LTM4622 Negative Output

Is it possible for LTM4622 to generate negative output? Just like the one described in LTM8025 or LTM8065 datasheets (attached)?

Thank you.

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  • Hi wtedjo, 

    Yes, the LTM4622 can also be used for negative output (inverting buck-boost) configuration. This is a dual part so both outputs will be negative (or you can float the other output if not needed). You can also refer to the LTM4625 demo board DC2721A-B for inverting configuration reference. 

    http://www.analog.com/media/en/technical-documentation/eval-board-schematic/DC2721A(A,B)-2-SCH.PDF

    Thanks. 

  • I just want to double check.

    In LTM4622, assuming the Rfb is set such that Vout1 = 3.0V and Vout2 = 2.0V in normal mode. Then, in negative configuration, Vout1 is connected to GND. The ground pin is now -3.0V and Vout2 is (-3.0V + 2.0V) = -1.0V. Therefore, I would have -1.0V and -3.0V outputs. Is that the correct assumption and would work for this specific model?

    Thanks.

  • Hi wtedjo, 

    Sorry for any confusion, I should have clarified that if using both outputs in neg. configuration that would normally be for the case that the output rails are being paralleled (ie for higher current capability).

    In the case of using both rails otherwise for this, the part cannot provide two different negative output voltages since the GND pins for channel 1 and channel 2 are internally tied. If one would try to generate two different negative outputs (ie ground Vout1 & Vout2) they would find the outputs would fight to try to regulate to their programmed output voltage.

    In your case where you only ground one of the outputs (ie Vout1) then you are correct Vout1 will regulate the correct output voltage, and Vout2 would regulate at programmed Vout1 + programmed Vout2. As you noted Vout2 voltage with respect to system ground is dependent on Vout1 voltage, so excursions on Vout1 voltage (ie load transient, start-up) will also show up on Vout2. 

    Thanks.