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High-side MOSFET driver without bootstrap?

B

Ban

Jan 1, 1970
0
Winfield said:
Tilmann Reh wrote...

No, the "charge pump" in the '4080 series works like most other
chips, and only charges an external capacitor (through an external
diode) on each cycle of the driver IC. So if it's continuously on,
the charge drains away and then a sad end to the story. You need a
part with an internal oscillator and charge-pump switch. There are
a few such parts.

Win,
you're getting old stating without looking into the datasheet.
There are even 2 charge pumps inside the 4081, each supplying 30-50uA. This
is enough to compensate for any losses, so the cap stays charged. If the
total gate capacity is much more than 1000pF, I would still add the Schottky
diode to charge the capacitor which should have 10-15 times the gate
capacity, 15nF in our example. Each time the switch is used the cap gets
recharged in less than a millisecond, so this would be perfectly adaequate
for the OP problem( in case the switching is "clean").
 
D

Daniel Haude

Jan 1, 1970
0
On 1 Jul 2004 17:52:06 -0700,
in Msg. said:
No, the "charge pump" in the '4080 series works like most other chips,
and only charges an external capacitor (through an external diode) on
each cycle of the driver IC. So if it's continuously on, the charge
drains away and then a sad end to the story. You need a part with an
internal oscillator and charge-pump switch. There are a few such parts.

What you describe here is what the HIP408x data sheets call
bootstrapping, and indeed it is the main source of energy for the
high-side gate drivers in normal switching apps. Yet the IC seems to
have some more to offer (HIP4081a app note (page 1, 2nd paragraph):

A combination of bootstrap and charge-pumping techniques
is used to power the circuitry which drives the upper halves
of the H-Bridge. The bootstrap technique supplies the high
instantaneous current needed for turning on the power
devices, while the charge pump provides enough current to
maintain bias voltage on the upper driver sections and
MOSFETs.

From page 4 of the same app note:

There are two charge pump circuits in the HIP4081A, one for
each of the two upper logic and driver circuits. Each charge
pump uses a switched capacitor doubler to provide about
30µA to 50µA of gate load current.

Another passage (p. 5)

Before discussing bootstrap circuit design in detail, it is
worth mentioning that it is possible to operate the HIP4081A
without a bootstrap circuit altogether. Even the bootstrap
capacitor, which functions to supply a reservoir of charge for
rapidly turning on the MOSFETs is optional in some cases.
In situations where very slow turn-on of the MOSFETs is tolerable,
one may consider omitting some or all bootstrap
components. Applications such as driving relays or lamp
loads, where the MOSFETs are switched infrequently and
switching losses are low, may provide opportunities for boot
strapless operation. Generally, loads with lots of resistance
and inductance are possible candidates.

Maybe the 408x will noe become even more favorites of yours?

--Daniel
 
W

Winfield Hill

Jan 1, 1970
0
R.Legg wrote...
14K files in 3.5G here.

My 18.4k files take 5GB of disk space. Hey, we should
consider sharing our files with an exchange of DVDs.
Have you organized your files by company name and part
number (which requires manually renaming many files)?

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
W

Winfield Hill

Jan 1, 1970
0
Ban wrote...
Win,
you're getting old stating without looking into the datasheet.
There are even 2 charge pumps inside the 4081, each supplying 30-50uA.

Well, I had forgotten this nice little factoid about the 4080 series.
But hopefully that has less to do with my advancing age (60 yrs) than
with my decade of use of these chips. At any rate I have recently felt
little need to go back to the depths of its data sheets and app notes
for my new 4080-series designs, but clearly such a cavalier attitude
about any familiar part means something important may be missed. :>)

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
F

Fred Bloggs

Jan 1, 1970
0
Winfield said:
Well, I had forgotten this nice little factoid about the 4080 series.
But hopefully that has less to do with my advancing age (60 yrs) than
with my decade of use of these chips.

It has to do with habituating this vegetable forum- a most dull place
and sewer of quasi-humanity suffering from a weakling preoccupation with
worthless minutiae that produces absolutely nothing. You would be better
off setting up a rocking chair on your lawn and watching the grass grow.
 
K

Klaus Vestergaard Kragelund

Jan 1, 1970
0
Winfield Hill said:
R.Legg wrote...

My 18.4k files take 5GB of disk space. Hey, we should
consider sharing our files with an exchange of DVDs.
Have you organized your files by company name and part
number (which requires manually renaming many files)?

Mine er organized like this:

www.microdesign.dk/tmp/datasheets.jpg

Cheers

Klaus
 
J

Jim Meyer

Jan 1, 1970
0
Tilmann Reh said:
Hello,

I am looking for a high-side MOSFET driver that is functionally
equivalent to the IR2117/18, but does not use a bootstrap supply
since I need a static on/off switch (and would like to avoid the
extra supply charge pump, if possible).

Take a look at the TLP191B-ND from Digi-Key. I've used it and it works.

Jim
 
W

Winfield Hill

Jan 1, 1970
0
Jim Meyer wrote...
Tilmann Reh wrote ...

Take a look at the TLP191B-ND from Digi-Key. I've used it and
it works.

The IR part I recommended earlier in this thread, the PVI5033
(they call it a "Photovoltaic Isolator"), may be better suited
for some applications, because it has some special circuitry to
rapidly discharge the FET's gate capacitance. As a result the
PVI5033 turns off much faster, 0.4ms vs. 3ms for the Toshiba
TLP191B (with 1000pF gate capacitance). This is required for
"break-before-make" circuits. But the TLP191B puts out more
gate current (55uA vs 5uA) and therefore turns on much faster,
0.2ms vs. 6ms for the PVI5033.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
J

James Meyer

Jan 1, 1970
0
Jim Meyer wrote...

The IR part I recommended earlier in this thread, the PVI5033
(they call it a "Photovoltaic Isolator"), may be better suited
for some applications,

Thanks,
- Win
I wonder what would happen if you used one of each. LEDs in series and
outputs in parallel.

Jim
 
W

Winfield Hill

Jan 1, 1970
0
James Meyer wrote...
Winfield Hill posted this:


I wonder what would happen if you used one of each. LEDs in series
and outputs in parallel.

Examining their relative properties, I had the same thought. I see
no reason it shouldn't work quite well, providing 0.2ms turn-on and
0.4ms turn-off for a 1000pF gate. Nice. One could add a resistor,
etc., in series with the TLP191B to delay turnon until after turnoff,
for applications that need this feature.

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)
 
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