Forums

guard rings

Started by Unknown April 10, 2021
Some schottky diodes have a PN junction in parallel, a "guard ring"
that acts like a parallel zener to improve ESD specs, and may help
with the fab somehow. That's OK, but at high currents the PN diode can
turn on, and it's slow to turn off and can even act like a
step-recovery diode.

I wonder if there is a way to tell, from the data sheets, if there is
a guard ring. VI curve? CV curve? ESD specs?

I'm pulsing a medium-small schottky pretty hard and I think I'm seeing
SRD effects. It's an ON SEMI RB520S30T1G.

The data sheet shows a recovery time test circuit, but no recovery
time spec! The latest data sheet is rev 11; you'd think someone might
have noticed the omission by now. But at the specified 10 mA test
current, the guard ring won't conduct; so why does a schottky have a
recovery time test circuit?

Grrrrr.





-- 

John Larkin      Highland Technology, Inc

The best designs are necessarily accidental.


  
On Saturday, April 10, 2021 at 12:49:02 PM UTC-4, jla...@highlandsniptechnology.com wrote:
> Some schottky diodes have a PN junction in parallel, a "guard ring" > that acts like a parallel zener to improve ESD specs, and may help > with the fab somehow. That's OK, but at high currents the PN diode can > turn on, and it's slow to turn off and can even act like a > step-recovery diode. > > I wonder if there is a way to tell, from the data sheets, if there is > a guard ring. VI curve? CV curve? ESD specs? > > I'm pulsing a medium-small schottky pretty hard and I think I'm seeing > SRD effects. It's an ON SEMI RB520S30T1G. > > The data sheet shows a recovery time test circuit, but no recovery > time spec! The latest data sheet is rev 11; you'd think someone might > have noticed the omission by now. But at the specified 10 mA test > current, the guard ring won't conduct; so why does a schottky have a > recovery time test circuit? > > Grrrrr.
Looks similar to this where they state it's 3ns. https://www.onsemi.com/pdf/datasheet/nsr0340p2-d.pdf
> > > > > > -- > > John Larkin Highland Technology, Inc > > The best designs are necessarily accidental.
On Saturday, April 10, 2021 at 12:49:02 PM UTC-4, jla...@highlandsniptechnology.com wrote:
> Some schottky diodes have a PN junction in parallel, a "guard ring" > that acts like a parallel zener to improve ESD specs, and may help > with the fab somehow. That's OK, but at high currents the PN diode can > turn on, and it's slow to turn off and can even act like a > step-recovery diode. > > I wonder if there is a way to tell, from the data sheets, if there is > a guard ring. VI curve? CV curve? ESD specs? > > I'm pulsing a medium-small schottky pretty hard and I think I'm seeing > SRD effects. It's an ON SEMI RB520S30T1G. > > The data sheet shows a recovery time test circuit, but no recovery > time spec! The latest data sheet is rev 11; you'd think someone might > have noticed the omission by now. But at the specified 10 mA test > current, the guard ring won't conduct; so why does a schottky have a > recovery time test circuit? > > Grrrrr. >
Looks like a first order capacitor charge to me. Don't have any idea how well that actually fits because it's just a sketch. That pulse generator has to be producing a current pulse.
> > > > -- > > John Larkin Highland Technology, Inc > > The best designs are necessarily accidental.
Am 10.04.21 um 18:48 schrieb jlarkin@highlandsniptechnology.com:
> Some schottky diodes have a PN junction in parallel, a "guard ring" > that acts like a parallel zener to improve ESD specs, and may help > with the fab somehow. That's OK, but at high currents the PN diode can > turn on, and it's slow to turn off and can even act like a > step-recovery diode. > > I wonder if there is a way to tell, from the data sheets, if there is > a guard ring. VI curve? CV curve? ESD specs?
HP/Avago used to write that in the data sheets or an app note.
> I'm pulsing a medium-small schottky pretty hard and I think I'm seeing > SRD effects. It's an ON SEMI RB520S30T1G.
30 pF @ 0V to 15 pF at some Volts. I heard that could happen (even in a usable way) with some PIN diodes.
> The data sheet shows a recovery time test circuit, but no recovery > time spec! The latest data sheet is rev 11; you'd think someone might > have noticed the omission by now. But at the specified 10 mA test > current, the guard ring won't conduct; so why does a schottky have a > recovery time test circuit?
It will need some recovery time also, albeit less. I did some push-pull frequency doublers recently. 100 -> 200 MHz was easy, but 200 -> 400 MHz had "effects". In the end it was good enough, but just barely. It looked like trr. 13 dBm in, still NOS Avago HSMS-282F. Gerhard
On Sat, 10 Apr 2021 19:43:05 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

