LTM4668A Multi-Channel Mode


I have the LTM4668A configured in dual-channel mode (1+2+4)/3 as described in Table 4. Configuration of Multi-Channel Parallel Operation. The high-current (3.6A) channel is not providing the expected output power, and I'm having a difficult time understanding why. I've done the following:

  1. Combined all 6 VIN pins for channels 1,2,4
  2. Combined all 6 VOUT pins for channels 1,2,4
  3. Combined all 3 RUN pins for channels 1,2,4 and set to VIN
  4. Added a feedback resistor (13.3K for 3.3V) for channel 1
  5. Set the feedback pins for channels 2 & 4 to INTVCC
  6. MODE/SYNC pin is grounded for Pulse Skipping Mode
  7. Combined all PGOOD pins for channels 1,2,4

I just realized #7 is not correct since the datasheet specifies PGOOD should only be used by the master (or channel 1). This would explain why PGOOD never asserts, but I'm curious if this has other consequences. I'm observing a voltage drop around 1.3A, which makes me think channels 2 & 4 are not operational. I should also mention that channel 3 is working as expected, and I also have a second part that's configured in quad-channel mode, which is also working.

Any other ideas would be appreciated. Thanks!