Monitoring circuit

This disclosure relates to I 2 C devices, more particularly, to I 2 C devices that automatically isolate themselves from the I 2 C bus in the event of a failure.

With the current I 2 C bus redundancy strategy, it is common to route two I 2 C buses to each field replaceable unit (FRU) included within a system. With this redundant topology, in the event that one I 2 C bus fails due to a short circuit occurring in one of the FRUs attached to one of the I 2 C buses (thus shorting the impacted I 2 C bus), access to the remaining FRUs (including the defective FRU itself provided the redundant I 2 C interface is operational) is maintained due to access being available via the redundant I 2 C bus.

However, one shortcoming of this design is the inability to determine which FRU has failed, as the only information that the field engineer knows is that one FRU on the I 2 C bus is shorting the I 2 C bus. Accordingly, the field engineer would need to remove each FRU on the impacted I 2 C bus, one at a time, and check the status of the impacted I 2 C bus during each removal to see if the impacted I 2 C bus was restored. As several I 2 C devices may be coupled to the impacted I 2 C bus, this could prove to be a time consuming and fallible procedure for the field engineer.

In a first implementation, a monitoring circuit monitors for the occurrence of a failure event on a data bus. The monitoring circuit includes a failure detection circuit for detecting the occurrence of the failure event within a device coupled to the data bus. An isolation circuit isolates the device from the data bus in response to the occurrence of the failure event.

One or more of the following features may be included. The failure detection circuit may include a delay circuit for delaying the isolation of the device from the data bus in response to the occurrence of the failure event. The delay circuit may include an RC circuit. The monitoring circuit may be included within the device. The monitoring circuit may include one or more switches for isolating the device from the data bus. The one or more switches may include one or more transistors. The data bus may be an I 2 C bus. The device may be an I 2 C device.

In another implementation, an I2C device is configured to be couplable to an I 2 C bus. The I 2 C device includes a failure detection circuit for detecting the occurrence of the failure event within the I 2 C device. An isolation circuit isolates the I 2 C device from the I 2 C bus in response to the occurrence of the failure event.

One or more of the following features may be included. A delay circuit may delay the isolation of the I 2 C device from the I 2 C bus in response to the occurrence of the failure event. The delay circuit may includes an RC circuit. The monitoring circuit may include one or more switches for isolating the I 2 C device from the I 2 C bus. The one or more switches may include one or more transistors.

In another implementation, a monitoring circuit monitors for the occurrence of a failure event on a data bus. The monitoring circuit includes a failure detection circuit for detecting the occurrence of the failure event within a device coupled to the data bus. An isolation circuit isolates the device from the data bus in response to the occurrence of the failure event. The failure detection circuit includes a delay circuit for delaying the isolation of the device from the data bus in response to the occurrence of the failure event.

One or more of the following features may be included. The delay circuit may include an RC circuit. The RC circuit may be configured to control the operation of a first switch within the failure detection circuit. The first switch may be configured to control at least a second switch within the isolation circuit. The at least a second switch may be configured to isolate the device from the data bus in response to the occurrence of the failure event. The monitoring circuit may be included within the device. At least one of the first switch and the at least a second switch may include one or more transistors. The data bus may be an I 2 C bus. The device may be an I 2 C device.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims.

FIG. 1 is a diagrammatic view of a single bus data system;

FIG. 2 is a diagrammatic view of a multi-bus data system;

FIG. 3A is a diagrammatic view of a first implementation of a monitoring circuit;

FIG. 3B is a diagrammatic view of an alternative implementation of the monitoring circuit of FIG. 3A ; and

FIG. 4 is an illustrative schematic diagram of the monitoring circuit of FIG. 3A or FIG. 3B .

Like reference symbols in the various drawings indicate like elements.

Referring to FIG. 1 , there is shown a system in which data bus 10 is used to connect multiple devices (e.g., device 12 ) within a computing system (e.g., computing system 14 ).

An example of data bus 10 is an I 2 C bus and an example of device 12 is an I 2 C device (e.g., DACs, ADCs, host adaptors, USB adapters, hardware monitor interfaces, diagnostic sensor interfaces, configuration data interfaces, and clock interfaces). As is known in the art, an I 2 C bus is a serial, multi-master, single-ended computer bus that allows communication between low-speed peripheral devices and a motherboard or embedded system. Typically, the I 2 C uses two bidirectional, open drain lines, namely a Serial Data Line (SDA, not shown) and a Serial Clock Line (SCL, not shown) that typically operate in the 3.3-5.0 VDC range.

