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LT3579 ±V topology and sync

Hello ADI/Linear folk!

We are planning to use the LT3579 x2 in a design that needs the following specs:

- Input voltage: Li-ion battery, 3.1V - 4.2V, but willing to consider ~3.4V - 4.2V.
- Output voltage ±12V
- output current per rail: 600mA
- output disconnect

Presently, our prototyped topology only regulates +rail using the config very similar to the 1MHz, 5V to ±12V Converter shown on page 36 of the LT3579 datasheet.  The optional feedback resistor between the + and - rails consumes too much power and is is not favorable to battery life.

It would be advantageous to have both rails regulated.   Since our power requirements push us to use qty 2 LT3579, it therefore seems prudent to switch topology and use the topology similar to the one mentioned in Figure 4 here:

Can our aforementioned specs instead be achieved with 2x LT3579 or 2x LT3579-1?  In this context, would the -1 model be better for sync'ing 2 LT2579s and to keep EMI low?

Also, the feedback resistor in Figure 4 of the above link appears to be a typo - it is on the wrong side of the inductor, when compared to inverting converter shown on page 34 of the 3579 datasheet.  Which one is correct?  I assume the latter.

Thanks in advance for your reply!

Kind Regards,

David McRell

  • Hi David,

    The application showed on Figure 4 of the article can be achieved by using either two LT3579s or two LT3579-1s. It is stated in the article that LT3579-1 was used since it features low input ripple so you might prefer that. 

    You are also correct that the feedback resistor is connected on the wrong side of the inductor in the article. The connection on page 34 of the datasheet is correct.