What temperature range and accuracy does FT18B20 specify?

The product specification lists -55 °C to +125 °C measurement range and ±0.5 °C accuracy from -10 °C to +70 °C in its feature summary.

Can FT18B20 operate without a local supply?

Yes. In parasite-power mode VDD is grounded and the device derives power from DQ, with a strong pullup required during conversions and EEPROM copies.

What resolution options are available?

The configuration register selects 9-, 10-, 11- or 12-bit resolution. Maximum conversion time ranges from 93.75 ms to 750 ms.

How are several FT18B20 devices addressed?

Each device has a unique 64-bit ROM code, and the 1-Wire ROM commands support search, match, skip and alarm-search operations.

FT18B20 Digital Thermometer

NYFEA FT18B20 combines direct-to-digital temperature measurement, user-selectable 9- to 12-bit resolution, a unique 64-bit ROM code, nonvolatile alarm thresholds, scratchpad memory and CRC-protected 1-Wire communication in a three-lead TO-92 package.

Product scope: the supplied specification lists a -55 °C to +125 °C measurement range, ±0.5 °C accuracy from -10 °C to +70 °C, and 2.5 V to 5.5 V operation. The DC table states ±0.5 °C through +85 °C; this page retains the narrower feature claim until the controlled specification is clarified.

Download FT18B20 Datasheet View 1-Wire Commands

This engineering selection page summarizes the supplied PDF. Use the controlled specification for final limits, timing, package tolerances and production release.

NYFEA FT18B20 1-Wire digital thermometer in a three-lead TO-92 package — FT18B20 TO-92 pin order, front view: pin 1 GND, pin 2 DQ and pin 3 VDD.

±0.5 °CFeature claim from -10 °C to +70 °C; review the specification note for the wider DC-table entry.

-55 °C to +125 °CSpecified measurement and operating range.

9- to 12-bitProgrammable resolution with 93.75 ms to 750 ms maximum conversion time.

2.5 V to 5.5 VExternal or parasite power, 1-Wire multidrop bus and unique 64-bit identity.

Product Overview and Selection Scope

FT18B20 is intended for direct digital temperature measurement on a single-drop or multidrop 1-Wire bus. Its ROM identity, alarm search, configurable conversion time and optional two-wire parasite-power connection suit distributed temperature sensing.

Digital temperature: -55 °C to +125 °C measurement range.
Accuracy: ±0.5 °C from -10 °C to +70 °C in the feature summary; ±1.5 °C over the full range in the DC table.
Resolution: user-selectable 9, 10, 11 or 12 bits; 12 bits after power-up.
1-Wire interface: one DQ signal plus ground, with multidrop device discovery.
Unique identity: 64-bit ROM with family code 28h, 48-bit serial number and CRC byte.
Alarm functions: nonvolatile high and low thresholds plus Alarm Search command.
Power options: 2.5 V to 5.5 V external supply or parasite power from DQ.
Robustness: the feature list states HBM 7000 V and MM 700 V ESD capability.

Selection boundaryAccuracy at the packaged component does not include enclosure gradients, cable effects, self-heating, placement, response lag, calibration policy or system-level EMC. Validate the complete assembly.

Pin Configuration and Functional Architecture

FT18B20 internal block diagram showing parasite power, 64-bit ROM, scratchpad, sensor, alarm, EEPROM and CRC functions — The FT18B20 architecture combines the sensor, ROM identity, scratchpad, configuration, alarm thresholds, two user EEPROM bytes and CRC generator.

Pin	Name	Type	Function	Design guidance
1	GND	Power	Ground reference	Use a low-impedance return to the host and bus pullup supply.
2	DQ	Bidirectional open drain	1-Wire data input/output; also supplies parasite power	Use a pullup sized for bus capacitance and timing. Provide a controlled strong pullup when parasite powered.
3	VDD	Power	Optional 2.5 V to 5.5 V external supply	Connect to GND for parasite-power operation.

Electrical and Temperature Performance

The DC table applies from -55 °C to +125 °C with VDD from 2.5 V to 5.5 V. Values below reproduce the supplied specification; verify ambiguous column placement against the controlled source before release.

Parameter	Condition	Minimum	Typical	Maximum	Unit
Supply voltage, VDD	External power	2.5	-	5.5	V
Pullup supply, VPU	Parasite power	2.5	-	5.5	V
Temperature error	-10 °C to +85 °C, DC table	-	-	±0.5	°C
Temperature error	-55 °C to +125 °C	-	-	±1.5	°C
Input LOW, VIL	DQ	-0.3	-	0.8	V
Input HIGH, VIH	External power	2.2	-	min(5.5, VDD + 0.3)	V
Sink current, IL	DQ at 0.4 V	4.0	-	-	mA
Standby current, IDDS	Up to +70 °C	-	750	1000	nA
Active current, IDD	VDD = 5 V	-	1.0	1.5	mA
Drift	1000 h at +125 °C, VDD = 5.5 V	-	-	±0.2	°C

FT18B20 typical error curve from 0 to 70 degrees Celsius — Typical error curve reproduced from the supplied specification. It is descriptive performance data, not a substitute for guaranteed limits.

