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TMUX1204: DCDC Power Supply with TMUX1204 MUX for Feedback Switching - Output Stuck at 2V

Shah Zaman
Prodigy 90 points
Part Number: TMUX1204

Tool/software:

I’m designing a variable-output DCDC supply using an XL4016 (FB reference = 1.25V) and a TMUX1204 multiplexer to switch between three operating modes. The MUX is controlled by an MCU via EN, A0, and A1 pins, but the output remains fixed at 2V regardless of the control logic. Replacing the TMUX1204 did not resolve the issue.

Setup:

  1. Feedback Configuration:

    • Mode 1 (2V Output): Feedback divider output FB_2V → TMUX1204 pin S1.
    • Mode 2 (6V Output): Feedback divider output FB_6V → TMUX1204 pin S3.
    • Mode 3 (CC/CV): Feedback signal CC/CV_FB → TMUX1204 pin S2.
    • TMUX1204 output D connects to the FB pin of the XL4016.
  2. The selection logic is:
  • When EN=1 and A0=0, A1=0: D connects to S1 (2V mode)
  • When EN=1 and A0=1, A1=0: D connects to S2 (CC/CV mode)
  • When EN=1 and A0=0, A1=1: D connects to S3 (6V mode)

However, I am encountering an issue: the output is always 2V, no matter what values I set for A0 and A1. Even when I set the MUX to select S3 (for 6V) by setting A0=0 and A1=1, the output remains 2V. Similarly, when I set the MUX to S2 (for CC/CV mode), the output remains 2V.Moreover, I observed that when I set EN=0 (disabling the MUX), the voltage at the D pin (FB input of the XL4016) is 1.25V and the output remains 2V. I have replaced the TMUX1204 but the problem persists.