FHT40 Digital Temperature and Humidity Sensor

Q: What are the specified FHT40 humidity and temperature accuracies?

The supplied specification lists typical relative-humidity accuracy of ±1.8%RH and typical temperature accuracy of ±0.2 °C. Maximum accuracy varies with humidity and temperature and must be checked against the specification curves.

Q: What supply-voltage range does FHT40 support?

The electrical-characteristics table specifies 1.6 V to 5.5 V, with 3.3 V used as the typical test condition.

Q: What I²C address and bus speed does FHT40 use?

The standard FHT40 ordering entry lists 7-bit address 0x44. The interface supports standard, fast and fast-mode-plus operation up to 1 MHz. The document mentions two configurable addresses but does not identify the alternate address or ordering method; confirm it before design release.

Q: Does FHT40 use clock stretching?

No. If conversion is not complete when the host sends the read header, the sensor returns NACK. The host must wait for the selected measurement duration or implement a controlled retry.

Q: How is FHT40 measurement data protected?

Each 16-bit temperature or humidity word is followed by an 8-bit CRC. The polynomial is 0x31, initialization is 0xFF, reflection is disabled and final XOR is 0x00.

Q: How are the raw FHT40 values converted?

Temperature in degrees Celsius is -45 + 175 × ST / 65535. Relative humidity is -6 + 125 × SRH / 65535 %RH. For ordinary reporting, crop calculated humidity to 0%RH through 100%RH.

Q: When should the integrated heater be used?

The heater can help remove condensed water and improve recovery in extended high humidity. It is not a normal temperature-control function, and sensor accuracy specifications do not apply while it is active.

Q: What heater limits must be respected?

Keep total heater duty cycle below 10%, operate it only below 65 °C ambient, keep total sensor temperature below 125 °C and design the supply for up to 70 mA at the highest heater setting.

Q: What external components are required?

The typical circuit shows a 100 nF bypass capacitor at VDD/VSS and 10 kΩ pull-ups on SDA and SCL. Final pull-up values must satisfy the actual bus voltage, capacitance, rise time, VOL and host current limits.

Q: What package and ordering code are specified?

FHT40 uses a 1.5 mm × 1.5 mm DFN-4 package. The ordering table lists FHT40-DD-TR, top marking F40, tape-and-reel packing and 2,000 units per reel.

NYFEA FHT40 combines a capacitive relative-humidity sensing element, temperature sensor, signal conditioning, calibration memory, digital processing, CRC-protected I²C interface and configurable on-chip heater in a 1.5 mm × 1.5 mm DFN-4 package.

Product scope: the supplied specification lists typical accuracy up to ±1.8 %RH and ±0.2 °C, 1.6 V to 5.5 V operation and I²C up to 1 MHz. Accuracy depends on environmental exposure, placement, thermal coupling, airflow, chemical contamination, condensation, assembly and host implementation. Validate the finished product under its real operating conditions.

Download FHT40 Product Specification PDF · 15 pages View I²C Commands and CRC

This page is an engineering selection summary. The controlled PDF remains the authority for limits, curves, footnotes, package tolerances and production release.

45-degree product view of the NYFEA FHT40 DFN-4 temperature and humidity sensor — 45-degree product view of the NYFEA FHT40 in a DFN-4 package. The supplied ordering table specifies FHT40-DD-TR and production top marking F40; confirm the controlled marking drawing for incoming inspection.

±1.8 %RH typicalRelative-humidity accuracy at the stated condition; consult the full tolerance maps.

±0.2 °C typicalTemperature accuracy with -40 °C to +125 °C specified measurement range.

I²C up to 1 MHzSix-byte measurement readout with CRC-8 after each 16-bit word.

1.6 V to 5.5 V0.1 µA typical idle current and 1.5 mm × 1.5 mm DFN-4 package.

Product Overview and Selection Scope

FHT40 is intended for compact digital temperature and relative-humidity measurement where low average current, CRC-protected output and a controllable recovery heater are useful. The finished system must provide the enclosure, environmental protection, calibration policy and safety functions required by its application.