>Am 10.04.21 um 18:48 schrieb jlarkin@highlandsniptechnology.com: >> Some schottky diodes have a PN junction in parallel, a "guard ring" >> that acts like a parallel zener to improve ESD specs, and may help >> with the fab somehow. That's OK, but at high currents the PN diode can >> turn on, and it's slow to turn off and can even act like a >> step-recovery diode. >> >> I wonder if there is a way to tell, from the data sheets, if there is >> a guard ring. VI curve? CV curve? ESD specs? > >HP/Avago used to write that in the data sheets or an app note. > > >> I'm pulsing a medium-small schottky pretty hard and I think I'm seeing >> SRD effects. It's an ON SEMI RB520S30T1G. > >30 pF @ 0V to 15 pF at some Volts.
Capacitance doesn't sound like "reverse recovery" to me. I can simulate the capacitance effects but the current spikes are huge in real life. Diode models don't include the fun stuff. I'll just have to try other diodes.
> >I heard that could happen (even in a usable way) with some PIN diodes.
PINs seem to have soft recoveries, unless you do the Grekhov trick.
> >> The data sheet shows a recovery time test circuit, but no recovery >> time spec! The latest data sheet is rev 11; you'd think someone might >> have noticed the omission by now. But at the specified 10 mA test >> current, the guard ring won't conduct; so why does a schottky have a >> recovery time test circuit? > >It will need some recovery time also, albeit less. I did some push-pull >frequency doublers recently. 100 -> 200 MHz was easy, but 200 -> 400 MHz >had "effects". In the end it was good enough, but just barely. It looked >like trr. 13 dBm in, still NOS Avago HSMS-282F.
Any estimate of peak current? They spec < 100 ps Trr, at 5 mA.
> >Gerhard
-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
jlarkin@highlandsniptechnology.com wrote:
> Some schottky diodes have a PN junction in parallel, a "guard ring" > that acts like a parallel zener to improve ESD specs, and may help > with the fab somehow. That's OK, but at high currents the PN diode can > turn on, and it's slow to turn off and can even act like a > step-recovery diode. > > I wonder if there is a way to tell, from the data sheets, if there is > a guard ring. VI curve? CV curve? ESD specs? > > I'm pulsing a medium-small schottky pretty hard and I think I'm seeing > SRD effects. It's an ON SEMI RB520S30T1G. > > The data sheet shows a recovery time test circuit, but no recovery > time spec! The latest data sheet is rev 11; you'd think someone might > have noticed the omission by now. But at the specified 10 mA test > current, the guard ring won't conduct; so why does a schottky have a > recovery time test circuit? > > Grrrrr.
What's the chance somebody there would even know? Like for old designed stuff, do any current employees even know how or why the designs exist the way they do, or undestand the test parameters being used to check parts? There's a vague claim that institutional knowledge is lost in 20 (or 30?) years. In the world of computers, it's way faster than that. I've come across a bunch of products where the manufacturer really has no idea what the specs even are, or how the thing even works.
On Sat, 10 Apr 2021 20:47:41 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

