TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 1
FEATURES
• Full interchangeability with no calibration
required in standard conditions
• Instantaneous desaturation after long periods in
saturation phase
• Compatible with automatized assembly
processes, including Pb free and reflow
processes
• Individual marking for compliance to stringent
traceability requirements
APPLICATIONS
• Home Appliance
• Medical
• Printers
• Humidifier
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with
Temperature output
• DFN type package
• Relative Humidity and Temperature Digital Output, I²C interface
• Fully calibrated
• Lead free sensor, reflow solderable
• Low power consumption
• Fast response time
The HTU21D(F) is a new digital humidity sensor with temperature output
by MEAS. Setting new standards in terms of size and intelligence, it is
embedded in a reflow solderable Dual Flat No leads (DFN) package with
a small 3 x 3 x 0.9 mm footprint. This sensor provides calibrated,
linearized signals in digital, I²C format.
HTU21D(F) digital humidity sensors are dedicated humidity and
temperature plug and play transducers for OEM applications where
reliable and accurate measurements are needed. Direct interface with a
micro-controller is made possible with the module for humidity and
temperature digital outputs. These low power sensors are designed for
high volume and cost sensitive applications with tight space constraints.
Every sensor is individually calibrated and tested. Lot identification is
printed on the sensor and an electronic identification code is stored on
the chip – which can be read out by command. Low battery can be
detected and a checksum improves communication reliability. The
resolution of these digital humidity sensors can be changed by command
(8/12bit up to 12/14bit for RH/T).
With MEAS’ improvements and miniaturization of this sensor, the
performance-to-price ratio has been improved – and eventually, any
device should benefit from its cutting-edge energy saving operation
mode.
Optional PTFE filter/membrane (F) protects HTU21D digital humidity
sensors against dust and water immersion, as well as against
contamination by particles. PTFE filter/membranes preserve a high
response time. The white PTFE filter/membrane is directly stuck on the
sensor housing. This membrane is allowing an IP67 compliant
protection.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 2
NOMENCLATURE
HTU2XY(F)
HTU2XY Modules HTU2XYF Modules
PERFORMANCE SPECS
Maximum Ratings
Graph above show peak conditions: less than 10% of the operating life
Exposure to absolute maximum rating conditions for extended periods may affect the sensor reliability.
Ratings
Symbol
Unit
Storage Temperature
Tstg
°C
Supply Voltage (Peak)
Vcc
Vdc
Humidity Operating Range
RH
%RH
Temperature Operating Range
Ta
°C
VDD to GND
V
Digital I/O pins (DATA/SCK) to VDD
V
Input current on any pin
mA
Humidity accuracy :
X = 0: +/-5%RH max tolerance @55%RH
= 1: +/-3%RH max tolerance @55%RH
Output Sensor:
Y = D/A for Digital, I2C protocol
= P for PWM interface, analog output
With embedded PTFE filter: HTU2XYF
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 3
ELECTRICAL AND GENERAL ITEMS
(@T = 25°C, @Vdd = 3V)
Characteristics
Symbol
Min
Typ
Max
Unit
Voltage Supply
VDD
1.5
3.0
3.6
V
Current
consumption (1)
Sleep mode
idd
0.02
0.14
µA
Measuring
300
450
500
µA
Power Dissipation
Sleep mode
0.06
0.5
µW
Average 8bit (2)
2.7
µW
Communication
digital 2-wire interface, I²C protocol
Heater
VDD=3V
5.5mW/ΔT=+0.5-1.5°C
Storage
-40°C/125°C
(1) Conditions: Vdd = 3V, SCK= 400kHz at 25°C
(2) Conditions: Vdd = 3V, SCK= 400kHz, Temp<60°C, duty cycle <10%
SENSOR PERFORMANCE
Relative Humidity
(@T = 25°C, @Vdd = 3V)
Characteristics
Symbol
Min
Typ
Max
Unit
Resolution
12 bits
0.04
%RH
8 bits
0.7
%RH
Humidity Operating Range
RH
0
100
%RH
Relative Humidity Accuracy
@25°C (20%RH to 80%RH)
typ
±2
%RH
max
See graph 1
%RH
Replacement
fully interchangeable
Temperature coefficient (from 0°C to 80°C)
Tcc
-0.15
%RH/°C
Humidity Hysteresis
±1
%RH
Measuring Time (1)
12 bits
14
16
ms
11 bits
7
8
ms
10 bits
4
5
ms
8 bits
2
3
ms
PSRR
±10
LSB
Recovery time after 150 hours of condensation
t
10
s
Long term drift
0.5
%RH/yr
Response Time (at 63% of signal) from 33 to 75%RH (2)
τRH
5
10
s
(1) Typical values are recommended for calculating energy consumption while maximum values shall be applied for calculating
waiting times in communication.
