The 12V level shifter saga

[Piotr Wyderski]

Hi,

I am working on a high-current 4-switch buck-boost converter. The
switches are psmnr70-40sshj, which -- with their 202nC gate charge --
makes the 12A gate driver MCP14A1202 a perfect spouse. The problem is
with passing the control signals to the upper switches. I want to have
true 100% duty cycle operation capability, which excludes AC coupling
techniques such as a signal transformer. The high-side switches float at
most 15V above the GND. Options:

1. Use a 1.5kV digital isolator. There are units capable of 7ns
propagation delay,
which makes a total end-to-end delay of about 33ns. Not bad, but I feel
it is heavily overengineered. In total that would make 4 gate driver ICs
+ 2 high-side isolators + 1 2-channel isolator to match the timing
between the high- and low-side paths. 7 ICs or 6, is the delay equalizer
is based on an RC delay + a Schmitt trigger.

2. Similar to the above, but use a half-bridge driver such as the LM5101
just as a level translator. 6 ICs in total and the propagation delays
are equalized out of the box. Disadvantage: the part is not stunningly fast
with its own 25ns propagation delay. The fastest HB gate driver I know
of, the LMG1210, has 10ns delay. OK, I tested the 5101 variant, works
nice up to 2MHz, but has 58ns end-to-end propagation delay... well, meh.

3. A *simple* solution based on discrete components. Total failure in
practice, really simple common-base units have ~400ns delay; the
best I could make was beyond the pain threshold complexity level and
was capable of 78ns, not including the output stage.

OK, I have a working solution (2), can go from 25 to 16ns translator
delay by replacing the LM5101 with MP18021 or switch to (1) and get
7..10ns, but I have a feeling that something is very wrong, because (3)
should be the solution.

Why is making a fast level shifter so notoriously difficult?
One interesting observation so far is that isolators are so much faster
than their non-isolated counterparts.

Best regards, Piotr

 

[Piotr Wyderski]

Winfield Hill wrote:

Dunno if you really need 12A gate switching, that gives
a full 10V gate drive in 10ns, way faster than you need.

202nC/12A=16.8ns. How did you get to a figure 68% better?

OK, going lower: the 1EDN7550 contains a level shifter, but its drive
strenght is 4A/8A. The 8A sink looks fine, but 4A source is 50.5ns, i.e.
1% of the switching period. Scope confirms the math, this is basically
the dV/dT as seen on the gate. This is a hard switching converted due to
its (relative) simplicity, so the switching losses will be plenty of watts.

Best regards, Piotr

 

On Sun, 2 Feb 2020 18:15:20 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

Winfield Hill wrote:

Dunno if you really need 12A gate switching, that gives
a full 10V gate drive in 10ns, way faster than you need.

202nC/12A=16.8ns. How did you get to a figure 68% better?

OK, going lower: the 1EDN7550 contains a level shifter, but its drive
strenght is 4A/8A. The 8A sink looks fine, but 4A source is 50.5ns, i.e.
1% of the switching period. Scope confirms the math, this is basically
the dV/dT as seen on the gate. This is a hard switching converted due to
its (relative) simplicity, so the switching losses will be plenty of watts.

Best regards, Piotr

I've been using discrete GaN fets (the EPC BGA parts) as mosfet and
SiC drivers. They are cheap and crazy fast and easy to drive.

A bit of series gate inductance can help too sometimes. It does the
classic thing, add a bit of delay but improves edge times.





--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Tim Williams]

Just how fast do you think you're going to be running this thing?

You at least need isolated drivers for the simple reason that you'll explode
the bootstrapped type in one cycle. Assuming you're running those bastards
anywhere near their ratings.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
news:r16jnd$1kki$1@gioia.aioe.org...

Hi,

I am working on a high-current 4-switch buck-boost converter. The switches
are psmnr70-40sshj, which -- with their 202nC gate charge --
makes the 12A gate driver MCP14A1202 a perfect spouse. The problem is with
passing the control signals to the upper switches. I want to have true
100% duty cycle operation capability, which excludes AC coupling
techniques such as a signal transformer. The high-side switches float at
most 15V above the GND. Options:

1. Use a 1.5kV digital isolator. There are units capable of 7ns
propagation delay,
which makes a total end-to-end delay of about 33ns. Not bad, but I feel it
is heavily overengineered. In total that would make 4 gate driver ICs + 2
high-side isolators + 1 2-channel isolator to match the timing between the
high- and low-side paths. 7 ICs or 6, is the delay equalizer
is based on an RC delay + a Schmitt trigger.

