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Design >> Analog Design >> The body diode of the power MOSFET Tr
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Message started by dandelion on Jan 28^th, 2008, 9:53pm

Title: The body diode of the power MOSFET Tr
Post by dandelion on Jan 28^th, 2008, 9:53pm

Hi,
In my design, the power MOSFET is integrated on the chip. We have the concern the body diode of the power MOSFET will have adverse effect for the performance.

I wonder if this effect can be represented in the simulation? Put another words, in normally, the body diode is imcluded in the BSIM spice model?

PLs. give me some advice.
Thanks

Title: Re: The body diode of the power MOSFET Tr
Post by thechopper on Jan 29^th, 2008, 3:38pm

Hi Dandelion,

I guess you are taking of the drain-body diode (I´m assuming an open-drain output stage). If that´s te case the answer is yes, it is included in the BSIM model.
Which is exactly the adverse effect you are expecting on the performance of such device? Is it ESD related?

If you could give us more details that would help us answer your question.
Thanks
Tosei

Title: Re: The body diode of the power MOSFET Tr
Post by dandelion on Jan 29^th, 2008, 6:23pm

thechopper wrote on Jan 29^th, 2008, 3:38pm:

Hi Tosei,
Thanks for the reply.

I am designing a class-d audio amplifier. because the output power is about 2W. The power mosfet is integrated into the chip.

we have the concern if the body diode will have any adverse effect on the performance. So, if this body diode is included in the spice model, it would be controllable for the front-end designs.

In fact, we have found some descranpancy between the simulation and the silicon measuremnts results. Mainly is at the overcurrent protection part and we are checking if this body diode is the culprit.

Thanks

Title: Re: The body diode of the power MOSFET Tr
Post by sheldon on Jan 31^st, 2008, 8:08am

Dandelion,

By the body diode are you referring to the body-drain diode or are you
using a triple well process [or BiCMOS process] with a buried N-Well? The
body-drain diode should be included in the bsim4 model, but the body well
due to the buried n-well probably is not included in the model. I have not
looked at the diode models in the bsim4 model. Usually when a parasitic
device is included in a compact model, the model is somewhat simplified
to optimize simulator performance. Is it possible to use an external model
for the body diode? An external diode model may contain more parameters
and allow for more accurate simulation. Does your foundry provide data on
effects like saturation recovery? Is it possible that device self heating is an
issue? Is the body diode the only protection device or are you using an
external Schottky as the main protection device?

Best Regards,

Sheldon

Title: Re: The body diode of the power MOSFET Tr
Post by dandelion on Jan 31^st, 2008, 8:54pm

sheldon wrote on Jan 31^st, 2008, 8:08am:

Hi sheldon,
Thanks for the reply. It is helpful to us.

As I know, our foundy did not provide the effects like saturation recovery.

In addtion, we exclude the possiblity of the self heating to the performance. For the overcurrent protection, we have another block to handle it. I am not clear the function of the body diode or the external Schottky for protecting the overcurrent. The only adverse effect as I know is its EMI effecr for the saturation recovery of body diiode.

In present, we have found the VDD/GND bounce maybe the cause of the fault. We are still checking it.

Rhanks