CN114866160A - Isolation protection circuit, module and chip of RS485 chip in acquisition terminal - Google Patents
Isolation protection circuit, module and chip of RS485 chip in acquisition terminal Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
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- H—ELECTRICITY
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Abstract
The invention belongs to the technical field of digital-analog hybrid and radio frequency integrated circuits, and particularly relates to an isolation protection circuit, a module and a chip of an RS485 chip in an acquisition terminal. The isolation protection circuit comprises an isolation filter circuit, a serial port end protection device and a differential end protection device. The isolation filter circuit comprises an isolation device and a filter device; the isolation device is electrically connected with the RS485 chip. The filter device includes a first filter circuit, a second filter circuit, and a third filter circuit. The serial port end protection device is connected to the serial port end interface of the RS485 chip and the isolation device. The serial port end protection device is used for discharging interference signals on the RS485 serial port pin. The differential side protection device is connected to the differential side A, B of the RS485 chip. The differential end protection device is composed of 4 current-limiting resistors, 3 transient suppression diodes, 2 ESD diodes, a pull-up resistor, a pull-down resistor, a thermistor and a capacitor. The invention solves the problems of insufficient communication stability and poor anti-interference performance of the RS485 interface.
Description
Technical Field
The invention belongs to the technical field of digital-analog hybrid and radio frequency integrated circuits, and particularly relates to an isolation protection circuit, a module and a chip of an RS485 chip in an acquisition terminal, and the RS485 chip integrated with the isolation protection chip.
Background
The power acquisition terminal equipment used on the power grid is usually designed in a product modularized mode, and the modularized power acquisition equipment is composed of a series of standard components with independent functions and independent input and output. The modular terminal design divides the power acquisition terminal into different components such as a power supply unit, a processing unit, a communication unit and a function unit, and the components are physically isolated from each other. In order to improve the isolation protection performance, the MCU of the acquisition terminal main control module can also use a power supply independent of other circuits. In order to prevent interference between other power circuits, some devices need to isolate signals from other circuits or interfaces.
The inside of the existing acquisition terminal is generally not provided with a protection device, and circuit communication is easily interfered. Part of the acquisition terminal circuits adopt the scheme of an isolation circuit, but the isolation circuit with a single function cannot meet the shielding requirement of RS485 diversified interference signals and cannot resist the impact of accumulated interference signals on a chip. In addition, by adding a protection module or a measure for shielding interference by a structure, the application cost is high, difficulty is brought to maintenance of a system using an RS485 communication interface, and the method is not suitable for large-scale popularization and application.
Disclosure of Invention
The problems that equipment adopting the existing RS485 interface for communication is easy to interfere, the communication stability is insufficient and the anti-interference performance is poor are solved; the invention relates to an isolation protection circuit, a module and a chip of an RS485 chip in an acquisition terminal, and the RS485 chip integrated with the isolation protection chip.
The invention is realized by adopting the following technical scheme:
the utility model provides an isolation protection circuit of RS485 chip among acquisition terminal, this isolation protection circuit includes isolation filter circuit, serial ports end protection device to and difference end protection device.
The isolation filter circuit comprises an isolation device and a filter device; the three-channel interface of the isolation device comprises an enabling end, a sending end and a receiving end. And three-channel interfaces of the isolating device are respectively and electrically connected with three corresponding interfaces of the serial port end in the RS485 chip. The filter device includes a first filter circuit, a second filter circuit, and a third filter circuit. The first filter circuit is connected to a power supply end of the isolation device and used for inhibiting the influence of surge voltage on RS 485. The second filter circuit is connected to the ground end of the isolation device and used for discharging the interference signals accumulated on the RS485 chip through the ground end. And the third filter circuit is connected to all interfaces of the electricity removal source end and the ground end of the isolation device and is used for removing high-frequency interference signals.
The serial port end protection device is connected to three interfaces in the serial port end where the RS485 chip and the isolation device are connected with each other. The serial port end protection device is used for discharging interference signals on the RS485 serial port pin.
