CN104821574A

CN104821574A - IIC bus interface electrostatic protection circuit

Info

Publication number: CN104821574A
Application number: CN201510273764.2A
Authority: CN
Inventors: 廖志梅
Original assignee: Guangzhou Correcttude Power Currency Electric Co Ltd
Current assignee: Guangzhou Correcttude Power Currency Electric Co Ltd
Priority date: 2015-05-26
Filing date: 2015-05-26
Publication date: 2015-08-05

Abstract

The invention discloses an IIC bus interface electrostatic protection circuit which is characterized in that SCL and SDA two lines of an IIC bus are respectively provided with a grounded TVS diode; and when static electricity is conducted to an IIC bus interface, the IIC bus interface generates a high voltage to the earth, and the TVS diode can immediately work a protection function to prevent the interface from being damaged due to rising of IIC bus interface voltage, and thus the circuit plays an electrostatic protection function on the IIC bus interface.

Description

A kind of electrostatic discharge protection circuit of iic bus interface

Technical field

The present invention relates to the electronic circuit containing iic bus interface, particularly a kind of IIC interface to element carries out electrostatic discharge protection circuit.

Background technology

At present, a large amount of use has peripheral components and the microprocessor communication of IIC interface in embedded systems, and such as eeprom chip, Flash chip, clock chip etc., both provide iic bus interface.The IIC interface of microcontroller (MCU) is used to be connected with the IIC interface of peripheral components in practical application, to realize the communication function of master-slave mode.

At present, outer member anti-interference is missed very deficient, usually mainly use pull-up resistor, decoupling capacitor and pcb board zone network to wrap up the measure of IIC order wire, increase antijamming capability, as Fig. 1.But, pull-up resistor is set, goes the measure such as lotus root electric capacity and zone network parcel, the anti-EMC interference performance of enhancing that only can be suitable, but little to the protection effect of electrostatic impact.Pull-up resistor is just clamped at high level by a resistance by uncertain signal, and resistance plays metering function simultaneously, and it is little to the protection effect of electrostatic impact.Though the high frequency spurs on the energy filter out power line of decoupling capacitor, does not have protective effect to two order wires of iic bus.The measure of pcb board zone network parcel IIC order wire, although can prevent the generation electromagnetic interference in neighbouring circuit and space, if the high pressure produced during electrostatic arrives communication line by the mode of conduction, parcel measure will be lost efficacy.Even if after adopting above-mentioned measure, in the use of reality and when carrying out electrostatic discharge testing, find that the IIC interface of MCU or peripheral components still often can be damaged by static electricity.And this damage is all permanent usually, also cannot recover even if again power on after power-off.Therefore in the recurrent occasion of electrostatic phenomenon or need the product carrying out strict electrostatic discharge testing, also need to increase other more effective safeguard measure to IIC interface.

Summary of the invention

The object of the present invention is to provide a kind of can effectively prevent iic bus interface in use and do electrostatic test experiment time damage iic bus interface electrostatic protection circuit, to make iic bus interface communication more practical, reliable.

The electrostatic discharge protection circuit of iic bus interface of the present invention; at the serial time clock line (SCL) of iic bus and serial data line (SDA) two lines, a Transient Suppression Diode (TVS pipe) is set all over the ground; the puncture voltage of this TVS pipe is less than the limiting voltage of shielded IIC interface, and is greater than the voltage that IIC interface normally works.

The electrostatic discharge protection circuit of iic bus interface of the present invention, when electrostatic is transmitted to IIC interface, IIC interface can produce high pressure over the ground, due to SCL(serial time clock line) and SDA(serial data line) company of being provided with ground TVS pipe, and be exceedingly fast due to the response speed of TVS pipe, for nanosecond, therefore when electrostatic conduction is come, IIC interface produces high pressure over the ground, this voltage is far longer than the puncture voltage of TVS pipe, just there is snowslide in TVS diode, be supplied to transient current super-low resistance path, consequently transient current is drawn away by diode, avoid protected IIC device, preventing IIC interface voltage from raising makes interface damage, thus electrostatic defending effect is served to iic bus interface.

Accompanying drawing explanation

Fig. 1 is a kind of electrostatic discharge protection circuit schematic diagram of existing iic bus interface.

Fig. 2 is the electrostatic discharge protection circuit schematic diagram of iic bus interface of the present invention.

Embodiment

As Fig. 2; the electrostatic discharge protection circuit of iic bus interface; it is characterized in that: the SCL(serial time clock line at iic bus) and SDA(serial data line) two bars lines arrange a Transient Suppression Diode (TVS pipe) all over the ground; the breakdown voltage value of this TVS pipe is less than the limiting voltage of shielded IIC interface, and is greater than the voltage that IIC interface normally works.As: when 24C512 chip application is under 3.3V voltage, its IIC interface greatest limit voltage is 6V, and the protection magnitude of voltage of TVS pipe now can be selected to be 5V.Corresponding TVS pipe model can be GBLC05C, and its breakdown voltage value is 5V, and junction capacitance is 3pF when 1MHz, and the capacitance of junction capacitance can not affect IIC and communicate normally.

When electrostatic is transmitted to IIC interface, IIC interface can produce high pressure over the ground, and this high pressure can produce expendable destruction to the IIC interface of chip.If add TVS pipe; because the response speed of TVS pipe is exceedingly fast (nanosecond); when electrostatic conduction is come, IIC interface produces high pressure over the ground, and this voltage is far longer than the puncture voltage of TVS pipe; just there is snowslide in TVS diode; be supplied to transient current super-low resistance path, consequently transient current is drawn away by diode, avoids protected IIC device; preventing IIC interface voltage from raising makes interface damage, and therefore serves electrostatic defending effect.

Claims

1. the electrostatic discharge protection circuit of an iic bus interface; it is characterized in that: at the serial time clock line (SCL) of iic bus and serial data line (SDA), a Transient Suppression Diode (TVS pipe) is set all over the ground; the puncture voltage of this TVS pipe is less than the limiting voltage of shielded IIC interface, and is greater than the voltage that IIC interface normally works.