(2) At 1m/s air flow
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 4
GRAPH 1 : RELATIVE HUMIDITY ERROR BUDGET CONDITIONS AT 25°C
▪ HTU21D(F) sensors are specified for optimum accuracy measurements within 5 to 95%RH.
▪ Operation out of this range (< 5% or > 95% RH, including condensation) is however possible.
TEMPERATURE COEFFICIENT COMPENSATION EQUATION
For other temperatures than 25°C, the following temperature coefficient compensation equation can be used and will
guarantee Relative Humidity accuracy given in table1, from 0°C to 80°C:
)(TfRHRH actualTdTcompensate
RHactualT Ambient humidity in %RH, computed from HTU21D(F) sensor
Tactual Humidity cell temperature in °C, computed from HTU21D(F) sensor
)(Tf
RH correction (in %RH) is a linear function of the temperature T (°C) as described below :
)25(*15.0)( TTf
0
1
2
3
4
5
6
7
8
9
10
010 20 30 40 50 60 70 80 90 100
Delta Relative Humidity (%RH)
Relative Humidity (%RH)
Maximal Tolerance
Typical Tolerance
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 5
TEMPERATURE
Characteristics
Symbol
Min
Typ
Max
Unit
Resolution
14 bit
0.01
°C
12 bit
0.04
°C
Temperature Operating Range
T
-40
+125
°C
Temperature Accuracy @25°C
typ
±0.3
°C
max
See graph 2
°C
Replacement
fully interchangeable
Measuring time (1)
14 bit
44
50
ms
13 bit
22
25
ms
12 bit
11
13
ms
11 bit
6
7
ms
PSSR
±25
LSB
Long term drift
0.04
°C/yr
Response Time (at 63% of signal) from 15°C to 45°C (2)
τT
10
s
(1) Typical values are recommended for calculating energy consumption while maximum values shall be applied for calculating
waiting times in communication.
(2) At 1m/s air flow
GRAPH 2 : TEMPERATURE ERROR BUDGET
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
-40 -20 0 20 40 60 80 100 120
Delta Temperature (°C)
Temperature (°C)
Maximal Tolerance
Typical Tolerance
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 6
USER GUIDE HTU21D(F)
Application Information
• Soldering instructions: Lead free reflow soldering recommended process
For soldering HTU21D (F) sensor standard reflow soldering ovens may be used.
HTU21D(F) sensor as a humidity sensitive component (as classified by IPC/JEDEC J-STD-020 or equivalent documented
procedure with peak temperature at 260°C during up to 30 seconds for Pb-free assembly in IR/convection reflow ovens) must
be handled in a manner consistent with IPC/JEDEC J-STD-033 or an equivalent documented procedure. IPC-1601 provides
humidity control, handling and packing of PCBs.
The HTU21D (F) sensor is qualified to withstand one lead free reflow soldering recommended process profile below according
to JEDEC standard.
Mount parts within 24 hours after printing solder paste to avoid potential dry up.
For manual soldering, contact time must be limited to 5 seconds at up to 350°C.
For the design of the HTU21D(F) sensor footprint, it is recommended to use dimensions according to figure below.
Recommended footprint for HTU21D(F) sensors. Values in mm.
No specific conditioning of devices is necessary after soldering process, either manual or reflow soldering. Optimized
performance in case of metrological measurements can be reached with stabilization of devices (24 hours at 25°C / 55%RH).
Similar process is advised after exposure of the devices to extreme relative humidity conditions.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 7
In no case, neither after manual nor reflow soldering, a board wash shall be applied. Therefore, it is strongly recommended to
use a “no-clean” solder paste. In case of applications with exposure of the sensor to corrosive gases or condensed water (i.e.
environments with high relative humidity) the soldering pads shall be sealed (e.g. conformal coating) to prevent loose contacts
or short cuts.
