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bitrex
Guest

Wed Jan 04, 2017 12:59 am   



Something seems wrong here but I can't place exactly what it is:

<http://www.edn.com/design/power-management/4443225/Body-diodes-simplify-UPS---energy-recovery-circuits>

Rob
Guest

Wed Jan 04, 2017 1:27 am   



bitrex <bitrex_at_de.lete.earthlink.net> wrote:
Quote:


It describes the way an APC UPS works.
See video #504 in the eevblog.

(it is presented as a design idea but actually it is patented by another
UPS company and probably licensed to APC)


Guest

Wed Jan 04, 2017 6:47 am   



On Wednesday, January 4, 2017 at 12:41:41 PM UTC+11, John Larkin wrote:
Quote:
On Tue, 03 Jan 2017 18:25:48 -0600, Tim Wescott <tim_at_seemywebsite.com
wrote:

On Tue, 03 Jan 2017 12:59:02 -0500, bitrex wrote:

Something seems wrong here but I can't place exactly what it is:

http://www.edn.com/design/power-management/4443225/Body-diodes-
simplify-UPS---energy-recovery-circuits

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want to
parallel the FETs with Schottky diodes, as they recover quicker. A FET
with a body diode that has slow recovery can become smoke pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.


So they can spray really high-frequency noise around the circuit?

Just what you want when you have to meet EMI standards.

--
Bill Sloman, Sydney

Tim Wescott
Guest

Wed Jan 04, 2017 7:25 am   



On Tue, 03 Jan 2017 12:59:02 -0500, bitrex wrote:

Quote:
Something seems wrong here but I can't place exactly what it is:

http://www.edn.com/design/power-management/4443225/Body-diodes-
simplify-UPS---energy-recovery-circuits


Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want to
parallel the FETs with Schottky diodes, as they recover quicker. A FET
with a body diode that has slow recovery can become smoke pretty quickly.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

John Larkin
Guest

Wed Jan 04, 2017 8:30 am   



On Tue, 03 Jan 2017 18:25:48 -0600, Tim Wescott <tim_at_seemywebsite.com>
wrote:

Quote:
On Tue, 03 Jan 2017 12:59:02 -0500, bitrex wrote:

Something seems wrong here but I can't place exactly what it is:

http://www.edn.com/design/power-management/4443225/Body-diodes-
simplify-UPS---energy-recovery-circuits

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want to
parallel the FETs with Schottky diodes, as they recover quicker. A FET
with a body diode that has slow recovery can become smoke pretty quickly.


Some mosfet body diodes make nice step-recovery diodes.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Winfield Hill
Guest

Wed Jan 04, 2017 11:14 pm   



bill.sloman_at_ieee.org wrote...
Quote:
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.


All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


--
Thanks,
- Win

John Larkin
Guest

Wed Jan 04, 2017 11:52 pm   



On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu>
wrote:

Quote:
bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

bitrex
Guest

Wed Jan 04, 2017 11:58 pm   



On 01/04/2017 11:52 AM, John Larkin wrote:
Quote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

John Larkin
Guest

Thu Jan 05, 2017 12:10 am   



On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?


My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

bitrex
Guest

Thu Jan 05, 2017 12:48 am   



On 01/04/2017 12:10 PM, John Larkin wrote:
Quote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?

John Larkin
Guest

Thu Jan 05, 2017 1:47 am   



On Wed, 4 Jan 2017 12:48:08 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/04/2017 12:10 PM, John Larkin wrote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?


I doubt it. The big spike sure looks like step recovery in the
substrate diode. The diode takes over from the low-side mosfet for
about 20 ns, then when the high-side fet turns on, the diode fights it
for a few ns, then snaps off.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

bitrex
Guest

Thu Jan 05, 2017 2:31 am   



On 01/04/2017 01:47 PM, John Larkin wrote:
Quote:
On Wed, 4 Jan 2017 12:48:08 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 12:10 PM, John Larkin wrote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?

I doubt it. The big spike sure looks like step recovery in the
substrate diode. The diode takes over from the low-side mosfet for
about 20 ns, then when the high-side fet turns on, the diode fights it
for a few ns, then snaps off.



If it is step recovery then the fact that they don't bring the source
connection on the high side switch out to a pin makes it seem like a SOL
situation with respect to trying some other simple tricks to mitigate it.

I remember reading some paper where EMI-making ringing on the output
node of a buck switcher of all types was canceled by sensing it thru a
capacitor, amplifying it and passing it through the other winding of a
common mode choke where the first winding was used as the energy-storage
inductor.

Seems like a lot of work, though...

John Larkin
Guest

Thu Jan 05, 2017 2:58 am   



On Wed, 4 Jan 2017 14:31:44 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/04/2017 01:47 PM, John Larkin wrote:
On Wed, 4 Jan 2017 12:48:08 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 12:10 PM, John Larkin wrote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?

I doubt it. The big spike sure looks like step recovery in the
substrate diode. The diode takes over from the low-side mosfet for
about 20 ns, then when the high-side fet turns on, the diode fights it
for a few ns, then snaps off.



