Hello, I wanted to see if I could soft-start a used OCXO (Trimble 34310) during warm-up. By default with an appropriately rated 12 VDC supply, the OCXO starts the heater at about 8 W, and eventually settles down to 2 W for 20-25 degC ambient temperature. Figure Attached. The good news is it does startup with either a current limited or power limited supply. Albeit, for the constant current case the start-up time is dramatically longer. Figures Attached. The bad news, but interesting tangent is that when this particular OCXO is soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output spectrum just the 10.9 MHz tone (and some noise from the banana clip-leads loop-antenna). So this is a bit of a pain for soft-starting because, although the oven eventually comes into regulation, the oscillator is running on the wrong frequency. I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a pretty great temperature probe of the crystal (literally). You can see the sinusoidal frequency disturbance of this tone has the same periodicity as that of the heater current (~50 s). So I don't know if the heater is oscillating at the uK level or mK level, will need to find out the tempCo of this crystal mode. Neat to see the oven dynamics. Hopefully once the oven is settled at temp, I can load switch the OCXO for 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a 10+ W rated supply it starts up on 10 MHz every time.

Hi A SC cut crystal has multiple resonance “modes” in can operate on. This is in addition to the normal set of fundamental, third overtone, fifth overtone and so on. For various interesting reasons the SC modes are called A, B and C. On a normal 10 MHz crystal, the “main mode” is the C mode. The A mode is well below this mode both in frequency and amplitude. The B mode is more problematic, It is 8 to 12% above the C mode in frequency and may be higher in amplitude (lower resistance) than the desired mode. The C mode has a “useful” third order temperature characteristic. The B mode has a fairly steep linear temp co. One of the classic design experiments on a SC based design is to force the oscillator onto the B mode. This lets you investigate the oven gain while running a temperature run. What you have likely done is to put the unit onto the B mode. Oscillators tend to be fractal when switching between modes. Minor startup issues can drive the circuit one way or the other. Once it gets onto a mode, it may be quite difficult to get it off of that mode …. Bob > On Apr 12, 2017, at 5:38 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > Hello, > > I wanted to see if I could soft-start a used OCXO (Trimble 34310) during > warm-up. By default with an appropriately rated 12 VDC supply, the OCXO > starts the heater at about 8 W, and eventually settles down to 2 W for > 20-25 degC ambient temperature. Figure Attached. > > The good news is it does startup with either a current limited or power > limited supply. Albeit, for the constant current case the start-up time is > dramatically longer. Figures Attached. > > The bad news, but interesting tangent is that when this particular OCXO is > soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious > overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output > spectrum just the 10.9 MHz tone (and some noise from the banana clip-leads > loop-antenna). So this is a bit of a pain for soft-starting because, > although the oven eventually comes into regulation, the oscillator is > running on the wrong frequency. > > I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a > pretty great temperature probe of the crystal (literally). You can see the > sinusoidal frequency disturbance of this tone has the same periodicity as > that of the heater current (~50 s). So I don't know if the heater is > oscillating at the uK level or mK level, will need to find out the tempCo > of this crystal mode. Neat to see the oven dynamics. > > Hopefully once the oven is settled at temp, I can load switch the OCXO for > 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a 10+ W > rated supply it starts up on 10 MHz every time. > <SoftStart2p5W.png><SoftStart300mA.png><Trimble10p9MHz_SpurMode.png><TrimbleSpur_Spectrum.png><TrimbleWarmupPower.png>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

