Latch effect (Latch Up) is the power source in parts of an apparatus cites the condition that low impedance method produces between foot and ground. This kind of circumstance general by spark incident (voltaic infuse or overvoltage) cause, but once spark, although touch hair condition to exist no longer, low impedance method still exists. Method of this kind of low impedance may be made the same score as a result of too big electricity water and cause systematic turbulence or disastrous damage. When designing circuit application, need ensures the tension that uses at parts of an apparatus and voltaic level accord with absolutely the biggest rating to ask.

 

When circuit is designed, can suggest to avoid latch problem under the consideration.

 

1.If produce latch as a result of electrify sort, can use diode and VDD series connection.

 

If allow when to await the digital input of parts of an apparatus or output to exceed VDD, can establish ties in VDD diode (following graphs use 1N914) will prevent SCR sparks and subsequently latch arises. Because diode can prevent parasitism,this is the base electric current of transverse PNP transistor brings a foot to pour out of from VDD, prevent SCR to spark thereby.

 

 

2.Xiaoteji diode adds DGND (digital ground) can prevent voltage to be not worth

 

If the digital input of parts of an apparatus is mixed,output at any time under DGND, so diode will lose the Xiaoteji that receives DGND repeatedly from these inputs or output effectively deflection clamp in – 0.3V comes – between 0.4V. This can prevent parasitism NPN transistor blast off extremely with base the knot guides, and return can spark in order to prevent SCR.

 

 

3.In DGND and ground of AGND (imitate) between join diode of Xiao Te radical

 

If DGND potential can exceed AGND 0.3V or more now and then, can be in parts of an apparatus brings what diode of Xiao Te radical places to prevent transistor of relevant parasitism NPN between the foot twice to guide. This provided the additional protection that prevents latch. In addition, additional diode can be in the retrorse and shunt-wound connective that mentions in front DGND of another direction admiral restricts AGND, reduced digital noise greatly so by the possibility of infuse parts of an apparatus.