Reply by Phil Hobbs ●December 14, 20172017-12-14
Modern buck regulators seem to have way too many features that I can't 
turn off or customize.

The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
short-circuit protection interval--it wouldn't start up into a 220 uF 
capacitor, even with a very light load.  Fortunately, switching to 22 uF 
fixed it, and I had some with the right footprint.

And then many go into stutter mode at light loads, e.g. the MCP16311. 
Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
throughout the load range, but the data sheet lies.  That bit me once 
when I was trying to make an isolated +24 -> +-5V converter for an 
industrial control system, using two coupled inductors.   Simulated 
great, but the undocumented stutter mode of the MCP16312 screwed it up.

Chips these days.

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
Reply by bitrex ●December 14, 20172017-12-14
On 12/14/2017 09:45 AM, Phil Hobbs wrote:

> Modern buck regulators seem to have way too many features that I can't 
> turn off or customize.
> 
> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
> short-circuit protection interval--it wouldn't start up into a 220 uF 
> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
> fixed it, and I had some with the right footprint.
> 
> And then many go into stutter mode at light loads, e.g. the MCP16311. 
> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
> throughout the load range, but the data sheet lies.  That bit me once 
> when I was trying to make an isolated +24 -> +-5V converter for an 
> industrial control system, using two coupled inductors.   Simulated 
> great, but the undocumented stutter mode of the MCP16312 screwed it up.
> 
> Chips these days.
> 
> Cheers
> 
> Phil Hobbs
> 


The fixed short-circuit protection interval thing that makes them fall 
over on start into large capacitances or cold resistive loads is 
annoying as fuk; I encountered that when building someone a circuit with 
Numitron tubes for a display. Used a boost module that should've had 
plenty of nominal current to drive the segments when hot, but wouldn't 
start up when they were cold.

The chip did have a "shutdown" pin though so I hacked it by using a CMOS 
555 and RC circuit to the control voltage input to send a ~5kHz square 
wave of increasing duty cycle to that pin over a couple seconds, and 
then shut off the oscillator once the rail was up.
Reply by George Herold ●December 14, 20172017-12-14
On Thursday, December 14, 2017 at 9:45:33 AM UTC-5, Phil Hobbs wrote:

> Modern buck regulators seem to have way too many features that I can't 
> turn off or customize.
> 
> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
> short-circuit protection interval--it wouldn't start up into a 220 uF 
> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
> fixed it, and I had some with the right footprint.
> 
> And then many go into stutter mode at light loads, e.g. the MCP16311. 
> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
> throughout the load range, but the data sheet lies.  That bit me once 
> when I was trying to make an isolated +24 -> +-5V converter for an 
> industrial control system, using two coupled inductors.   Simulated 
> great, but the undocumented stutter mode of the MCP16312 screwed it up.
> 
> Chips these days.

Grin, On the glass half full front, at least there are these IC's.  
What if you had to design it all with discretes?  

I'm beating my head on some unknown bit of stray capacitance.  The first 
circuit worked, the second doesn't.  The second pcb now looks like a 
battle field of blue jumper wires. I've got it isolated to an inch of trace,
but I can't see how it couples.... oh a new idea... I think I'm going to
redo the pcb, but I'd like to understand a bit more what I did wrong.  

George H.    

> 
> 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
Reply by Phil Hobbs ●December 14, 20172017-12-14
On 12/14/2017 11:09 AM, George Herold wrote:

> On Thursday, December 14, 2017 at 9:45:33 AM UTC-5, Phil Hobbs wrote:
>> Modern buck regulators seem to have way too many features that I can't 
>> turn off or customize.
>>
>> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
>> short-circuit protection interval--it wouldn't start up into a 220 uF 
>> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
>> fixed it, and I had some with the right footprint.
>>
>> And then many go into stutter mode at light loads, e.g. the MCP16311. 
>> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
>> throughout the load range, but the data sheet lies.  That bit me once 
>> when I was trying to make an isolated +24 -> +-5V converter for an 
>> industrial control system, using two coupled inductors.   Simulated 
>> great, but the undocumented stutter mode of the MCP16312 screwed it up.
>>
>> Chips these days.
> Grin, On the glass half full front, at least there are these IC's.  
> What if you had to design it all with discretes?  


Quit being so offensively reasonable. ;)

This one would probably work using an astable driving a PMOS at fixed
duty cycle, followed by an LC lowpass (which is really all a buck is)
and an LM1117 (or zener plus metal-can 2N2222) for regulation.


> 
> I'm beating my head on some unknown bit of stray capacitance.  The first 
> circuit worked, the second doesn't.  The second pcb now looks like a 
> battle field of blue jumper wires. I've got it isolated to an inch of trace,
> but I can't see how it couples.... oh a new idea... I think I'm going to
> redo the pcb, but I'd like to understand a bit more what I did wrong.  


