PNDS / Marking codes / 55

Identify an unknown SMD part: marking code “55”

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.

18 candidates 7 with manufacturer source-traceable

Candidate part numbers

Part number	Manufacturer	Package	Mapping source
BAT15-055R	INFINEON	SOT173	Public marking directory
BAT15-055S	INFINEON	SOT173	Public marking directory
BAT17-05	INFINEON	SOT-23	Public marking directory
R3111Q551B	RICOH ^*	SC-82AB	Public marking directory
RN5RF55AA	RICOH ^*	SOT-23-5	Public marking directory
RN5RZ55AA	RICOH ^*	SOT-23-5	Public marking directory
UDZS16B	ROHM	—	Public marking directory
CHDTC123JMPT	—	SOT-723 18ta - 3a Chm	Public marking directory
EDZ16B	—	SOD-523	Public marking directory
ELM9855BB	—	SOT-23 16cg VR1 3d Elm	Public marking directory
FSD273TA-A	—	SOT-323	Public marking directory
Gali-55	—	SOT-89	Public marking directory
HMSZ5255B	—	SOD-323	Public marking directory
TCMM5Z3V9	—	SOD-523	Public marking directory
TDZ16B	—	—	Public marking directory
VDZS16B	—	—	Public marking directory
XC6221D431NR	—	SSOT-24	Public marking directory
ZD5255BS2	—	SOD-323	Public marking directory

How we narrow this down

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

51 5A 5B 5C 5D 52 5H 56 5E 5F

Still not sure what the part is?

Send the code, package and a photo through the BOM hub — our engineers cross-check it against datasheets and sourcing records.

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.