>jlarkin@highlandsniptechnology.com wrote: >> Some schottky diodes have a PN junction in parallel, a "guard ring" >> that acts like a parallel zener to improve ESD specs, and may help >> with the fab somehow. That's OK, but at high currents the PN diode can >> turn on, and it's slow to turn off and can even act like a >> step-recovery diode. >> >> I wonder if there is a way to tell, from the data sheets, if there is >> a guard ring. VI curve? CV curve? ESD specs? >> >> I'm pulsing a medium-small schottky pretty hard and I think I'm seeing >> SRD effects. It's an ON SEMI RB520S30T1G. >> >> The data sheet shows a recovery time test circuit, but no recovery >> time spec! The latest data sheet is rev 11; you'd think someone might >> have noticed the omission by now. But at the specified 10 mA test >> current, the guard ring won't conduct; so why does a schottky have a >> recovery time test circuit? >> >> Grrrrr. > >What's the chance somebody there would even know? Like for old >designed stuff, do any current employees even know how or why the >designs exist the way they do, or undestand the test parameters being >used to check parts? There's a vague claim that institutional >knowledge is lost in 20 (or 30?) years. In the world of computers, >it's way faster than that. I've come across a bunch of products where >the manufacturer really has no idea what the specs even are, or how >the thing even works.
I was recently looking for a fast single LVDS receiver chip, and tried OnSemi. Their web site is basically useless. If I search for "lvds receiver" I get over 4000 irrelevent hits. I emailed their tech support and they found one quad part. I found a good single, FIN1002, by googling. It's an old Fairchild part, so maybe the Fairchild people who knew about this stuff are gone. The TI/Burr Brown situation is similar. Nobody knows anything.
John Larkin <jlarkin@highland_atwork_technology.com> wrote:

> On Sat, 10 Apr 2021 20:47:41 +0000 (UTC), Cydrome Leader > <presence@MUNGEpanix.com> wrote: > >>jlarkin@highlandsniptechnology.com wrote: >>> Some schottky diodes have a PN junction in parallel, a "guard ring" >>> that acts like a parallel zener to improve ESD specs, and may help >>> with the fab somehow. That's OK, but at high currents the PN diode can >>> turn on, and it's slow to turn off and can even act like a >>> step-recovery diode. >>> >>> I wonder if there is a way to tell, from the data sheets, if there is >>> a guard ring. VI curve? CV curve? ESD specs? >>> >>> I'm pulsing a medium-small schottky pretty hard and I think I'm seeing >>> SRD effects. It's an ON SEMI RB520S30T1G. >>> >>> The data sheet shows a recovery time test circuit, but no recovery >>> time spec! The latest data sheet is rev 11; you'd think someone might >>> have noticed the omission by now. But at the specified 10 mA test >>> current, the guard ring won't conduct; so why does a schottky have a >>> recovery time test circuit? >>> >>> Grrrrr. >> >>What's the chance somebody there would even know? Like for old >>designed stuff, do any current employees even know how or why the >>designs exist the way they do, or undestand the test parameters being >>used to check parts? There's a vague claim that institutional >>knowledge is lost in 20 (or 30?) years. In the world of computers, it's >>way faster than that. I've come across a bunch of products where the >>manufacturer really has no idea what the specs even are, or how the >>thing even works. > > I was recently looking for a fast single LVDS receiver chip, and tried > OnSemi. Their web site is basically useless. If I search for "lvds > receiver" I get over 4000 irrelevent hits. I emailed their tech > support and they found one quad part. > > I found a good single, FIN1002, by googling. It's an old Fairchild > part, so maybe the Fairchild people who knew about this stuff are > gone. The TI/Burr Brown situation is similar. Nobody knows anything.
Try Octopart. They give Datasheets, Distributors, MOQ, Price. You can give a part number or a general description: https://octopart.com/search?q=LVDS+receiver&currency=USD&specs=0 The FIN1002 is slow. 400 MHz instead of 600 MHz: https://octopart.com/search?q=FIN1002&currency=USD&specs=0 Findchips cannot find the FIN1002, but gives a substitute that doesn't exist in Octopart: https://www.findchips.com/search/FIN002 Not very useful... -- The best designs occur in the theta state. - sw
On Sat, 10 Apr 2021 09:48:49 -0700, jlarkin@highlandsniptechnology.com
wrote:

