Forums

boost-converter trouble

Started by Winfield Hill November 20, 2018
 I encountered an unexpected boost-converter failure mode.

 My beehive monitor runs from 5V, 0.25A USB power, or from
 a 3.7V Li-Ion cell.  A pulsed 25mA LED current source runs
 off 14V, using a compact sot-23-6 TPS61040 boost converter,
 which makes its boost switching cycles only when needed.
 It takes 125mA average from a 3.7V supply during the pulse.
 E.g., with 250mA peak sawtooth charging currents.  Here we
 have cycles of the '61040's 400mA peak-current setpoint.

 For the 50ms between LED pulsing, I disabled the converter.
 After enabling for a new burst, the converter would quickly
 re-establish +14.0 volts.  After spending time measuring dark
 levels, LED pulsing is started.  But the TPS61040 failed to
 keep up, and the 14V bus could decay to about 11V, damaging
 LED output, before it finally recovered and enforced 14V.

 The cause?  The TPS61040 has a soft-start function.  This is
 desirable, given limited current availability from USB power.
 It sets the ramp current to 100mA for 256 cycles, and 200mA
 for 256 more cycles.  But the '61040 doesn't need a full 512
 cycles to restore its output to 14V, which means when it was
 finally expected to deliver full power, it could not do so.

 One solution is to stop disabling the converter, and leave
 it on continuously.  Thankfully it only needs 28uA to run.
 But this means a PCB roach wire.  There might be a software
 solution.  Early operating regimes didn't have the problem.
 Making the change allows full operating mode freedom.


-- 
 Thanks,
    - Win
Ah yes, the sausage is leaking out...

(Ever more, these days, designs are -- I assume -- driven by digital 
engineers, following specs written by other digital engineers, few if any of 
whom have a nuanced, general understanding of control theory or DSP.  It's 
all sausage inside.  You don't want to see it getting made.

Such a device is presented in such-and-such way, following a block diagram, 
and seemingly emulating an analog chip (which would do the same job with 
fewer transistors, but higher development costs).  But because of all these 
compromises, there are innumerable hidden states, which if the end user 
stays within the spec's expected operating envelope, never show up, but when 
you have situations like this, well... the ugliness spills out.)

It bothers me that, e.g., their "Eco-Boost" (some TPS54xxx's and such) 
controllers are reasonably nice, yet, when they go to burst mode, they don't 
slow down (the analog version), or pulse skip (the simple digital version), 
no, they have an internal oscillator and counter keeping state, and a mux to 
select a different tap from the [binary] divider, so the frequency only goes 
down in halves.  But no one noticed that that's a horrible nonlinearity in 
an otherwise reasonable control loop, so, that's what made it into 
production.