2. Similar to the above, but use a half-bridge driver such as the LM5101
just as a level translator. 6 ICs in total and the propagation delays are
equalized out of the box. Disadvantage: the part is not stunningly fast
with its own 25ns propagation delay. The fastest HB gate driver I know of,
the LMG1210, has 10ns delay. OK, I tested the 5101 variant, works nice up
to 2MHz, but has 58ns end-to-end propagation delay... well, meh.

3. A *simple* solution based on discrete components. Total failure in
practice, really simple common-base units have ~400ns delay; the
best I could make was beyond the pain threshold complexity level and
was capable of 78ns, not including the output stage.

OK, I have a working solution (2), can go from 25 to 16ns translator delay
by replacing the LM5101 with MP18021 or switch to (1) and get 7..10ns, but
I have a feeling that something is very wrong, because (3) should be the
solution.

Why is making a fast level shifter so notoriously difficult?
One interesting observation so far is that isolators are so much faster
than their non-isolated counterparts.

Best regards, Piotr

 

[Piotr Wyderski]

Tim Williams wrote:

> Just how fast do you think you're going to be running this thing?

200kHz is the assumed frequency, but since the control is going to be
digital anyway, I hear the mermaid singing "Variable Frequency Drive".
At least in several steps. This is to handle the low load conditions
with a a nice CCM.

50+25ns offered by the 4A floating driver looks disapointing.

You at least need isolated drivers for the simple reason that you'll
explode the bootstrapped type in one cycle.

Already prototyped, tested and eager to source power. This solves the
100% duty cycle as well, as pass-through mode should be quite a typical
case.

> Assuming you're running those bastards anywhere near their ratings.

50-80A in one direction, 10A in the other.

Best regards, Piotr

 

On Mon, 3 Feb 2020 04:38:55 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

Just how fast do you think you're going to be running this thing?

You at least need isolated drivers for the simple reason that you'll explode
the bootstrapped type in one cycle. Assuming you're running those bastards
anywhere near their ratings.

Tim

A PV optocoupler or a cheap dc/dc can furnish a small amount of
isolated power to keep a bootstrap alive.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Michael Kellett]

On 02/02/2020 13:44, Piotr Wyderski wrote:

Hi,

I am working on a high-current 4-switch buck-boost converter. The
switches are psmnr70-40sshj, which -- with their 202nC gate charge --
makes the 12A gate driver MCP14A1202 a perfect spouse. The problem is
with passing the control signals to the upper switches. I want to have
true 100% duty cycle operation capability, which excludes AC coupling
techniques such as a signal transformer. The high-side switches float at
most 15V above the GND. Options:

1. Use a 1.5kV digital isolator. There are units capable of 7ns
propagation delay,
which makes a total end-to-end delay of about 33ns. Not bad, but I feel
it is heavily overengineered. In total that would make 4 gate driver ICs
+ 2 high-side isolators + 1 2-channel isolator to match the timing
between the high- and low-side paths. 7 ICs or 6, is the delay equalizer
is based on an RC delay + a Schmitt trigger.

2. Similar to the above, but use a half-bridge driver such as the LM5101
just as a level translator. 6 ICs in total and the propagation delays
are equalized out of the box. Disadvantage: the part is not stunningly fast
with its own 25ns propagation delay. The fastest HB gate driver I know
of, the LMG1210, has 10ns delay. OK, I tested the 5101 variant, works
nice up to 2MHz, but has 58ns end-to-end propagation delay... well, meh.

3. A *simple* solution based on discrete components. Total failure in
practice, really simple common-base units have ~400ns delay; the
best I could make was beyond the pain threshold complexity level and
was capable of 78ns, not including the output stage.

OK, I have a working solution (2), can go from 25 to 16ns translator
delay by replacing the LM5101 with MP18021 or switch to (1) and get
7..10ns, but I have a feeling that something is very wrong, because (3)
should be the solution.

Why is making a fast level shifter so notoriously difficult?
One interesting observation so far is that isolators are so much faster
than their non-isolated counterparts.