• Storage Conditions and Handling Instructions
It is recommended to store HTU21D(F) sensor in its original packaging at following conditions: Temperature shall be in the
range of -40°C – 125°C.
• Temperature Effects
Relative humidity reading strongly depends on temperature. Therefore, it is essential to
keep humidity sensors at the same temperature as the air of which the relative humidity is
to be measured.
In case of testing or qualification the reference sensor and test sensor must show equal
temperature to allow for comparing humidity readings.
The HTU21D(F) sensor should be mounted in a way that prevents heat transfer from
electronic sensor or that keeps it as low as possible. Advice can be ventilation, reduction of
copper layers between the HTU21D(F) sensor and the rest of the PCB or milling a slit into
the PCB around the sensor (1mm minimum width).
Example of HTU21D(F) sensor mounting
with slits mills to minimize heat transfer
• Materials Used for Sealing / Mounting
For sealing and gluing (use sparingly), use high filled epoxy for electronic packaging and silicone. For any specific material
please request to humidity.application@meas-spec.com.
Window must remain uncovered.
• Wiring Considerations and Signal Integrity
Carrying the SCK and DATA signal parallel and in close proximity (e.g. in wires) for more than 10 cm may result in cross talk
and loss of communication.
This may be resolved by routing VDD and/or GND between the two data signals and/or using shielded cables. Furthermore,
slowing down SCK frequency will possibly improve signal integrity.
Power supply pins (VDD, GND) must be bypassed with a 100nF capacitor if wires are used. Capacitor should be placed as
close as possible to the sensor.
• ESD (ElectroStatic Discharge)
ESD immunity is qualified according to:
▪ JEDEC JESD22-A114 method (Human Body Model at ±4kV) for pads & open window
▪ JEDEC JESD22-A115 method (Machine Model ±200V)
▪ ESDA ESD-STM5.3.1-1999 and AEC-Q100-011 (charged device model, 750V corner pins, 500V other pins)
Latch-up immunity is provided at a force current of ±100mA with Tamb=25°C according to JEDEC JESD78. For exposure
beyond named limits the sensor need additional protection circuit.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 8
INTERFACE SPECIFICATION
Typical application circuit, including pull-up resistor Rp and decoupling of VDD and GND by a capacitor.
• Power Pins (VDD, GND)
The supply voltage of HTU21D(F) sensors must be in the range of 1.5VDC - 3.6VDC. Recommended supply voltage is 3VDC
(regulated).
However the typical application circuit includes a pull-up resistor R on data wire and a 100nF decoupling capacitor between
VDD and GND, placed as close as possible to the sensor.
• Serial clock input (SCK)
SCK is used to synchronize the communication between microcontroller and HTU21D(F) sensor. Since the interface consists
of fully static logic there is no minimum SCK frequency.
• Serial data (DATA)The DATA pin is used to transfer data in and out of the device. For sending a command to the
HTU21D(F) sensor, DATA is valid on the rising edge of SCK and must remain stable while SCK is high. After the
falling edge of SCK, the DATA value may be changed. For safe communication DATA shall be valid tSU and tHD
before the rising and after the falling edge of SCK, respectively. For reading data from the HTU21D(F) sensor, DATA
is valid tVD after SCK has gone low and remains valid until the next falling edge of SCK.
An external pull-up resistor (e.g. 10kΩ) on SCK is required to pull the signal high only for open collector or open drain
technology microcontrollers. In most of the cases, pull-up resistors are internally included in I/O circuits of microcontrollers.