Accuracy wording requires confirmationThe feature page states ±0.5 °C from -10 °C to +70 °C, while the DC-characteristics table states -10 °C to +85 °C. This page uses the narrower range in headline claims and exposes the table entry here for engineering review.

Temperature Data, Resolution and Scratchpad Memory

After Convert T [44h], the signed temperature result is placed in scratchpad bytes 0 and 1. At 12-bit resolution, one LSB equals 0.0625 °C. The power-on temperature-register value is +85 °C and should not be treated as a fresh measurement.

R1	R0	Resolution	Temperature increment	Maximum conversion time
0	0	9 bit	0.5 °C	93.75 ms
0	1	10 bit	0.25 °C	187.5 ms
1	0	11 bit	0.125 °C	375 ms
1	1	12 bit	0.0625 °C	750 ms

Scratchpad map

Byte	Content	Access and persistence
0	Temperature LSB	Read only; updated by conversion.
1	Temperature MSB	Read only; signed two's-complement result.
2	TH alarm threshold	Writable; backed by EEPROM.
3	TL alarm threshold	Writable; backed by EEPROM.
4	Configuration register	R1/R0 select resolution; backed by EEPROM.
5	Reserved	Internal use.
6–7	User bytes	Writable user EEPROM storage.
8	Scratchpad CRC	Read only; CRC over bytes 0 through 7.

12-bit temperature: T (°C) = signed 16-bit register value × 0.0625

1-Wire Signaling and Timing

The bus master initiates reset, write and read time slots. FT18B20 responds to reset with a presence pulse. Data transfers are least-significant bit first.

FT18B20 1-Wire write-zero, read-zero, reset and presence-detect timing diagrams — 1-Wire time-slot, reset and presence-detect waveforms reproduced from the supplied specification.

Timing parameter	Symbol	Minimum	Maximum	Unit
Time slot	tSLOT	60	120	µs
Recovery time	tREC	1	-	µs
Write-0 LOW	tLOW0	60	120	µs
Write-1 LOW	tLOW1	1	15	µs
Read data valid	tRDV	-	15	µs
Reset LOW	tRSTL	480	1000	µs
Reset HIGH	tRSTH	480	-	µs
Presence-detect HIGH	tPDHIGH	15	60	µs
Presence-detect LOW	tPDLOW	60	240	µs

ROM and Function Command Set

ROM commands

Command	Code	Use	Boundary
Search ROM	F0h	Discover the ROM codes of devices on a multidrop bus.	Repeat the search cycle until every device is identified.
Read ROM	33h	Read one device's 64-bit ROM code.	Use only when exactly one slave is present.
Match ROM	55h	Select one device by its ROM code.	Other devices wait for the next reset.
Skip ROM	CCh	Address all devices without a ROM code.	Do not follow with Read Scratchpad on a multidrop bus.
Alarm Search	ECh	Discover devices whose latest conversion set an alarm flag.	Run another conversion after changing TH or TL.

Function commands

Command	Code	Function	Engineering note
Convert T	44h	Start one temperature conversion.	Use a strong pullup within 10 µs when parasite powered.
Write Scratchpad	4Eh	Write TH, TL, configuration and user bytes.	Transmit least-significant bit first; complete required bytes before reset.
Read Scratchpad	BEh	Read up to nine scratchpad bytes including CRC.	The master may reset early if only part is required.
Copy Scratchpad	48h	Copy writable scratchpad values to EEPROM.	For parasite power, apply strong pullup within 10 µs for at least 10 ms.
Recall E²	B8h	Reload EEPROM values into scratchpad.	Read slots return 0 while busy and 1 when complete.
Read Power Supply	B4h	Detect parasite-powered devices.	Parasite-powered devices pull DQ LOW during the following read slot.

External and Parasite Power

FT18B20 parasite-power circuit with MOSFET strong pullup — Parasite power: connect VDD to GND and switch in a strong pullup during conversions and EEPROM copies.

FT18B20 externally powered circuit with a 4.7 kiloohm 1-Wire pullup — External supply: VDD is powered locally and the 1-Wire bus remains available during conversion.

Strong pullup timing: enable it within 10 µs after Convert T or Copy Scratchpad in parasite mode.
Bus availability: no other 1-Wire traffic can occur while the strong pullup is active.
High temperature: parasite power is not recommended above +100 °C because leakage can disrupt communication.
Mode discovery: use Skip ROM followed by Read Power Supply when the mix of powered devices is unknown.