Yeah, you learn a lot from those post-mortems.  Using SiGe:C BJTs is an
education in layout all by itself.

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
https://hobbs-eo.com
Reply by John Larkin ●December 14, 20172017-12-14
On Thu, 14 Dec 2017 09:45:17 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:


>Modern buck regulators seem to have way too many features that I can't 
>turn off or customize.
>
>The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
>short-circuit protection interval--it wouldn't start up into a 220 uF 
>capacitor, even with a very light load.  Fortunately, switching to 22 uF 
>fixed it, and I had some with the right footprint.
>
>And then many go into stutter mode at light loads, e.g. the MCP16311. 
>Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
>throughout the load range, but the data sheet lies.  That bit me once 
>when I was trying to make an isolated +24 -> +-5V converter for an 
>industrial control system, using two coupled inductors.   Simulated 
>great, but the undocumented stutter mode of the MCP16312 screwed it up.
>
>Chips these days.
>
>Cheers
>
>Phil Hobbs


My latest fave is the TPS54302. It's a 6-pin SOT23, nice and dumb, and
behaves very well.

There is no usable model (Web-bench never works for me) so I had to
breadboard the various compensations, but that's done now.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics
Reply by Phil Hobbs ●December 14, 20172017-12-14
On 12/14/2017 12:17 PM, John Larkin wrote:

> On Thu, 14 Dec 2017 09:45:17 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> Modern buck regulators seem to have way too many features that I can't 
>> turn off or customize.
>>
>> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
>> short-circuit protection interval--it wouldn't start up into a 220 uF 
>> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
>> fixed it, and I had some with the right footprint.
>>
>> And then many go into stutter mode at light loads, e.g. the MCP16311. 
>> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
>> throughout the load range, but the data sheet lies.  That bit me once 
>> when I was trying to make an isolated +24 -> +-5V converter for an 
>> industrial control system, using two coupled inductors.   Simulated 
>> great, but the undocumented stutter mode of the MCP16312 screwed it up.
>>
>> Chips these days.
>>
> 
> My latest fave is the TPS54302. It's a 6-pin SOT23, nice and dumb, and
> behaves very well.
> 
> There is no usable model (Web-bench never works for me) so I had to
> breadboard the various compensations, but that's done now.
> 
> 

Looks like a nice part, but distributor stock appears to be very thin.

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
https://hobbs-eo.com
Reply by John Larkin ●December 14, 20172017-12-14
On Thu, 14 Dec 2017 14:40:49 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:


>On 12/14/2017 12:17 PM, John Larkin wrote:
>> On Thu, 14 Dec 2017 09:45:17 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> 
>>> Modern buck regulators seem to have way too many features that I can't 
>>> turn off or customize.
>>>
>>> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
>>> short-circuit protection interval--it wouldn't start up into a 220 uF 
>>> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
>>> fixed it, and I had some with the right footprint.
>>>
>>> And then many go into stutter mode at light loads, e.g. the MCP16311. 
>>> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode 
>>> throughout the load range, but the data sheet lies.  That bit me once 
>>> when I was trying to make an isolated +24 -> +-5V converter for an 
>>> industrial control system, using two coupled inductors.   Simulated 
>>> great, but the undocumented stutter mode of the MCP16312 screwed it up.
>>>
>>> Chips these days.
>>>
>> 
>> My latest fave is the TPS54302. It's a 6-pin SOT23, nice and dumb, and
>> behaves very well.
>> 
>> There is no usable model (Web-bench never works for me) so I had to
>> breadboard the various compensations, but that's done now.
>> 
>> 
>Looks like a nice part, but distributor stock appears to be very thin.
>
>Cheers
>
>Phil Hobbs


I'd better check on that. It's very similar to the AOZ part but, of
course, different pinout.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by Tim Williams ●December 14, 20172017-12-14
The fancier synchronous controllers allow you to run in full-wave mode, and 
some of the regular-switch kinds too.  They're usually the upscale ones that 
feel like giving you those extra control pins to play with.  So, they may 
break whatever budget or layout size restrictions you had.

That short protection mode is good to know about, thanks.  Seems like I see 
that on chips with poor (or no) current limiting, or fixed timing designs 
(like a peak current mode controller, that turns on /every/ cycle and for at 
least a minimum pulse width, hence not actually limiting current into a 
short).  I mean, even my discrete designs deal with that problem, but alas, 
we're stuck with ICs in practical designs.

What's so bad about burp-ripple in an "industrial control system"?  In your 
low noise opto gadgets, I can see that, but..?

Tim

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

"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message 
news:9qmdnXVbc4rjE6_HnZ2dnUU7-bnNnZ2d@supernews.com...