Tim

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

"Winfield Hill" <hill@rowland.harvard.edu> wrote in message 
news:pt2k45010b4@drn.newsguy.com...
> I encountered an unexpected boost-converter failure mode. > > My beehive monitor runs from 5V, 0.25A USB power, or from > a 3.7V Li-Ion cell. A pulsed 25mA LED current source runs > off 14V, using a compact sot-23-6 TPS61040 boost converter, > which makes its boost switching cycles only when needed. > It takes 125mA average from a 3.7V supply during the pulse. > E.g., with 250mA peak sawtooth charging currents. Here we > have cycles of the '61040's 400mA peak-current setpoint. > > For the 50ms between LED pulsing, I disabled the converter. > After enabling for a new burst, the converter would quickly > re-establish +14.0 volts. After spending time measuring dark > levels, LED pulsing is started. But the TPS61040 failed to > keep up, and the 14V bus could decay to about 11V, damaging > LED output, before it finally recovered and enforced 14V. > > The cause? The TPS61040 has a soft-start function. This is > desirable, given limited current availability from USB power. > It sets the ramp current to 100mA for 256 cycles, and 200mA > for 256 more cycles. But the '61040 doesn't need a full 512 > cycles to restore its output to 14V, which means when it was > finally expected to deliver full power, it could not do so. > > One solution is to stop disabling the converter, and leave > it on continuously. Thankfully it only needs 28uA to run. > But this means a PCB roach wire. There might be a software > solution. Early operating regimes didn't have the problem. > Making the change allows full operating mode freedom. > > > -- > Thanks, > - Win
On Tuesday, November 20, 2018 at 10:41:10 PM UTC-5, Winfield Hill wrote:
> I encountered an unexpected boost-converter failure mode. > > My beehive monitor runs from 5V, 0.25A USB power, or from > a 3.7V Li-Ion cell. A pulsed 25mA LED current source runs > off 14V, using a compact sot-23-6 TPS61040 boost converter, > which makes its boost switching cycles only when needed. > It takes 125mA average from a 3.7V supply during the pulse. > E.g., with 250mA peak sawtooth charging currents. Here we > have cycles of the '61040's 400mA peak-current setpoint. > > For the 50ms between LED pulsing, I disabled the converter. > After enabling for a new burst, the converter would quickly > re-establish +14.0 volts. After spending time measuring dark > levels, LED pulsing is started. But the TPS61040 failed to > keep up, and the 14V bus could decay to about 11V, damaging > LED output, before it finally recovered and enforced 14V. > > The cause? The TPS61040 has a soft-start function. This is > desirable, given limited current availability from USB power. > It sets the ramp current to 100mA for 256 cycles, and 200mA > for 256 more cycles. But the '61040 doesn't need a full 512 > cycles to restore its output to 14V, which means when it was > finally expected to deliver full power, it could not do so. > > One solution is to stop disabling the converter, and leave > it on continuously. Thankfully it only needs 28uA to run. > But this means a PCB roach wire. There might be a software > solution. Early operating regimes didn't have the problem. > Making the change allows full operating mode freedom.
So? The soft start is only 512us. Cyclically disable the chip as originally planned but then delay the LED current pulse by 1ms after the 61040 is EN'ed.
> > > -- > Thanks, > - Win
On 11/20/18 10:40 PM, Winfield Hill wrote:
> I encountered an unexpected boost-converter failure mode. > > My beehive monitor runs from 5V, 0.25A USB power, or from > a 3.7V Li-Ion cell. A pulsed 25mA LED current source runs > off 14V, using a compact sot-23-6 TPS61040 boost converter, > which makes its boost switching cycles only when needed. > It takes 125mA average from a 3.7V supply during the pulse. > E.g., with 250mA peak sawtooth charging currents. Here we > have cycles of the '61040's 400mA peak-current setpoint. > > For the 50ms between LED pulsing, I disabled the converter. > After enabling for a new burst, the converter would quickly > re-establish +14.0 volts. After spending time measuring dark > levels, LED pulsing is started. But the TPS61040 failed to > keep up, and the 14V bus could decay to about 11V, damaging > LED output, before it finally recovered and enforced 14V. > > The cause? The TPS61040 has a soft-start function. This is > desirable, given limited current availability from USB power. > It sets the ramp current to 100mA for 256 cycles, and 200mA > for 256 more cycles. But the '61040 doesn't need a full 512 > cycles to restore its output to 14V, which means when it was > finally expected to deliver full power, it could not do so. > > One solution is to stop disabling the converter, and leave > it on continuously. Thankfully it only needs 28uA to run. > But this means a PCB roach wire. There might be a software > solution. Early operating regimes didn't have the problem. > Making the change allows full operating mode freedom. > >
Yeah, and the datasheets lie through their teeth, especially about forced-PWM vs stutter mode at low output current. I don't ever use new switcher parts without prototyping them. 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
On 20 Nov 2018 19:40:53 -0800, Winfield Hill
<hill@rowland.harvard.edu> wrote:

