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Author Topic: NCP driver sucks  (Read 2015 times)

Offline OgreVorbis

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NCP driver sucks
« on: October 13, 2019, 1749 UTC »
I'm on my 4th revision of my PCB and the first one was the best. On the first one, I used TC4452 because I didn't know about the IXDD614 at that point. After that I found out about the NCP and thought it would be better than the 614 and so I built my last three PCBs based on it. It was a big mistake and I wasted so much time on it and now if I want to use the 614s, I have to basically start over at square one. So I am giving up for at least a year. It pisses me off because I'm not the type to be able to put something like this down, but it's not worth it to get angry over something like this.

BTW: The waves going in and out of them are square as can be (as square as the crystal source which is connected with very short straight traces).

So what's wrong with them?
1. They get dangerously hot at 12V and above - they may do 15V with a heatsink on top, but they were emitting a smell like they were about to pop (and I did pop several).
2. The datasheet (especially the truth table) is either just really confusing or the design is just wrong. Based on the truth table, there is no way to use the inverting input as the output will always be low. I found this to be the case in practice also.

So yeah, I think it will work with GaN cause they only need about 8V, but if you got it working with SiC at higher voltages, then you must have magical powers.

So for now, I'm just going to use my original design board that works good below 5 MHz. I guess I won't be on the 'fun' band any time soon lol  :)

EDIT:

Here's the datasheet: https://www.onsemi.com/pub/Collateral/NCP81074-D.PDF

Truth table page 5.
« Last Edit: October 13, 2019, 1758 UTC by OgreVorbis »
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Offline Azimuth Coordinator

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Re: NCP driver sucks
« Reply #1 on: October 13, 2019, 2154 UTC »
I think the issue is the frequency your trying to use the device at..  looks like max Ft is 2Mhz Should be fine for AM 550Khz to 1700Khz  But not for 6Mhz +
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Offline redhat

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Re: NCP driver sucks
« Reply #2 on: October 13, 2019, 2323 UTC »
For the record, all these parts are spec'd to 2 MHz...that is all.  In the early days of using power conversion parts, I quickly found that the DIP package parts smoke driving anything over 1 MHz.  I switched to tabbed devices and all my problems went away...sortof.  It did take a bit of fiddling with different parts until I settled on the '614's.  in most applications, you can use the TO-263 version up to about 9 MHz or so, depending on what you are trying to drive.  My fets are about 1000pf each and the 614's will happily drive them to about that, maybe more with decreased performance and more heat.  I'm not sure if there is much of a performance difference between the 4452's and the '614's but the heatsink tab on the latter is tied internally to VSS, which makes layout and thermal management easier.

Fall is here, and 4 MHz historically has worked much better for me than 6 MHz when the leaves start to fall  8)

+-RH
« Last Edit: October 14, 2019, 0232 UTC by redhat »
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Offline Stretchyman

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Re: NCP driver sucks
« Reply #3 on: October 14, 2019, 0608 UTC »
The NCP's are fine to beyond 14MHz driving GaN.

The issues arrive from driving Qg and the SiC's I use, C3M0280090D have a Qg of 9.5nC. (GaNs have Qg of 6nC)

Power required to drive FET is QgxfxV, so 9.5e-9x7e6x12 = 800mW so they get a bit warm but are fine.

Apart from one op blowing the sh*t out of the whole Tx by powering it with A.C. I've never had one blow.

Are you using the same SiC FETs?

Str.
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Offline OgreVorbis

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Re: NCP driver sucks
« Reply #4 on: October 14, 2019, 1147 UTC »
Thanks for the replies!

The NCP's are fine to beyond 14MHz driving GaN.

The issues arrive from driving Qg and the SiC's I use, C3M0280090D have a Qg of 9.5nC. (GaNs have Qg of 6nC)

Power required to drive FET is QgxfxV, so 9.5e-9x7e6x12 = 800mW so they get a bit warm but are fine.

Apart from one op blowing the sh*t out of the whole Tx by powering it with A.C. I've never had one blow.

Are you using the same SiC FETs?

Str.

Yes, that's the one I'm using.

There must be some small difference about my PCB that's making it not work, but it's just too marginal. 800mW in that SOIC-8 seems like a lot. In my situation they are also hand soldered, so the dissipation through the pins is probably not as good as if I had used solder paste.

If I was going to continue this, it wouldn't be hard to make a GaN version of the board because it would just require swapping the drain and source pins. Then the NCPs would run easily with a lot of headroom.

So then the only problem I would have is getting the inverted inputs on them to work.

Stretchy: Have you used the inverting inputs on these? How do you wire it up? I tried connecting the inverted input to the crystal and grounding the non-inverted input, but the output stays low. I have the two OUTH and OUTL tied together, but I think it's wrong. How should it be connected for inverting? Like I said the datasheet is no help and the truth table doesn't make sense. There is no diagram of how to use the inverted input and clearly it's not just a matter of connecting the input to it.