The differential side protection device is connected to the differential side A, B of the RS485 chip. The differential end protection device is composed of 4 current limiting resistors R4, R6, R91, R92, 3 transient suppression diodes TVS1, TVS2, TVS3, 2 ESD diodes D11 and D17, a pull-up resistor R24, a pull-down resistor R24, a thermistor PTC1 and a capacitor C7. In the differential end protection device, one end of R4 is connected with one differential interface B of an RS485 chip, and the other end of R4 is connected with R91 and PTC1 in series. The other end of the PTC1 serves as an external port of the differential interface B. One end of the R6 is connected with the other differential interface A of the RS485 chip, the other end of the R6 is connected with the R92 in series, and the other end of the R92 is used as an external port of the differential interface A. One end of D11 is connected between R4 and R91, and the other end is virtual ground. One end of D17 is connected between R5 and R92, and the other end is virtual ground. The 3 transient suppression diodes TVS1, TVS2, and TVS3 are connected in series with each other and connected at both ends to a virtual ground. The intermediate nodes of TVS1 and TVS2 are electrically connected to the intermediate nodes of R92 and PTC 1. The intermediate nodes of TVS2 and TVS3 are electrically connected to the node of R92 that is the differential interface A terminated end. One end of the pull-down resistor R23 is connected with the differential interface B of the RS485 chip, and the other end is connected with the virtual ground. One end of the pull-up resistor R24 is connected with the differential interface B of the RS485 chip, and the other end is connected with a power supply. One end of the capacitor C7 is connected to the power supply end of the RS485 chip, and the other end is connected to virtual ground.
As a further improvement of the invention, the serial port end protection device comprises 3 ESD diodes and 1 resistor R93, wherein two ESD diodes are respectively connected in series to the transmitting end and the receiving end of the RS485 chip, and the third ESD diode is connected in parallel with the resistor R93 and then connected in series to the enabling end of the RSA485 chip; the other ends of the three ESD diodes are all connected with a virtual ground.
As a further improvement of the invention, the isolation device adopts a transmission device with two paths and six channels; the isolation device supports simultaneous connection with two RS485 chips.
As a further improvement of the invention, the second filter circuit adopts a safety capacitor C99, one end of the C99 is connected and grounded with the ground end of one path of the isolation device, and the other end of the C99 is connected and grounded with the ground end of the other path of the isolation device.
As a further improvement of the invention, the safety capacitor C99 adopts a Y capacitor with the specification of 1000 PF/4000V.
As a further improvement of the invention, the first filter circuit comprises two groups, and both the two groups are formed by connecting a current-limiting resistor and a capacitor in series. Two power ends of the isolating device are respectively connected to nodes connected between the current-limiting resistors and the capacitors in the two groups of first filtering circuits. In the two groups of first filter circuits, the other ends of the capacitors are grounded, and the other ends of the current-limiting resistors are connected with a power supply.
As a further improvement of the invention, the third filter circuit is an RC filter circuit formed by connecting a resistor and a capacitor in series. In the third filter circuit, the other end of the resistor is electrically connected with the isolation device, and the other end of the capacitor is used as an external port of the isolation device.
As a further improvement of the invention, the isolation device adopts a Na8262 six-channel digital isolator. The model of a transient suppression diode in the differential end protection device is SMAJ60 CA; the nominal resistance of the thermistor PTC1 is between 30-60 omega.
The invention also comprises an isolation protection module of the RS485 chip in the acquisition terminal, wherein the isolation protection module adopts the circuit layout of the isolation protection circuit and is used for carrying out isolation protection on the RS485 chip. The isolation protection module comprises an isolation filtering unit, a serial port end protection unit and a differential end protection unit.
The isolation filtering unit consists of an isolation circuit, a first filtering subunit, a second filtering subunit and a third filtering subunit. The isolation circuit adopts a digital isolator with two paths and six channels. The first filtering subunit comprises two groups which are respectively connected to two power supply ends of the isolating device, and the first filtering subunit is used for inhibiting the influence of the surge voltage on the RS 485. The second filtering subunit is connected between two ground ends of the isolation device and used for releasing the interference signals accumulated on the RS485 chip out through the ground ends. The third filter subunit adopts a plurality of independent RC filter circuits and is connected to all interfaces of the isolating device except the power supply end and the ground end. The third filtering subunit is used for removing the high-frequency interference signal.
The serial port end protection unit is connected to three interfaces in the serial port end where the RS485 chip and the isolation circuit are connected with each other. The serial port end protection device is used for discharging interference signals on the RS485 serial port pin.
The differential end protection unit is connected to the differential end A, B of the RS485 chip and used for protecting the RS485 chip from the impact of transient high-voltage spike pulses.
