Finding LTspice Models

On Monday, May 4, 2020 at 7:27:25 PM UTC-4, bitrex wrote:
> On 5/4/2020 12:09 PM, Ricky C wrote:
> > On Monday, May 4, 2020 at 7:25:05 AM UTC-4, piglet wrote:
> >> On 04/05/2020 10:41 am, Ricky C wrote:
> >>> Now I need to find a logic family that works from 4 volts down to under 2 volts and doesn't draw excess current.  I did a quick look at LVC and with 2 volt inputs it's starting to draw excess current.  I'll check the old CD4000 family to see if that will work below 2 volts Vdd.
> >>>
> >>
> >> CD4000 might work that low but be very feeble, think Rdson values in
> >> tens of kilo-ohm.  30+ year old 74HC (not HCT) parts are spec'd for Vdd
> >> 2V and will work much lower (with worsening performance).
> >>
> >> I had 74HC163 counters that retained internal states right down to Vdd
> >> of 50mV (yes - millivolts)
> >>
> >> piglet
> > 
> > I realized the required logic is even simpler than I thought.  Once I made a state diagram I realized one of the two FFs controlling the indicators can actually be removed as the output was essentially the same as an input.  That leaves one FF to control the other indicator which can be muted.
> > 
> > Taking advantage of wire and diode connections allows the transistor based FF to be set and reset on the same net.  Then the mute control drives a transistor which acts as an AND gate combining the mute signal with the alarm signal to drive the indicator.
> > 
> > So as long as the functionality doesn't change, this is a pretty simple solution.
> > 
> 
> To get flip-flops with guaranteed operation down below 2 volts you'll 
> have to use something a little exotic like these Fairchild/ON 
> "TinyLogic" parts with guaranteed down to 1.65:
> 
> <https://www.mouser.com/datasheet/2/308/NC7SZ74-D-1812305.pdf>
> 
> They are very nice high-performance flops though the US8 package is a 
> little tedious to hand-solder to a surfboard for prototyping, use a 
> microscope if you have one and are gonna do that.

Thanks for the info.  "Below 2 volts" is just that I don't want the thing going crazy.  The sounder is rated for 2 to 4 volts, so I am basing my power life on that range, charging the supercap up to 4 volts and running it down as long as it works.  

I actually simplified the logic a bit.  I had been looking at two FFs to control the alarm state as well as the mute for the audio alarm.  But once I tried implementing it I found a number of nice simplifications so the circuit is just one FF (implemented with two transistors and a transistor to act as an AND gate to combine the alarm with the mute signal for the sounder.  The run time with 2.5 F is 20 minutes... just meeting the requirement.  If I want to extend the time I can pulse the alarm by some duty cycle which might make it more apparent.  Then I need something additional to create the pulsing.  A 555 timer seems overkill, but maybe it is perfect kill?  I believe there is a CMOS version that runs at very low currents.  Maybe not all that low.  I'm finding 100 uA at 5 volts.  I'd like to at least find low double digits uA.  

I need to ask more about the alarm requirements, but I think they want me to define them. 

-- 

  Rick C.

  +- Get 1,000 miles of free Supercharging
  +- Tesla referral code - https://ts.la/richard11209