N°
Function
Comment
1
DATA
Data bit-stream
2
GND
Ground
3
NC
Must be left unconnected
4
NC
Must be left unconnected
5
VDD
Supply Voltage
6
SCK
Selector for RH or Temp
PAD
Ground or unconnected
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 9
ELECTRICAL CHARACTERISTICS
• Input/output DC characteristics
(VDD=3V, Temperature=25°C unless otherwise noted)
Characteristics
Symbol
Min
Typ
Max
Unit
Low level output
voltage
VDD=3V
-4mA<IOL<0mA
VOL
0
-
0.4
V
High level output voltage
VOH
70%VDD
-
VDD
V
Low level input voltage
VIL
0
-
30%VDD
V
High level input voltage
VIH
70%VDD
-
VDD
V
• Timing specifications of digital input/output pads for I²C fast mode
Characteristics
Symbol
Min
Typ
Max
Unit
SCK frequency
fSCK
0
-
0.4
MHz
SCK high time
tSCKLH
0.6
-
-
µs
SCK low time
tSCLL
1.3
-
-
µs
DATA set-up time
tSU
100
-
-
ns
DATA hold-time
tHD
0
-
900
ns
DATA valid-tile
tVD
0
-
400
ns
SCK/DATA fall time
tF
0
-
100
ns
SCK/DATA rise time
tR
0
-
300
ns
Capacitive load on bus line
CB
0
-
500
pF
• Timing diagram for digital input/output pads
DATA directions are seen from the HTU21D(F) sensor. DATA line in bold is controlled by the sensor. DATA valid read time is
triggered by falling edge of anterior toggle.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 10
COMMUNICATION PROTOCOL WITH HTU21D(F) SENSOR
• Start-up sensor
The HTU21D(F) sensor requires a voltage supply between 1.5V and 3.6V. After power up, the device needs at most 15ms
while SCK is high for reaching idle state (sleep mode), i.e to be ready accepting commands from the MCU. No command
should be sent before that time. Soft reset is recommended at start, refer p.13.
• Start sequence (S)
To initiate transmission, a start bit has to be issued. It consists of a lowering of the DATA line while SCK
is high followed by lowering SCK.
• Stop sequence (P)
To stop transmission, a stop bit has to be issued. It consists of a heightening of the DATA line while SCK
is high preceded by a heightening of the SCK.
HTU21D(F) SENSOR LIST OF COMMANDS AND REGISTER ADRESSES
For sample source code, please request to pic.info@te.com
• Sending a command
After sending the start condition, the subsequent I²C header consist of a 7-bit I²C device address 0x40 and a DATA direction bit
(‘0’ for Write access : 0x80). The HTU21D(F) sensor indicates the proper reception of a byte by pulling the DATA pin low (ACK
bit) after the falling edge of the 8th SCK clock. After the issue of a measurement command (0xE3 for temperature, 0xE5 for
relative humidity), the MCU must wait for the measurement to complete. The basic commands are given in the table below:
• Hold/No Hold master modes
There are two different operation modes to communicate with the HTU21D(F) sensor: Hold Master mode and No Hold Master
mode.
In the first case, the SCK line is blocked (controlled by HTU21D(F) sensor) during measurement process while in the second
case the SCK line remain open for other communication while the sensor is processing the measurement.
No Hold Master mode allows for processing other I²C communication tasks on a bus while the HTU21D(F) sensor is
measuring. A communication sequence of the two modes is available below.
In the Hold Master mode, the HTU21D(F) pulls down the SCK line while measuring to force the master into a wait state. By
releasing the SCK line, the HTU21D(F) sensor indicates that internal processing is completed and that transmission may be
continued.
In the No Hold Master mode, the MCU has to poll for the termination of the internal processing of the HTU21D(F) sensor. This
is done by sending a start condition followed by the I²C header (‘1’ for Read access: 0x81) as shown below. If the internal
processing is finished, the HTU21D(F) sensor acknowledges the poll of the MCU and data can be read by the MCU. If the
measurement processing is not finished, the HTU21D(F) sensor answers no ACK bit and start condition must be issued once
more.
Command
Code
Comment
Trigger Temperature Measurement
0xE3
Hold master
Trigger Humidity Measurement
0xE5
Hold master
Trigger Temperature Measurement
0xF3
No Hold master
Trigger Humidity Measurement
0xF5
No Hold master
Write user register
0xE6
Read user register
0xE7
Soft Reset
0xFE
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 11
For both modes, since the maximum resolution of the measurement is 14 bits, the two last least significant bits (LSBs, bits 43
and 44) are used for transmitting status information. Bit 1 of the two LSBs indicates the measurement type (‘0’: temperature,
‘1’: humidity). Bit 0 is currently not assigned. (Refer to Diagnostic Status for more information)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S
1
0
0
0
0
0
0
0
ACK
1
1
1
0
0
1
0
1
ACK
I²C address + write
Command (see table p.9)
19
20
21
22
23
24
25
26
27
S
1
0
0
0
0
0
0
1
ACK
Measurement
I²C address + read
Hold during measurement
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
0
1
1
1
1
1
0
0
ACK
1
0
0
0
0
0
1
0
ACK
Data (MSB)
Data (LSB)
Status
46
47
48
49
50
51
52
53
54
1
0
0
1
0
1
1
1
NACK
P
Checksum
Hold Master communication sequence
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S
1
0
0
0
0
0
0
0
ACK
1
1
1
1
0
1
0
1
ACK
I²C address + write
Command (see table p.9)
19
20
21
22
23
24
25
26
27
Measurement
S
1
0
0
0
0
0
0
1
NACK
measuring
I²C address + read
19
20
21
22
23
24
25
26
27
Measurement
S
1
0
0
0
0
0
0
1
ACK
continue measuring
I²C address + read
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
0
1
1
1
1
1
0
0
ACK
1
0
0
0
0
0
1
0
ACK
Data (MSB)
Data (LSB)
Status
46
47
48
49
50
51
52
53
54
1
0
0
1
0
1
1
1
NACK
P
Checksum
No Hold Master communication sequence
Grey blocks are controlled by HTU21D(F) sensor.