    Best regards, Piotr

Would these be any use to you:

Infineon 1EDN7550, 8A/4A, true differential input with 150V common mode
range.

MK

 

[Piotr Wyderski]

Michael Kellett wrote:

Would these be any use to you:

Infineon 1EDN7550, 8A/4A, true differential input with 150V common mode
range.

Yes, this was my starting point. Works as advertised, i.e. the 4A
current looks a tad too low. The 8A rail is fine.

Best regards, Piotr

 

On Monday, February 3, 2020 at 4:16:40 PM UTC-5, Piotr Wyderski wrote:

Michael Kellett wrote:

Would these be any use to you:

Infineon 1EDN7550, 8A/4A, true differential input with 150V common mode
range.

Yes, this was my starting point. Works as advertised, i.e. the 4A
current looks a tad too low. The 8A rail is fine.

Best regards, Piotr

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
>--+---R1---+--->
| |
'---|<---'

But John's photovoltaic-augmented bootstrap is good, too.

Cheers,
James Arthur

 

On Tuesday, February 4, 2020 at 3:34:51 AM UTC-5, Piotr Wyderski wrote:

dagmargoodboat@yahoo.com wrote:

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
--+---R1---+---
| |
'---|<---'

This is a nice idea, but I am not sure what is simple nowadays.
For ~10A peak collector current and hundreds of kHz the transistor
cannot be a randomly picked unit. While there are good Zetex parts,
e.g. ZTXN25020, they are not exactly cheap and it still makes 3 parts.

10A peak collector current is easily met with a wide range of
medium-hefty transistors. OnSemi and Zetex lo-sat units are a
good start.

Including the 2x33kOhm resistors required by 1EDN7550 and the driver
itself it makes 6 parts per channel. Times 4 channels, it is 24 parts.
Using MCP14A1202 as a 12A booster and L5101 as a level
translator/pre-driver, makes 6 parts in total at about the same cost.

Best regards, Piotr

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

These other guys give you the drive, but without the level-
translation or the swing.

It's an interesting ballgame, and it's your swing.

Cheers,
James Arthur

 

[Piotr Wyderski]

dagmargoodboat@yahoo.com wrote:

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

I don't want the full allowed gate swing for efficiency and reliability
reasons. Just the bare minimum, which is 0-10V typically.

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

Exactly, with a minor remark that the floating gate driver supply is
already there, powering 6 SiC transistors. So adding two more windings
to the transformer is not an issue. The (now rectifying) diode and the
capacitor need to be there in the bootstrapped configuration as well,
so half a meter of 0.2mm TIW wire it is all it costs.

> It's an interesting ballgame, and it's your swing.

I don't consider this exchange of ideas a game, as I can't come up with
a satisfying winning criteria. My findings I wanted to share are:

Surprise #1: there are no (or I am unable to find, which is the same in
practice) fast non-isolated level translators that can operate in the
30V VDD range. Just lots of (useless) glue logic translators with 6V
VDD_MAX.

Surprise #2: If a HB MOSFET driver is used to do the translation, the
existing isolated translators can be 2-3 times faster.

Surprise #3: making a discrete level translators out of a small number
of cheap parts is very difficult at the required level of frequency and
dV/dt. For me it had been a no-brainer till I had to make one. This
adds a lot of respect to John's picosecond circuits and sheds some light
on the baroque complexity thereof.

Best regards, Piotr

 

On Tue, 4 Feb 2020 10:13:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, February 4, 2020 at 3:34:51 AM UTC-5, Piotr Wyderski wrote:
dagmargoodboat@yahoo.com wrote:

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
--+---R1---+---
| |
'---|<---'

This is a nice idea, but I am not sure what is simple nowadays.
For ~10A peak collector current and hundreds of kHz the transistor
cannot be a randomly picked unit. While there are good Zetex parts,
e.g. ZTXN25020, they are not exactly cheap and it still makes 3 parts.

10A peak collector current is easily met with a wide range of
medium-hefty transistors. OnSemi and Zetex lo-sat units are a
good start.

Including the 2x33kOhm resistors required by 1EDN7550 and the driver
itself it makes 6 parts per channel. Times 4 channels, it is 24 parts.
Using MCP14A1202 as a 12A booster and L5101 as a level
translator/pre-driver, makes 6 parts in total at about the same cost.