Pullup value requires bus-level validationThe circuit figures show 4.7 kΩ, while narrative timing examples refer to 5 kΩ and 1 kΩ. Select the weak pullup from supply voltage, cable length, device count, capacitance, rise time and sink-current limits; treat 4.7 kΩ only as the supplied circuit example.

CRC and Data Integrity

The 64-bit ROM ends with a CRC byte calculated over its first 56 bits. Scratchpad byte 8 contains a CRC over bytes 0 through 7. The master must calculate and compare CRC values before accepting identity, temperature, alarm or configuration data.

CRC polynomial: x⁸ + x⁵ + x⁴ + 1
Normal polynomial representation: 0x31 · LSB-first reflected implementation: 0x8C

ROM layout: 8-bit family code 28h, 48-bit serial number, 8-bit CRC.
Scratchpad: eight data bytes followed by one CRC byte.
Bit order: feed the least-significant bit first, matching the 1-Wire transfer order.
Host responsibility: the device does not stop a command sequence when the host detects a CRC mismatch.

TO-92 Package and Ordering

FT18B20 TO-92 package drawing and dimensions — TO-92 package drawing reproduced from the supplied specification. Use the controlled drawing when creating the production CAD library.

Symbol	Minimum	Maximum	Unit	Description
A	3.300	3.700	mm	Body profile dimension shown in end view.
D	4.300	4.700	mm	Body width.
E	4.300	4.700	mm	Body height in front view.
e	1.270 typical		mm	Adjacent lead pitch.
e1	2.440	2.640	mm	Outer lead span.
L	14.100	14.500	mm	Lead length.

Ordering information

Purchase number	Device	Package	Standard packing quantity	Remarks
FT18B20	FT18B20	TO-92	2,000	Bulk

Application Guidance and Design Limitations

The supplied specification lists temperature control, industrial systems, consumer goods, grain temperature measurement, thermometers and general thermal systems.

Temperature ControlClosed-loop control after validating latency, hysteresis, placement and fail-safe behavior.

Industrial SystemsDistributed monitoring with cable, grounding, surge and EMC validation.

Consumer GoodsDigital sensing where enclosure gradients and internal heat sources are controlled.

Grain MonitoringMultidrop probes after cable length, moisture protection and serviceability tests.

ThermometersDisplay and logging instruments with defined calibration and error handling.

System qualificationThe application list does not establish functional-safety, automotive, medical, food-contact or regulatory qualification. Confirm environmental sealing, isolation, calibration, diagnostics and compliance for the finished product.

FT18B20 Engineering FAQs

What are the specified FT18B20 temperature range and accuracy?

The feature summary lists -55 °C to +125 °C and ±0.5 °C from -10 °C to +70 °C. The DC table extends its ±0.5 °C line to +85 °C and lists ±1.5 °C over the full range; confirm that discrepancy before publishing a wider accuracy claim.

What supply range does FT18B20 support?

External VDD and parasite-power pullup supply are specified from 2.5 V to 5.5 V.

Can FT18B20 operate with only two wires?

Yes. In parasite-power mode, connect VDD to GND and use DQ plus GND. A strong pullup is required during temperature conversion and EEPROM copy operations.

What resolution should firmware select?

Use 9, 10, 11 or 12 bits to trade conversion time against resolution. Maximum conversion times are 93.75, 187.5, 375 and 750 ms respectively.

How can several FT18B20 devices share one bus?

Each device has a unique 64-bit ROM code. Search ROM discovers devices and Match ROM selects one. Skip ROM can trigger simultaneous conversion, but must not precede Read Scratchpad when several devices could answer.

What does the +85 °C reading mean after power-up?

The temperature register initializes to +85 °C. Firmware should issue Convert T, wait for completion and verify CRC before treating the value as a current measurement.

How does alarm search work?

After each conversion, FT18B20 compares the result with nonvolatile TH and TL thresholds. Alarm Search returns only devices whose latest conversion is at or beyond a programmed threshold.

How is received data checked?

Verify the ROM CRC and the ninth scratchpad byte with polynomial x⁸ + x⁵ + x⁴ + 1. Reject or retry data when the host-calculated CRC does not match.

Is parasite power suitable above +100 °C?

The specification advises against parasite power above +100 °C because increased leakage may prevent reliable communication. Use external VDD where those temperatures are possible.

What package and order quantity are specified?

The ordering table lists FT18B20 in a three-pin TO-92 package, bulk packed with a standard packing quantity of 2,000.

Technical source and design authority

This page summarizes FT18B20_datasheet.pdf for component evaluation and engineering reference. It does not replace the complete controlled product specification. Confirm the current revision, accuracy wording, timing, bus pullup, command sequence, EEPROM endurance, package tolerances, assembly process and qualification requirements before production release.

Download FT18B20 Product Specification Contact NYFEA for Product Support