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DC2844A/ LTM4680 two phase load current sharing

Hi,

I am testing LTM4680 demo board DC2844A in a interleaved two phase buck operation, but I noticed significant current imbalance according to the telmetry reading. Here is what I did:

1. I followed the schematic instruction to short some signals. 

2. I changed both VOUT_COMMAND to 1.8V.  

But it does not ensure currenet sharing (at no load, I can see one phase curent is negative! ) . I want to know what else do I need to do to ensure current sharing.

  • Could you give a specific number about the current imbalance between those 2 phases? According to the test data I have, the current difference between 2-phase is about 2~3A. So at no load condition, one phase current could be negative. That is possible, as long as the sum of 2 phases' current is about 0.

    For 2-phase single output operation, we have to make sure the VOUT_COMMAND of each phase is the same. 

    (1) Update the NVM to make it configured as single output

    (2) Meanwhile, remove the following resistors: R93, R3, R28, R29, R30 and R31. Just leave them open.

  • Thanks for replying! I see about 2-3A on the demo board. However on the board I designed with four phase (2 modules), I see one module with 500mA and one modue with 2A (is it because of inductor tolerance?) . Is this module peak current or average current controlled? 2-3A imbalance can affect light load efficiency a lot. Is there a fix to this? 

  • For LTM4680, it is a peak current mode controlled module. As you mentioned, there is a part to part variation. Some parts can achieve very good current balance, and some parts have 2~3A current difference. DCR sensing is used inside the module. The DCR value varies from part to part as well. The variation of DCR value is a major contribution to the imbalance of 2-phase current. There is no fix to this 2~3A  current imbalance so far.