For Hold Master sequence, bit 45 may be changed to NACK followed by a stop condition to omit checksum transmission.
For No Hold Master sequence, if measurement is not completed upon “read” command, sensor does not provide ACK on bit
27 (more of these iterations are possible). If bit 45 is changed to NACK followed by stop condition, checksum transmission is
omitted.
In those examples, the HTU21D(F) sensor output is SRH = ‘0111’1100’1000’0000 (0x7C80). For the calculation of physical
values status bits must be set to ‘0’. Refer to “Conversion of signal outputs” section p.16.
The maximum duration for measurement depends on the type of measurement and resolution chosen. Maximum values shall
be chosen for the communication planning of the MCU. Refer to the table p.4 and p.6 regarding measuring time specifications.
I²C communication allows for repeated start conditions without closing prior sequence with stop condition.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 12
• Diagnostic Status
Status Bit are implemented for internal diagnostic and data information (RH or Temperature)
Diagnostic State “00” is triggered when:
• sensor displays values ≤ -6%RH or values ≤ -46,85°C
• sensor is in open circuit condition
Diagnostic State “11” is triggered when:
• sensor displays values ≥ 119 %RH or values ≥ 128,87°C
• sensor is in short circuit condition
DATA MSB
DATA LSB
Status Bit
00 00 00 00
00 00 00
00
Diag State (Open circuit)
XX XX XX XX
XX XX XX
00
Temperature data
XX XX XX XX
XX XX XX
10
Humidity data
11 11 11 11
11 11 11
11
Diag State (Short Circuit)
A sensor is defective, only if the diagnostic state remains when external conditions change.
• Soft reset
This command is used for rebooting the HTU21D(F) sensor switching the power off and on again. Upon reception of this
command, the HTU21D(F) sensor system reinitializes and starts operation according to the default settings with the exception
of the heater bit in the user register. The soft reset takes less than 15ms.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S
1
0
0
0
0
0
0
0
ACK
1
1
1
1
1
1
1
0
ACK
P
I²C address + write
Soft Reset Command
Grey blocks are controlled by HTU21D(F) sensor.
• User register
The content of user register is described in the table below. Reserved bits must not be changed and default values of
respective reserved bits may change over time without prior notice. Therefore, for any writing to user register, default values of
reserved bits must be read first.
The “End of Battery” alert/status is activated when the battery power falls below 2.25V.
The heater is intended to be used for functionality diagnosis: relative humidity drops upon rising temperature. The heater
consumes about 5.5mW and provides a temperature increase of about 0.5-1.5°C.
OTP reload is a safety feature and load the entire OTP settings to the register, with the exception of the heater bit, before
every measurement. This feature is disabled per default and it is not recommended for use. Please use soft reset instead as it
contains OTP reload.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 13
Bit
#Bits
Description/Coding
Default
7,0
2
Measurement resolution
Bit 7
Bit 0
RH
Temp
0
0
12 bits
14 bits
0
1
8 bits
12 bits
1
0
10 bits
13 bits
1
1
11 bits
11 bits
‘00’
6
1
Status: End of Battery(1)
‘0’: VDD>2.25V
‘1’: VDD<2.25V
‘0’
3, 4, 5
3
Reserved
‘0’
2
1
Enable on-chip heater
‘0’
1
1
Disable OTP reload
‘1’
(1) This status bit is updated after each measurement
Cut-off value for “End of Battery” signal may vary by ±0.1V.
