Gate and source of P-channel mosfet breakdown

[ericgibbs]

it is absolutely possible.

So you are REALLY saying you DONT know.

In that case why did you bother to post.?

 

[millwood]

So you are REALLY saying you DONT know.

I am sorry that you have been confused, but I failed to understand how you can be confused by something this simple.

In that case why did you bother to post.?

to help you with your problems?

 

[millwood]

Thanks Eric.
I can manage to add attachment per your direction.Thank you very much.
I just issued a new post whose title is:Making a output voltage,Would you like to review it when are feel free.Thanks in advance.

take a look at the datasheet for the mosfets used. they should have a body diode in their and you need to make sure that the reverse em will not damage the body diode. if not, put some diodes on those mosfets.

 

[ericgibbs]

I am sorry that you have been confused, but I failed to understand how you can be confused by something this simple.
to help you with your problems?

Once again you say you have failed to understand.

I can see, myself and others are wasting our time trying to get any sense out of you, so you are best ignored.

 

[millwood]

Once again you say you have failed to understand.

yeah. how could something so simple be so startling to you?

I can see, myself and others are wasting our time trying to get any sense out of you, so you are best ignored.

sure you can see, that doesn't make true what you say you saw.

 

[Pommie]

If this troll doesn't get banned then you are going to loose a lot of good posters.

Mike.

 

[kchriste]

Getting back to the blown FETs.
What are the part number of both the P and N channel FETs on the diagram? The datasheet, and knowing the voltage of Vbat, might give us more of a clue.
I know it has been mentioned that the failure points towards a gate-source breakdown, but this circuit could self destruct when it is used. ie: If both PWM inputs are low, nothing happens. If only one PWM input is "high" the motor will run and nothing bad should happen. If both PWM inputs are "high" then all four FETs are turned on and smoke happens!

 

[smanches]

Two good app notes I just found all about MOSFETs.

https://www.electro-tech-online.com/custompdfs/2009/07/an-936.pdf

https://www.fairchildsemi.com/an/AN/AN-9010.pdf#page=16

The one from Fairchild is much more in depth. They both go over possible failure points.

 

[mneary]

In the circuit shown, no bulk bypass is shown on Vbatt. If this isn't close enough to the H-bridge or has been altogether forgotten, then Vbatt will be spiking seriously. The P-channel devices will get the worst of it, and will die very quickly.

If Vbatt is 12V or so (gotta guess), and guessing that the motor is less than 6A (R45 is .02 ohms 0.5W) I would use 220µF in parallel with a couple of 1µF ceramics.

[edit] I should mention if Vbatt is an automotive supply, then 14.4V is too close to the breakdown rating of a lot of mosfets and the design needs surgery. I cannot find a listing for a GB3318 or GA3055 mosfet, am I reading them correctly or are these house numbers?[/edit]

 

[wealth210]

Thank you for your reply.I admit that I can't express my problem in detail,so let you have trobule in understanding.
I decide to update my problem later,hope you can give me more analysis and comment.Once again,I learn a lot from you.Thank you very much.

Best regards

 

[ericgibbs]

Thank you for your reply.I admit that I can't express my problem in detail,so let you have trobule in understanding.
I decide to update my problem later,hope you can give me more analysis and comment.Once again,I learn a lot from you.Thank you very much.

Best regards

hi wealth,

It would help if you posted the specification of the P and N MOS fets, also the Vbat voltage.

 

[wealth210]

Hi Eric
1. VBAT is 9.6V.
2. GB3318 datasheet is belowing:
BVDss is -25V, Rds(on) is 150mohm,Id is -10A.
3. GJ3055s datasheet is belowing:
BVDss is 20V, Rds(on) is 25mohm,Id is 18A.
detail please refer to the attachment,there is only GJ3055s specification.I will add GB3318 specification here when I get it.
One more thing need you know,the bad mosfet is only GB3318,not GJ3055s.

 

[wealth210]

update my problem: Gate and source of mosfet is short

My problem is that the PCBA whose the bad PMOS
(GB3318) can be pick out by the testing jig.Now I need to analyse why the mosfet GB3318 is damage.
The testing jig setting is belowing:
1.DC Power supply is 10V~15V，often use 12V.there is stable voltage output 6V to PCBA VBAT.That means 6v to the PCBA.

2.Use 11ohm 10W resistor replace of the motor,so there is no motor in the testing jig.My understanding is no reverse EM on the PCBA.

3. IC PWM comes from Logic IC,there only one channel IC PWM will output high level.Two channel IC PWM have never output high level at the same time.

4.Severals E.Cap(220uf and 470uf) connect VBAT to ground.

That's all.would you like to hele me ananlyse why GB3318 mosfet is damage.its Gate and Source is short.

 

[OutToLunch]

what is the failure rate?

can you post some captured waveforms while in test? Show the gate, drain and source of the PFET simultaneously (can be referenced to ground) while switching on and when turning off. If you have 4 channels, show the gate of the lower FET as well.

 

[ericgibbs]

hi wealth,
Please confirm that this LTspice simulator circuit represents the PCBA.

I know that these are not your FET's I will modify them later.

 

[mvs sarma]

How that 11 ohms is decided?
It cant be motors dc resistance
We have to take impedance into consideration and change it to a higher value, i suppose

 

[ericgibbs]

How that 11 ohms is decided?
It cant be motors dc resistance
We have to take impedance into consideration and change it to a higher value, i suppose

from the OP's posts: its a test rig that is using the 11R.

2.Use 11ohm 10W resistor replace of the motor,so there is no motor in the testing jig.My understanding is no reverse EM on the PCBA.

 

[mvs sarma]

from the OP's posts: its a test rig that is using the 11R.

I saw it Eric, but he forgot that the inductors he used in series are enough to create the back emf. perhaps the motor is substituted by the combination of these inductors and the 11 ohm.
However 5.6uH is too small to be expected as Motor simulator.

 

[ericgibbs]

I saw it Eric, but he forgot that the inductors he used in series are enough to create the back emf. perhaps the motor is substituted by the combination of these inductors and the 11 ohm.
However 5.6uH is too small to be expected as Motor simulator.

hi Sarma,
As its a R/C toy car, I suspect those 6.5uH inductors are for radio RF suppression.

From the initial tests I have done, it appears that theP MOS fets are failing at power on due to poor circuit design.?

 

[mvs sarma]

hi Sarma,
As its a R/C toy car, I suspect those 6.5uH inductors are for radio RF suppression.

From the initial tests I have done, it appears that theP MOS fets are failing at power on due to poor circuit design.?

If so why only p mos?