TINA/Spice/TLV2372: Schmitt Trigger Oscillator

Mike Jung

Intellectual 700 points

Part Number: TLV2372
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Dear all.

I have any question for schmitt trigger oscillator using TLV2372.

non-inverting input is 82kohm & 820kohm, inverting input is 20k & 200nF and Vcc is 5V.

Tina simulation is good ocillation but of the actual boards, 15 out of 50 units do not work.

it work when 10V & 4Mohm are connected at 820kohm to insert divider voltage to non inverting input.

when this point is added, simulation doesn't work.

my question are below

1) is it possible to use resistance to solve this problem?

2) what is the fundamental problem?

3) Can a oscillation waveform change depending on temperature?

Thanks

over 8 years ago

0 Ron Michallick over 8 years ago

TI__Guru**** 164846 points

Mike,

For this type of oscillator, the non-inverting input voltage for both output VOL and VOH sets the two thresholds for the RC capacitor voltage delay on inverting input. If I read your text correctly, the upper threshold is 455mV and the lower threshold is 0mV.

If this is true, the samples of one polarity Vos (input offset error) will toggle before 0mV and samples with the other polarity of Vos will need a small negative voltage at inverting input (up to -5mV) to toggle output.

Therefore the lower threshold (at non-inverting input) has to be at least +5mV

3) I would expect that capacitance change with temperature would be the biggest factor.

0 Mike Jung over 8 years ago in reply to Ron Michallick

Intellectual 700 points

Thanks your reply.

I don't understand perfectly, lower threshold has to be at least +5mV.
In other word, should we make 5mV instead of 455mV ?

Thanks.