Best regards, Piotr

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

These other guys give you the drive, but without the level-
translation or the swing.

It's an interesting ballgame, and it's your swing.

Cheers,
James Arthur

Another highside driver trick, if you don't have outrageous swing, is
to use a few resistors to turn a cheap LVDS line receiver into a high
cmrr line receiver, to ride on the source of, and drive, the highside
mosfet, or SiC, or whatever. You still need some isolated power,
although it might work bootstrapped.

We pay 40 cents for DS90LV012. If someone changed the part number and
sold it as a <2ns RRIO comparator, they would charge 8 times as much.
I suspect that some people already do that.

I have a wonderful, brutal GaN-based highside mosfet driver but it's
too good to post in public.




--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

On Wednesday, February 5, 2020 at 2:08:19 AM UTC-5, Piotr Wyderski wrote:

dagmargoodboat@yahoo.com wrote:
AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

I don't want the full allowed gate swing for efficiency and reliability
reasons. Just the bare minimum, which is 0-10V typically.

+10V at the gate doesn't work if, as you describe, you want the
source to output +15V. You need 25V swing.

+15v >---. .-+--------> Vout
| V |
- - - Q1
.-----.
|
drive >-------'

But if you floated the driver using +15V for GND and <10V higher>
for Vcc, you'd still have to drive the gate to 0V in order to turn
Q1 off. That's a mess.

So, the only choice is to run the driver from a floating supply
referenced to Vout. And then you need a logic-level translator.

Which isn't that hard, but it's going to be pretty nigh unto
impossible to satisfy your desire to do it with zero parts
and zero cost.

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

Exactly, with a minor remark that the floating gate driver supply is
already there, powering 6 SiC transistors. So adding two more windings
to the transformer is not an issue. The (now rectifying) diode and the
capacitor need to be there in the bootstrapped configuration as well,
so half a meter of 0.2mm TIW wire it is all it costs.

If that's the case, why not make a floating bootstrap supply in
lieu of the usual bootstrap cap -- thus meeting your d.c. operation
spec. -- then find an integrated driver to supply the logic-level
translation?

If you're dead-set on 12A drive but can't find it, you might
consider paralleling drivers. That gets you lots of gate drive
with no extra discretes, a fairly clean solution.

It's an interesting ballgame, and it's your swing.

I don't consider this exchange of ideas a game, as I can't come up with
a satisfying winning criteria. My findings I wanted to share are:

Surprise #1: there are no (or I am unable to find, which is the same in
practice) fast non-isolated level translators that can operate in the
30V VDD range. Just lots of (useless) glue logic translators with 6V
VDD_MAX.

Surprise #2: If a HB MOSFET driver is used to do the translation, the
existing isolated translators can be 2-3 times faster.

Surprise #3: making a discrete level translators out of a small number
of cheap parts is very difficult at the required level of frequency and
dV/dt. For me it had been a no-brainer till I had to make one. This
adds a lot of respect to John's picosecond circuits and sheds some light
on the baroque complexity thereof.

Best regards, Piotr

Cheers,
James Arthur

 

[Piotr Wyderski]

dagmargoodboat@yahoo.com wrote:

+10V at the gate doesn't work if, as you describe, you want the
source to output +15V. You need 25V swing.

From the very beginning I have wanted a floating driver, not the
solution you refer to. E ~ C*V^2 and I have just too
much charge to transfer even at the mere 10V already. Going to 25V would
make the situation 5 times worse.

So, the only choice is to run the driver from a floating supply
referenced to Vout. And then you need a logic-level translator.

Yes, this has always been the way I wanted it.
> Which isn't that hard

I beg to disagree. Nanosecond-level of rise/fall time and delay below
20ns make a discrete level translator very difficult to design. The best
I have done has 78ns propagation delay, which makes a description based
on the geological time scale relevant.

but it's going to be pretty nigh unto
impossible to satisfy your desire to do it with zero parts
and zero cost.

Cost is a secondary issue, but part count is not, as it directly impacts
reliability.

If that's the case, why not make a floating bootstrap supply in
lieu of the usual bootstrap cap -- thus meeting your d.c. operation
spec. -- then find an integrated driver to supply the logic-level
translation?