Reserved bits must not be changed.
OTP reload active loads default settings after each time a measurement command is issued.
• I²C communication reading and writing the user register example
In this example, the resolution is set to 8 bits / 12 bits (for RH/Temp) from default configuration.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
S
1
0
0
0
0
0
0
0
ACK
1
1
1
0
0
1
1
1
ACK
I²C address + write
Read Register Command
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
S
1
0
0
0
0
0
0
1
ACK
0
0
0
0
0
0
1
0
NACK
I²C address + read
Register content
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
S
1
0
0
0
0
0
0
0
ACK
1
1
1
0
0
1
1
0
ACK
I²C address + write
Write Register Command
55
56
57
58
59
60
61
62
63
0
0
0
0
0
0
1
1
ACK
P
Register Content to be written
Grey blocks are controlled by HTU21D(F) sensor.
• CRC Checksum
HTU21D(F) sensor provides a CRC-8 checksum for error detection. The polynomial used is X8 + X5 + X4 + 1.
Basic Considerations
CRC stands for Cyclic Redundancy Check. It is one of the most effective error detection schemes and requires a minimal
amount of resources.
The types of errors that are detectable with CRC that is implemented in HTU21D(F) sensors are:
• Any odd number of errors anywhere within the data transmission
• All double-bit errors anywhere within the transmission
• Any cluster of errors that can be contained within an 8-bit window (1-8 bits incorrect)
• Most larger clusters of errors
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
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A CRC is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw
data.
Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of
their contents; on retrieval the calculation is repeated, and corrective action can be taken against presumed data corruption if
the check values do not match.
CRCs are so called because the check (data verification) value is a redundancy (it expands the message without adding
information) and the algorithm is based on cyclic codes. CRCs are popular because they are simple to implement in binary
hardware, easy to analyze mathematically, and particularly good at detecting common errors caused by noise in transmission
channels. Because the check value has a fixed length, the function that generates it is occasionally used as a hash function.
CRC for HTU21D(F) sensors using I²C Protocol
When HTU21D(F) sensors are run by communicating with the standard I²C protocol, an 8-bit CRC can be used to detect
transmission errors. The CRC covers all read data transmitted by the sensor. CRC properties for HTU21D(F) sensors
communicating with I²C protocol are listed in the table below.
CRC with I²C protocol
Generator polynomial
X8 + X5 + X4 + 1
Initialization
0x00
Protected data
Read data
Final Operation
none
CRC calculation
To compute an n-bit binary CRC, line the bits representing the input in a row, and position the (n+1)-bit pattern representing
the CRC's divisor (called a "polynomial") underneath the left-hand end of the row.
This is first padded with zeroes corresponding to the bit length n of the CRC.
If the input bit above the leftmost divisor bit is 0, do nothing. If the input bit above the leftmost divisor bit is 1, the divisor is
XORed into the input (in other words, the input bit above each 1-bit in the divisor is toggled). The divisor is then shifted one bit
to the right, and the process is repeated until the divisor reaches the right-hand end of the input row.
Since the left most divisor bit zeroed every input bit it touched, when this process ends the only bits in the input row that can
be nonzero are the n bits at the right-hand end of the row. These n bits are the remainder of the division step, and will also be
the value of the CRC function.
The validity of a received message can easily be verified by performing the above calculation again, this time with the check
value added instead of zeroes. The remainder should equal zero if there are no detectable errors.
CRC examples
The input message 11011100 (0xDC) will have as result 01111001 (0x79).
The input message 01101000 00111010 (0x683A: 44.8%RH) will have as result 01111100 (0x7C).
The input message 01001110 10000101 (0x4E85: 7.04°C) will have as result 01101011 (0x6B).
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
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CONVERSION OF SIGNAL OUTPUTS
Default resolution is set to 12-bit relative humidity and 14-bit temperature readings. Measured data are transferred in two byte
packages, i.e. in frames of 8-bit length where the most significant bit (MSB) is transferred first (left aligned). Each byte is followed
by an acknowledge bit. The two status bits, the last bits of LSB, must be set to ‘0’ before calculating physical values.
