Unused IMON Pins on the LPTM21L / L-ASC10: Ground or Float?
Question: When the IMON (current monitor) feature is not used, should the IMONP and IMONN pins be tied to ground or left floating?
The hardware checklist specifies handling for unused VMON pins but not for IMON pins.
Answer: Leave unused IMON pins floating (unconnected). Do not tie them to ground, VCC, or a resistor.
Why this is safe:
The LPTM21L evaluation board reference design shows both IMONP and IMONN unconnected — this is the intended configuration when the feature is unused.Neither the datasheet nor the hardware checklist requires these pins to be pulled down or grounded.
IMON pins are high-impedance, input-only current-sense inputs. They passively monitor current and do not drive internal logic, so a floating state does not cause instability or unpredictable operation the way an undriven enable/shutdown pin would.
Note on VMON vs. IMON: The checklist calls out VMON because pin-handling requirements differ by function. The absence of an IMON instruction is not an oversight in intent — floating is the correct state for unused IMON pins.
Design guidance:
- Do not connect IMONP/IMONN to GND, VCC, or any external resistor unless a specific application requires it.
- Do not add pull-up or pull-down resistors.
- Leave the pins unconnected on the PCB, matching the evaluation board.
- Keep the layout clear of unintended traces or connections near these pins.
In summary:
For the LPTM21L / L-ASC10, unused IMON pins should be left floating. Grounding, biasing, or adding resistors is unnecessary and not required by the datasheet or hardware checklist — the evaluation board reference design confirms floating as the intended configuration. Designers can leave these pins unconnected with confidence, simplifying layout and reducing component count.
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