On 5/5/2020 2:14 AM, Ricky C wrote:
> On Monday, May 4, 2020 at 7:27:25 PM UTC-4, bitrex wrote:
>> On 5/4/2020 12:09 PM, Ricky C wrote:
>>> On Monday, May 4, 2020 at 7:25:05 AM UTC-4, piglet wrote:
>>>> On 04/05/2020 10:41 am, Ricky C wrote:
>>>>> Now I need to find a logic family that works from 4 volts down to under 2 volts and doesn't draw excess current.  I did a quick look at LVC and with 2 volt inputs it's starting to draw excess current.  I'll check the old CD4000 family to see if that will work below 2 volts Vdd.
>>>>>
>>>>
>>>> CD4000 might work that low but be very feeble, think Rdson values in
>>>> tens of kilo-ohm.  30+ year old 74HC (not HCT) parts are spec'd for Vdd
>>>> 2V and will work much lower (with worsening performance).
>>>>
>>>> I had 74HC163 counters that retained internal states right down to Vdd
>>>> of 50mV (yes - millivolts)
>>>>
>>>> piglet
>>>
>>> I realized the required logic is even simpler than I thought.  Once I made a state diagram I realized one of the two FFs controlling the indicators can actually be removed as the output was essentially the same as an input.  That leaves one FF to control the other indicator which can be muted.
>>>
>>> Taking advantage of wire and diode connections allows the transistor based FF to be set and reset on the same net.  Then the mute control drives a transistor which acts as an AND gate combining the mute signal with the alarm signal to drive the indicator.
>>>
>>> So as long as the functionality doesn't change, this is a pretty simple solution.
>>>
>>
>> To get flip-flops with guaranteed operation down below 2 volts you'll
>> have to use something a little exotic like these Fairchild/ON
>> "TinyLogic" parts with guaranteed down to 1.65:
>>
>> <https://www.mouser.com/datasheet/2/308/NC7SZ74-D-1812305.pdf>
>>
>> They are very nice high-performance flops though the US8 package is a
>> little tedious to hand-solder to a surfboard for prototyping, use a
>> microscope if you have one and are gonna do that.
> 
> Thanks for the info.  "Below 2 volts" is just that I don't want the thing going crazy.  The sounder is rated for 2 to 4 volts, so I am basing my power life on that range, charging the supercap up to 4 volts and running it down as long as it works.
> 
> I actually simplified the logic a bit.  I had been looking at two FFs to control the alarm state as well as the mute for the audio alarm.  But once I tried implementing it I found a number of nice simplifications so the circuit is just one FF (implemented with two transistors and a transistor to act as an AND gate to combine the alarm with the mute signal for the sounder.  The run time with 2.5 F is 20 minutes... just meeting the requirement.  If I want to extend the time I can pulse the alarm by some duty cycle which might make it more apparent.  Then I need something additional to create the pulsing.  A 555 timer seems overkill, but maybe it is perfect kill?  I believe there is a CMOS version that runs at very low currents.  Maybe not all that low.  I'm finding 100 uA at 5 volts.  I'd like to at least find low double digits uA.
> 
> I need to ask more about the alarm requirements, but I think they want me to define them.
> 

Flops and logic made from discrete BJTs doesn't sound particularly 
low-power to me. There is a CMOS 555 but as you say it's not 
particularly cheap or low-current, me being me I'd think about using the 
low-power ATTiny variant that will run down to 1.8 volts, when it's not 
doing anything it can be put in the deep sleep and draw only nA.

There's a circuit for a one-shot/timer on page 21 of the Lm13700 
datasheet that draws (almost) zero stand-by current and triggers on 2 
volts. The 13700 requires about 3-ish volt supply to operate properly 
but looking at the circuit and the internal schematic of the 13700 I 
suspect it would work OK with a lower supply rail if the output was 
bootstrapped to the positive rail to boost its own supply as the output 
is positive-going.

On Tuesday, May 5, 2020 at 12:43:22 PM UTC-4, bitrex wrote:
> On 5/5/2020 2:14 AM, Ricky C wrote:
> > On Monday, May 4, 2020 at 7:27:25 PM UTC-4, bitrex wrote:
> >> On 5/4/2020 12:09 PM, Ricky C wrote:
> >>> On Monday, May 4, 2020 at 7:25:05 AM UTC-4, piglet wrote:
> >>>> On 04/05/2020 10:41 am, Ricky C wrote:
> >>>>> Now I need to find a logic family that works from 4 volts down to under 2 volts and doesn't draw excess current.  I did a quick look at LVC and with 2 volt inputs it's starting to draw excess current.  I'll check the old CD4000 family to see if that will work below 2 volts Vdd.
> >>>>>
> >>>>
> >>>> CD4000 might work that low but be very feeble, think Rdson values in
> >>>> tens of kilo-ohm.  30+ year old 74HC (not HCT) parts are spec'd for Vdd
> >>>> 2V and will work much lower (with worsening performance).
> >>>>
> >>>> I had 74HC163 counters that retained internal states right down to Vdd
> >>>> of 50mV (yes - millivolts)
> >>>>
> >>>> piglet
> >>>
> >>> I realized the required logic is even simpler than I thought.  Once I made a state diagram I realized one of the two FFs controlling the indicators can actually be removed as the output was essentially the same as an input.  That leaves one FF to control the other indicator which can be muted.
> >>>
> >>> Taking advantage of wire and diode connections allows the transistor based FF to be set and reset on the same net.  Then the mute control drives a transistor which acts as an AND gate combining the mute signal with the alarm signal to drive the indicator.
> >>>
> >>> So as long as the functionality doesn't change, this is a pretty simple solution.
> >>>
> >>
> >> To get flip-flops with guaranteed operation down below 2 volts you'll
> >> have to use something a little exotic like these Fairchild/ON
> >> "TinyLogic" parts with guaranteed down to 1.65:
> >>
> >> <https://www.mouser.com/datasheet/2/308/NC7SZ74-D-1812305.pdf>
> >>
> >> They are very nice high-performance flops though the US8 package is a
> >> little tedious to hand-solder to a surfboard for prototyping, use a
> >> microscope if you have one and are gonna do that.
> > 
> > Thanks for the info.  "Below 2 volts" is just that I don't want the thing going crazy.  The sounder is rated for 2 to 4 volts, so I am basing my power life on that range, charging the supercap up to 4 volts and running it down as long as it works.
> > 
> > I actually simplified the logic a bit.  I had been looking at two FFs to control the alarm state as well as the mute for the audio alarm.  But once I tried implementing it I found a number of nice simplifications so the circuit is just one FF (implemented with two transistors and a transistor to act as an AND gate to combine the alarm with the mute signal for the sounder.  The run time with 2.5 F is 20 minutes... just meeting the requirement.  If I want to extend the time I can pulse the alarm by some duty cycle which might make it more apparent.  Then I need something additional to create the pulsing.  A 555 timer seems overkill, but maybe it is perfect kill?  I believe there is a CMOS version that runs at very low currents.  Maybe not all that low.  I'm finding 100 uA at 5 volts.  I'd like to at least find low double digits uA.
> > 
> > I need to ask more about the alarm requirements, but I think they want me to define them.
> > 
> 
> Flops and logic made from discrete BJTs doesn't sound particularly 
> low-power to me. 

