MSP430 ESD protection

david sun77114 said:

I have a MSP430F2370 design require Air 15K discharge.

 Hi David are you asking about how to pass air discharge ESD test?

 This is different from selecting ESD model but you need a circuitry that react dissipating ESD when spark begin from external body to board and your system has to survive intact. Passing also FCC/CE certification require some filtering that also help remove that problem too.

 If you try protect it just by inserting some TVS, when voltage reach upper or lower threshold the parasitic thyristor get fired and MSP connect VCC to GND shutting down or destroying if power is not limited.

 So use some RLC circuit to limit energy/ filter out RF and ESD from reaching input pin. Add  a charge decoupling network from msp ground and front panel. Some good ESD manual on how to can help you then your design can also withstand a more strong discharge undisturbed by.

Hi Roberto,

Thank you very much, I know ESD solution can not be answered by yes or no,  initially I only want to get a generic suggestion or rule of thumb. seems to me you are an expert of ESD topic, I feel lucky that I can ask you some detailed questions. 

1. I just read SLAA530. in page 26, there are Figure 20(b) shows 8000V  I-IEC pulse curve. this must be a 8000V contact model waveform. how does Air discharge looks like. I guess the current should be much lower for Air discharge, at least I hope so, because our device is only required Air discharge.

2. let assume all circuits will be optimized to MSP430 depend on the TVS being selected, what is the side effect if I change the TVS from 12V breakdown to 6V. 

looking forward for your reply

 Hi David, I read you are dealing about 8KV discharge model but on first one you required 15KV, current of air discharge doesn't change by selecting TVS voltage, can be much lower by parallel capacitor and RC decoupling from panels and shielding.

 Good PCB design also is the primary goal, ESD and EMF components must be closer one to other and just connected to one point of a SOLID ground plane.

 Never run long traces on ground plane never open large area on it. If you had more than one ground plane connect them in one point and in the case of galvanic separated add an RC coupling to avoid spark and current spikes too.

 As you can see from the good document you pointed me asking for a reply it depend on where discharge can hit your circuits from box cables or direct reradiation.

 Are you planning to pass ESD level 1 or 2? Is your system cabinet metal or plastic?

Exposed to external discharge: Cables, push button, led LCD other?

 ESD on cables can be reduced by LRC EMF circuits too, TVS can reduce spikes but RF filter definitively reduce energy and smooth down pulse too requiring a small TVS. 6V TVS present more capacitance, check ESR on datasheet, if ESR increase this scenario can be more worst with 6V TVS than 12V ones.

 If subsystem are included what about certification ESD certification?

Hi Roberto,

let me simplify my question, I have two TVS diodes, all parameters are same, except the break down voltage, one is 6V, one is 12V. for MSP430F powered by 3.0V. which one should I choose? why?

thank you very much,

David Sun

 Hi David you must choose the one with less ESR, the pulse current is the same for both 6 or 12V TVS breakdown voltage so the worst parameter came from voltage across ESR, 12V BD with 1Ohm ESR is better than 6V BD with 2Ohm ESR. If all parameter but BD voltage are the same then if ESR meet the requirement both can suffice for protection from ESD. Post the part number and what discharge path you need protect from and I can see which one perform better.

I try to insert a schematic in this post, but the insert image and file function doesn't work for my win7 computer.  let me explain the circuit here, some port (P4.1, P4.2) of MSP430F2274 in my application will connect to a external port directly, because there are current drive out, so no resistor or inductor in between. I would like to put a ESD TVS on these ports to provide +/- 15K air discharge protection.

we are using a TVS from Central semiconductor, PN CMNTVS12V, it has a 12V breakdown voltage, it will meet the 15K Air at most of the time. but failure( system reboot) happens in very rare case. I hope to change to a TI true IEC61000-4-2( level 4) parts will improve the performance.

the candidates are TPD4E001( 11V breakdown), TPD4S009(9V breakdown ), TPD8E003(6V breakdown).

the signal is in Khz domain, so the bandwidth or speed of the TVS is not required.

thank you very much for your help.

David

thank you very much for your suggestions. 

 Just for please tell me if the suggestion solve your problem or need more assistance. ESD and EMF problem are to be solved in front of system to see all interaction but some more refinement can also be done by pictured scenario.