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LM25149-Q1EVM-2100: LM25149-Q1

Part Number: LM25149-Q1EVM-2100
Other Parts Discussed in Thread: LM25149-Q1

Hi Team,

1. Do you have a reference schematic with dual-phase operation?

2. How to build a dual-phase board by modifying 2 LM25149-Q1 EVMs?

Thanks,

Lisheng

  • Hi Sheng

    Sorry there is no reference schematic with dual-phase for now.

    To build dual-phase board using EVMs, you should try following steps:

    Remove Primary PG pullup resistor R12;

    Unpower Secondary AEF (Remove C1 and C3);

    Change Primary RCNFG to 54.9kΩ or 71.5kΩ. Change secondary RCNFG to 90.9kΩ (see Table 8-4 in datasheet)

    Tie COMP together;

    Tie VOUT together;

    Tie Primary PG to Secondary PFM/SYNC;

    Hope that can help.

    Best regards.

  • And the final version of datasheet will be updated and will contain the reference circuit.

  • Hi Gui,

    Thank you for your response. 

    1. Per the current datasheet, seems like we need to use the voltage divider (R20&R22) on the Primary board only,  and remove the R20& R22 from the Secondary board. Also, on the Secondary board, we need to tie the FB Pin to VDDA Pin.  Could you help confirm this?

    2. Since the EXTCOMPs are tied together, can we use only 1 set of loop compensator?  For example, can we keep the R18, C35 and C37 of the Primary board only, and delete the R18, C35 and C37 of the Secondary Board?

    3. Should we tie the 2 VINs together for the dual-phase operation?  

    4. Based on the datasheet, R20 is recommended at around 100k. Can we reduce R20, for example around 5k, and change R22 accordingly?  Is there any concerns? 

    Lisheng

  • Hi Lisheng,

    1. Yes, use the FB voltage divider on the primary to set the output voltage, remove the divider of the secondary.

    The FB of the secondary will control PFM or FPWM for the secondary. The secondary FB should match the primary PFM pin setting, tie FB2 to either VDDA2 or GND.

    2. Yes only use one loop compensation network. You can remove R18 and C37 from the secondary. You may want to a small value on C35 for noise filtering.

    3. Yes use the same VIN for both boards.

    4. Smaller FB resistors on the divider should be fine, however it will increase VOUT IQ.

    Hope this helps,

    -Orlando

  • Hi Orlando, Gui,

    Appreciate your help!

    Thanks,

    Lisheng