For the record, all these parts are spec'd to 2 MHz...that is all.  In the early days of using power conversion parts, I quickly found that the DIP package parts smoke driving anything over 1 MHz.  I switched to tabbed devices and all my problems went away...sortof.  It did take a bit of fiddling with different parts until I settled on the '614's.  in most applications, you can use the TO-263 version up to about 9 MHz or so, depending on what you are trying to drive.  My fets are about 1000pf each and the 614's will happily drive them to about that, maybe more with decreased performance and more heat.  I'm not sure if there is much of a performance difference between the 4452's and the '614's but the heatsink tab on the latter is tied internally to VSS, which makes layout and thermal management easier.

Fall is here, and 4 MHz historically has worked much better for me than 6 MHz when the leaves start to fall  8)

+-RH

Eventually some day when I have more time, it's clear to me that the 614s combined with GaN are probably the best, most durable and fool proof way. I love how the tabs are grounded on the 614s and the transphorm GaN. All fets should be that way.
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Offline Stretchyman

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Re: NCP driver sucks
« Reply #5 on: October 14, 2019, 1228 UTC »
The design I use uses the AD9850 PCB's on Ebay and they O/P opposite phases already so I've no need to invert.

I'll have a look at your 'problem'....

.................................................

OK, tie the O/P's together, ground the I/P you don't want to use, drive the other.

That should give opposing O/P's.

Str.
« Last Edit: October 14, 2019, 1241 UTC by Stretchyman »
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Offline OgreVorbis

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Re: NCP driver sucks
« Reply #6 on: October 14, 2019, 1456 UTC »
The design I use uses the AD9850 PCB's on Ebay and they O/P opposite phases already so I've no need to invert.

I'll have a look at your 'problem'....

.................................................

OK, tie the O/P's together, ground the I/P you don't want to use, drive the other.

That should give opposing O/P's.

Str.

Right, that's what I did and none of the inverted ones are working. They are always low. I checked with a scope right on the output of them.

If I fix this, maybe it will work  :o Even with only one side of the amp firing, I am getting almost exactly 50% efficiency, so I think if I can make the other side work it should be pretty good.
I found that 10V may actually be enough for the drivers. It doesn't seem to lower the output/efficiency until I go to 9V or less.

I don't know if you checked the image of the board, but here it is. You can see the subtle change on the drivers for each side.

Thanks for the help stretchy.

« Last Edit: October 14, 2019, 1501 UTC by OgreVorbis »
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Offline redhat

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Re: NCP driver sucks
« Reply #7 on: October 14, 2019, 1541 UTC »
Maybe you have to tie the positive input pins high to get the inverter function to work?

+-RH
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Offline OgreVorbis

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Re: NCP driver sucks
« Reply #8 on: October 14, 2019, 1548 UTC »
Maybe you have to tie the positive input pins high to get the inverter function to work?

+-RH

Now that I look at it again, yeah, I think you're right.
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Offline Stretchyman

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Re: NCP driver sucks
« Reply #9 on: October 14, 2019, 1639 UTC »
Yes indeed!

If you 'translate' the truth table.....

Drive the '-' I/P on both sides but pull up the '+' I/P on one side and down on the other side.

What RH said!

Sounds like your nearly there....

Str.
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Offline JimIO

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Re: NCP driver sucks
« Reply #10 on: October 14, 2019, 1812 UTC »
It's called a truth table because it is.    8)

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Offline OgreVorbis

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Re: NCP driver sucks
« Reply #11 on: October 15, 2019, 0016 UTC »
Drive the '-' I/P on both sides but pull up the '+' I/P on one side and down on the other side.

Sounds more complicated than necessary. Do I need to do it that way?
Alright the modification has been made. I just connected the non-inverted input to 5V and drive the inverted input only.

« Last Edit: October 15, 2019, 0024 UTC by OgreVorbis »
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Offline Stretchyman

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Re: NCP driver sucks
« Reply #12 on: October 15, 2019, 0502 UTC »
On one side only..

Ok, does it work??

Str.
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Offline OgreVorbis

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Re: NCP driver sucks
« Reply #13 on: October 15, 2019, 1112 UTC »
On one side only..

Ok, does it work??

Str.

Well, the non-inverted side already works fine (with less than 12V). After reading the truth table again, I don't see why this wouldn't work. Unfortunately, the only way to find out is to send for the PCBs again. I'm just going to go for it. It's only $35 for 6 of them and it's not something I can hack onto my current board because those pins are grounded, so I can't just connect a wire there; I have to get new PCBs. And I shouldn't need pullups or pulldowns because that pin should always be high.
« Last Edit: October 15, 2019, 1117 UTC by OgreVorbis »
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Offline Monophonia

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Re: NCP driver sucks
« Reply #14 on: October 15, 2019, 1354 UTC »
I have used the NCP up to 7.290 in the past. Inverting and non-inverting. What keeps them from frying is a few ohms between the driver and the SiC gate.