Forums

boost-converter trouble

Started by Winfield Hill November 20, 2018
On Wed, 21 Nov 2018 10:25:10 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>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.
Known as a "hysteretic-mode converter". They're fairly common these days, usually called something like "D-Cap" control.
On Wed, 21 Nov 2018 22:21:19 -0500, krw@notreal.com wrote:

>On Wed, 21 Nov 2018 10:25:10 -0800, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>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. > >Known as a "hysteretic-mode converter". They're fairly common these >days, usually called something like "D-Cap" control.
You can make a schmitt fire in fixed-width pulses, which becomes a frequency control loop, not hysteretic. Each shot dumps a pretty much equal bump of energy into the load. Hysteretic works fairly well in a buck switcher, less well (or not at all) in boost mode. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Wednesday, November 21, 2018 at 3:24:36 PM UTC-5, Winfield Hill wrote:
> 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.
Okay, I see now. I don't like this TPS61040, they're using a really inferior methodology for soft start just so they can include it in their highlighted marketing bullets. The better engineered parts terminate soft start when the output reaches full voltage, along with output voltage status outputs, the TPS kluge does not, it just hangs in soft start mode until whenever. As for better engineered parts with approximately the same meta-scale parametrics but better control, like internal oscillators, you have the Microchip MCP1650/51/52/53, http://ww1.microchip.com/downloads/en/DeviceDoc/21876B.pdf with cost about 25% more in quantities of 1000, but still purrretty cheap. Then there is this premium performance Austria Microsystems part, AS1340 and AS1344, https://ams.com/as1340. Price is not so bad. The only question is who are Austria Microsystems. https://ams.com/about-ams Most of these parts have soft start current limits way bigger than the TPS, even though the output current rating is about the same. The way you're using the TPS now, which is effectively bypassing soft start, may run into problems with incomplete utilization of the full battery capacity. The partially discharged battery always has issues with output impedance and time response to surges, which may trip your UVLO and cause a restart, all this happening just when you start powering your LEDs, and you're back to square one. Just something else to be tested... I take it you're driving 4x white LEDs in series.
> > > -- > Thanks, > - Win
bloggs.fredbloggs.fred@gmail.com wrote...
> > On Wednesday, Winfield Hill wrote: >> bloggs.fredbloggs.fred@gmail.com wrote... >>> On Tuesday, Winfield Hill wrote: >>>> I encountered an unexpected boost-converter failure mode. >>>> [ snip ] >>>> The cause? The TPS61040 has a soft-start function. ... >>> >>> 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. ... > > Okay, I see now. I don't like this TPS61040, they're using a > really inferior methodology for soft start just so they can > include it in their highlighted marketing bullets. The better > engineered parts terminate soft start when the output reaches > full voltage, along with output voltage status outputs, > the TPS kluge does not, it just hangs in soft start mode > until whenever.
Yes, really bad.
> As for better engineered parts ...
Thanks for the suggested parts. Unfortunately I'm stuck with only a small amount of space, and therefore only considered sot-23 package parts. I had gathered a huge list of candidate datasheets in my computer, but it's the little unknown gotchas that lurk behind one's design choices that rise up and bite. There may be a great sot-23 alternate, but after 3 pcb passes, 15 boards assembled, and a season of live beehive experience, I had hoped to be done with the hardware optimization phase. It's working OK now, at the expense of 10 to 20% wasted power.
> I take it you're driving 4x white LEDs in series.
Actually, there are eight IR proximity-sensor LEDs in series. There are 48 proximity sensors for 24 bee-trip channels, and we scan all of the channels 20 times a second. Sensing is with 96 measured (on and off) analog ADC reflection levels. It works well even with sunlight shining into the channels. -- Thanks, - Win
On 21 Nov 2018 12:26:36 -0800, Winfield Hill
<hill@rowland.harvard.edu> 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.
Uncovered.....or created? Preferred because a lower power consumption was theoretically possible? RL
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.
What is the cheapest uP that has an ADC input? One of those and a three cent mosfet would make a nice boost switcher; just needs a little code. 30 cents for the uP and fet and a diode maybe. Serial interface is probably free. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 11/22/18 12:46 PM, John Larkin wrote:
> 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. > > What is the cheapest uP that has an ADC input? One of those and a > three cent mosfet would make a nice boost switcher; just needs a > little code. 30 cents for the uP and fet and a diode maybe. Serial > interface is probably free. > >
I really like the LPC802, at 50 cents in reels. 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 Thu, 22 Nov 2018 09:46:35 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>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. > >What is the cheapest uP that has an ADC input? One of those and a >three cent mosfet would make a nice boost switcher; just needs a >little code. 30 cents for the uP and fet and a diode maybe. Serial >interface is probably free.
<https://www.microchip.com/design-centers/8-bit/pic-mcus/device-selection/pic16f15386>
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message 
news:taqdvd983sbci31sulfkda0fagihjvm603@4ax.com...
> What is the cheapest uP that has an ADC input? One of those and a > three cent mosfet would make a nice boost switcher; just needs a > little code. 30 cents for the uP and fet and a diode maybe. Serial > interface is probably free.
Guessing, cheapest with >200kSps isn't going to be as competitive as you're thinking. That's basically what the stupid phaux-analog controllers are anyways.
>:(
Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
On Thursday, November 22, 2018 at 11:09:31 PM UTC+1, Tim Williams wrote:
> "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message > news:taqdvd983sbci31sulfkda0fagihjvm603@4ax.com... > > What is the cheapest uP that has an ADC input? One of those and a > > three cent mosfet would make a nice boost switcher; just needs a > > little code. 30 cents for the uP and fet and a diode maybe. Serial > > interface is probably free. > > Guessing, cheapest with >200kSps isn't going to be as competitive as you're > thinking. > > That's basically what the stupid phaux-analog controllers are anyways. > >:( >
Silabs Busybee EFM8BB1, comes in at below 20 cents, and has 800kSa ADC, plus deadtime enabled timer, 2% voltage reference Cheers Klaus