> I encountered an unexpected boost-converter failure mode. > > My beehive monitor runs from 5V, 0.25A USB power, or from > a 3.7V Li-Ion cell. A pulsed 25mA LED current source runs > off 14V, using a compact sot-23-6 TPS61040 boost converter, > which makes its boost switching cycles only when needed. > It takes 125mA average from a 3.7V supply during the pulse. > E.g., with 250mA peak sawtooth charging currents. Here we > have cycles of the '61040's 400mA peak-current setpoint. > > For the 50ms between LED pulsing, I disabled the converter. > After enabling for a new burst, the converter would quickly > re-establish +14.0 volts. After spending time measuring dark > levels, LED pulsing is started. But the TPS61040 failed to > keep up, and the 14V bus could decay to about 11V, damaging > LED output, before it finally recovered and enforced 14V. > > The cause? The TPS61040 has a soft-start function. This is > desirable, given limited current availability from USB power. > It sets the ramp current to 100mA for 256 cycles, and 200mA > for 256 more cycles. But the '61040 doesn't need a full 512 > cycles to restore its output to 14V, which means when it was > finally expected to deliver full power, it could not do so. > > One solution is to stop disabling the converter, and leave > it on continuously. Thankfully it only needs 28uA to run. > But this means a PCB roach wire. There might be a software > solution. Early operating regimes didn't have the problem. > Making the change allows full operating mode freedom.
Is there a uP? Make your own software controlled boost converter maybe. Mosfet, inductor, diode. I've done converters using a schmitt-trigger gate as the control element. Sort of fun. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
bloggs.fredbloggs.fred@gmail.com wrote...
> > On Tuesday, Winfield Hill wrote: >> I encountered an unexpected boost-converter failure mode. >> [ snip ] >> >> For the 50ms between LED pulsing, I disabled the converter. >> After enabling for a new burst, the converter would quickly >> re-establish +14.0 volts. After spending time measuring dark >> levels, LED pulsing is started. But the TPS61040 failed to >> keep up, and the 14V bus could decay to about 11V, damaging >> LED output, before it finally recovered and enforced 14V. >> >> The cause? The TPS61040 has a soft-start function. This is >> desirable, given limited current availability from USB power. >> It sets the ramp current to 100mA for 256 cycles, and 200mA >> for 256 more cycles. But the '61040 doesn't need a full 512 >> cycles to restore its output to 14V, which means when it was >> finally expected to deliver full power, it could not do so. >> >> One solution is to stop disabling the converter, and leave >> it on continuously. Thankfully it only needs 28uA to run. >> But this means a PCB roach wire. There might be a software >> solution. Early operating regimes didn't have the problem. >> Making the change allows full operating mode freedom. > > So? The soft start is only 512us. Cyclically disable the chip > as originally planned but then delay the LED current pulse by > 1ms after the 61040 is EN'ed.
That would work if the TPS61040 had an oscillator. Instead it only makes cycles as needed, and without a load, 512 cycles aren't needed. One software solution is to run it at full load for 1 to 2ms before using it. But that wastes much more power, 16mW, than simply leaving the converter on all the time, 0.1 mW. -- Thanks, - Win
Phil Hobbs wrote...
> > Yeah, and the datasheets lie through their teeth, > especially about forced-PWM vs stutter mode at low > output current. I don't ever use new switcher parts > without prototyping them.
This one passed multiple prototyping tests. Then a new preferred software scheme uncovered the issue. -- Thanks, - Win
On 11/21/18 3:26 PM, Winfield Hill wrote:
> Phil Hobbs wrote... >> >> Yeah, and the datasheets lie through their teeth, >> especially about forced-PWM vs stutter mode at low >> output current. I don't ever use new switcher parts >> without prototyping them. > > This one passed multiple prototyping tests. Then a > new preferred software scheme uncovered the issue. > >
Someone has defined history as "one damned thing after another." ;) 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
On Wed, 21 Nov 2018 15:29:55 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/21/18 3:26 PM, Winfield Hill wrote: >> Phil Hobbs wrote... >>> >>> Yeah, and the datasheets lie through their teeth, >>> especially about forced-PWM vs stutter mode at low >>> output current. I don't ever use new switcher parts >>> without prototyping them. >> >> This one passed multiple prototyping tests. Then a >> new preferred software scheme uncovered the issue. >> >> >Someone has defined history as "one damned thing after another." ;)
I should hope so. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Wed, 21 Nov 2018 15:29:55 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/21/18 3:26 PM, Winfield Hill wrote: >> Phil Hobbs wrote... >>> >>> Yeah, and the datasheets lie through their teeth, >>> especially about forced-PWM vs stutter mode at low >>> output current. I don't ever use new switcher parts >>> without prototyping them. >> >> This one passed multiple prototyping tests. Then a >> new preferred software scheme uncovered the issue. >> >> >Someone has defined history as "one damned thing after another." ;)
<https://www.amazon.com/ODTAA/dp/B0028OSB9S/ref=sr_1_4?s=books&ie=UTF8&qid=1542856396&sr=1-4&keywords=odtaa>