> Modern buck regulators seem to have way too many features that I can't 
> turn off or customize.
>
> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed 
> short-circuit protection interval--it wouldn't start up into a 220 uF 
> capacitor, even with a very light load.  Fortunately, switching to 22 uF 
> fixed it, and I had some with the right footprint.
>
> And then many go into stutter mode at light loads, e.g. the MCP16311. Its 
> brother, the MCP16312, is claimed to stay in vanilla PWM mode throughout 
> the load range, but the data sheet lies.  That bit me once when I was 
> trying to make an isolated +24 -> +-5V converter for an industrial control 
> system, using two coupled inductors.   Simulated great, but the 
> undocumented stutter mode of the MCP16312 screwed it up.
>
> Chips these days.
>
> 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
>
Reply by Phil Hobbs ●December 14, 20172017-12-14
On 12/14/2017 04:42 PM, John Larkin wrote:

> On Thu, 14 Dec 2017 14:40:49 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> On 12/14/2017 12:17 PM, John Larkin wrote:
>>> On Thu, 14 Dec 2017 09:45:17 -0500, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>> Modern buck regulators seem to have way too many features that I can't
>>>> turn off or customize.
>>>>
>>>> The otherwise very nice AOZ1282-1 snookered me by having a 600-us fixed
>>>> short-circuit protection interval--it wouldn't start up into a 220 uF
>>>> capacitor, even with a very light load.  Fortunately, switching to 22 uF
>>>> fixed it, and I had some with the right footprint.
>>>>
>>>> And then many go into stutter mode at light loads, e.g. the MCP16311.
>>>> Its brother, the MCP16312, is claimed to stay in vanilla PWM mode
>>>> throughout the load range, but the data sheet lies.  That bit me once
>>>> when I was trying to make an isolated +24 -> +-5V converter for an
>>>> industrial control system, using two coupled inductors.   Simulated
>>>> great, but the undocumented stutter mode of the MCP16312 screwed it up.
>>>>
>>>> Chips these days.
>>>>
>>>
>>> My latest fave is the TPS54302. It's a 6-pin SOT23, nice and dumb, and
>>> behaves very well.
>>>
>>> There is no usable model (Web-bench never works for me) so I had to
>>> breadboard the various compensations, but that's done now.
>>>
>>>
>> Looks like a nice part, but distributor stock appears to be very thin.
>>
>> Cheers
>>
>> Phil Hobbs
> 
> I'd better check on that. It's very similar to the AOZ part but, of
> course, different pinout.
> 
> 

Yeah, there's a big run on quite a few chips at the moment, it seems. 
The AOZ1282-1 is in "full production" but nobody has any more till at 
least January.  It's the 400 mA, 1-MHz version of the vanilla 1282, 
which is a 1A, 500 kHz part.  Faster is nice when you're coming off a 
24V rail.

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
Reply by Phil Hobbs ●December 14, 20172017-12-14
On 12/14/2017 04:57 PM, Tim Williams wrote:


> 
> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in
> message news:9qmdnXVbc4rjE6_HnZ2dnUU7-bnNnZ2d@supernews.com...
>> Modern buck regulators seem to have way too many features that I
>> can't turn off or customize.
>> 
>> The otherwise very nice AOZ1282-1 snookered me by having a 600-us 
>> fixed short-circuit protection interval--it wouldn't start up into
>> a 220 uF capacitor, even with a very light load.  Fortunately,
>> switching to 22 uF fixed it, and I had some with the right
>> footprint.
>> 
>> And then many go into stutter mode at light loads, e.g. the
>> MCP16311. Its brother, the MCP16312, is claimed to stay in vanilla
>> PWM mode throughout the load range, but the data sheet lies.  That
>> bit me once when I was trying to make an isolated +24 -> +-5V
>> converter for an industrial control system, using two coupled
>> inductors.   Simulated great, but the undocumented stutter mode of
>> the MCP16312 screwed it up.
>> 
>> Chips these days.



> The fancier synchronous controllers allow you to run in full-wave
> mode, and some of the regular-switch kinds too.  They're usually the
> upscale ones that feel like giving you those extra control pins to
> play with. So, they may break whatever budget or layout size
> restrictions you had.
> 
> That short protection mode is good to know about, thanks.  Seems like
> I see that on chips with poor (or no) current limiting, or fixed
> timing designs (like a peak current mode controller, that turns on
> /every/ cycle and for at least a minimum pulse width, hence not
> actually limiting current into a short).  I mean, even my discrete
> designs deal with that problem, but alas, we're stuck with ICs in
> practical designs.
> 
> What's so bad about burp-ripple in an "industrial control system"?
> In your low noise opto gadgets, I can see that, but..?


I was using it to make an isolated supply, so I need it to keep on 
PWMing under all circumstances.  (It was a 'flybuck' design.)  The main 
output didn't need much current.

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