On Fri, 14 Nov 2014 13:16:37 -0800 (PST),
bloggs.fredbloggs.fred@gmail.com wrote:
>On Wednesday, November 12, 2014 5:39:44 PM UTC-5, John Larkin wrote:
>> I need a mosfet gate driver, to drive two n-fets in a half-bridge
>> (totem pole) config, 5 volts nom in, with some sort of bootstrap for
>> the upper fet gate. Switcher output will be around 2.5 volts at 5
>> amps, so the gate drives don't have to be monstrous.
>>
>> I've been working with LTC4442 on a breadboard, but it's really
>> erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
>> up ugly. It's especially bad if Vcc gets much over 5 volts. I think
>> the anti-shoot-through circuit is too smart or something.
>>
>> I don't have the paddle grounded, which could be part of the problem
>> maybe. Maybe it wants that extra ground connection. It's hard to do
>> that on a breadboard. But the ground pin doesn't look very noisy.
>>
>> Any suggested parts?
>
>Are the FETs extra large? This chip performance peaks at 3nF, and that's with everything laid out perfectly with low to nonexistent series inductance. The back GND pad floating could easily interfere with switching performance at its advertized speed.
Grounding the power pad can only help. I've got it working OK now, so
it should be better on a proper PC board.
I'm switching at 1.5 MHz, 4 or 5 amps, so things are inherently
radical.
The LTC4442 is cute in that the input pin has different thresholds for
turning on the upper and lower fets. So if you drive it with an RC in
series with the input, you can control the both-fets-off deadtime.
Combine that with gate resistors, and you get some knobs to turn to
trade off noise/efficiency/whatever, to get out of trouble maybe.
FDT439N mosfets seem about right. 1 volt threshold and then 17 (17!) S
transconductance.
You call me a "mechanic", but this stuff is fun. Some people,
architects and civil engineers and even some artists, never get really
involved in their own medium... don't handle the stuff themselves.
Rocket Scientists don't get to ride on rockets. Dremeling and
soldering and scoping is cool.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by John Larkin●November 15, 20142014-11-15
On Fri, 14 Nov 2014 11:39:16 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Wed, 12 Nov 2014 14:39:36 -0800, John Larkin
><jlarkin@highlandtechnology.com> wrote:
>
>>
>>
>>I need a mosfet gate driver, to drive two n-fets in a half-bridge
>>(totem pole) config, 5 volts nom in, with some sort of bootstrap for
>>the upper fet gate. Switcher output will be around 2.5 volts at 5
>>amps, so the gate drives don't have to be monstrous.
>>
>>I've been working with LTC4442 on a breadboard, but it's really
>>erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
>>up ugly. It's especially bad if Vcc gets much over 5 volts. I think
>>the anti-shoot-through circuit is too smart or something.
>>
>>I don't have the paddle grounded, which could be part of the problem
>>maybe. Maybe it wants that extra ground connection. It's hard to do
>>that on a breadboard. But the ground pin doesn't look very noisy.
>>
>>Any suggested parts?
>
>From the data sheet...
>
>GND (Pin 4, Exposed Pad Pin 9): Chip Ground. The exposed
>pad must be soldered to the PCB ground for electrical
>contact and for rated thermal performance.
>
>Maybe devise a spring clip to contact the back-side pad in your
>breadboard?
>
> ...Jim Thompson
Too late!
https://dl.dropboxusercontent.com/u/53724080/Protos/D200_BB_3.jpg
It's on the SO adapter, upper left. All wired in.
It seems to be working at 5 volts, and I got some SOT223 nfets that
are happy with that much gate drive. It rings a bit on the edges, but
a proper PCB layout may fix that.
The driver's not getting hot at 1.5 MHz, so I'm OK on the breadboard.
I need some SO adapters with the power paddle connection, vias to the
bottom maybe.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by ●November 14, 20142014-11-14
On Friday, November 14, 2014 7:53:55 PM UTC+1, klaus.k...@gmail.com wrote:
> With only 5 volts in, can't you roll your own? Small boost or charge capacitor supply to make a 15V rail and a capacitor coupled gate drive. (You need to be sure you don't have nasty transients on the 5V input
>
On Fri, 14 Nov 2014 13:23:09 -0800, Bill Martin <wwm@wwmartin.net>
wrote:
>On 11/14/2014 11:37 AM, Jim Thompson wrote:
>> On Fri, 14 Nov 2014 13:52:55 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 11/12/2014 05:39 PM, John Larkin wrote:
>>>>
>>>>
>>>> I need a mosfet gate driver, to drive two n-fets in a half-bridge
><SNIP>
>>
>> Been trying to find a picture, without success, of an
>> over-top-dead-center clamp that I used in my Motorola days to press a
>> flat pack down on a PCB to test it without soldering.
>>
>> ...Jim Thompson
>>
>Take a look at Carr-Lane website, toggle clamps.
>
>-bill
There you go...
<http://www.ebay.com/itm/like/291262881110?lpid=82>
We had a "well" that the package body fell into to align the leads
easily.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Bill Martin●November 14, 20142014-11-14
On 11/14/2014 11:37 AM, Jim Thompson wrote:
> On Fri, 14 Nov 2014 13:52:55 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 11/12/2014 05:39 PM, John Larkin wrote:
>>>
>>>
>>> I need a mosfet gate driver, to drive two n-fets in a half-bridge
<SNIP>
>
> Been trying to find a picture, without success, of an
> over-top-dead-center clamp that I used in my Motorola days to press a
> flat pack down on a PCB to test it without soldering.