The invention also comprises an isolation protection chip which is formed by packaging the isolation protection circuit of the RS485 chip in the acquisition terminal. The pin of the isolation protection chip comprises: the device comprises a power supply end pin, a ground end pin, a virtual ground pin, two differential interface pins and three serial port pins.
And the power supply end pin is connected to the VCC pin of the RS485 chip and is used for connecting a power supply.
One ground pin is used for the ground.
And the virtual ground pin is connected to the GND pin of the RS485 chip and is used for connecting virtual ground.
And the two differential interface pins are respectively and electrically connected with the differential interfaces A and B in the RS485 chip.
The three serial port pins comprise a sending terminal pin, a receiving terminal pin and an enabling terminal pin. The enabling terminal pin is used for being electrically connected with the RE pin and the DE pin of the RS485 chip; the pin of the sending terminal is used for being electrically connected with the DI pin of the RS485 chip; and the receiving terminal pin is used for being electrically connected with an RO pin of the RS485 chip.
The invention also comprises an RS485 chip, wherein the RS485 chip is integrated with the isolation protection chip and has an isolation protection function, so that the communication stability and the anti-interference capability are improved.
The technical scheme provided by the invention has the following beneficial effects:
1. the isolation protection circuit of the invention adds an ESD protection diode at A, B differential interfaces of the RS485 chip, a serial port sending end, a serial port receiving end and an enabling end, thereby protecting the RS485 chip from the interference of external pulse group coupling interference, static discharge interference, static electricity and other high-frequency signals. When the RS485 interface is misconnected to a strong electric wire, the ESD2 part serves as a first-stage protection, and the PTC2 serves as a thermistor, so that the whole RS485 can be protected from being burnt out by strong electricity. Through setting up the TVS pipe, can be in a safety range by the speed restriction of PS level excessive voltage to play the effect of protection back circuit, three transient state suppression diodes TVS1, TVS2 and TVS3 are put in this position, can protect the circuit to avoid surge overvoltage signal to dash the sign. By arranging two ESD diodes D11 and D17 in parallel in the circuit, the circuit can be protected from high-frequency signals. The TVS has large absorbed energy, slow response and small absorption capacity of the ESD diode, is suitable for surge protection, but has high reaction speed and is suitable for electrostatic occasions, so that the ESD2 partially protects the first stage by adopting the ESD diode and the TVS simultaneously, and can shield external pulse group coupling interference and static discharge interference. In addition, the ESD1 part is used as a second-stage protection, and three ESD tubes D13, D16 and D18 are adopted to protect the RS485 chip from high-frequency signals such as static electricity.
2. The isolation protection circuit of the invention is additionally provided with RC filter circuits at the input end and the output end of the capacitive isolation device respectively, thereby protecting communication from interference. The chip is prevented from being damaged due to the impact current.
3. In the method provided by the invention, proper safety capacitors are additionally arranged at the two ends of the optical coupling grounding of the capacitive isolator, and the charges accumulated by circuit interference signals are quickly released by the safety capacitors, so that the stability of the transmitted signals is improved, and the anti-interference capability of the chip is improved.
4. The scheme provided by the invention can provide an all-dimensional signal anti-interference effect for the RS485 chip, greatly improves the isolation protection performance of the chip, and can be integrated into the existing chip or the existing equipment, thereby reducing the installation cost of the equipment and improving the maintainability of the product.
Drawings
Fig. 1 is a detailed circuit diagram of an isolation protection circuit of an RS485 chip in an acquisition terminal according to embodiment 1 of the present invention.
Fig. 2 is a schematic diagram of the series capacitor in the isolation device to implement high voltage isolation in embodiment 1 of the present invention.
Fig. 3 is a schematic connection diagram of functional modules of an isolation protection module of an RS485 chip in an acquisition terminal according to embodiment 2 of the present invention.
Fig. 4 is a schematic structural diagram of an isolation protection chip of an RS485 chip in an acquisition terminal and pins thereof according to embodiment 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
The embodiment provides an isolation protection circuit of an RS485 chip in an acquisition terminal, which comprises an isolation filter circuit, a serial port end protection device and a differential end protection device.