Relative humidity: 0 %RH to 100 %RH specified range, 0.01 %RH resolution and ±1.8 %RH typical accuracy.
Temperature: -40 °C to +125 °C specified range, 0.01 °C resolution and ±0.2 °C typical accuracy.
Low power: 0.1 µA typical idle current; 0.4 µA average at 1 Hz in low-repeatability mode.
Repeatability choices: high, medium and low modes trade measurement time against repeatability and current.
Digital integrity: CRC-8 protects each temperature and humidity word during I²C readout.
Integrated heater: three power levels and two durations for condensation removal and high-humidity recovery.
Traceability and qualification: the feature list states NIST traceability and JEDEC JESD47 qualification.
Compact assembly: 1.5 mm × 1.5 mm DFN-4, MSL 1, tape-and-reel ordering.

Selection boundaryTypical accuracy is not a universal maximum. Review the humidity/temperature tolerance maps, response time, drift, chemical exposure, self-heating and mechanical placement before setting an end-product accuracy claim.

Pin Configuration and Functional Architecture

FHT40 DFN-4 pin assignment and internal functional architecture — FHT40 combines humidity and temperature sensing, ADC, calibration, processing, heater, reset, register and I²C interface functions.

Pin	Name	Type	Function	PCB guidance
1	SDA	Bidirectional digital	I²C serial data	Open-drain bus; connect to VDD through the selected pull-up resistor.
2	SCL	Digital input	I²C serial clock	Connect to VDD through the selected pull-up resistor; the sensor does not clock-stretch.
3	VDD	Power	1.6 V to 5.5 V supply	Place the 100 nF bypass capacitor beside VDD and VSS.
4	VSS	Power	Ground reference	Use a short, low-impedance return and keep heat sources away from the sensor.

Electrical Characteristics and Measurement Timing

Unless otherwise stated, the electrical table applies across -40 °C to +125 °C and VDD from 1.6 V to 5.5 V. Typical conditions are +25 °C and 3.3 V.

Parameter	Condition	Minimum	Typical	Maximum	Unit
Supply voltage, VDD	Operating	1.6	3.3	5.5	V
Power-on reset level, VPOR	Supply threshold	0.8	-	1.0	V
Supply slew rate	VDD,slew	-	-	20	V/ms
Idle current	No measurement active	0.08	0.10	0.15	µA
Measurement current	During conversion	-	300	500	µA
Average current	High / medium / low repeatability	-	2.0 / 1.2 / 0.4	-	µA
LOW input voltage, VIL	SDA or SCL	0	-	0.3 × VDD	V
HIGH input voltage, VIH	SDA or SCL	0.7 × VDD	-	VDD	V
Pull-up resistance, R_P	SDA or SCL; no additional source-table condition	390	-	-	Ω
Bus capacitance	Cb	-	-	400	pF

Absolute maximum ratings and robustness

Parameter	Minimum	Maximum / rating	Unit	Engineering interpretation
Operating-condition temperature	-40	+125	°C	Listed in the absolute-maximum table; performance still follows the specified measurement limits and curves.
Junction temperature	-	+150	°C	Stress limit.
Storage temperature	-40	+150	°C	Stress limit; recommended storage conditions are narrower.
HBM electrostatic discharge	-	±7000	V	Per ANSI/ESDA/JEDEC JS-001.
Latch-up	-	±200	mA	Per JESD78, Class IA.

Absolute maximum ratings define stress boundaries and do not guarantee normal operation or measurement accuracy at those limits.

System timing

Operation	Mode or condition	Typical	Maximum	Unit
Power-up	After hard reset and VDD > VPOR	0.3	1.0	ms
Soft reset	Command 0x94	-	1.0	ms
Measurement	Low repeatability	1.3	1.6	ms
Measurement	Medium repeatability	3.7	4.5	ms
Measurement	High repeatability	6.9	8.3	ms
Heater pulse	Short / long command	0.1 / 1.0	Defined by command	s

Pull-up value requires system calculationThe electrical table lists R_P = 390 Ω minimum without an additional condition, while the typical circuit shows 10 kΩ on SDA and SCL. Select each pull-up from bus voltage, total capacitance, rise-time limit, V_OL margin and sink-current capability. Treat 10 kΩ as the supplied reference-circuit value.

