Wondering if the sync on the lt1054 is really working as intended

[Polymer]

I've got an oscilloscope now, so can poke around and see what is going on.
The interpretation of what I am seeing - well - a lot to learn there ...
Looking to cut down on noise.

I thought that synchronising the inverter chip meant that it is switched off
at the moments when the decay signal is being evaluated.

Are my thoughts way off or is this synchronisation some kind of MD voodoo I can't
get my head around?

The datasheet suggests something very different, sorta like on the MPP as far as I can see,
but not quite.

Anyway, I measured PIN 7 Osc, 2 and 4 on the LT1054 in relationship to Pin 6 of the 5534.

Here's a 4 pic overlay of the four signals:



Any thoughts about this? Thanks.

[Davor]

Thanks for the pic, I was wondering the same. Considering its price it does terrible job.

[waltr]

The scope trace of pin 7 doesn't look correct.
This should pulse with the Coil Pulse. Possibly R25 value is too large.

I have been using the 7660A and it runs at the Coil TX rate. The LT1054 should do the same.
This makes the DC-DC frequency the same as the TX pulse rate and that is what keeps the DC-DC switching noise out of the RX.

Try reducing R25 from 2.2Meg to 100k or even 10k.

[Qiaozhi]

The internal oscillator of the LT1054 runs at 25kHz, which is much higher than the TX pulse rate. If you try to use the TX oscillator as the external clock for the LT1054, it will fail to work properly. To get around this problem, both the MPP and Baracuda allow the voltage converter to operate with its internal oscillator, but use the TX oscillator to pause the converter during the TX-on pulse. In this way the two oscillators will be "sort of" synchronized. i.e. the relationship between the two oscillators will be consistently the same during each TX period. This is a better solution than allowing the voltage converter to free-run, such that the two oscillators are asynchronous.

The idea isn't to "keep the DC-DC switching noise out of the RX", but to simply keep the DC-DC switching noise consistent from one cycle to the next.

[kt315]

set C21 to 4700pF, then 0.47uF and give the pics.

[waltr]

The idea isn't to "keep the DC-DC switching noise out of the RX", but to simply keep the DC-DC switching noise consistent from one cycle to the next.

Qiaozhi
Thanks for the explanation of how the LT1054 works with a PI MD.
Of course this explanation makes sense and what the scope traces Polymer posted do.

[Polymer]

The internal oscillator of the LT1054 runs at 25kHz, which is much higher than the TX pulse rate. If you try to use the TX oscillator as the external clock for the LT1054, it will fail to work properly. To get around this problem, both the MPP and Baracuda allow the voltage converter to operate with its internal oscillator, but use the TX oscillator to pause the converter during the TX-on pulse. In this way the two oscillators will be "sort of" synchronized. i.e. the relationship between the two oscillators will be consistently the same during each TX period. This is a better solution than allowing the voltage converter to free-run, such that the two oscillators are asynchronous.

The idea isn't to "keep the DC-DC switching noise out of the RX", but to simply keep the DC-DC switching noise consistent from one cycle to the next.

George, Thank you so much for the straightforward explanation!

Is there any way to do it better ... rather than trying to re-invent the wheel.
What I mean is there any tried and tested way to at least have the 1054 switched off
when "measuring" the main decay (would that make sense?)

[Polymer]

set C21 to 4700pF, then 0.47uF and give the pics.

C21 is already set to 0.47uF. You have no oscilloscope What would be the lesson here?

[kt315]

on original board C21 is 4700pF.

[Andi68]

4700pF= 4,7nF

[kt315]

4700pF= 4,7nF

DO YOU NEED THE PIC GUY????

[Andi68]

I know this pic with the Wima

[Andi68]

The good old Wima- C10=4,7nF

[Qiaozhi]

The original Anchor Baracuda used 0.47uF (470nF), which is the same for ApBerg's version, and the Geotech Baracuda.
I don't know where the value of 4700pF comes from?

[Qiaozhi]

George, Thank you so much for the straightforward explanation!

Is there any way to do it better ... rather than trying to re-invent the wheel.
What I mean is there any tried and tested way to at least have the 1054 switched off
when "measuring" the main decay (would that make sense?)

To be honest, I cannot detect any difference between having the boost converter free-running and having it synchronized. So blanking during the main sample (and presumably also during the EFE sample) would gain very little, if anything.