NFETs with 1 Mohm resistors are adequately low power.  I had them on the board anyway so why not use them for a FF?  I like keeping the BOM short. 


> There is a CMOS 555 but as you say it's not 
> particularly cheap or low-current, me being me I'd think about using the 
> low-power ATTiny variant that will run down to 1.8 volts, when it's not 
> doing anything it can be put in the deep sleep and draw only nA.

Yeah, I hate to use an MCU when it's not really required.  So far the circuit has gotten simpler rather than more complex.  Realizing I didn't need a three state FSM was a help.  A two state mute circuit is simpler.  I'm looking at implementing that with a cap, but that requires nA currents and I have little confidence since a fingerprint in the wrong place can cause a failure. 


> There's a circuit for a one-shot/timer on page 21 of the Lm13700 
> datasheet that draws (almost) zero stand-by current and triggers on 2 
> volts. The 13700 requires about 3-ish volt supply to operate properly 
> but looking at the circuit and the internal schematic of the 13700 I 
> suspect it would work OK with a lower supply rail if the output was 
> bootstrapped to the positive rail to boost its own supply as the output 
> is positive-going.

Doesn't look so good to me.  I can kill power to the device entirely since it has to be run from its own regulator.  It's the active current that is important.  Ten or twenty uA is not bad since the  load it is controlling is 3 mA.  I'm thinking it can be pulsed on for a second and off for up to 9 seconds and still be effective, but that's a question that I'll need to get some feedback on.  

I know I am over thinking this design, but I don't really have many requirements.  I think I'm expected to figure them out myself. 

For grins I took a look at FFs and found an 74HCS72 single dual with negative edge trigger which is required unless I add an inverter or use a cap to couple a signal transition to a clear input.  I'm looking at that and it looks pretty good.  The second FF could be used with a pair of resistors, capacitors and diodes to make an oscillator, no?  Every input to the device has a Schmitt trigger so a slow transition won't cause noise!  

-- 

  Rick C.

  ++ Get 1,000 miles of free Supercharging
  ++ Tesla referral code - https://ts.la/richard11209

I've looked into a CMOS FF and it is a nice choice instead of the two NFETs and two resistors.  The NFETs would have worked just fine, but I can get two FFs in a single package and use the other one for something else.  Also it is pretty easy to assure the FF starts in the right state. 

I even rigged up a serviceable emulation of the FF using the LTspice digital library.  I was ready to run the simulation and I got an error that wasn't clear.  Turns out the library I got for the TI regulator is encrypted!!!  WTF!!!  Why does TI have such a hard on to interfere with using LTspice.  I mean really!  TINA has lost the war.  The world is an LTspice domain and that's a natural fact.  

The TI wasn't a perfect fit anyway.  It is only specified down to 2.2 volts and I want the design to work down to 2.  I spent a couple of hours looking but did not find one part at Digikey that matched all my requirements.  I found a couple that were really close.  One had a disturbing overshoot when enabled.  I am using the LDO to prevent the 5 volts on the supercap from damaging the sounder which is rated for 2 to 4 volts.  If it overshoots to 4.6 volts, that defeats the point!  

The device also needs to have very low drop out at low currents, 4 mA and low double digit uA of supply (ground) current when operating.  The main thing though is to maintain the drop out voltage down to 2.0 volts or even lower.  

I found one that did everything perfectly, but it is only available in fixed voltages.  Mouser will order the 4.0 volt part and say you can buy qty 1.  I don't know the lead time and I'm not sure I won't have to buy the reel. 

I'll try again Thursday when I have time to work on this again. 

-- 

  Rick C.

  --- Get 1,000 miles of free Supercharging
  --- Tesla referral code - https://ts.la/richard11209