1. Record the Missing-Supply Situation
A switch can be unselected while its supply remains present, or it can have no supply while another part of the circuit still presents a signal. These situations ask different questions. Establish which one the application requires before comparing devices. A normal routing description explains a selected connection; it does not automatically describe the same signal terminals after the switch supply disappears.
Describe the signal-producing side and the circuit that receives the switched signal. Then identify which supply is absent in the proposed situation. This distinguishes a signal that remains present at an unpowered switch from a circuit in which everything has shut down. The requirement should concern the actual signal path and its power context, rather than an informal instruction to keep the switch off.
Keep this question separate from reverse-current protection in a power load switch. Both discussions can mention an absent supply or unwanted powering, but the functions being selected differ. Here the object of review is the analog signal path through a signal switch. A description of protection between a load switch's power input and output does not establish the behavior of those analog connections.
2. Read the Named Powered-Off Scope
TI's TMUX1574 product description identifies powered-off protection on the signal path and states that it provides isolation when the supply voltage is removed. The same description places a boundary on the signals covered. Preserve both parts of that statement. The feature is useful evidence for the named device and documented situation, rather than permission to leave the remaining signal conditions unspecified.
Compare the application's required signal conditions with the exact candidate's powered-off description. The relevant question is whether the documented protection addresses the signal that can remain present while that candidate lacks supply. Keeping the requirement in this form prevents a general protection headline from being treated as an unlimited input rating or as evidence for a different member of a switch family.
Use the manufacturer's original functional terminology when discussing a candidate. Isolation in this signal-path description should not be promoted into a galvanic barrier specification. It also supplies no measured result for the customer's board. If the application needs additional leakage, loading or transition evidence, identify the exact requirement for further review instead of interpreting the word isolation as a complete answer to those separate questions.
3. Keep Logic Fail-Safe and Routing Separate
The TMUX1574 description separately explains fail-safe logic on its control inputs, allowing control voltages to be applied before the supply pin. That is a control-side statement. Powered-off protection concerns the signal path when supply is removed. A sourcing comparison should retain the distinction even when both features appear together in the product summary, because the circuit may require one behavior without having established the other.
Ask which connection the requirement addresses whenever a supplier uses a phrase such as safe when unpowered. Is the concern a driven logic control input, a signal arriving at a switched terminal, or the route selected during normal powered operation? Assign the supporting manufacturer statement to that connection and state. This makes the comparison specific without interpreting a physical pin diagram or prescribing a power sequence.
Ordinary route selection remains relevant when the device is powered, but it answers another part of the switch requirement. Retain the required connections separately from the missing-supply condition. Neither a familiar switching category nor the expected control interpretation demonstrates powered-off protection. Conversely, the presence of powered-off protection does not establish every routing, control or operating requirement of a proposed replacement.
4. Preserve Candidate State Gaps
A focused engineering comparison can distinguish the intended powered route, the signal that may remain at the device without supply, and any control input that may already be driven. These are separate functional requirements, rather than repeated versions of one off-state checkbox. Attach the exact candidate's supporting descriptions to the relevant requirement so that a reviewer can see which function each statement actually addresses.
Keep supply removal and the transitions around it distinguishable. A statement describing a documented missing-supply condition does not, by itself, establish the complete behavior throughout shutdown or restoration. Where that matters to the circuit, request the applicable exact-device evidence. The comparison should preserve that additional decision without turning a product summary into a timing recommendation, connection procedure or completed assessment of the customer's sequence.
The resulting sourcing requirement should identify the required signal-path protection and its documented operating scope, while retaining control-side and ordinary-routing decisions separately. A candidate with an unresolved condition can still be identified for review, with that exception visible. Approval of its use belongs with the circuit requirement; a familiar package or protection label cannot settle an absent-supply question that the available evidence does not cover.
Sources and further reading
TI's product-description core supports the distinction between powered-off signal-path protection and control-input fail-safe logic. No full-datasheet review, physical pin interpretation, board result or current availability is claimed.