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What precision of the OSC in LT8390?

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tony_lth

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Hi, ALL,
I designed a RF module pwoered by LT8390.
It has a internal OSC, which decided by a external RT pin resistor.
the follwoing picture is the RT resistor vs. switching freq.
So,
1. Could any one estimate the switching freq pricision? I guess it is a RC OSC, right?
2. What freq precision difference between the different date/patch produced LT8390 with the same RT resistor?
3. What freq precision difference between 200K and 180K RT resistors?
Many thanks.
Best,
Tony Liu
 

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I would not rely on the internal oscillator of a switched mode power supply IC for any degree of precision, they are not designed for it.
Look at page 5 of the data sheet under Oscillator for some indication of frequency accuracy, 400kHz +/-20kHz for a 100k resistor.
If you need the switching frequency to be stable, synchronise it with a known external source.
 
I want to use 180K and 200K resistors for two LT8390 ICs in the same module.
I hope that the two switching freqs are not overlap by 180K and 200K.
But I am not sure about it. That is what I worry about.

- - - Updated - - -

From the table, for 180K, estimated switching freq1 is 250K, with 5% tolerance, i.e. 237K-263K.
For 200K, switching freq2 is 225K, with 5% tolerance, i.e. 212K-238K.
So the swicthing freqs may overlap.
 

Clear specification, +/- 5% accuracy. If that's not sufficient, sync with external reference.

- - - Updated - - -

Clear specification, +/- 5% accuracy. If that's not sufficient, sync with external reference.

So the swicthing freqs may overlap.
Yes. Typically you can expect better accuracy, but you can't rely on it.
 
Hi,

I want to use 180K and 200K resistors for two LT8390 ICs in the same module.
I hope that the two switching freqs are not overlap by 180K and 200K.

Call me pessimistic, but I´d say there is a good chance that both oscillators lock.


Klaus
 

Oscillator frequency can be synchronized by an external oscillator so multiple IC can be fed from a single source.Page 18
 

Oscillator frequency can be synchronized by an external oscillator so multiple IC can be fed from a single source.Page 18
But if multiple ICs be fed from a single source, the switching freqs should be same, that can increase the risk for spurs or desense, right?
 

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