As shown in fig. 1, the isolation filter circuit includes an isolation device and a filter device. Specifically, the isolation device in this embodiment is a U8 chip in the circuit diagram. The isolation circuit adopts a transmission device with two paths and six channels; the circuit model is Na 8262; the isolating device supports simultaneous connection with two RS485 chips, and the RS485 chip corresponds to a U2 chip in a circuit diagram and is MAX3082 ESA. The three-channel interface of the isolation device comprises an enabling end RN, a transmitting end TX and a receiving end RX. And three-channel interfaces of the isolating device are respectively and electrically connected with three corresponding interfaces of the serial port end in the RS485 chip.
Isolation is a method of preventing dc interference between two parts of a system, or interfering ac currents, while allowing signals to be transmitted normally in the two parts of the system. This isolation would be required to cut the ground loop in the communication network from communicating with the high-end equipment in order to protect the operator from damage to the expensive processors in the high-voltage system. Digital isolators are the best choice, such as SPI, UART, I2C, RS-485 and CAN, in many different system applications, including industrial automation systems, motor drives, medical devices, solar inverters, power supplies and hybrid electric vehicles.
Referring to fig. 2, the isolation device may use silicon dioxide (SiO) 2 ) As dielectrics used in signal isolation and digital isolators. High voltage isolation is typically achieved using two silicon dioxide capacitors in series, i.e., one on each side of the isolation gate. Compared to inductive-based (magnetic isolation) isolators and conventional optocouplers, SiO 2 The dielectric strength provided is highest, does not degrade from exposure to ambient humidity, and can have an isolation lifetime of greater than 100 years.
The filter device in this embodiment includes a first filter circuit, a second filter circuit, and a third filter circuit. The first filter circuit is connected to the power supply terminal of the isolation device, corresponding to the partial circuit in the region of RC1 in fig. 1. The first filter circuit is used for suppressing the influence of the surge voltage on the RS 485. The isolation device is considered to have two outputs and can support the connection of two RS485 chips. In the present embodiment, the first filter circuits are also provided in two sets. The two groups of first filtering currents are formed by connecting a current-limiting resistor and a capacitor in series. Two power ends of the isolating device are respectively connected to nodes connected between the current-limiting resistors and the capacitors in the two groups of first filtering circuits. In the two groups of first filter circuits, the other ends of the capacitors are grounded, and the other ends of the current-limiting resistors are connected with a power supply.
The second filter circuit in this embodiment is connected to the ground of the isolation device. And the second filtering current is used for discharging the interference signals accumulated on the RS485 chip through the ground end. As shown in the RC2 area in fig. 1, the second filtering circuit employs a regulated capacitor C99, one end of C99 is connected and grounded to the ground of one of the paths of the isolation device, and the other end of C99 is connected and grounded to the ground of the other path of the isolation device. In the embodiment, the safety capacitor C99 adopts a Y capacitor with the specification of 1000 PF/4000V.
In this embodiment, both the first filter circuit and the second filter circuit can function as an RC low-pass filter. The capacitive element has characteristics of passing high frequency and blocking low frequency. The RC filter utilizes the characteristic of the capacitive element to introduce a high-frequency signal into the ground, and only a low-frequency signal is left in the circuit, so that the aim of removing the high-frequency signal in the circuit is fulfilled.
The third filter circuit is connected to all interfaces of the neutralization end and the ground end of the isolation device and used for discharging the charges accumulated at the ground end of the RS485 circuit. The third filter circuit is an RC filter circuit formed by a resistor and a capacitor connected in series as shown in the area of RC3 in fig. 1. In the third filter circuit, the other end of the resistor is electrically connected with the isolation device, and the other end of the capacitor is used as an external port of the isolation device.
In this embodiment, the third filter circuit uses the coupling effect of the Y capacitor to connect the two circuits, allowing the ac signal to pass through and transmit to the next stage circuit, thereby discharging the interference energy above the virtual ground to the real ground, and transmitting the interference energy, thereby protecting the circuit components of the RS485 part.
The serial port end protection device is connected to three interfaces in the serial port end where the RS485 chip and the isolation device are connected with each other. The serial port end protection device is used for discharging interference signals on the RS485 serial port pin. Specifically, as shown in the ESD1 part in fig. 1, the serial port protection device includes 3 ESD diodes and 1 resistor R93, two of the ESD diodes are respectively connected in series to the transmitting end and the receiving end of the RS485 chip, and the third ESD diode is connected in parallel to the resistor R93 and then connected in series to the enable end of the RSA485 chip; the other ends of the three ESD diodes are all connected with a virtual ground.
