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LM70880-Q1: In case of Dual Output - How can I connect 2 devices?

Chase Jeong
Mastermind 7485 points
Part Number: LM70880-Q1

Tool/software:

Dear TI experts,

My customer wants to use 2 LM70880-Q1 in one PCB.

And they want to connect these 2 LM70880-Q1 because of the performance of EMC,EMI, etc.

I checked the datasheet but there are only the example of single output/dual phase operation in PFM/FPWM mode, not for dual output.

Is there any reference or application notes for dual output so I can refer the routing of SYNCOUT and SYNCIN pin?

Please check this issue. Thanks.

  • 0
    TI__Genius 11405 points

    Hi Chase,

    I am a bit confused on the application here - by dual output - do you mean that the two converters are connected in parallel? (The outputs of the two are shorted so that there is better current sharing between the two).

    Any reason why the customer doesn't want to do the interleaved operation of the device? 

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    Mastermind 7485 points

    Dear Taru,

    Thank you for your support.

    My customer wants to use 2 LM70880-Q1 separately, they just worried about bad EMC performance if they use 2 LM70880-Q1 in one PCB.

    So they expected that if they connect 2 ICs by SYNCIN and SYNCOUT pin then they expect better EMC performance.

    But Still I am not sure that it would be work or not.

    So please just let me clear - Is this effective way to connect 2 ICs for better EMC performance?

    or Do you have better way for my customer?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Genius 11405 points

    Hi Chase, 

    I think it is a good idea to do a SYNC IN and SYNCOUT for both designs. 

    The customer needs to ensure that the passives they choose are in accordance to the fsw of the design. The constraint here would be that both the LM70880-Q1 will have to work at the same fsw for this to work. Also, the compensation of the two designs needs to be different (if using external compensation). 

    Other than this, standard recommendations for good EMC performance applies - like proper layout, input EMI filter, etc. Customer can refer to www.ti.com/.../slyy208.pdf

    Thanks,

    Best Regards,

    Taru

  • 0 in reply to Taru Kapoor
    Mastermind 7485 points

    Dear Taru,

    Thank you for your support.

    I understand that I should not just connect 2 devices, and have to add some passive components like R,L,C.

    Do you have any example schematic tor the use of my customer? It would be better to assume 2.2MHz fsw.

    Please check this issue. Thanks.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Genius 11405 points

    Hi Chase, 

    I don't have any example schematic - but the implementation should be fairly straightforward - design your two converters separately and then finally connect the SYNCOUT and SYNCIN between the two. What you are basically getting is a Clock signal (180 degrees out of phase). This clock signal can then be used to synchronize the other buck converter. 

    The customer can refer to this app note to understand sync operation between two buck converter with different rails. https://www.ti.com/lit/an/slvaeg8/slvaeg8.pdf

    Finally, you can also share the schematic, once done, with us and we can review and get back to you.

    Thanks,

    Best Regards,

    Taru