As far as I know, there are no integrated drivers able to work with
sufficiently high common mode input voltage AND capable of 10A+
source/sink. To be specific, there is exactly one such a driver
(UCC5390SC), but it is for IGBT and has UVLO of 12V, which is beyond
the required 10V operation with an option to lower that, if performance
is satisfactory.

If you're dead-set on 12A drive but can't find it, you might
consider paralleling drivers. That gets you lots of gate drive
with no extra discretes, a fairly clean solution.

Indeed, it is an option. But then it means a) doubling the number of
drivers (8 ICs in place of 6) and b) propagation time spread: 4A + 4A
doesn't mean 8A (simultaneously). Have a look at 1EDN7550, for instance:
38 to 55ns propagation delay range -- that is whopping 17ns, equal to
the total switching time at 12A. Better to use a single power stage like
the Microchip's 0902 or 1202 with no dispersion issues.

Best regards, Piotr

 

On Wednesday, February 5, 2020 at 10:43:56 AM UTC-5, jla...@highlandsniptechnology.com wrote:

On Tue, 4 Feb 2020 10:13:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, February 4, 2020 at 3:34:51 AM UTC-5, Piotr Wyderski wrote:
dagmargoodboat@yahoo.com wrote:

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
--+---R1---+---
| |
'---|<---'

This is a nice idea, but I am not sure what is simple nowadays.
For ~10A peak collector current and hundreds of kHz the transistor
cannot be a randomly picked unit. While there are good Zetex parts,
e.g. ZTXN25020, they are not exactly cheap and it still makes 3 parts.

10A peak collector current is easily met with a wide range of
medium-hefty transistors. OnSemi and Zetex lo-sat units are a
good start.

Including the 2x33kOhm resistors required by 1EDN7550 and the driver
itself it makes 6 parts per channel. Times 4 channels, it is 24 parts.
Using MCP14A1202 as a 12A booster and L5101 as a level
translator/pre-driver, makes 6 parts in total at about the same cost.

Best regards, Piotr

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

These other guys give you the drive, but without the level-
translation or the swing.

It's an interesting ballgame, and it's your swing.

Cheers,
James Arthur

Another highside driver trick, if you don't have outrageous swing, is
to use a few resistors to turn a cheap LVDS line receiver into a high
cmrr line receiver, to ride on the source of, and drive, the highside
mosfet, or SiC, or whatever. You still need some isolated power,
although it might work bootstrapped.

We pay 40 cents for DS90LV012. If someone changed the part number and
sold it as a <2ns RRIO comparator, they would charge 8 times as much.
I suspect that some people already do that.

I have a wonderful, brutal GaN-based highside mosfet driver but it's
too good to post in public.

I bought some GaN FETs for that high-side driver I was toying with
a few years ago, but I've still not ever powered them up. The BGA
looked intimidating at first, but I've since hand-reworked some
chip scale / die packaged parts ... (that was a huge pain, but after
many tries it did finally work).

It's truly amazing that our craft is still advancing so rapidly
on so many fronts, so many years on.

Cheers,
James Arthur

 

On Wednesday, February 5, 2020 at 1:35:59 PM UTC-5, Piotr Wyderski wrote:

dagmargoodboat@yahoo.com wrote:

+10V at the gate doesn't work if, as you describe, you want the
source to output +15V. You need 25V swing.

From the very beginning I have wanted a floating driver, not the
solution you refer to. E ~ C*V^2 and I have just too
much charge to transfer even at the mere 10V already. Going to 25V would
make the situation 5 times worse.

So, the only choice is to run the driver from a floating supply
referenced to Vout. And then you need a logic-level translator.

Yes, this has always been the way I wanted it.
Which isn't that hard

I beg to disagree. Nanosecond-level of rise/fall time and delay below
20ns make a discrete level translator very difficult to design. The best
I have done has 78ns propagation delay, which makes a description based
on the geological time scale relevant.

Over the past few years I've designed and am still actively
extending a line of pulse generators that produce kilovolt
pulses with nanosecond rise and fall times from logic-level
inputs. So I feel at least somewhat familiar with the
issues attending high-speed level translation.

I'm confident your problem could be solved with discretes. It
would take a bit of doing. But what I don't know is how to do
it more simply than the single BJT booster you've already
rejected for being too complex.

but it's going to be pretty nigh unto
impossible to satisfy your desire to do it with zero parts
and zero cost.

