Forums

Buck switcher chips

Started by Phil Hobbs July 19, 2013
So we've got the +-40V sorted out, thanks to all.  The next bit to 
re-examine is the two buck regulators, both LM2594s, one for +5 and one 
for -15.

The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in 
stock.  The ONsemi clone, LM2594D, is only 64 cents, but it looks like 
Digikey is the only distributor with any stock, and they have less than 
one reel.

I like the medium-old bipolar switchers, because their nice slow edges 
make me less worried about switching junk getting into my low level 
circuitry.

Any idea why the ONsemi ones are both cheap and apparently unpopular?

Any suggestions for buck chips that will handle at least 40V and 0.5 A?

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
On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So we've got the +-40V sorted out, thanks to all. The next bit to >re-examine is the two buck regulators, both LM2594s, one for +5 and one >for -15. > >The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >Digikey is the only distributor with any stock, and they have less than >one reel. > >I like the medium-old bipolar switchers, because their nice slow edges >make me less worried about switching junk getting into my low level >circuitry. > >Any idea why the ONsemi ones are both cheap and apparently unpopular? > >Any suggestions for buck chips that will handle at least 40V and 0.5 A? > >Cheers > >Phil Hobbs
Have you checked the ON Semi site? It could be that the LM2594 is being discontinued. Use an LM339 and be safe ;-) Reminds me of a design of mine that produced both +5V and -12V... http://www.analog-innovations.com/SED/OldStyleBuckSwitcherWithAddedNegativeOutput.pdf What are the relative loads on your +5V and -15V? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | 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.
On 07/19/2013 01:59 PM, Jim Thompson wrote:
> On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> So we've got the +-40V sorted out, thanks to all. The next bit to >> re-examine is the two buck regulators, both LM2594s, one for +5 and one >> for -15. >> >> The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >> stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >> Digikey is the only distributor with any stock, and they have less than >> one reel. >> >> I like the medium-old bipolar switchers, because their nice slow edges >> make me less worried about switching junk getting into my low level >> circuitry. >> >> Any idea why the ONsemi ones are both cheap and apparently unpopular? >> >> Any suggestions for buck chips that will handle at least 40V and 0.5 A? >> >> Cheers >> >> Phil Hobbs > > Have you checked the ON Semi site? It could be that the LM2594 is > being discontinued. > > Use an LM339 and be safe ;-) > > Reminds me of a design of mine that produced both +5V and -12V... > > http://www.analog-innovations.com/SED/OldStyleBuckSwitcherWithAddedNegativeOutput.pdf > > What are the relative loads on your +5V and -15V? > > ...Jim Thompson >
I looked on the ONsemi site, and they're discontinuing the DIP package but not (so far) the SO8. The +5 load is relatively light--it's running a 3.3V LDO for a small ARM with a bit of external flash and sram, some optos, a display, and an FDTI chip. So maybe 200 mA. The -15 can be at least that, because there are beefy op amps driving series-terminated 50 ohm BNCs that somebody might decide to terminate in 50 ohms. But no more than 250 mA. 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
On Fri, 19 Jul 2013 14:06:45 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 07/19/2013 01:59 PM, Jim Thompson wrote: >> On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> So we've got the +-40V sorted out, thanks to all. The next bit to >>> re-examine is the two buck regulators, both LM2594s, one for +5 and one >>> for -15. >>> >>> The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >>> stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >>> Digikey is the only distributor with any stock, and they have less than >>> one reel. >>> >>> I like the medium-old bipolar switchers, because their nice slow edges >>> make me less worried about switching junk getting into my low level >>> circuitry. >>> >>> Any idea why the ONsemi ones are both cheap and apparently unpopular? >>> >>> Any suggestions for buck chips that will handle at least 40V and 0.5 A? >>> >>> Cheers >>> >>> Phil Hobbs >> >> Have you checked the ON Semi site? It could be that the LM2594 is >> being discontinued. >> >> Use an LM339 and be safe ;-) >> >> Reminds me of a design of mine that produced both +5V and -12V... >> >> http://www.analog-innovations.com/SED/OldStyleBuckSwitcherWithAddedNegativeOutput.pdf >> >> What are the relative loads on your +5V and -15V? >> >> ...Jim Thompson >> > >I looked on the ONsemi site, and they're discontinuing the DIP package >but not (so far) the SO8. > >The +5 load is relatively light--it's running a 3.3V LDO for a small ARM >with a bit of external flash and sram, some optos, a display, and an >FDTI chip. So maybe 200 mA. > >The -15 can be at least that, because there are beefy op amps driving >series-terminated 50 ohm BNCs that somebody might decide to terminate in >50 ohms. But no more than 250 mA. > >Cheers > >Phil Hobbs
My parasitic scheme only works with loads on the negative supply that are lower than that of the +5V. In my case I had ~5A on the +5V and ~100mA on the -12V. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | 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.
On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So we've got the +-40V sorted out, thanks to all. The next bit to >re-examine is the two buck regulators, both LM2594s, one for +5 and one >for -15. > >The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >Digikey is the only distributor with any stock, and they have less than >one reel. > >I like the medium-old bipolar switchers, because their nice slow edges >make me less worried about switching junk getting into my low level >circuitry. > >Any idea why the ONsemi ones are both cheap and apparently unpopular? > >Any suggestions for buck chips that will handle at least 40V and 0.5 A? > >Cheers > >Phil Hobbs
We use LM2574/SO14 and LM2576HV/TO263. Nice and slow. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
John Larkin <jlarkin@highlandtechnology.com> writes:

