Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
1999-05-05
2001-11-27
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
C327S379000, C327S546000
Reexamination Certificate
active
06324044
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to controller area network (CAN) systems and, more particularly, to a transceiver for use in a CAN employing low voltage components for high speed performance configured to handle high voltage transients.
BACKGROUND OF THE INVENTION
Controller area network (CAN) systems are currently being implemented as common networking systems for automotive and industrial applications. In a typical automotive application, the CAN provides a two (or one) wire link that can be routed around the entire vehicle. This link may illustratively be terminated by 120 ohm loads at each end. A CAN provides a lightweight and cost effective means for the vehicle's central processing unit to communicate with satellite peripheral modules, e.g., dome lamps, door modules, headlight modules, taillight modules, anti-skid braking system (ABS) modules, airbag modules, etc. The CAN wire itself is specified by the International Standards Organization (ISO) for at least a ten meter length. Unfortunately, this long wire acts as an ideal antenna that can be subject to automotive-type transients, as well as industrial-type transients, such as electromagnetic interference (EMI) and electrostatic discharge (ESD).
In order to operate in the harsh environments of automotive and industrial settings, a CAN transceiver must successfully withstand these high voltage transients and must be capable of handling the standard automotive requirements of double battery and 40 volt load dump. It must also withstand shorts from the CAN wire to V
cc
, ground and V
bat
, and any other power supply associated with the system. These requirements are typically specified as the ability to survive voltages on the CAN wire(s) between +40 and −6 volts.
A controller area network (CAN) transceiver in accordance with the prior art is shown in FIG.
1
. It consists of a CAN-H driver and a CAN-L driver. CAN-H uses a pnp (or a PMOS) transistor as an active device, while CAN-L uses an npn (or an NMOS) transistor as an active device. In order to obtain high speed and symmetry, it is desirable to use low voltage, matched components. However, in this configuration, these low voltage components cannot withstand high voltage conditions due to gate oxide integrity issues and drain-to-source breakdown voltage limitations. High voltage components are not desirable for CAN applications due to their larger gate capacitances, and hence their slower operation. These high voltage components also incur a considerable silicon area penalty.
In a differential CAN driver of the types described in relation to the prior art and the present invention, there is a need to match the impedances of the two legs during switching and during the dominant state, and to match the timing of the two switching devices.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, there is disclosed herein a controlled area network (CAN) driver which provides improved symmetry between its differential output signals and which provides protection for its low voltage devices from voltage transients occurring on its output lines.
Further in accordance with the present invention, a plurality of CAN drivers are serially interconnected to form a driver system, wherein each downstream driver stage receives a time-delayed form of the digital input signal, each stage providing a time-delayed contribution to the differential output signals of the overall driver system.
REFERENCES:
patent: 5050190 (1991-09-01), Shimada et al.
patent: 5357518 (1994-10-01), Peter
patent: 5539778 (1996-07-01), Kienzler et al.
patent: 6115831 (2000-09-01), Hanf et al.
Baldwin David J.
Devore Joseph A.
Legat Timothy J.
Pauletti Timothy P.
Teggatz Ross E.
Brady III W. James
Leja Ronald W.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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