Cost is a secondary issue, but part count is not, as it directly impacts
reliability.

If that's the case, why not make a floating bootstrap supply in
lieu of the usual bootstrap cap -- thus meeting your d.c. operation
spec. -- then find an integrated driver to supply the logic-level
translation?

As far as I know, there are no integrated drivers able to work with
sufficiently high common mode input voltage AND capable of 10A+
source/sink. To be specific, there is exactly one such a driver
(UCC5390SC), but it is for IGBT and has UVLO of 12V, which is beyond
the required 10V operation with an option to lower that, if performance
is satisfactory.

If you're dead-set on 12A drive but can't find it, you might
consider paralleling drivers. That gets you lots of gate drive
with no extra discretes, a fairly clean solution.

Indeed, it is an option. But then it means a) doubling the number of
drivers (8 ICs in place of 6) and b) propagation time spread: 4A + 4A
doesn't mean 8A (simultaneously). Have a look at 1EDN7550, for instance:
38 to 55ns propagation delay range -- that is whopping 17ns, equal to
the total switching time at 12A. Better to use a single power stage like
the Microchip's 0902 or 1202 with no dispersion issues.

Best regards, Piotr

Cheers,
James Arthur

 

[Phil Hobbs]

On 2020-02-06 12:01, dagmargoodboat@yahoo.com wrote:

On Wednesday, February 5, 2020 at 10:43:56 AM UTC-5, jla...@highlandsniptechnology.com wrote:
On Tue, 4 Feb 2020 10:13:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, February 4, 2020 at 3:34:51 AM UTC-5, Piotr Wyderski wrote:
dagmargoodboat@yahoo.com wrote:

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
--+---R1---+---
| |
'---|<---'

This is a nice idea, but I am not sure what is simple nowadays.
For ~10A peak collector current and hundreds of kHz the transistor
cannot be a randomly picked unit. While there are good Zetex parts,
e.g. ZTXN25020, they are not exactly cheap and it still makes 3 parts.

10A peak collector current is easily met with a wide range of
medium-hefty transistors. OnSemi and Zetex lo-sat units are a
good start.

Including the 2x33kOhm resistors required by 1EDN7550 and the driver
itself it makes 6 parts per channel. Times 4 channels, it is 24 parts.
Using MCP14A1202 as a 12A booster and L5101 as a level
translator/pre-driver, makes 6 parts in total at about the same cost.

Best regards, Piotr

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

These other guys give you the drive, but without the level-
translation or the swing.

It's an interesting ballgame, and it's your swing.

Cheers,
James Arthur

Another highside driver trick, if you don't have outrageous swing, is
to use a few resistors to turn a cheap LVDS line receiver into a high
cmrr line receiver, to ride on the source of, and drive, the highside
mosfet, or SiC, or whatever. You still need some isolated power,
although it might work bootstrapped.

We pay 40 cents for DS90LV012. If someone changed the part number and
sold it as a <2ns RRIO comparator, they would charge 8 times as much.
I suspect that some people already do that.

I have a wonderful, brutal GaN-based highside mosfet driver but it's
too good to post in public.

I bought some GaN FETs for that high-side driver I was toying with
a few years ago, but I've still not ever powered them up. The BGA
looked intimidating at first, but I've since hand-reworked some
chip scale / die packaged parts ... (that was a huge pain, but after
many tries it did finally work).

It's truly amazing that our craft is still advancing so rapidly
on so many fronts, so many years on.

Cheers,
James Arthur

A couple of years ago, I was the defence's expert on the patent
infringement side of the Waymo v. Uber case ($2.3B ask). In the process
I got to take apart and deliberately blow up some of Uber's best lidar
TX sections.

Like most such, they use a GaN FET to dump a few-nanofarad cap into an
Osram stacked laser. Doing some modelling based on my measurements, the
total inductance of that discharge loop was less than 400 picohenries,
about half in the drain circuit and half in the source. Not bad a-tall.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Thu, 6 Feb 2020 09:01:51 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Wednesday, February 5, 2020 at 10:43:56 AM UTC-5, jla...@highlandsniptechnology.com wrote:
On Tue, 4 Feb 2020 10:13:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, February 4, 2020 at 3:34:51 AM UTC-5, Piotr Wyderski wrote:
dagmargoodboat@yahoo.com wrote:

A simple one-BJT booster fixes that.