In this embodiment, although the ESD diode has a small absorption capacity, it has a fast response speed, and is suitable for static electricity and other situations. By adopting the three ESD diodes D13, D16 and D18, the RS485 chip can be protected from high-frequency signals such as static electricity.
The differential side protection device is connected to the differential side A, B of the RS485 chip. The differential end protection device is composed of 4 current limiting resistors R4, R6, R91, R92, 3 transient suppression diodes TVS1, TVS2, TVS3, 2 ESD diodes D11 and D17, a pull-up resistor R24, a pull-down resistor R24, a thermistor PTC1 and a capacitor C7. The model number of the transient suppression diode in the differential end protection device is 5MAJ60 CA; the nominal resistance of the thermistor PTC1 can be between 30-60 omega and will not be described in detail.
As shown in the ESD2 part of fig. 1, in the differential-end protection device, one end of R4 is connected to one of the differential interfaces B of the RS485 chip, and the other end of R4 is connected in series with R91 and PTC 1. The other end of the PTC1 serves as an external port for the differential interface B. One end of the R6 is connected with the other differential interface A of the RS485 chip, the other end of the R6 is connected with the R92 in series, and the other end of the R92 is used as an external port of the differential interface A. One end of D11 is connected between R4 and R91, and the other end is virtual ground. One end of D17 is connected between R5 and R92, and the other end is virtual ground. The 3 transient suppression diodes TVS1, TVS2, and TVS3 are connected in series with each other and connected to a virtual ground at both ends. The intermediate nodes of TVS1 and TVS2 are electrically connected to the intermediate nodes of R92 and PTC 1. The intermediate nodes of TVS2 and TVS3 are electrically connected to the node of R92 that is the differential interface A terminated end. One end of the pull-down resistor R23 is connected with the differential interface B of the RS485 chip, and the other end is connected with the virtual ground. One end of the pull-up resistor R24 is connected with the differential interface B of the RS485 chip, and the other end is connected with a power supply. One end of the capacitor C7 is connected to the power supply end of the RS485 chip, and the other end is connected to virtual ground.
In this embodiment, the TVS functions to change the impedance value between the two terminals from high impedance to low impedance at PS second level speed when the two terminals are subjected to transient high energy impact, so as to absorb a transient large current, and clamp the voltage across the terminals to a predetermined value, thereby protecting the following precision components from the impact of transient high voltage spike, and the three transient suppression diodes TVS1, TVS2 and TVS3 are placed at this position, mainly protecting the circuit from the signal impact of surge overvoltage signal; d11 and D17 are ESD diodes which are connected in parallel in the circuit and protect the circuit from high frequency signals. The TVS has large energy absorption, slow response and high response speed, is suitable for surge protection, and is suitable for electrostatic occasions.
Example 2
On the basis of the circuit designed in embodiment 1, the present embodiment further includes an isolation protection module of an RS485 chip in the acquisition terminal, where the isolation protection module adopts the circuit layout of the isolation protection circuit in embodiment 1 and is used to perform isolation protection on the RS485 chip.
The isolation protection module in this embodiment includes three different circuit units, namely an isolation filtering unit, a serial port protection unit, and a differential port protection unit. In fact, the isolation protection module can adopt the circuit in embodiment 1, and can also adopt other signal chips or circuits with different specifications and the same performance.
As shown in fig. 3, the isolation filtering unit is composed of an isolation circuit, a first filtering subunit, a second filtering subunit, and a third filtering subunit. The isolation circuit adopts a digital isolator with two paths and six channels. The first filtering subunit comprises two groups which are respectively connected to two power supply ends of the isolating device, and the first filtering subunit is used for inhibiting the influence of the surge voltage on the RS 485. The second filtering subunit is connected between two ground ends of the isolation device and used for releasing the interference signals accumulated on the RS485 chip out through the ground ends. The third filter subunit adopts a plurality of independent RC filter circuits and is connected to all interfaces of the isolating device except the power supply end and the ground end. The third filtering subunit is used for removing the high-frequency interference signal.
The serial port end protection unit is connected to three interfaces in the serial port end where the RS485 chip and the isolation circuit are connected with each other. The serial port end protection device is used for discharging interference signals on the RS485 serial port pin.
The differential end protection unit is connected to the differential end A, B of the RS485 chip and used for preventing the RS485 circuit from being interfered by pulse groups and static discharge and burning out components and parts by strong electricity.