Accordingly, in the event that either of SDL or SDA included within an I 2 C data bus is tied/shorted to ground (as represent by short 16 ), communication with the devices coupled to the I 2 C bus is interrupted until the fault is corrected. Therefore, in the event that short 16 within device 12 results in either or both of the SDA and/or SCL within data bus 10 being tied/shorted to ground, communication with any of the devices (e.g., devices 12 , 18 , 20 , 22 ) coupled to data bus 10 would also be interrupted (as data bus 10 would cease to operate).

While the previous discussion concerns an I 2 C data bus, it is understood that the I 2 C data bus is being used solely for illustrative purposes and the above-discussion is equally applicable to other forms of buses (such as USB).

Referring also to FIG. 2 , there is shown a bus configuration that allows for continued communication with the devices coupled to a data bus after the occurrence of a device failure that results in the data bus being tied/shorted to ground. Specifically, a second, redundant data bus may be included that may continue to operate after the failure of the device that rendered the first data bus inoperable. For example, a pair of data buses (e.g., data busses 100 , 102 ) may be coupled to each device (e.g., devices 104 , 106 , 108 , 110 ) included within the computing system.

Therefore, in the event that short 112 within device 108 results in either or both of the SDA and/or SCL within e.g., data bus 102 being tied/shorted to ground, communication with any of the other devices (e.g., devices 104 , 106 , 110 ) within the system would be maintained. Specifically, while the occurrence of short 112 may disrupt communications on data bus 102 , redundant data bus 100 would continue to operate. Accordingly, devices 104 , 106 , 110 would be capable of continued communication via data bus 100 . However, as long as short 112 exists, data bus 102 would be down.

Referring also to FIGS. 3A-3B , there is shown various implementations of a monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ) that may allow for detection of a failure event (e.g., short 112 ) within a device (e.g., device 108 ) coupled to a data bus, such as data bus 100 and/or data bus 102 . In response to the detection of such a failure event, the monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ) may isolate the device (e.g., device 108 ) from the data bus (e.g., data bus 100 and/or data bus 102 ) in response to the occurrence of the failure event (e.g., short 112 ).

The manner in which the monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ) is configured may vary depending upon the specific application. For example, the monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ) may be configured to be external to the device (e.g., as illustrated with monitoring circuits 150 , 152 ). Accordingly and in this configuration, the data bus (e.g., data bus 100 and/or data bus 102 ) may be coupled to the monitoring circuit (e.g., monitoring circuit 150 and/or monitoring circuit 152 , respectively), and the monitoring circuit (e.g., monitoring circuit 150 and/or monitoring circuit 152 ) may be coupled to the device (e.g., device 108 ).

Alternatively, the monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ) may be configured to be included within the device (e.g., as illustrated with monitoring circuits 154 , 156 ). Accordingly and in this configuration, the data bus (e.g., data bus 100 and/or data bus 102 ) may be coupled to the device (e.g., device 108 ) and may pass through the appropriate internal monitoring circuits (e.g., monitoring circuit 154 for data bus 100 and monitoring circuit 152 for data bus 102 ).

In the event of a failure event (e.g., short 112 ) within device 108 coupled to e.g., data bus 100 and/or data bus 102 , one or more of monitoring circuit 150 , 152 , 154 , 156 may be isolate the failed device (e.g., device 108 ) from the appropriate data bus (e.g., data bus 100 and/or data bus 102 ). For illustrative purposes, monitoring circuits 150 , 154 are shown to be in a conducting state, while monitoring circuits 152 , 156 are shown to be in an isolating state (e.g., due to the occurrence of short 112 ).

Referring also to FIG. 4 , there is shown an exemplary schematic view of one implementation 200 of the above-described monitoring circuit (e.g., monitoring circuit 150 , 152 , 154 , 156 ).

Monitoring circuit 200 may include failure detection circuit 202 that may be configured to detect the occurrence of the failure event (e.g., short 112 ) within a device (e.g., device 108 ) coupled to the data bus (e.g., data bus 100 and/or data bus 102 ). In response to the detection of such a failure event (e.g., short 112 ), isolation circuit 204 may isolate the device (e.g., device 108 ) from the data bus (e.g., data bus 100 and/or data bus 102 ) so that the utility of the data bus may be restored.