> On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>So we've got the +-40V sorted out, thanks to all. The next bit to >>re-examine is the two buck regulators, both LM2594s, one for +5 and one >>for -15. >> >>The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >>stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >>Digikey is the only distributor with any stock, and they have less than >>one reel. >> >>I like the medium-old bipolar switchers, because their nice slow edges >>make me less worried about switching junk getting into my low level >>circuitry. >> >>Any idea why the ONsemi ones are both cheap and apparently unpopular? >> >>Any suggestions for buck chips that will handle at least 40V and 0.5 A? >> >>Cheers >> >>Phil Hobbs > > We use LM2574/SO14 and LM2576HV/TO263. Nice and slow.
I tend to go the other way! Higher magnetics frequencies are easier to filter and are attentuated more by groundplanes. The fall in PSRR of the opamps gets compensated by the improvement in local filtering. Works best when signals are relatively slow I suppose, slower that the SMPS. -- John Devereux
On Fri, 19 Jul 2013 19:56:22 +0100, John Devereux
<john@devereux.me.uk> wrote:

>John Larkin <jlarkin@highlandtechnology.com> writes: > >> On Fri, 19 Jul 2013 13:47:06 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>>So we've got the +-40V sorted out, thanks to all. The next bit to >>>re-examine is the two buck regulators, both LM2594s, one for +5 and one >>>for -15. >>> >>>The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >>>stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >>>Digikey is the only distributor with any stock, and they have less than >>>one reel. >>> >>>I like the medium-old bipolar switchers, because their nice slow edges >>>make me less worried about switching junk getting into my low level >>>circuitry. >>> >>>Any idea why the ONsemi ones are both cheap and apparently unpopular? >>> >>>Any suggestions for buck chips that will handle at least 40V and 0.5 A? >>> >>>Cheers >>> >>>Phil Hobbs >> >> We use LM2574/SO14 and LM2576HV/TO263. Nice and slow. > >I tend to go the other way! Higher magnetics frequencies are easier to >filter and are attentuated more by groundplanes. The fall in PSRR of the >opamps gets compensated by the improvement in local filtering. > >Works best when signals are relatively slow I suppose, slower that the >SMPS.
We've seen fast switchers, things with a couple ns edges, spray spikes all over a board, through paths that aren't visible on schematics. Synchronous switchers are especially evil. I recently spun the layout on this http://www.highlandtechnology.com/DSS/T346DS.shtml to reduce switcher noise, for a customer who is doing really sensitive RF stuff. The major bad guys were LTC3411s. And one of my favorite waveforms, from an LM3102. The substrate diode step-recovery behavior is clear. https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/LM3102_Switcher_Rise.JPG This freaked out opamps clear across the board, with no obvious connection to this switcher. We're probably talking something over 1e9 amps/second here. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Phil Hobbs wrote:
> So we've got the +-40V sorted out, thanks to all. The next bit to > re-examine is the two buck regulators, both LM2594s, one for +5 and one > for -15. > > The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in > stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like > Digikey is the only distributor with any stock, and they have less than > one reel. > > I like the medium-old bipolar switchers, because their nice slow edges > make me less worried about switching junk getting into my low level > circuitry. > > Any idea why the ONsemi ones are both cheap and apparently unpopular? > > Any suggestions for buck chips that will handle at least 40V and 0.5 A? >