Example 3
The embodiment further comprises an isolation protection chip, wherein the isolation protection chip is formed by packaging an isolation protection circuit of the RS485 chip in the acquisition terminal according to the embodiment 1. And the packaging mode of the chip is easier for popularization and application of the isolation protection circuit. And finally integrated into devices such as acquisition devices. The maintainability of the equipment is improved.
As shown in fig. 4, the pin of the isolation protection chip includes: the device comprises a power supply end pin, a ground end pin, a virtual ground pin, two differential interface pins and three serial port pins.
And the power supply end pin is connected to the VCC pin of the RS485 chip and is used for being connected with a power supply.
One ground pin is used for the ground.
And the virtual ground pin is connected to the GND pin of the RS485 chip and is used for connecting virtual ground.
And the two differential interface pins are respectively and electrically connected with the differential interfaces A and B in the RS485 chip.
The three serial port pins comprise a sending terminal pin, a receiving terminal pin and an enabling terminal pin. The enabling terminal pin is used for being electrically connected with the RE pin and the DE pin of the RS485 chip; the pin of the sending terminal is used for being electrically connected with the DI pin of the RS485 chip; and the receiving terminal pin is used for being electrically connected with an RO pin of the RS485 chip.
Example 4
On the basis of the foregoing embodiment, this embodiment further provides an RS485 chip, and the RS485 chip is integrated as the isolation protection chip in embodiment 3 to from taking isolation protection function, improving communication stability and interference killing feature.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. An isolation protection circuit of an RS485 chip in an acquisition terminal is characterized by comprising
An isolation filter circuit including an isolation device and a filter device; the three-channel interface of the isolation device comprises an enabling end, a sending end and a receiving end; three-channel interfaces of the isolation device are electrically connected with three corresponding interfaces of the serial port end in the RS485 chip respectively; the filter device comprises a first filter circuit, a second filter circuit and a third filter circuit; the first filter circuit is connected to a power supply end of the isolation device and used for inhibiting the influence of impulse voltage on RS 485; the second filter circuit is connected to the ground end of the isolation device and used for releasing the interference signals accumulated on the RS485 chip out through the ground end; the third filter circuit is connected to all interfaces of the electricity removal source end and the ground end of the isolation device and is used for removing high-frequency interference signals;
the serial port end protection device is connected to three interfaces in the serial port end where the RS485 chip and the isolation device are connected with each other; the serial port end protection device is used for discharging interference signals on an RS485 serial port pin; and
a differential end protection device; which is connected to the differential terminal A, B of the RS485 chip; the differential end protection device is composed of 4 current-limiting resistors R4, R6, R91, R92, 3 transient suppression diodes TVS1, TVS2, TVS3, 2 ESD diodes D11 and D17, a pull-up resistor R24, a pull-down resistor R24, a thermistor PTC1 and a capacitor C7; in the differential end protection device, one end of R4 is connected with one differential interface B of an RS485 chip, and the other end of R4 is connected with R91 and PTC1 in series in sequence; the other end of the PTC1 is used as an external port of the differential interface B; one end of the R6 is connected with the other differential interface A of the RS485 chip, the other end of the R6 is connected with the R92 in series, and the other end of the R92 is used as an external port of the differential interface A; one end of D11 is connected between R4 and R91, and the other end is connected to virtual ground; one end of D17 is connected between R5 and R92, and the other end is virtual ground; the 3 transient suppression diodes TVS1, TVS2, and TVS3 are connected in series with each other, and both ends are connected to virtual ground; the intermediate nodes of TVS1 and TVS2 are electrically connected with the intermediate nodes of R92 and PTC 1; the intermediate nodes of the TVS2 and the TVS3 are electrically connected with the node of the R92 which is used as the external terminal of the differential interface A; one end of the pull-down resistor R23 is connected with a differential interface B of the RS485 chip, and the other end of the pull-down resistor R23 is connected with a virtual ground; one end of the pull-up resistor R24 is connected with the differential interface B of the RS485 chip, and the other end of the pull-up resistor R24 is connected with a power supply; one end of the capacitor C7 is connected to the power supply end of the RS485 chip, and the other end is connected to virtual ground.
2. The isolation protection circuit of the RS485 chip in the collection terminal according to claim 1, wherein: the serial port end protection device comprises 3 ESD diodes and 1 resistor R93, wherein two ESD diodes are respectively connected in series to the transmitting end and the receiving end of the RS485 chip, and the third ESD diode is connected in parallel with the resistor R93 and then connected in series to the enabling end of the RSA485 chip; the other ends of the three ESD diodes are all connected with a virtual ground.