10.9 MHz is likely the B-mode of the SC cut. (It's a different mode, not a different overtone). This mode has a tempco of 20 ppm and is used to do thermometry. IMHO, there is NO excuse for the oscillator designer to design an oscillator that doesn't oscillate unconditionally in the right mode. NONE! What was the actual manufacturer of the OCXO? (AFAIK, Trimble doesn't make their own). My old boss at Zeta Labs (a really great boss) used to walk up to people who were testing their latest circuit and momentarily turn down the current limit on each of the power supplies to see if the circuit recovered correctly. It often didn't, and then it was back to the drawing board... Rick On 4/12/2017 2:38 PM, Scott Stobbe wrote: > Hello, > > I wanted to see if I could soft-start a used OCXO (Trimble 34310) during > warm-up. By default with an appropriately rated 12 VDC supply, the OCXO > starts the heater at about 8 W, and eventually settles down to 2 W for > 20-25 degC ambient temperature. Figure Attached. > > The good news is it does startup with either a current limited or power > limited supply. Albeit, for the constant current case the start-up time is > dramatically longer. Figures Attached. > > The bad news, but interesting tangent is that when this particular OCXO is > soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious > overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output > spectrum just the 10.9 MHz tone (and some noise from the banana clip-leads > loop-antenna). So this is a bit of a pain for soft-starting because, > although the oven eventually comes into regulation, the oscillator is > running on the wrong frequency. > > I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a > pretty great temperature probe of the crystal (literally). You can see the > sinusoidal frequency disturbance of this tone has the same periodicity as > that of the heater current (~50 s). So I don't know if the heater is > oscillating at the uK level or mK level, will need to find out the tempCo > of this crystal mode. Neat to see the oven dynamics. > > Hopefully once the oven is settled at temp, I can load switch the OCXO for > 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a 10+ W > rated supply it starts up on 10 MHz every time. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

On 4/12/17 7:14 PM, Richard (Rick) Karlquist wrote: > 10.9 MHz is likely the B-mode of the SC cut. > (It's a different mode, not a different overtone). > This mode has a tempco of 20 ppm and is used > to do thermometry. > > IMHO, there is NO excuse for the oscillator > designer to design an oscillator that doesn't > oscillate unconditionally in the right mode. > NONE! What was the actual manufacturer of > the OCXO? (AFAIK, Trimble doesn't make their > own). > > My old boss at Zeta Labs (a really great boss) > used to walk up to people who were testing > their latest circuit and momentarily turn > down the current limit on each of the power > supplies to see if the circuit recovered > correctly. It often didn't, and then it > was back to the drawing board... > These days, a common trap is when you've got a DC/DC converter on the input - with a soft start, the current goes huge, causing all kinds of problems. (I'm in the middle of closing a failure report on just such a sensitivity - an unexpected interaction between the source DC/DC converter and the load DC/DC converter..)

Bob, Rick, my use of modes vs overtones was loose, you guys are spot on. That's a fun challenge, suppressing a mode 10% higher in frequency. That's a bit of a fussy LC filter/trap. So if I assume the tempCo of the B-mode to be 20 ppm/degC, that would mean the heater servo has a sustained oscillation of about 250 udegC all day long. Power cycling for 100 ms isn't long enough for the crystal motion to die out, 200 ms seems to do it, which ~2 MCycles. At which point it runs on the 10MHz C-Mode as desired. I couldn't say who Trimble went with, to me its an ebay special :), but photo attached anyways. When the supply is current or power limited the effective supply slew rate is something like 1 mV/s, and under these conditions, at least this particular unit starts up on B-mode every time. Running one of these on a USB supply (5V, 500mA = 2.5W) is looking plausible. On Wed, Apr 12, 2017 at 9:30 PM, Bob kb8tq <kb8tq@n1k.org> wrote: > Hi > > A SC cut crystal has multiple resonance “modes” in can operate on. This is > in addition to the > normal set of fundamental, third overtone, fifth overtone and so on. For > various interesting reasons > the SC modes are called A, B and C. On a normal 10 MHz crystal, the “main > mode” is the C mode. The > A mode is well below this mode both in frequency and amplitude. The B mode > is more problematic, It is > 8 