Failure detection circuit 202 may include delay circuit 206 that may be configured to delay the isolation of the device (e.g., device 108 ) from the data bus (e.g., data bus 100 and/or data bus 102 ) in response to the occurrence of the failure event (e.g., short 112 ). One exemplary embodiment of delay circuit 206 is an RC circuit. Monitoring circuit 200 (e.g., within failure detection circuit 202 and/or isolation circuit 204 ) may include one or more switches (e.g., transistors 208 , 210 , 212 , 214 ) for isolating the device (e.g., device 108 ) from the data bus (e.g., data bus 100 and/or data bus 102 ) in response to the occurrence of the failure event (e.g., short 112 ).

Assume for illustrative purposes that short 112 occurs (e.g., a failure occurs within device 108 ), which draws the data bus (e.g., data bus 100 and/or data bus 102 ) down to ground, thus rendering the data bus (e.g., data bus 100 and/or data bus 102 ) inoperable. Accordingly, as the data bus is now at zero potential, the voltage drop across resistor 216 , resistor 218 , and diode 220 are all reduced to zero. Accordingly, the voltage at the base of transistor 212 will also be zero, thus shutting off transistor 212 . An example of transistor 212 is an NPN bipolar transistor, such as an MMBT222A transistor manufactured by Fairchild Semiconductor. An example of diode 220 is a BAT54LP diode manufactured by Diodes Incorporated. Exemplary values of resistors 216 , 218 are 100 K and 120 K respectively.

Prior to being shut off, transistor 212 tied junction 222 to ground, thus ensuring that transistor 214 was off. However, once transistor 212 shuts off, junction 222 is no longer tied to ground and capacitor 224 will begin to charge via resistor 226 . The rate at which capacitor 224 charges is controlled by the RC time constant of capacitor 224 and resistor 226 . Exemplary values of capacitor 224 and resistor 226 are 1.0 microfarad and 200 Kohm respectively. An exemplary value of resistor 228 is 1.0 Mohm.

Assuming the above-described values, delay circuit 206 would have a delay factor of approximately 40 milliseconds. Accordingly, if a failure event is sensed, the isolation of the device from the data bus would be delayed by approximately 40 milliseconds to avoid false trigger events that may be caused by the normal 10 millisecond low level times that occur when the I 2 C bus is operating at 100 kilohertz.

Once capacitor 224 is sufficiently charged, transistor 214 will turn on, thus tying voltage source G 1 to ground. An example of transistor 214 is an NPN bipolar transistor, such as an MMBT222A transistor manufactured by Fairchild Semiconductor.

Once voltage source G 1 is tied to ground, transistors 208 , 210 will shut off, thus opening the connection between data bus 100 and/or data bus 102 and (in this example) device 108 , thus isolating device 108 from data bus 100 and/or data bus 102 . An example of transistors 208 , 210 is an N Channel MOSFET, such as a 2N7002E transistor manufactured by Diodes Incorporated. Accordingly, even though device 108 has failed, since monitoring circuit 200 sensed the failure and isolated device 108 from data bus 100 and/or data bus 102 , data bus 100 and/or data 102 may continue to function after the failure of device 108 .

Further, if a two bus system is utilized (as shown in FIGS. 2 , 3 A, & 3 B, while the failed device will be isolated from the impacted bus, the device will still be able to communicate via the non-impacted bus (assuming that the failure within the device was not substantial enough to impact both buses). Accordingly, with the exception of the failed device, all devices on the system would be visible on both buses. However, the failed device would only be visible on the non-impacted bus. Accordingly, by determining which device is only visible on one bus, the identity of the failed device may be quickly determined.

Resistors 230 , 232 may function as pull-up resistors that may provide the necessary voltage drop between their respective voltage source and data bus 100 , 102 . Further, resistors 232 , 234 may form a voltage divider circuit to properly bias the gate of transistor 208 . Exemplary values of resistors 230 , 232 , 234 are 10 Kohm, 10 Kohm, and 10 Kohm respectively. An example of diode 236 is a BAT54LP diode manufactured by Diodes Incorporated. An exemplary value of voltage source V cc may be in the range of 3.3-5.0 VDC. An exemplary value of voltage source G 1 may be in the range of 3.3-5.0 VDC. An exemplary value of voltage source V 3 may be in the range of 3.3-5.0 VDC.

The above-described monitoring circuits (e.g., monitoring circuit 150 , 152 , 154 , 156 ) are described as being utilized within a dual (i.e., redundant) bus system, this is for illustrative purposes only and is not intended to be a limitation of this disclosure, as other configuration are possible and are considered to be within the scope of this disclosure. For example, such monitoring circuits (e.g., monitoring circuit 150 , 152 , 154 , 156 ) may be utilized within a single (e.g., non-redundant) bus system.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.