Vcc
|
|/
.------|
| |>.
| .3 |
--+---R1---+---
| |
'---|<---'

This is a nice idea, but I am not sure what is simple nowadays.
For ~10A peak collector current and hundreds of kHz the transistor
cannot be a randomly picked unit. While there are good Zetex parts,
e.g. ZTXN25020, they are not exactly cheap and it still makes 3 parts.

10A peak collector current is easily met with a wide range of
medium-hefty transistors. OnSemi and Zetex lo-sat units are a
good start.

Including the 2x33kOhm resistors required by 1EDN7550 and the driver
itself it makes 6 parts per channel. Times 4 channels, it is 24 parts.
Using MCP14A1202 as a 12A booster and L5101 as a level
translator/pre-driver, makes 6 parts in total at about the same cost.

Best regards, Piotr

AIUI, "The high-side switches float at most 15V above the GND",
combined with your FET, means you need 0-25V swing at the gate,
which the MCP14A1202 cannot do (unless you float it).

One of the many bootstrapped drivers would give you the
level-translation and swing, but you might need a booster to
get the drive. And you'd need to augment the bootstrap with
an external arrangement, to use at d.c.

These other guys give you the drive, but without the level-
translation or the swing.

It's an interesting ballgame, and it's your swing.

Cheers,
James Arthur

Another highside driver trick, if you don't have outrageous swing, is
to use a few resistors to turn a cheap LVDS line receiver into a high
cmrr line receiver, to ride on the source of, and drive, the highside
mosfet, or SiC, or whatever. You still need some isolated power,
although it might work bootstrapped.

We pay 40 cents for DS90LV012. If someone changed the part number and
sold it as a <2ns RRIO comparator, they would charge 8 times as much.
I suspect that some people already do that.

I have a wonderful, brutal GaN-based highside mosfet driver but it's
too good to post in public.

I bought some GaN FETs for that high-side driver I was toying with
a few years ago, but I've still not ever powered them up. The BGA
looked intimidating at first, but I've since hand-reworked some
chip scale / die packaged parts ... (that was a huge pain, but after
many tries it did finally work).

The EPC parts are hard to handle but otherwise wonderful. They need
just a few volts of gate drive, switch super hard and fast, and have
near zero Cd-g. Incredibly, they don't offer eval boards, so we had to
make our own just to connect to them.

It's truly amazing that our craft is still advancing so rapidly
on so many fronts, so many years on.

Cheers,
James Arthur

Electronics as such is over 100 years old, and we get a continuous and
nicely paced series of new toys and tools.

But where are my diamond transistors?

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[whit3rd]

On Thursday, February 6, 2020 at 11:57:55 AM UTC-8, John Larkin wrote:

Electronics as such is over 100 years old, and we get a continuous and
nicely paced series of new toys and tools.

But where are my diamond transistors?

The oxidation of C doesn't make a suitable insulator/passivated surface,
so it's gonna take more than a little engineering to do this.

Mechanical engineering with diamond is a bit easier; read about it here

<https://www.goodreads.com/book/show/827.The_Diamond_Age>

 

[Phil Hobbs]

On 2020-02-06 16:16, whit3rd wrote:

On Thursday, February 6, 2020 at 11:57:55 AM UTC-8, John Larkin wrote:


Electronics as such is over 100 years old, and we get a continuous and
nicely paced series of new toys and tools.

But where are my diamond transistors?

The oxidation of C doesn't make a suitable insulator/passivated surface,
so it's gonna take more than a little engineering to do this.

Old-timey planar processing is far from the whole story these
days--folks are using most of the periodic table for various tasks in
silicon.

Many of the advantages of planar processing (especially the reduction of
surface recombination and other stuff like that) can be reproduced using
epitaxy to do junction isolation, with deposited films on top of that.

I have no idea how far folks have got with epitaxial processing of
diamond, but "no good oxide" is no longer a cogent argument against a
semiconductor system, and hasn't been for a good many years.

Cheers

Phil Hobbs
(Who used to do his own silicon processing, back in the tunnel junction
days.)

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com