Heater-duration inconsistency in the source PDFThe command table defines short and long heater operations as 0.1 s and 1 s. The separate system-timing table prints 0.9 / 1.0 / 1.1 s for both its “long pulse” and “short pulse” rows. This page uses the command-table durations for command identification; confirm the short-pulse timing with NYFEA before a timing-critical release.

Relative-Humidity and Temperature Performance

The tabulated values below are sensor-level specifications. The curves show how typical and maximum accuracy change near the ends of the measurement ranges, and the typical-accuracy tolerance map defines the FHT40 relative-humidity bands from 0 °C to 85 °C.

RH parameter	Value	Unit
Typical accuracy	±1.8	%RH
Repeatability, high / medium / low	0.08 / 0.15 / 0.25	%RH
Resolution	0.01	%RH
Hysteresis at +25 °C	±0.8	%RH
Specified range	0 to 100	%RH
Response time, t_63%	4	s
Typical long-term drift	<0.3	%RH/year

Temperature parameter	Value	Unit
Typical accuracy	±0.2	°C
Repeatability, high / medium / low	0.04 / 0.07 / 0.10	°C
Resolution	0.01	°C
Specified range	-40 to +125	°C
Response time, t_63%	2	s
Typical long-term drift	<0.03	°C/year

Redrawn FHT40 relative-humidity and temperature accuracy curves — Engineering redraw of PDF Figures 2 and 4. Curve coordinates are approximate readings from the supplied plots; the controlled PDF remains the numerical authority.

Redrawn FHT40 typical relative-humidity accuracy tolerance map from zero to eighty-five degrees Celsius — Engineering redraw of the typical-accuracy map in PDF Figure 3: ±3.0 %RH at 0–5 %RH and 95–100 %RH, ±2.0 %RH at 5–25 %RH and 75–95 %RH, and ±1.8 %RH at 25–75 %RH over 0–85 °C.

Accuracy and response-time boundaryResponse time changes with PCB copper, airflow, enclosure design, protective membranes, thermal mass and nearby heat sources. Verify static error, time response and recovery behavior in the assembled product.

I²C Communication, Measurement Readout and CRC-8

Every transfer starts with START and ends with STOP. The host writes one command, waits for conversion, then reads temperature MSB/LSB/CRC followed by humidity MSB/LSB/CRC. The final byte is terminated with NACK and STOP. An acknowledged read header clears the stored measurement after that read, so the host must validate and retain the complete six-byte frame.

FHT40 I2C measurement transaction, six-byte read order and CRC-8 parameters — Validate both CRC bytes and handle conversion-time NACK explicitly. FHT40 does not support clock stretching.

Address boundaryThe product feature list says two configurable I²C addresses, but the supplied ordering information identifies the standard FHT40 at 0x44 and does not document the alternate address selection. Do not assume an address other than 0x44 without controlled confirmation.

Command Set, Raw-Value Conversion and Reset

Command	Function	Returned bytes	Engineering note
0xFD	Measure T and RH, high repeatability	6	Maximum measurement time 8.3 ms.
0xF6	Measure T and RH, medium repeatability	6	Maximum measurement time 4.5 ms.
0xE0	Measure T and RH, low repeatability	6	Maximum measurement time 1.6 ms.
0x89	Read unique serial number	6	Two 16-bit words, each followed by CRC.
0x94	Soft reset	ACK	Allow up to 1 ms before the next command.
0x39 / 0x32	200 mW heater for 1 s / 0.1 s	6	High-repeatability result after heating.
0x2F / 0x24	110 mW heater for 1 s / 0.1 s	6	Typical power at VDD = 3.3 V.
0x1E / 0x15	20 mW heater for 1 s / 0.1 s	6	Respect heater duty-cycle and ambient limits.

Relative humidity: RH = -6 + 125 × S_RH / 65535 %RH
Temperature: T = -45 + 175 × S_T / 65535 °C
Temperature: T = -49 + 315 × S_T / 65535 °F

The RH equation can produce values below 0 %RH or above 100 %RH. Retain uncropped values only for diagnostic analysis; crop ordinary reported RH to 0 %RH through 100 %RH.