3. The isolation protection circuit of the RS485 chip in the acquisition terminal according to claim 1, wherein: the isolation device adopts a transmission device with two paths and six channels; the isolation device supports simultaneous connection with two RS485 chips;
the second filter circuit adopts a safety capacitor C99, wherein one end of the C99 is connected and grounded with the ground end of one path of the isolation device, and the other end of the C99 is connected and grounded with the ground end of the other path of the isolation device.
4. The isolation protection circuit of the RS485 chip in the collection terminal according to claim 3, wherein: the safety capacitor C99 adopts a Y capacitor with the specification of 1000 PF/4000V.
5. The isolation protection circuit of the RS485 chip in the acquisition terminal according to claim 3, wherein: the first filter circuit comprises two groups, and the two groups are formed by connecting a current-limiting resistor and a capacitor in series; two power supply ends of the isolating device are respectively connected to nodes connected between the current-limiting resistors and the capacitors in the two groups of first filtering circuits; in the two groups of first filter circuits, the other ends of the capacitors are grounded, and the other ends of the current-limiting resistors are connected with a power supply.
6. The isolation protection circuit of the RS485 chip in the acquisition terminal according to claim 5, wherein: the third filter circuit is formed by connecting a resistor and a capacitor in series to form an RC filter circuit; in the third filter circuit, the other end of the resistor is electrically connected with the isolation device, and the other end of the capacitor is used as an external port of the isolation device.
7. The isolation protection circuit of the RS485 chip in the acquisition terminal according to claim 1, wherein: the isolation device adopts a Na8262 six-channel digital isolator; the model of a transient suppression diode in the differential end protection device is 5MAJ60 CA; the nominal resistance of the thermistor PTC1 is between 30-60 omega.
8. The utility model provides an isolation protection module of RS485 chip among collection terminal which characterized in that: the circuit layout of the isolation protection circuit is adopted, and the isolation protection circuit is used for isolating and protecting an RS485 chip; the isolation protection module comprises
The isolation filtering unit consists of an isolation circuit, a first filtering subunit, a second filtering subunit and a third filtering subunit; the isolation circuit adopts a digital isolator with two paths and six channels; the first filtering subunits comprise two groups which are respectively connected to two power supply ends of the isolation device, and the first filtering subunits are used for inhibiting the influence of impulse voltage on RS 485; the second filtering subunit is connected between two ground ends of the isolation device and used for releasing the interference signals accumulated on the RS485 chip out through the ground ends; the third filter subunit adopts a plurality of independent RC filter circuits and is connected to all interfaces of the electricity removal end and the ground end of the isolation device; the third filtering subunit removes high-frequency interference signals;
the serial port end protection unit is connected to three interfaces in the serial port end where the RS485 chip and the isolation circuit are connected with each other; the serial port end protection unit is used for discharging interference signals on an RS485 serial port pin; and
a differential end protection unit; which is connected to the differential terminal A, B of the RS485 chip; and the differential end protection unit is used for protecting the RS485 chip from the impact of instantaneous high-voltage spike pulse.
9. An isolation protection chip, characterized in that, it is packaged by the isolation protection circuit of the RS485 chip in the acquisition terminal according to any one of claims 1 to 7; the pin of the isolation protection chip comprises:
a power supply end pin which is connected with the VCC pin of the RS485 chip and is used for connecting a power supply;
a ground pin for grounding;
the virtual ground pin is connected to the GND pin of the RS485 chip and is used for connecting virtual ground;
the two differential interface pins are used for being electrically connected with the differential interfaces A and B in the RS485 chip;
the three serial port pins comprise a sending terminal pin, a receiving terminal pin and an enabling terminal pin; the enabling terminal pin is used for being electrically connected with RE and DE pins of the RS485 chip; the pin of the sending end is used for being electrically connected with a DI pin of the RS485 chip; and the receiving terminal pin is used for being electrically connected with an RO pin of the RS485 chip.
10. An RS485 chip is characterized in that: the RS485 chip is integrated with the isolation protection chip of claim 9 and has an isolation protection function, so that the communication stability and the anti-interference capability are improved.
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| CN114866160B (en) | 2024-02-06 |
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