1.

As shown, the Schmitt trigger buffer 210 receives a signal output from the USB connector 102 as an input. The output of the Schmitt trigger buffer 210 is input to the high enable three-phase buffer 211. An enable pin of the high enable three-phase buffer 211 is connected to the USBPUEN 105 of the SOC 120. In addition, the output of the enable three-phase buffer 211 is connected to the USBSENSE 107 and also to the first pull-down resistor 212.

The first pull down resistor 212 is attached to set an initial state of the three-phase buffer 211, and the second pull down resistor 209 of FIG. It is used to discharge the charged charge according to the cable line charge phenomenon that occurs when inserted into the connector. The second pull down resistor 209 is connected to a capacitor 103 which is added to eliminate the ripple phenomenon.

The power applied to the SOC 120 may be independently supplied or may be based on VBUS. In the case of FIG.

Hereinafter, a specific operation of the USB device of FIG. 2 will be described.

In the present embodiment, the output from the USBPUEN port 105 is connected to an enable pin of the three-phase buffer 211 for detecting a USB connection regardless of a USB cable connection time and a USB device boot time. do.

In general, since the initial value of the USBPUEN port 105 is a low drive, the three-phase buffer 211 is disabled and the output is floating. That is, the three-phase buffer 211 operates in a high impedance state due to the signal of the USBPUEN 105, in which case the output of the three-phase buffer may be in an indeterminate state. In addition, this indeterminate state may cause a problem in which the SUBSENSE 107 cannot perform accurate USB connection detection.

In other words, in order to detect the attachment of the USB cable, a rising edge, that is, a state change from low to high, is required. That is, in order to accurately detect the attachment of the USB cable, it is necessary to set the initial state of the three-phase buffer 211. To this end, a first pull-down 212 resistor is attached to the output of the three-phase buffer 211, through which the output of the three-phase buffer 211 is initially low. Is maintained.

Through this initial state setting, the USBSENSE 107 is kept low unless the state of the USBPUEN 105 becomes high in the above-mentioned 'C' and 'D' cases.

That is, after the booting of the slave 130 device, if the USBPUEN 105 is driven high due to the initialization of the system, the three-phase buffer 211 is enabled in the 'C' case. Because of the transition to, a rising edge occurs when the USB cable is inserted to detect the connection of the USB cable.

In addition, in the 'D' case, the input of the three-phase buffer 211 is already high, but the state of the three-phase buffer 211 is not until the initialization of the slave device 130 is completed. As it is still disabled (not initialized yet, the USBPUEN 105 does not change the state of the three-phase buffer 211 to enabled) and is pulled down by the first pull-down resistor 212. The output of the three-phase buffer 211 is kept low. When the initialization of the system is completed, since the USBPUEN 105 is driven high, the three-phase buffer 211 is enabled only after the system initialization, in which case the three-phase buffer 211 ) Is input to the USBSENSE 107 port.

The above is summarized as follows.

In this embodiment, due to the structure as shown in FIG. 2, it is possible to set the output value of the three-phase buffer 211 to low. That is, when the system has not yet been initialized, the output of the three-phase buffer 211 is low regardless of the input of the three-phase buffer 211 (that is, the output of the 210 element). In addition, since the USBPUEN 105 does not change the state of the three-phase buffer 211 until the initialization of the slave 130 device is completed, the initialization of the three-phase buffer 211 is completed. The output is still low. Then, when the initialization of the slave device 130 is terminated, the state of the three-phase buffer 211 is switched to enable. In the case of D described above, a high is already input to the input terminal of the 211 device before initialization, but only a low is output to the output terminal of the 211 device due to the characteristics of the 211 device described above. Then, when initialization is completed, high is output to the output terminal of the 211 element. That is, since the output of the 211 device is changed from low to high, the USBSENSE 107 can detect the change of the rising edge to accurately detect the USB connection.

2, the input of the three-phase buffer 211 is 5V, but since the buffer itself has a tolerance of 5V, the output of the buffer in the 3.3V system is 3.3. V. That is, it performs the function of a level translator.

As described above, in order to sufficiently remove ripples that may occur in the VBUS when attaching / detaching the USB cable, attach a capacitor 103 having a capacitance value of a predetermined size or more, and A second pull down resistor 209 is attached to discharge the charge. The resistance value of the second pull down resistor 209 may be determined in consideration of a limit value of an externally provided current. That is, when there is a limit on the upper limit of the current provided from the outside according to the conventional standard, it is preferable that the second pull-down resistor 209 is determined to be above the preset threshold so as not to exceed this upper limit. Preferably, the resistance value has a large value of several hundred kohm.

Hereinafter, operation by the Schmitt trigger buffer 210 added to the apparatus of FIG. 2 will be described. When VBUS is directly input to the three-phase buffer 211 in FIG. 2, an unstable oscillation may occur due to an undefined region according to a noise margin of the buffer.

The general operation of the three-phase buffer 211 is as follows. In general, in a 3.3V buffer, when a power supply of 2 volts or more is input, it is recognized as high and outputs a specific first voltage corresponding to high. In addition, when a power supply of 0.8 volts or less is input, it is recognized as a low and outputs a specific second voltage corresponding to the low. In this case, an input of 0.8 to 2 volts cannot be recognized as low or high, so this region is called an undefined region.