to 12% above the C mode in frequency and may be higher in amplitude > (lower resistance) than the > desired mode. > > The C mode has a “useful” third order temperature characteristic. The B > mode has a fairly steep linear > temp co. One of the classic design experiments on a SC based design is to > force the oscillator onto the > B mode. This lets you investigate the oven gain while running a > temperature run. What you have likely > done is to put the unit onto the B mode. > > Oscillators tend to be fractal when switching between modes. Minor startup > issues can drive the circuit > one way or the other. Once it gets onto a mode, it may be quite difficult > to get it off of that mode …. > > Bob > > > On Apr 12, 2017, at 5:38 PM, Scott Stobbe <scott.j.stobbe@gmail.com> > wrote: > > > > Hello, > > > > I wanted to see if I could soft-start a used OCXO (Trimble 34310) during > > warm-up. By default with an appropriately rated 12 VDC supply, the OCXO > > starts the heater at about 8 W, and eventually settles down to 2 W for > > 20-25 degC ambient temperature. Figure Attached. > > > > The good news is it does startup with either a current limited or power > > limited supply. Albeit, for the constant current case the start-up time > is > > dramatically longer. Figures Attached. > > > > The bad news, but interesting tangent is that when this particular OCXO > is > > soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious > > overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output > > spectrum just the 10.9 MHz tone (and some noise from the banana > clip-leads > > loop-antenna). So this is a bit of a pain for soft-starting because, > > although the oven eventually comes into regulation, the oscillator is > > running on the wrong frequency. > > > > I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a > > pretty great temperature probe of the crystal (literally). You can see > the > > sinusoidal frequency disturbance of this tone has the same periodicity as > > that of the heater current (~50 s). So I don't know if the heater is > > oscillating at the uK level or mK level, will need to find out the tempCo > > of this crystal mode. Neat to see the oven dynamics. > > > > Hopefully once the oven is settled at temp, I can load switch the OCXO > for > > 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a > 10+ W > > rated supply it starts up on 10 MHz every time. > > <SoftStart2p5W.png><SoftStart300mA.png><Trimble10p9MHz_SpurMode.png>< > TrimbleSpur_Spectrum.png><TrimbleWarmupPower.png>_______ > ________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

Hi It’s a good bet that there is at least one regulator IC inside any modern OCXO. As you slowly ramp the input voltage on a regulator, various odd things may or may not happen. A 1 mv / s ramp on the outside can be “who knows what” at the oscillator level. That said, slow voltage ramps are a really good way to put all sorts of oscillator circuits into really odd modes. Clock oscillators (XO’s) and MCU built in clock circuits very definitely fall into this category. The same sort of “who knows what” problem also gets into the rest of the circuit. A limited supply might work fine nine times out of ten or 99 out of 100. On the odd time out, something goes poof ! Bob > On Apr 12, 2017, at 11:40 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > Bob, Rick, my use of modes vs overtones was loose, you guys are spot on. > > > That's a fun challenge, suppressing a mode 10% higher in frequency. That's > a bit of a fussy LC filter/trap. > > So if I assume the tempCo of the B-mode to be 20 ppm/degC, that would mean > the heater servo has a sustained oscillation of about 250 udegC all day > long. > > Power cycling for 100 ms isn't long enough for the crystal motion to die > out, 200 ms seems to do it, which ~2 MCycles. At which point it runs on the > 10MHz C-Mode as desired. > > I couldn't say who Trimble went with, to me its an ebay special :), but > photo attached anyways. > > When the supply is current or power limited the effective supply slew rate > is something like 1 mV/s, and under these conditions, at least this > particular unit starts up on B-mode every time. > > Running one of these on a USB supply (5V, 500mA = 2.5W) is looking > plausible. > > On Wed, Apr 12, 2017 at 9:30 PM, Bob kb8tq <kb8tq@n1k.org> wrote: > >> Hi >> >> A SC cut crystal has multiple resonance “modes” in can operate on. This is >> in addition to the >> normal set of fundamental, third overtone, fifth overtone and so on. For >> various interesting reasons >> the SC modes are called A, B and C. On a normal 10 MHz crystal, the “main >> mode” is the C mode. The >> A mode is well below this mode both in frequency and amplitude. The B mode >> is more problematic, It is >> 8 to 12% above the C mode in frequency and may be higher in amplitude >> (lower resistance) than the >> desired mode. >> >> The C mode has a “useful” third order temperature characteristic. The B >> mode has a fairly steep linear >> temp co. One of the classic design experiments on a SC based design is to >> force the oscillator onto the >> B mode. This lets you investigate the oven gain while running a >> temperature run. What you have likely >> done is to put the unit onto the B mode. >> >> Oscillators tend to be fractal when switching between modes. Minor startup >> issues can drive the circuit >> one way or the other. Once it gets onto a mode, it may be quite difficult >> to get it off of that mode …. >> >> Bob >> >>> On Apr 12, 2017, at 5:38 PM, Scott Stobbe <scott.j.stobbe@gmail.com> >> wrote: >>> >>> Hello, >>> >>> I wanted to see if I could soft-start a used OCXO (Trimble 34310) during >>> warm-up. By default with an appropriately rated 12 VDC supply, the OCXO >>> starts the heater at about 8 W, and eventually settles down to 2 W for >>> 20-25 degC ambient temperature. Figure Attached. >>> >>> The good news is it does startup with either a current limited or power >>> limited supply. Albeit, for the constant current case the start-up time >> is >>> dramatically longer. Figures Attached. >>> >>> The bad news, but interesting tangent is that when this particular OCXO >> is >>> soft-started, it doesn't oscillate at 10 MHz! It starts up on a spurious >>> overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output >>> spectrum just the 10.9 MHz tone (and some noise from the banana >> clip-leads >>> loop-antenna). So this is a bit of a pain for soft-starting because, >>> although the oven eventually comes into regulation, the oscillator is >>> running on the wrong frequency. >>> >>> I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a >>> pretty great temperature probe of the crystal (literally). You can see >> the >>> sinusoidal frequency disturbance of this tone has the same periodicity as >>> that of the heater current (~50 s). So I don't know if the heater is >>> oscillating at the uK level or mK level, will need to find out the tempCo >>> of this crystal mode. Neat to see the oven dynamics. >>> >>> Hopefully once the oven is settled at temp, I can load switch the OCXO >> for >>> 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a >> 10+ W >>> rated supply it starts up on 10 MHz every time. >>> <SoftStart2p5W.png><SoftStart300mA.png><Trimble10p9MHz_SpurMode.png>< >> TrimbleSpur_Spectrum.png><TrimbleWarmupPower.png>_______ >> ________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > <TrimbleSpur_HeaterOsc.png><OCXO_34310.JPG>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

On 4/13/17 6:17 AM, Bob kb8tq wrote: > Hi > > It’s a good bet that there is at least one regulator IC inside any modern OCXO. > As you slowly ramp the input voltage on a regulator, various odd things may > or may not happen. A 1 mv / s ramp on the outside can be “who knows what” > at the oscillator level. That said, slow voltage ramps are a really good way to put > all sorts of oscillator circuits into really odd modes. Clock oscillators (XO’s) and MCU > built in clock circuits very definitely fall into this category. > > The same sort of “who knows what” problem also gets into the rest of the circuit. > A limited supply might work fine nine times out of ten or 99 out of 100. On the > odd time out, something goes poof ! > > Bob This is a known problem with many FPGAs, particularly those which configure themselves from on or off-board flash memory. They have all sorts of little sequencers internally which are driven by (very non-time-nuts-quality) oscillators. And even some non-flash based anti-fuse parts: https://www.microsemi.com/document-portal/doc_view/130010-ac344-board-level-considerations-for-power-up-and-power-down-of-rtax-s-sl-fpgas

