Identify an unknown SMD part: marking code “FF”

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.

22 candidates 10 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
BBY65-02V	INFINEON	SC79	Public marking directory
BCV27	FSC	SOT-23	Public marking directory
BD4925FVE	ROHM *	VSOF-5	Public marking directory
BD4925G	ROHM *	SSOP-5	Public marking directory
BFQ18A	NXP	SOT-89	Public marking directory
MAX6314US42D4-T	MAX *	SOT-143	Public marking directory
MAZD091	PANASONIC *	—	Public marking directory
RN1911FS	TOS	—	Public marking directory
UNR221Z	PANASONIC *	SC-59	Public marking directory
UNR521Z	PANASONIC *	SOT-523	Public marking directory
2SC5569	—	SOT-89	Public marking directory
ELM7625LDB	—	SOT-23 16vdc VD7 3d Elm	Public marking directory
ELM99151B	—	SOT-89	Public marking directory
R1141Q251D	—	SOT-143R	Public marking directory
RP130Q171B	—	SC-82AB	Public marking directory
RT9808-17CV	—	SOT-23 16vdb VD6 3a Rct	Public marking directory
UN221Z	—	SC-59	Public marking directory
UN521Z	—	SOT-523	Public marking directory
XC6127C26ANR	—	SSOT-24	Public marking directory
XC6127N26FNR	—	SSOT-24	Public marking directory
XC6223E321NR-G	—	SSOT-24	Public marking directory
Z1SMA-51	—	DO-214AC	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 “F”

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.