To accommodate/adapt any process variation (nominal capacitance value of the humidity die), tolerances of the sensor above
100%RH and below 0%RH must be considered. As a consequence:
▪ 118%RH corresponds to 0xFF which is the maximum RH digital output that can be sent out from the ASIC.
RH output can reach 118%RH and above this value, there will have a clamp of the RH output to this value.
▪ -6%RH corresponds to 0x00 which is the minimum RH digital output that can be sent out from the ASIC. RH
output can reach -6%RH and below this value, there will have a clamp of the RH output to this value.
• Relative Humidity conversion
With the relative humidity signal output SRH, the relative humidity is obtained by the following formula (result in %RH), no
matter which resolution is chosen:
16
2
1256RH
S
RH
In the example given p.10, the transferred 16-bit relative humidity data is 0x7C80: 31872. The relative humidity results to be
54.8%RH.
• Temperature conversion
The temperature T is calculated by inserting temperature signal output STemp into the following formula (result in °C), no
matter which resolution is chosen:
16
2
72.17585.46 Temp
S
Temp
APPLICATION: DEW POINT TEMPERATURE MEASUREMENT
The dew point is the temperature at which the water vapor in the air becomes saturated and condensation begins.
The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current
air temperature. Relative humidity of 100% indicates that the dew point is equal to the current temperature (and the air is
maximally saturated with water). When the dew point stays constant and temperature increases, relative humidity will
decrease.
Dew point temperature of the air is calculated using Ambient Relative Humidity and Temperature measurements from
HTU21D(F) sensor with following formulas given below:
Partial Pressure (PPTamb) formula from Ambient Temperature:
)(
10 CTamb
B
A
Tamb
PP
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
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Dew point Temperature (Td) formula from Partial Pressure (PPTamb):
PPTamb Partial Pressure in mmHg at ambient temperature (Tamb)
RHamb Ambient humidity in %RH, computed from HTU21D(F) sensor
Tamb Humidity cell temperature in °C, computed from HTU21D(F) sensor
Td Calculated Dew Point in °C
A, B, C Constants: A=8.1332; B=1762.39; C=235.66
PACKAGE OUTLINE
• HTU21D Sensor Dimensions
C
A
PP
RH
B
T
Tamb
amb
d
100
log10
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
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Dimensions are given in mm, tolerances are ±0.1mm. The die pad (thermal center pad) is internally connected to GND.
• HTU21DF Sensor Dimensions
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
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Dimensions are given in mm, tolerances are ±0.1mm. The die pad (thermal center pad) is internally connected to GND.
• Packaging Type
HTU21D(F) sensors are provided in DFN packaging. DFN stands for Dual Flat No leads.
The HTU21D(F) sensor chip is mounted to a lead frame made of Cu and plated with Ni/Pd/Au. Chip and lead frame are over
molded by green epoxy-based mold compound. Please note that side walls of sensors are diced and hence lead frame at
diced edge is not covered with respective protective coating.
The total weight of the sensor is 0.025g.
• Traceability Information
All HTU21D(F) sensors are laser marked with an alphanumeric, five-digit code on the sensor as pictured below.
The marking on the HTU21D(F) sensor consists of two lines with five digits each:
• The first line denotes the sensor type: HTU21.
• The second line denotes several information as:
o The first digit of the second line defines the output mode:
D or A = digital and I²C
• D : ±2%RH typical / ±3%RH max from 20%RH to 80%RH
• A : ±2%RH typical / ±3%RH max from 15%RH to 90%RH
P = PWM
o The second digit defines the manufacturing year: 3 = 2013, 4 = 2014, etc.
o The last three digits represent an alphanumeric tracking code. That code represents the day of the
year.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
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Laser marking on HTU21D(F) sensor
Reels are also labeled, as displayed below and give additional traceability information.
With:
2X: Sensor Type (21 for HTU21)
Y: Output mode (D/A = Digital, P = PWM)
(F): Sensor with PTFE membrane option
TTTTTTTTT: MEAS Traceability Code
QQQQ: Quantity per reel (400, 1500 or 5000 units)
YY: Last two digits of the year
DDD: Day of the year
HTU21
D3157
HTU21
D3157
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
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• Tape and Reel Packaging
HTU21D(F) sensors are shipped in tape & reel packaging, sealed into antistatic ESD bags.
Standard packaging sizes are 400, 1500 and 5000 units per reel. Each reel contains 440mm (55 pockets) header tape and
200mm (25 pockets) trailer tape. The drawing of the packaging tapes with sensor orientation is shown in the picture below.