>
> ...Jim Thompson
>
Take a look at Carr-Lane website, toggle clamps.
-bill
Reply by ●November 14, 20142014-11-14
On Wednesday, November 12, 2014 5:39:44 PM UTC-5, John Larkin wrote:
> I need a mosfet gate driver, to drive two n-fets in a half-bridge
> (totem pole) config, 5 volts nom in, with some sort of bootstrap for
> the upper fet gate. Switcher output will be around 2.5 volts at 5
> amps, so the gate drives don't have to be monstrous.
>
> I've been working with LTC4442 on a breadboard, but it's really
> erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
> up ugly. It's especially bad if Vcc gets much over 5 volts. I think
> the anti-shoot-through circuit is too smart or something.
>
> I don't have the paddle grounded, which could be part of the problem
> maybe. Maybe it wants that extra ground connection. It's hard to do
> that on a breadboard. But the ground pin doesn't look very noisy.
>
> Any suggested parts?
Are the FETs extra large? This chip performance peaks at 3nF, and that's with everything laid out perfectly with low to nonexistent series inductance. The back GND pad floating could easily interfere with switching performance at its advertized speed.
>
>
> --
>
> John Larkin Highland Technology, Inc
> picosecond timing precision measurement
>
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com
Reply by Jim Thompson●November 14, 20142014-11-14
On Fri, 14 Nov 2014 13:52:55 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>On 11/12/2014 05:39 PM, John Larkin wrote:
>>
>>
>> I need a mosfet gate driver, to drive two n-fets in a half-bridge
>> (totem pole) config, 5 volts nom in, with some sort of bootstrap for
>> the upper fet gate. Switcher output will be around 2.5 volts at 5
>> amps, so the gate drives don't have to be monstrous.
>>
>> I've been working with LTC4442 on a breadboard, but it's really
>> erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
>> up ugly. It's especially bad if Vcc gets much over 5 volts. I think
>> the anti-shoot-through circuit is too smart or something.
>>
>> I don't have the paddle grounded, which could be part of the problem
>> maybe. Maybe it wants that extra ground connection. It's hard to do
>> that on a breadboard. But the ground pin doesn't look very noisy.
>>
>> Any suggested parts?
>>
>>
>
>I usually put a blob of solder on the pad, and another one on the board.
> Then I melt the board side with the iron lying almost flat, set the
>chip on top of the iron till both sides are melted, and pull the iron
>out. Usually works pretty well--it's how I heat-sink LM78xx regulators
>in breadboards. Not exactly a production-worthy technique, but I've
>never had one die yet.
>
>Cheers
>
>Phil Hobbs
Been trying to find a picture, without success, of an
over-top-dead-center clamp that I used in my Motorola days to press a
flat pack down on a PCB to test it without soldering.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by ●November 14, 20142014-11-14
With only 5 volts in, can't you roll your own? Small boost or charge capacitor supply to make a 15V rail and a capacitor coupled gate drive. (You need to be sure you don't have nasty transients on the 5V input
Regards
Klaus
Reply by Phil Hobbs●November 14, 20142014-11-14
On 11/12/2014 05:39 PM, John Larkin wrote:
>
>
> I need a mosfet gate driver, to drive two n-fets in a half-bridge
> (totem pole) config, 5 volts nom in, with some sort of bootstrap for
> the upper fet gate. Switcher output will be around 2.5 volts at 5
> amps, so the gate drives don't have to be monstrous.
>
> I've been working with LTC4442 on a breadboard, but it's really
> erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
> up ugly. It's especially bad if Vcc gets much over 5 volts. I think
> the anti-shoot-through circuit is too smart or something.
>
> I don't have the paddle grounded, which could be part of the problem
> maybe. Maybe it wants that extra ground connection. It's hard to do
> that on a breadboard. But the ground pin doesn't look very noisy.
>
> Any suggested parts?
>
>
I usually put a blob of solder on the pad, and another one on the board.
Then I melt the board side with the iron lying almost flat, set the
chip on top of the iron till both sides are melted, and pull the iron
out. Usually works pretty well--it's how I heat-sink LM78xx regulators
in breadboards. Not exactly a production-worthy technique, but I've
never had one die yet.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by Jim Thompson●November 14, 20142014-11-14
On Wed, 12 Nov 2014 14:39:36 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:
>
>
>I need a mosfet gate driver, to drive two n-fets in a half-bridge
>(totem pole) config, 5 volts nom in, with some sort of bootstrap for
>the upper fet gate. Switcher output will be around 2.5 volts at 5
>amps, so the gate drives don't have to be monstrous.
>
>I've been working with LTC4442 on a breadboard, but it's really
>erratic. Sometimes it's beautiful, and sometimes the gate drive breaks
>up ugly. It's especially bad if Vcc gets much over 5 volts. I think
>the anti-shoot-through circuit is too smart or something.
>
>I don't have the paddle grounded, which could be part of the problem
>maybe. Maybe it wants that extra ground connection. It's hard to do
>that on a breadboard. But the ground pin doesn't look very noisy.
>
>Any suggested parts?
From the data sheet...
GND (Pin 4, Exposed Pad Pin 9): Chip Ground. The exposed
pad must be soldered to the PCB ground for electrical
contact and for rated thermal performance.
Maybe devise a spring clip to contact the back-side pad in your
breadboard?
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.