Reset paths

Soft reset: send command 0x94.
I²C general-call reset: send 0x06 to address 0x00; this affects every compatible device on the bus.
Power cycle: power down while pulling SCL and SDA LOW as described in the supplied specification.
Abort: an active sensor command can be aborted by soft reset or I²C general-call reset.

Integrated Heater Operation and Reliability Limits

FHT40 heater command sequence, use cases and duty-cycle limits — The heater runs before a high-repeatability measurement and then switches off. Sensor specifications do not apply during heating.

Do not use the heater as a calibration shortcutHeating changes the local temperature and relative humidity and can create thermomechanical offset. Use it only within the stated thermal and lifetime limits, then allow the assembly to return to equilibrium before using readings for control or accuracy claims.

Typical Application Circuit, PCB Placement and Exposure Control

FHT40 typical I2C circuit with pull-up resistors and 100 nanofarad bypass capacitor — Reference connection: independent pull-ups on SDA and SCL, plus a 100 nF local supply bypass capacitor.

Separate from heat sources: keep the sensor away from regulators, processors, displays, batteries and high-current copper.
Expose it to representative air: prevent stagnant pockets and isolate the sensing opening from board coatings, adhesives and enclosure walls.
Protect during assembly: use an ESD-protected area and do not contaminate the sensing surface with flux, solvent or cleaning residue.
Control I²C edges: choose pull-ups from bus capacitance and timing rather than copying one resistor value across all boards.
Budget heater current: local supply impedance must not allow the highest-power pulse to reset the sensor or disturb other circuitry.
Validate condensation recovery: test the complete vent, membrane, airflow path and heater duty cycle under the intended environmental profile.

Chemical-exposure warningThe specification identifies acetone, isopropanol, ethanol, toluene and related volatile chemicals as possible causes of irreversible RH offset. Review conformal coatings, adhesives, cleaning agents, enclosure outgassing and storage materials.

DFN-4 Package, Land Pattern, Tape-and-Reel and Ordering

FHT40 1.5 millimeter DFN-4 dimensions, exposed thermal-pad zone, recommended land pattern and tape-and-reel data — Package and land-pattern reconstruction from the supplied specification. The source calls the central underside feature an exposed thermal-pad zone; use the controlled drawing to determine its PCB treatment and release the CAD library.

Package dimensions

Symbol	Description	Minimum	Nominal / BSC / REF	Maximum	Unit
A	Overall height	0.49	0.54	0.59	mm
A1	Standoff	0	0.02	0.05	mm
b	Terminal width	0.25	0.30	0.35	mm
b1	Terminal feature	-	0.21 REF	-	mm
c	Terminal thickness	-	0.152 REF	-	mm
D / E	Body length / width	1.45	1.50	1.55	mm
D2	Exposed-zone length	0.90	1.00	1.10	mm
E2	Exposed-zone width	0.30	0.40	0.50	mm
e	Terminal pitch	-	0.80 BSC	-	mm
K	Terminal-to-zone spacing	-	0.25 REF	-	mm
L	Terminal length	0.25	0.30	0.35	mm
R	Corner radius	-	0.10 REF	-	mm
ØS / ØS1	Sensing-opening diameters	-	0.60 / 0.50 BSC	-	mm
h1	Opening-related height	-	0.13 nominal	-	mm

The recommended land pattern shows 1.4 mm centre span, 0.8 mm row span and 0.5 mm × 0.3 mm pads. Release the CAD footprint only against the controlled package drawing.

Ordering and handling

Item	Specified value	Release note
Ordering code	FHT40-DD-TR	Standard FHT40, 7-bit address 0x44, tape-and-reel packing.
Package	DFN-4, 1.5 mm × 1.5 mm	Four peripheral contacts plus a central zone labelled “EXPOSED THERMAL PAD ZONE” in the source drawing; confirm its PCB disposition before footprint release.
Top marking	F40 + YWWD trace code	Verify the pin-1 laser mark and lot traceability during incoming inspection.
Standard packing quantity	2,000 units	The ordering table specifies 2K; the carrier-tape page also describes a 10K, 13-inch reel option.
Moisture sensitivity	MSL 1	The document states one-year storage under the recommended conditions.
Recommended storage	10 °C to 50 °C; 20 %RH to 65 %RH	Keep components in their original packaging before use.