>Some schottky diodes have a PN junction in parallel, a "guard ring" >that acts like a parallel zener to improve ESD specs, and may help >with the fab somehow. That's OK, but at high currents the PN diode can >turn on, and it's slow to turn off and can even act like a >step-recovery diode. > >I wonder if there is a way to tell, from the data sheets, if there is >a guard ring. VI curve? CV curve? ESD specs? > >I'm pulsing a medium-small schottky pretty hard and I think I'm seeing >SRD effects. It's an ON SEMI RB520S30T1G. > >The data sheet shows a recovery time test circuit, but no recovery >time spec! The latest data sheet is rev 11; you'd think someone might >have noticed the omission by now. But at the specified 10 mA test >current, the guard ring won't conduct; so why does a schottky have a >recovery time test circuit? > >Grrrrr.
I started running across Trr specs for SBDs by Matsushita/Panasonic some years ago. In fact, it was hard to determine whether some parts were schottky or not, just from their data sheets. Even harder when, in some specific cases, the title missed this info, as a typo. I assume that it simply indicates the parts' performance when inserted into a Trr test jig, with defined If, di/dt, etc. The part capacitance, and possibly physical package constraints, generate a recognizable current reversal and recovery current peak that can be related to the conventional diode recovery measurement form/profile. When pulsing parts, it's probably best to characterize performance in-circuit, rather than depend on data sheets to give all the answers, as these are characterized for conventional use. I'm unaware of guard ring parasitic conduction as ever being considered as a practical occurance in SBDs. Their effects predominate in reverse bias, after all. RL
On Sun, 11 Apr 2021 02:04:37 -0400, legg <legg@nospam.magma.ca> wrote:

>On Sat, 10 Apr 2021 09:48:49 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>Some schottky diodes have a PN junction in parallel, a "guard ring" >>that acts like a parallel zener to improve ESD specs, and may help >>with the fab somehow. That's OK, but at high currents the PN diode can >>turn on, and it's slow to turn off and can even act like a >>step-recovery diode. >> >>I wonder if there is a way to tell, from the data sheets, if there is >>a guard ring. VI curve? CV curve? ESD specs? >> >>I'm pulsing a medium-small schottky pretty hard and I think I'm seeing >>SRD effects. It's an ON SEMI RB520S30T1G. >> >>The data sheet shows a recovery time test circuit, but no recovery >>time spec! The latest data sheet is rev 11; you'd think someone might >>have noticed the omission by now. But at the specified 10 mA test >>current, the guard ring won't conduct; so why does a schottky have a >>recovery time test circuit? >> >>Grrrrr. > >I started running across Trr specs for SBDs by Matsushita/Panasonic >some years ago. In fact, it was hard to determine whether some >parts were schottky or not, just from their data sheets. Even harder >when, in some specific cases, the title missed this info, as a typo. > >I assume that it simply indicates the parts' performance when inserted >into a Trr test jig, with defined If, di/dt, etc. > >The part capacitance, and possibly physical package constraints, >generate a recognizable current reversal and recovery current >peak that can be related to the conventional diode recovery >measurement form/profile. > >When pulsing parts, it's probably best to characterize performance >in-circuit, rather than depend on data sheets to give all the >answers, as these are characterized for conventional use. > >I'm unaware of guard ring parasitic conduction as ever being >considered as a practical occurance in SBDs. Their effects >predominate in reverse bias, after all. > >RL
Well, you wouldn't have to look farther than wikipedia to get a mention of Trr occurance at higher SBD forward voltage drops. Higher voltage SBDs, with higher normal forward voltages, have to resort to different methods of guard ring formation to avoid this issue. RL