LMC555: Looking for a spice model to estimate power consumption in real design

Rick Collins

Part Number: LMC555
Other Parts Discussed in Thread: TLC555

I am working on a very low power design and I need to optimize my circuit for power consumption. I have a spice model with LTspice, but it is for a bipolar device with high current draw. I need a model that is fairly accurate on the internal power consumption of the LMC555 timer chip. I see where someone asked about a model some four or five years ago. Any progress since then?

over 5 years ago

0 Ron Michallick over 5 years ago

TI__Guru**** 165376 points

Hello Rick,

Welcome to the e2e forum. There still is no LMC555 model, but there is a TLC555 model. TLC555 is a little higher typical current (on data sheet) than LMC555. The supply current is not modelled well.

The data sheet 'Is' current will be useful. If the operating frequency is higher then the current will be higher.

0 Rick Collins over 5 years ago in reply to Ron Michallick

Prodigy 80 points

Hi Ron,

Thnaks for the reply. I tried downloading the TLC555 model, but it doesn't seem to run. I get this error.

---------------------------
LTspice XVII
---------------------------
WARNING: Can't resolve .param nz=0.3/(vt*log(1+5.0m/isz))

Select OK to continue the simulation with
the default model or Cancel to quit now.
---------------------------
OK Cancel
---------------------------

It is referring to line 320 in the file. Searching the file I see VT used in various places, but not defined anywhere. Is this a bug in the simulation or is VT a predefined quantity that is not available in LTspice?

Rick Collins

0 Ron Michallick over 5 years ago in reply to Rick Collins

TI__Guru**** 165376 points

Rick,

VT is a thermal voltage (25mV at 20C). See this post for the reasoning and solution.

https://e2e.ti.com/support/tools/sim-hw-system-design/f/234/t/640955

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LMC555: Looking for a spice model to estimate power consumption in real design