Identify an unknown SMD part: marking code “18A”

Packages rarely print the full part number. The marking below is shared by several part numbers — use the package, pin count and the manufacturer family together to narrow it down, then confirm against the datasheet.

15 candidates 7 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
1.5SMC18A	ON	DO-214AB	Public marking directory
18C	MCC	SMAJP4KE20A	Public marking directory
CMPZ5221B	CSC CENTRAL SEMIC.CORP.	SOT-23	Public marking directory
MMBZ5221B	DIODES	SOT-23 16dc - 3a,3c F,Mot	Public marking directory
MMQA18V	ON *	SC-74	Public marking directory
P4SMA18A	LITTELFUSE	DO-214AC	Public marking directory
P6SMBJ18A	LITTLE	DO-214AA	Public marking directory
AAT60018A-S15	—	SOT-143	Public marking directory
AAT60018A-S16	—	SOT-89	Public marking directory
AAT60018A-S2	—	SOT-23 16vdb VD6 3d Aat	Public marking directory
GLZ18A	—	SOD-80	Public marking directory
HMBZ5221B	—	SOT-23 16dc - 3a Hsn	Public marking directory
TK74018L	—	SOT-23L-8	Public marking directory
XC6102B441MR	—	SOT-23-5	Public marking directory
ZD5221BN3	—	SOT-23	Public marking directory

How we narrow this down

1. Package first — SOT-23 vs SOD-123 vs SC-59 eliminates most candidates immediately.
2. Pin count and body size — a 3-pin SOT-23 LDO cannot be a 6-pin dual transistor.
3. Marking style — laser-marked parts are usually newer production; ink marking often indicates older or second-source vendors.
4. Circuits around it — a part sitting on a rail with an inductor is a regulator, not a diode.
5. Datasheet check — every credible candidate lists its marking scheme in the “marking information” section.

FAQ

• Same code, several parts — which one do I actually have? Compare package + pin count + surrounding circuit; if it still fits two parts, request a sample verification before production.
• Can I substitute between the candidates? No — the same marking may sit on electrically different parts. Always match the electrical spec sheet, not just the marking.
• Where do these mappings come from? Public SMD marking directories and historical stock tables; each row keeps its source so you can trace it.

Other codes starting with “1”

How these mappings are compiled: public SMD marking directories plus our own stock records. Each row keeps its original reference internally, so any mapping can be traced on request. ^* Manufacturer derived from the part-number family (some directory entries carry no manufacturer) — treat it as a lead, not a datasheet fact. Markings are indicative only — confirm with the physical batch marking and the original datasheet before ordering.