Hereinafter, the mechanism of malfunction according to the above-mentioned undefined region will be described.

When a rising edge occurs due to the USB cable attached, a fast response is shown as shown in FIG. 3. On the other hand, when the falling edge (falling edge) occurs due to the USB cable disconnection shows a response as shown in V (a) of FIG. That is, the discharge is improved to some extent by the second pull-down resistor 209 added according to the present embodiment, but the discharge is still slowed by the RC time constant (approximately hundreds of usec) according to 103 elements and 209 elements. Will be done. Of course, if the values of 103 and 209 elements are adjusted, a faster response can be achieved. However, since the values of 103 and 209 elements must be considered for ripple and discharge, there are limitations in adjusting the values of 103 and 209 elements. In Figure 3, V (a) represents the input waveform of the Schmitt trigger buffer 210 when the USB cable is attached, V (b) shows the output waveform of the Schmitt trigger buffer 210 when the USB cable is attached, V (c) shows the output waveform of the three-phase buffer 211 when a USB cable is attached.

When the Schmitt trigger buffer 210 is omitted, the waveform generated by the USB cable disconnection will be described in more detail as follows.

In FIG. 4, V (a) shows the VBUS waveform when the USB cable is disconnected, and V (c) shows the output waveform of the three-phase buffer 211 if the Schmitt trigger buffer 210 is not present and the USB cable is disconnected. V _TH1 is the maximum input (eg 2.0 volts) of the undefined region described above, and V _TH2 is the minimum input (eg 0.8 volts) of the undefined region described above.

When the V (a) waveform of FIG. 4 is directly input to the three-phase buffer 211, unstable oscillation occurs in the response of V (c). More specifically, the undefined region V _TH1 of the three-phase buffer 211. To V _TH2 ), such as V (c). This oscillation causes multiple rising and falling edges to cause a malfunction that recognizes multiple USB connections / disconnects.

Thus, in order to prevent this, a Schmitt trigger buffer 210 is attached to the input terminal of the three-phase buffer 211. The Schmitt trigger buffer 210 is a bi-stable device and has hysteresis as shown in FIG. 5. That is, when the input voltage increases from 0 to over V _TH4 , high is outputted, and when the input voltage decreases from high input voltage to V _TH3 , low is outputted.

Thus, since only two states of the input voltage are low or high, V (b) is high before V _TH3 as shown in FIG. 6 for the slow falling edge by VBUS. ) And then goes low. When such an output is input to the three-phase buffer 211, V (c) of FIG. 6 is output. Therefore, it is possible to solve the problem of unstable oscillation caused by the undefined region of the three-phase buffer.

5 is a diagram illustrating hysteresis of an output voltage according to an input voltage of a Schmitt trigger buffer. In addition, V _TH3 represents a threshold voltage at which the output voltage starts to become high when the input voltage increases in the Schmitt trigger buffer, and V _TH4 represents a low output voltage when the input voltage decreases in the Schmitt trigger buffer. threshold voltage that starts to be low).

In Figure 6, V (a) shows the input waveform of the Schmitt trigger buffer when the USB cable is removed, V (b) shows the output waveform of the Schmitt trigger buffer when the USB cable is removed, V (c) shows the output waveform of the three-phase buffer when the USB cable is removed.

Those skilled in the art through the above description can be seen that various changes and modifications can be made without departing from the spirit of the present invention. Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification but by the claims.

The effects of the present invention are as follows.

First, accurate connection detection is possible by generating the rising edge of USB VBUS, whether the USB cable is already connected before system power on or after system power on.

Second, it prevents very slow falling edges caused by the charge remaining on the USB cable at the time of disconnecting the USB cable.

Third, even though the VBUS pull-down resistor is attached, it prevents unstable output caused by some RC time constant.

Claims (5)

A tri-state buffer receiving an input signal corresponding to an externally provided USB power source; A first pull-down resistor connected to the output of the three-phase buffer to set an initial value of the three-phase buffer; A bi-stable buffer connected to an input of the three-phase buffer to remove oscillation by an undefined region of the three-phase buffer; A USB connection sensing module configured to detect a USB connection through a rising edge or a falling edge output from the three-phase buffer; And Ripple and discharge processing module for ripple removal and discharge to the USB power supply USB device that can detect the USB connection made. The method of claim 1, An enable pin of the three-phase buffer is connected to a USB pull-up enable port for controlling a pull-up operation of a data line transmitting USB data. A USB device capable of detecting a USB connection. The method of claim 1, The bistable buffer, Outputs a low for a rising input from a low value to a specific first threshold voltage, a high for a corresponding input above the first threshold voltage, and a high Outputting high for an input falling from a value to a particular second threshold voltage, and outputting low for an input falling below the second threshold voltage A USB device capable of detecting a USB connection. The method of claim 1, The bistable buffer is a Schmitt trigger buffer, The ripple and discharge processing module includes a capacitor and a second pull down resistor. A USB device capable of detecting a USB connection. The method of claim 1, A system on chip (SOC) module including the USB connection sensing module is to receive a power source other than the USB power source. A USB device capable of detecting a USB connection.

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