A high-impedance state control circuit for rs-485 transceiver

A RS-485 and control circuit technology, applied to electrical components, transmission systems, etc., can solve the problems of limited use scenarios, and the difficulty of ESD voltage reaching 15,000 volts, and achieve the effect of increasing ESD voltage

Active Publication Date: 2022-06-21
苏州灵天微半导体科技有限公司
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] The RS-485 chip must be in a high-impedance state after the output drive is turned off. At this time, the voltage range it can withstand is stipulated in the protocol as -7v~12v. The existing RS-485 chip usually uses CMOS output, and the negative voltage will cause The parasitic diode of the NMOS tube is turned on and thus clamped, and a high voltage input greater than the power supply voltage will cause the parasitic diode between the drain and the N well to conduct
[0004] The current solution on the market is to connect a reverse diode to the output port to block the output port, form a connection with the parasitic diode, and block the voltage clamping; this method makes the ESD voltage of the two output ports of the bus A / B very low. It is difficult to reach 15,000 volts, which limits many usage scenarios

Method used

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  • A high-impedance state control circuit for rs-485 transceiver
  • A high-impedance state control circuit for rs-485 transceiver

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Embodiment Construction

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

[0018] When the high-impedance state control circuit is implemented, based on the isolation process, it is necessary to separate the N well and the first NMOS of the PMOS devices such as the first PMOS transistor, the second PMOS transistor, the third PMOS transistor, the fourth PMOS transistor and the fifth PMOS transistor. The P wells of NMOS such as the second NMOS transistor, the third NMOS transistor, the fourth NMOS transistor, and the fifth NMOS transistor are floated to block the clamping of the parasitic diode between the substrate and the well.

[0019] This example refers to F...

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Abstract

The invention relates to a high-impedance state control circuit for an RS-485 transceiver, comprising an RS-485 output drive module and a high-impedance state control module; the bus output stage of the RS-485 output drive module is electrically connected to an NPN Transistor and PNP triode, the high-impedance state control module is used to make the NPN triode and PNP triode all cut off when the RS-485 output drive module is enabled; a kind of RS-485 transceiver according to the present invention The high-impedance state control circuit uses a transistor as the bus output stage and a high-impedance state control module. In the range of A / B common mode level -7v ~ 12v, it controls the output of the RS-485 transceiver to be high when it is enabled and closed. The resistance state greatly increases the ESD voltage of the two output ports of the bus A / B, which meets the requirements of most applications.

Description

technical field [0001] The invention relates to an RS-485 transceiver, in particular to a high-impedance state control circuit for the RS-485 transceiver. Background technique [0002] RS-485 is a standard that defines the electrical characteristics of drivers and receivers in balanced digital multipoint systems, as defined by the Telecommunications Industry Association and the Electronics Industry Alliance. Digital communication networks using this standard can effectively transmit signals under long-distance conditions and in environments with high electronic noise; RS-485 makes it possible to connect to local networks and to configure multi-drop communication links. [0003] The RS-485 chip must be in a high-impedance state after the output driver is turned off. At this time, the voltage range protocol it can withstand is -7v ~ 12v. The existing RS-485 chip usually uses CMOS output. Negative voltage will cause The parasitic diode of the NMOS transistor is turned on and t...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H04B1/40H04B1/401
CPCH04B1/40H04B1/401
Inventor 顾永兴
Owner 苏州灵天微半导体科技有限公司
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