Source-document clarificationThe absolute-maximum table contains an “ALERT Pin Voltage” entry, while the four-pin pin table defines only SDA, SCL, VDD and VSS. FHT40 has no ALERT pin in the supplied pinout. Confirm this apparent family-table carryover before controlled release.

Application Guidance and Design Limitations

The supplied specification lists automotive cabin, industrial control, smart home, consumer electronics and medical devices. These are application categories, not product- or system-level qualification claims.

Automotive CabinCabin climate or comfort sensing only after component qualification, placement, condensation and EMC validation.

Industrial ControlMonitor local air conditions with protection from corrosive gases, washdown, coating and hot equipment.

Smart HomeUse in thermostats, ventilation and indoor monitors after enclosure airflow and self-heating tests.

Consumer electronics climate monitoring icon

Consumer ElectronicsCompact low-power sensing for devices where display, battery and processor heat are isolated.

Medical equipment environmental sensing icon

Medical DevicesEnvironmental sensing only; no medical, diagnostic, life support or functional-safety qualification is stated.

Qualification boundaryValidate accuracy, calibration policy, EMC, ESD, condensation, chemical compatibility, cleaning, biocompatibility where applicable, fault handling and regulatory requirements in the finished product.

FHT40 Engineering FAQs

What are the specified FHT40 humidity and temperature accuracies?

The supplied specification lists typical relative-humidity accuracy of ±1.8 %RH and typical temperature accuracy of ±0.2 °C. Maximum accuracy varies with humidity and temperature and must be checked against the specification curves.

What supply-voltage range does FHT40 support?

The electrical-characteristics table specifies 1.6 V to 5.5 V, with 3.3 V used as the typical test condition.

What I²C address and bus speed does FHT40 use?

The standard FHT40 ordering entry lists 7-bit address 0x44. The interface supports Standard-mode, Fast-mode and Fast-mode Plus operation up to 1 MHz. The document mentions two configurable addresses but does not identify the alternate address or ordering method; confirm it before design release.

Does FHT40 use clock stretching?

No. If conversion is not complete when the host sends the read header, the sensor returns NACK. The host must wait for the selected measurement duration or implement a controlled retry.

How is FHT40 measurement data protected?

Each 16-bit temperature or humidity word is followed by an 8-bit CRC. The polynomial is 0x31, initialization is 0xFF, reflection is disabled and final XOR is 0x00.

How are the raw FHT40 values converted?

Temperature in degrees Celsius is -45 + 175 × ST / 65535. Relative humidity is -6 + 125 × SRH / 65535 %RH. For ordinary reporting, crop calculated humidity to 0 %RH through 100 %RH.

When should the integrated heater be used?

The heater can help remove condensed water and improve recovery after extended high-humidity exposure. Use it as a controlled recovery function; sensor accuracy specifications do not apply while it is active.

What heater limits must be respected?

Keep total heater duty cycle below 10%, operate it only below 65 °C ambient, keep total sensor temperature below 125 °C and design the supply for up to 70 mA at the highest heater setting.

What external components are required?

The typical circuit shows a 100 nF bypass capacitor at VDD/VSS and 10 kΩ pull-ups on SDA and SCL. Final pull-up values must satisfy the actual bus voltage, capacitance, rise time, VOL and host current limits.

What package and ordering code are specified?

FHT40 uses a 1.5 mm × 1.5 mm DFN-4 package. The ordering table lists FHT40-DD-TR, top marking F40, tape-and-reel packing and 2,000 units per reel.

Can FHT40 be exposed to solvents or cleaning chemicals?

Avoid close or prolonged exposure to volatile solvents and organic compounds such as acetone, isopropanol, ethanol and toluene. The document warns that these can cause irreversible humidity-reading shifts.

Technical source and design authority

This page summarizes FHT40_datasheet.pdf, whose internal part number is FHT40, for component evaluation and engineering reference. It does not replace the complete controlled product specification. Confirm the current revision, ordering code, I²C address, accuracy curves, commands, timing, heater limits, chemical exposure, package tolerances, land pattern, assembly process and qualification requirements before production release.

Download FHT40 Product Specification Contact NYFEA for Product Support