I can't say I have run into that issue with a MCU as most 21st century ones have a decent POR and Brown out detect (which typically burns 10x more current than a 32k XO + RTC, and may get switched off in battery applications, and then problems can occur). What does seem to come up is stuff hanging off non-always on power rails (ADC,DAC,Sensors,etc), leakage and back-feeding onto their dedicated supply has them try to startup on leakage but there isn't enough leakage to actually power the device. They may issue the on die reset once and then the supply collapses all the flops lose their reset state, but the IC dosen't try to reset again. Fortunately, you can buy a bunch of LDOs which include a small discharge FET to help this case as well as others. On Thu, Apr 13, 2017 at 9:17 AM, Bob kb8tq <kb8tq@n1k.org> wrote: > Hi > > It’s a good bet that there is at least one regulator IC inside any modern > OCXO. > As you slowly ramp the input voltage on a regulator, various odd things may > or may not happen. A 1 mv / s ramp on the outside can be “who knows what” > at the oscillator level. That said, slow voltage ramps are a really good > way to put > all sorts of oscillator circuits into really odd modes. Clock oscillators > (XO’s) and MCU > built in clock circuits very definitely fall into this category. > > The same sort of “who knows what” problem also gets into the rest of the > circuit. > A limited supply might work fine nine times out of ten or 99 out of 100. > On the > odd time out, something goes poof ! > > Bob > > > On Apr 12, 2017, at 11:40 PM, Scott Stobbe <scott.j.stobbe@gmail.com> > wrote: > > > > Bob, Rick, my use of modes vs overtones was loose, you guys are spot on. > > > > > > That's a fun challenge, suppressing a mode 10% higher in frequency. > That's > > a bit of a fussy LC filter/trap. > > > > So if I assume the tempCo of the B-mode to be 20 ppm/degC, that would > mean > > the heater servo has a sustained oscillation of about 250 udegC all day > > long. > > > > Power cycling for 100 ms isn't long enough for the crystal motion to die > > out, 200 ms seems to do it, which ~2 MCycles. At which point it runs on > the > > 10MHz C-Mode as desired. > > > > I couldn't say who Trimble went with, to me its an ebay special :), but > > photo attached anyways. > > > > When the supply is current or power limited the effective supply slew > rate > > is something like 1 mV/s, and under these conditions, at least this > > particular unit starts up on B-mode every time. > > > > Running one of these on a USB supply (5V, 500mA = 2.5W) is looking > > plausible. > > > > On Wed, Apr 12, 2017 at 9:30 PM, Bob kb8tq <kb8tq@n1k.org> wrote: > > > >> Hi > >> > >> A SC cut crystal has multiple resonance “modes” in can operate on. This > is > >> in addition to the > >> normal set of fundamental, third overtone, fifth overtone and so on. For > >> various interesting reasons > >> the SC modes are called A, B and C. On a normal 10 MHz crystal, the > “main > >> mode” is the C mode. The > >> A mode is well below this mode both in frequency and amplitude. The B > mode > >> is more problematic, It is > >> 8 to 12% above the C mode in frequency and may be higher in amplitude > >> (lower resistance) than the > >> desired mode. > >> > >> The C mode has a “useful” third order temperature characteristic. The B > >> mode has a fairly steep linear > >> temp co. One of the classic design experiments on a SC based design is > to > >> force the oscillator onto the > >> B mode. This lets you investigate the oven gain while running a > >> temperature run. What you have likely > >> done is to put the unit onto the B mode. > >> > >> Oscillators tend to be fractal when switching between modes. Minor > startup > >> issues can drive the circuit > >> one way or the other. Once it gets onto a mode, it may be quite > difficult > >> to get it off of that mode …. > >> > >> Bob > >> > >>> On Apr 12, 2017, at 5:38 PM, Scott Stobbe <scott.j.stobbe@gmail.com> > >> wrote: > >>> > >>> Hello, > >>> > >>> I wanted to see if I could soft-start a used OCXO (Trimble 34310) > during > >>> warm-up. By default with an appropriately rated 12 VDC supply, the OCXO > >>> starts the heater at about 8 W, and eventually settles down to 2 W for > >>> 20-25 degC ambient temperature. Figure Attached. > >>> > >>> The good news is it does startup with either a current limited or power > >>> limited supply. Albeit, for the constant current case the start-up time > >> is > >>> dramatically longer. Figures Attached. > >>> > >>> The bad news, but interesting tangent is that when this particular OCXO > >> is > >>> soft-started, it doesn't oscillate at 10 MHz! It starts up on a > spurious > >>> overtone at 10.9 MHz. There isn't even a hint of 10 MHz in the output > >>> spectrum just the 10.9 MHz tone (and some noise from the banana > >> clip-leads > >>> loop-antenna). So this is a bit of a pain for soft-starting