• Packaging reels
For 400 and 1500 units: outside diameter of 7” (178mm) and a 1/2” (13mm) diameter arbor hole.
For 5000 units: outside diameter of 13” (330mm) and a 1/2” (13mm) diameter arbor hole.
• Handling / Storage recommendations
In order to use and preserve the high quality performance of the HTU21 humidity and temperature sensor, the following
recommendations have to be followed concerning storage and packaging.
Please read the paragraph below carefully and note that all precautions are applicable for design phases, production phases
as well as in case of returned material to Measurement Specialties.
When sensors are not used or assembled, we recommend to store them in their original sealed anti ESD packaging. If sensors
have been removed from their original packaging, we recommend to keep them into anti static shielded ESD bags.
Such SMD sensors is classified MSL level 1 according to IPC/JEDEC J-STD-020.1 for storage, packaging and handling.
We recommend a shelf life of 1 year in following conditions of temperature and relative humidity ≤30°C 85%RH.
USER DIRECTION
OF UNREELING
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
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Protection against ESD mandatory
ORDERING INFORMATIO
** HTU21D – I.C 21D RH/T DIGITAL **
Package: TAPE AND REEL M.P.Q OF 400 PIECES, 1500 PIECES or 5000 PIECES
▪ HPP845E031R4 - I.C 21D RH/T DIGITAL in tape and reel of 400 pieces
▪ HPP845E031R1 - I.C 21D RH/T DIGITAL in tape and reel of 1500 pieces
▪ HPP845E031R5 - I.C 21D RH/T DIGITAL in tape and reel of 5000 pieces
** HTU21DF – I.C 21DF RH/T DIGITAL with ptfe membrane **
Package: TAPE AND REEL M.P.Q OF 400 PIECES, 1500 PIECES or 5000 PIECES
▪ HPP845E131R4 - I.C 21DF RH/T DIGITAL in tape and reel of 400 pieces
▪ HPP845E131R1 - I.C 21DF RH/T DIGITAL in tape and reel of 1500 pieces
▪ HPP845E131R5 - I.C 21DF RH/T DIGITAL in tape and reel of 5000 pieces
** I.C 21D DEMOKIT – WPP100B001: BLE Sensor Tag Demo for use with free Android or iOS application **
** I.C 21D DEMOKIT – WPP109B001: BLE Sensor Tag Demo for use with USB dongle Key for Windows PC **
For detailed information, please request to pic.info@te.com.
HTU21D(F) RH/T SENSOR IC
Digital Relative Humidity sensor with Temperature output
TE CONNECTIVITY SENSORS /// HTU21D(F) RH/T SENSOR IC 05/2017
Page 22
Edition
Comments
Who
Date
0
Document creation
D. LE GALL
April 12
A
General update
D. LE GALL-ZIRILLI
February 13
2
HTU21DF product with embedded PTFE membrane
reference added, Storage conditions after soldering process
updated (typing error), ESD performances updated,
complementary information on RH output signal in
“Conversion of signal outputs” paragraph, information on tape
and reel packaging added, HTU21D demokit availability
information added.
D. LE GALL-ZIRILLI
July 13
3
Correction of I²C communication reading and writing,
correction of soldering peak temperature
M.ROBERT
October 2013
4
Obsolescence of HTU21S (SDM interface) version
External package dimensions update
M.ROBERT
January 2014
5
Part number and designation modification
M.ROBERT
April 2014
6
General update
M.ROBERT
October 2014
7
Diagnostic paragraph added
MSL level 1 informed
Sensor dimension updated
DEMOKIT ordering information updated
P.METRAL
December 2015
8
CRC example correction.
P.METRAL
February 2016
NORTH AMERICA
Measurement Specialties, Inc.,
a TE Connectivity company
Tel: 800-522-6752 (option 2)
Email: customercare.ando@te.com
EUROPE
MEAS France SAS,
a TE Connectivity company
Tel: 800-440-5100
Email: customercare.tlse@te.com
ASIA
Measurement Specialties (China) Ltd.,
a TE Connectivity company
Tel: 0400-820-6015
Email: customercare.chdu@te.com
TE.com/sensorsolutions
Measurement Specialties, Inc., a TE Connectivity company.
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