There's always the old MC34063, almost dates back to Methusaleh, which can be had for slightly above $0.10 in qties: http://www.st.com/web/en/resource/technical/document/datasheet/CD00001232.pdf The BD9876 is around $0.50, more efficient, but you'd have to see if ok for the inverter job: http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9876efj-e.pdf The others I have encountered are mostly over a Dollar. If you can stomach an external FET there may be some further penny-pinching possible in case the MC34063 is not to your liking. -- Regards, Joerg http://www.analogconsultants.com/
On 07/19/2013 03:32 PM, Joerg wrote:
> Phil Hobbs wrote: >> So we've got the +-40V sorted out, thanks to all. The next bit to >> re-examine is the two buck regulators, both LM2594s, one for +5 and one >> for -15. >> >> The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >> stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >> Digikey is the only distributor with any stock, and they have less than >> one reel. >> >> I like the medium-old bipolar switchers, because their nice slow edges >> make me less worried about switching junk getting into my low level >> circuitry. >> >> Any idea why the ONsemi ones are both cheap and apparently unpopular? >> >> Any suggestions for buck chips that will handle at least 40V and 0.5 A? >> > > There's always the old MC34063, almost dates back to Methusaleh, which > can be had for slightly above $0.10 in qties: > > http://www.st.com/web/en/resource/technical/document/datasheet/CD00001232.pdf > > The BD9876 is around $0.50, more efficient, but you'd have to see if ok > for the inverter job: > > http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9876efj-e.pdf > > The others I have encountered are mostly over a Dollar. If you can > stomach an external FET there may be some further penny-pinching > possible in case the MC34063 is not to your liking. >
I see that there's a 150 kHz version of the 34063 as well, the NCP3063, which might be a win at 37 cents in hundreds. The switch burden voltage is quite a bit higher than the TI part, and it has an external current limit, which is obviously more accurate, but bumps the switch drop up to 1.6V, which is a chunk. (I'm quite fond of the LM2594--I still wish I knew why the On Semi one is half the price.) 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
Phil Hobbs wrote:
> On 07/19/2013 03:32 PM, Joerg wrote: >> Phil Hobbs wrote: >>> So we've got the +-40V sorted out, thanks to all. The next bit to >>> re-examine is the two buck regulators, both LM2594s, one for +5 and one >>> for -15. >>> >>> The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in >>> stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like >>> Digikey is the only distributor with any stock, and they have less than >>> one reel. >>> >>> I like the medium-old bipolar switchers, because their nice slow edges >>> make me less worried about switching junk getting into my low level >>> circuitry. >>> >>> Any idea why the ONsemi ones are both cheap and apparently unpopular? >>> >>> Any suggestions for buck chips that will handle at least 40V and 0.5 A? >>> >> >> There's always the old MC34063, almost dates back to Methusaleh, which >> can be had for slightly above $0.10 in qties: >> >> http://www.st.com/web/en/resource/technical/document/datasheet/CD00001232.pdf >> >> >> The BD9876 is around $0.50, more efficient, but you'd have to see if ok >> for the inverter job: >> >> http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9876efj-e.pdf >> >> >> The others I have encountered are mostly over a Dollar. If you can >> stomach an external FET there may be some further penny-pinching >> possible in case the MC34063 is not to your liking. >> > > I see that there's a 150 kHz version of the 34063 as well, the NCP3063, > which might be a win at 37 cents in hundreds. The switch burden voltage > is quite a bit higher than the TI part, and it has an external current > limit, which is obviously more accurate, but bumps the switch drop up to > 1.6V, which is a chunk. >
The current sense only adds 200mV. The switch drop is a pain but you'll have that in almost almost all slow and old regulators.
> (I'm quite fond of the LM2594--I still wish I knew why the On Semi one > is half the price.) >
One way to find out would be to ask a TI app engineer :-) -- Regards, Joerg http://www.analogconsultants.com/