because, > >>> although the oven eventually comes into regulation, the oscillator is > >>> running on the wrong frequency. > >>> > >>> I'm not sure what the tempCo of the 10.9 MHz crystal mode is, but its a > >>> pretty great temperature probe of the crystal (literally). You can see > >> the > >>> sinusoidal frequency disturbance of this tone has the same periodicity > as > >>> that of the heater current (~50 s). So I don't know if the heater is > >>> oscillating at the uK level or mK level, will need to find out the > tempCo > >>> of this crystal mode. Neat to see the oven dynamics. > >>> > >>> Hopefully once the oven is settled at temp, I can load switch the OCXO > >> for > >>> 10 or 100 ms and get it to startup on the correct 10 MHz mode. With a > >> 10+ W > >>> rated supply it starts up on 10 MHz every time. > >>> <SoftStart2p5W.png><SoftStart300mA.png><Trimble10p9MHz_SpurMode.png>< > >> TrimbleSpur_Spectrum.png><TrimbleWarmupPower.png>_______ > >> ________________________________________ > >>> time-nuts mailing list -- time-nuts@febo.com > >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com > >> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > <TrimbleSpur_HeaterOsc.png><OCXO_34310.JPG>_______________ > ________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

Hi If your MCU has a POR that resets the internal oscillator that’s an unusual part. Most of them I’ve seen simply reset the CPU…..Once the 8 MHz crystal oscillator is running at 37 to 53 MHz (or KHz) it may or may not ever return to 8 MHz on it’s own. Yes, you need to get into some nutty (as in volt per second) rates to see a lot of this kind of thing. It’s not a common thing to run into on a real design and it is even less common to see it tested for. Unfortunately there are a few fields / companies where really slow supply ramps are “the way it’s done”. Needless to say, they have a lot of fun getting stuff to work right. Bob > On Apr 13, 2017, at 1:41 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > I can't say I have run into that issue with a MCU as most 21st century ones > have a decent POR and Brown out detect (which typically burns 10x more > current than a 32k XO + RTC, and may get switched off in battery > applications, and then problems can occur). What does seem to come up is > stuff hanging off non-always on power rails (ADC,DAC,Sensors,etc), leakage > and back-feeding onto their dedicated supply has them try to startup on > leakage but there isn't enough leakage to actually power the device. They > may issue the on die reset once and then the supply collapses all the flops > lose their reset state, but the IC dosen't try to reset again. > > Fortunately, you can buy a bunch of LDOs which include a small discharge > FET to help this case as well as others. >

On Wed, 12 Apr 2017 20:18:38 -0700, you wrote: >On 4/12/17 7:14 PM, Richard (Rick) Karlquist wrote: >> 10.9 MHz is likely the B-mode of the SC cut. >> (It's a different mode, not a different overtone). >> This mode has a tempco of 20 ppm and is used >> to do thermometry. >> >> IMHO, there is NO excuse for the oscillator >> designer to design an oscillator that doesn't >> oscillate unconditionally in the right mode. >> NONE! What was the actual manufacturer of >> the OCXO? (AFAIK, Trimble doesn't make their >> own). >> >> My old boss at Zeta Labs (a really great boss) >> used to walk up to people who were testing >> their latest circuit and momentarily turn >> down the current limit on each of the power >> supplies to see if the circuit recovered >> correctly. It often didn't, and then it >> was back to the drawing board... >> > >These days, a common trap is when you've got a DC/DC converter on the >input - with a soft start, the current goes huge, causing all kinds of >problems. > >(I'm in the middle of closing a failure report on just such a >sensitivity - an unexpected interaction between the source DC/DC >converter and the load DC/DC converter..) Linear regulators with foldback current limiting and sometimes safe operating area protection can do the same thing with unfriendly loads. Safe operating area protection becomes a problem when the input to output voltage difference is large lowering the current limit at low output voltages. A more insidious problem and design mistake has sometimes occurs with thermal protection. If the thermal protection does not have enough hysteresis, then the regulator cannot "hard start" into a heavy load at high temperature and turns itself into a temperature controlled oven.