New 555 Spice Model

"Jim Thompson" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

Hello Jim,

Thanks a lot for this model.

I have made an example with your model and uploaded it to the Yahoo group.

Files > Lib > CMOS Timers TLC555, TLC556, LMC555 > Example LMC555

Best regards, Helmut

Thanks, Helmut!

Let me know of any complaints! ...Jim Thompson

"Jim Thompson" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

Hello Jim,

I have to use ".ic V(timing_cap)=0" to get the simulation quickly started.

Best regards, Helmut

Same here. Otherwise the latch doesn't know "high" from "low" ;-)

Or just RESETbar to initialize. ...Jim Thompson

Hi Jim,

Thanks for taking the time to create this model. I was doing some experimenting with it and comparing it to the standard bipolar 555 model, and noticed that the CMOS model seems to have significantly greater shoot-through current than the bipolar model. I haven't used a CMOS 555 or measured those currents "in real life", so I'm curious if that is a real difference, or perhaps the bipolar 555 models don't model it effectively?

Can't say about this specific family, but we had a HORRIBLE experience last year with a recent 5 V single-gate part, in the 74LVC1G family. We had a pair of analog comparators and a gate and FF from this family in each channel of a circuit, packing 32 channels per 6-layer board. We tried all SORTS of schemes to isolate the triggering of one channel from others. Eventually, I thought to try measuring the shoot-through pulses of the parts. I measured them as a complete channel, so it was one gate PLUS one FF. I was able to estimate the shoot-through current at 2 A for about 2 ns! Yikes, 2 AMPS!!! No WONDER it was crapping up the analog section.

So, I started scanning data sheets for low equivalent switching capacitance, and found some 3.3 V parts that showed much lower equiv capacitance. That was the 74AUP1G family. I had to use 3 parts to get the gating configuration I needed, and re-design the whole board to run off 3.3 V instead of 5 V, but in the end it was a much cleaner board, as well as fixing the inter-channel interference problem. These chips are so quiet I can't really measure the shoot-through pulse. With the others, I observed a substantial Voltage dip in the local decoupling caps.

I kind of think the 74LVC1G parts had some really crummy design, and made no effort whatsoever to control the turn-on and turn-off times of the output stage transistors, just had one driver stage feeding both P- and N-channel devices. My guess is that the 74AUP1G parts have separate drivers for the P- and N-channel output transistors and have some R-C tweaking via sizing the drivers so that they can tune the turn-on and turn-off precisely to get rid of shoot-through.

I was astounded at 2 A shoot-throughs, and can imagine this could bite even a purely digital design, even if only in the EMI compliance area. Man, a 2 A pulse at some clock frequency could really turn into a major transmitter!

Jon

I sized my CMOS devices based on source and sink current of the output at VCC=+5V for the _LMC555_ chip... Intersil datasheet was used only for structural ideas.

I simulate 7-8mA "shoot-thru" depending on direction of transition. Which, for CMOS with considerable source sink capability, seems pretty normal to me. Width at the 50% point of overlap current is 8.5ns, TF/TR at output ~ 7.3ns

What does "...significantly greater shoot-through current than the bipolar model" mean? ...Jim Thompson

Sorry for the delay in my reply, I didn't realize the thread was still active. Here's what I get using LTSpice with the test circuit:

The pulses appear to be about 100 ns wide. It probably is really better than the bipolar 555, because looking at the graph on the Maxim datasheet I don't believe the bipolar 555 model included with LTSpice is modeling the supply spikes accurately.

My mistake, I think the pulses are shorter than that. It's a little tricky measuring them in LTSpice.

On Thu, 24 Mar 2011 12:33:07 -0400, Bitrex wrote:

. . .

--- Here's the circuit I'm using to test Linear's NE555 model:

Version 4 SHEET 1 880 748 WIRE 224 192 -128 192 WIRE 544 192 448 192 WIRE -128 256 -128 192 WIRE -80 256 -128 256 WIRE 32 256 0 256 WIRE 64 256 32 256 WIRE 224 256 144 256 WIRE 512 256 448 256 WIRE 32 320 32 256 WIRE 176 320 32 320 WIRE 224 320 176 320 WIRE 608 320 448 320 WIRE 480 384 448 384 WIRE 608 416 608 320 WIRE 176 480 176 320 WIRE 512 480 512 256 WIRE 512 480 176 480 WIRE 544 496 544 192 WIRE -128 512 -128 256 WIRE 480 512 480 384 WIRE 480 512 -128 512 WIRE -128 528 -128 512 WIRE 176 544 176 480 WIRE -128 624 -128 608 WIRE 176 624 176 608 WIRE 176 624 -128 624 WIRE 544 624 544 576 WIRE 544 624 176 624 WIRE 608 624 608 496 WIRE 608 624 544 624 WIRE -128 688 -128 624 FLAG -128 688 0 SYMBOL Misc\\NE555 336 288 M0 SYMATTR InstName U1 SYMBOL voltage -128 512 M0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL res -96 240 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 58 VTop 0 SYMATTR InstName R1 SYMATTR Value 40k SYMBOL res 48 240 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 19.8k SYMBOL res 624 400 M0 WINDOW 0 -45 40 Left 0 WINDOW 3 -59 71 Left 0 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL cap 192 544 M0 WINDOW 0 -33 32 Left 0 WINDOW 3 -39 58 Left 0 SYMATTR InstName C1 SYMATTR Value 1e-7 SYMBOL res 528 480 R0 SYMATTR InstName R4 SYMATTR Value 1 TEXT 88 656 Right 0 !.tran .1 startup uic TEXT 456 176 Left 0 ;1 TEXT 456 240 Left 0 ;2 TEXT 456 304 Left 0 ;3 TEXT 456 360 Left 0 ;4 TEXT 200 368 Left 0 ;5 TEXT 200 304 Left 0 ;6 TEXT 200 240 Left 0 ;7 TEXT 200 176 Left 0 ;8

I've just posted a query to:

for clarification re. the accuracy of the model, and I'll post what comes back as soon as I get it.

Maybe Helmut will post here first.

-- JF

The NE555 model in LTspice is virtually all behavioral modeling. Just a quick observation of the switches (6 Ohms) suggest a whopping spike ;-) ...Jim Thompson

"John Fields" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

Hello John,

The NE555 in the Misc-folder of LTspice may be just a gift from Mike. I guess he made it because so many people asked for a 555. LTC doesn't have a 555. So we can't expect that Mike spends time to tweak the model for shoot-through current.

I tried a little bit with a capacitive load. Adding 100pF to the output has given a significant current peak in the power supply (V-source). Maybe this is a reasonable workaround if somebody wants it more realistic..

Best regards, Helmut