If it is step recovery then the fact that they don't bring the source
connection on the high side switch out to a pin makes it seem like a SOL
situation with respect to trying some other simple tricks to mitigate it.


Yup. The fix is to use some other part.

IC designers need more critical design reviews, for things like this,
and latchup, and other weird effects.

Quote:

I remember reading some paper where EMI-making ringing on the output
node of a buck switcher of all types was canceled by sensing it thru a
capacitor, amplifying it and passing it through the other winding of a
common mode choke where the first winding was used as the energy-storage
inductor.

Seems like a lot of work, though...


The current spikes must be huge. There is probably no reasonable way
to fix this one.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

bitrex
Guest

Thu Jan 05, 2017 4:51 am   



On 01/04/2017 02:58 PM, John Larkin wrote:
Quote:
On Wed, 4 Jan 2017 14:31:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 01:47 PM, John Larkin wrote:
On Wed, 4 Jan 2017 12:48:08 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 12:10 PM, John Larkin wrote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?

I doubt it. The big spike sure looks like step recovery in the
substrate diode. The diode takes over from the low-side mosfet for
about 20 ns, then when the high-side fet turns on, the diode fights it
for a few ns, then snaps off.



If it is step recovery then the fact that they don't bring the source
connection on the high side switch out to a pin makes it seem like a SOL
situation with respect to trying some other simple tricks to mitigate it.

Yup. The fix is to use some other part.

IC designers need more critical design reviews, for things like this,
and latchup, and other weird effects.


I remember years ago trying to use a Maxim part that was originally a
Dallas Semi part, I think it was the DS1077 SPI-programmable clock
oscillator.

A neat part, except for the fact that the example code in the datasheet
didn't work, and the way they said the chip was addressed over SPI by a
uP seemed to bear...no resemblance to reality.

"Designing" with it basically meant hunting through Wordpress blogs
trying to find someone who'd managed to suffer through the process before.

John Larkin
Guest

Thu Jan 05, 2017 4:54 am   



On Wed, 4 Jan 2017 16:51:06 -0500, bitrex
<bitrex_at_de.lete.earthlink.net> wrote:

Quote:
On 01/04/2017 02:58 PM, John Larkin wrote:
On Wed, 4 Jan 2017 14:31:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 01:47 PM, John Larkin wrote:
On Wed, 4 Jan 2017 12:48:08 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 12:10 PM, John Larkin wrote:
On Wed, 4 Jan 2017 11:58:44 -0500, bitrex
bitrex_at_de.lete.earthlink.net> wrote:

On 01/04/2017 11:52 AM, John Larkin wrote:
On 4 Jan 2017 08:14:07 -0800, Winfield Hill <hill_at_rowland.harvard.edu
wrote:

bill.sloman_at_ieee.org wrote...
John Larkin wrote:
Tim Wescott wrote:

Old hat. To be used with caution, because not all body diodes are
created equal -- for some fast switching regulators you really want
to parallel the FETs with Schottky diodes, as they recover quicker.
A FET with a body diode that has slow recovery can become smoke
pretty quickly.

Some mosfet body diodes make nice step-recovery diodes.

So they can spray really high-frequency noise around the circuit?
Just what you want when you have to meet EMI standards.

All MOSFETs do that, to one degree or another. Some have
added soft-recovery diodes in parallel with the body diode,
which helps, but designers of half-bridge stages, etc.,
are always struggling to prevent body-diode conduction,
or limit its current*time, or slow switching, or snub any
voltage spike from the sudden high dI/dt at snap off.
The problem is worse at maximum switched current. And
most off-line designs can't use added Schottky diodes,
since high-voltage versions have too high an ON voltage.


This is a really classic SRD waveform:

https://dl.dropboxusercontent.com/u/53724080/Parts/LM3102_SwitcherRise.JPG

This switcher is basically unusable. A paralleled external schottky
only helped some.


Didn't someone post a "design idea" here once where the cutoff ringing
from the leakage L of a flyback was recovered into the output rail, somehow?

My pic was of a synchronous buck regulator, so there was no leakage
inductance. The big-slam risetime may well have been scope+probe
limited. The spike messed up opamps all over the board.


Would adding some R in series with the high-side bootstrap cap make a
difference?

I doubt it. The big spike sure looks like step recovery in the
substrate diode. The diode takes over from the low-side mosfet for
about 20 ns, then when the high-side fet turns on, the diode fights it
for a few ns, then snaps off.



If it is step recovery then the fact that they don't bring the source
connection on the high side switch out to a pin makes it seem like a SOL
situation with respect to trying some other simple tricks to mitigate it.

Yup. The fix is to use some other part.

IC designers need more critical design reviews, for things like this,
and latchup, and other weird effects.

I remember years ago trying to use a Maxim part that was originally a
Dallas Semi part, I think it was the DS1077 SPI-programmable clock
oscillator.

A neat part, except for the fact that the example code in the datasheet
didn't work, and the way they said the chip was addressed over SPI by a
uP seemed to bear...no resemblance to reality.

"Designing" with it basically meant hunting through Wordpress blogs
trying to find someone who'd managed to suffer through the process before.


One good maxim is

Never Buy Maxim.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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