SENSIRION SHT3x Temperature and Humidity Sensors Instruction Manual

SHT3x – SHT4x Transition Guide for Analog Sensors
Boarding the new flagship RH/T sensor generation
SHT3x
SHT4x
Instruction Manual

SHT3x Temperature and Humidity Sensors

• Improved accuracy and robustness
• Higher driving strength
• Powerful internal heater for self-decontamination and creep prevention
• Superior versatility and technology from two decades of sensor development

Abstract
Introduced as a highly versatile humidity (RH) and temperature (T) sensor platform, the SHT3x family already enables outstanding sensing performance for several years. Sensirion now proudly features its all-new flagship sensors from the SHT4x family, which profit from about two decades of RH/T sensor development. Dedicated to best-in-class performance, smallest footprint, and attractive pricing, our new SHT4x sensors are the products of choice for many SHT3x applications. In particular, the SHT4x outperforms the SHT3x in every aspect and offers versatile add-ons, such as a powerful heater for self- decontamination, conformal coating protection, or filter membranes. Moreover, the latest analog output circuitry enables reduced the PSRR (Power Supply Rejection Ratio) and further increase of the driving strength of the load.

Important changes

Dimensions (mm3)
Pin assignment| 2.5 x 2.5 x 0.9
8 pins| 1.5 x 1.5 x 0.5
4 pins
Interface| 5 Analog output characteristics| 5 Analog output characteristics
Supply voltage (V)| 2.4 — 5.5| 4.5 — 5.5
Av. current (AA)| 220| 520
Typ. RH accuracy (%RH)| ±3.0| ±2.5
Typ. T accuracy (°C)| ±0.3| ±0.3
Response time r63% (s)
Additional features| 8
Heater for plausibility checks only.| 6
Powerful heater with A T60°C
Full condensation robustness

General

This document first highlights the new features and differences from the previous generation. It then aims to provide a high-level guideline to replace SHT3x with sensors from the SHT4x family and outlines important differences to be considered in design-in processes.

Performance Comparison

2.1 Relative Humidity and Temperature

Relative humidity
RH accuracy1| Typ.| ±3| ±2.5| %RH
Repeatability2| | 0.1| 0.5| %RH
Resolution3| –| 0.01| 0.01| %RH
Hysteresis| –| ±0.8| ±0.8| %RH
Specified range4| extended5| 0 to 100| 0 to 100| %RH
Response time,| r 63%| 8| 6| s
Long-term drift,| Typ.| <0.25| <0.25| %RH/y
Sensitivity| VDD = 5.0 V| 40| 40| mV/%RH
Condensation behavior| Droplet formation| Slight signal drop| No signal drop| –
Temperature
T Accuracy1| Typ.| ±0.3| ±0.3|
Repeatability2| –| 0.06| 0.1| °C
Resolution3| –| 0.01| 0.01| °C
Specified range4| –| -40 to +125| -40 to +125| °C
Response time,| T 63%| >2| 2| s
Long-term drift,| Typ.| < 0.03| < 0.03| °C/y
Sensitivity| VDD = 5.0 V| 23.| 23| mV/°C

Table 1. Humidity and temperature specifications of the SHT3x and SHT4x, where bold values highlight important differences. For further details, kindly refer to the SHT3x and SHT4x datasheets.

1. For definition of typ. accuracy, please refer to the document “Sensirion Humidity Sensor Specification Statement”.
2. The stated repeatability is 3 times the standard deviation (3σ) of multiple consecutive measurement values at constant conditions and is a measure for the noise on the physical sensor output.
3. Resolution of A/D converter.
4. Specified range refers to the range for which the humidity or temperature sensor specification is guaranteed.
5. For details about recommended humidity and temperature operating range, please refer to the SHT4x Datasheet.
6. Time for achieving 63% of a humidity step function, valid at 25°C and 1 m/s airflow. Humidity response time in the application depends on the design-in of thesensor.
7. Typical value for operation in normal RH/T operating range. Max. value is < 0.5 %RH/y. Value may be higher in environments with vaporized solvents, out-gassingtapes, adhesives, packaging materials, etc. For more details, please refer to Handling Instructions.
8. Temperature response time depends on heat conductivity of sensor substrate and design-in of sensor in application.
9. Max. value is < 0.04°C/y.

2.2 Electrical Characteristics

Slew rate change of
the supply voltage| ,
VDD.slew| | –| –| 20| | –| 20| V/ms
Supply current| /DD| Measurement| –| 220| 300| –| 520| tbd| pA
Resistive load to VSS| RL| | 50| >1000| –| 1| –| –| ko
Capacitive load| CL| | 1| 4.| 5| –| –| 100| nF
Application circuit
design| –| –| Largely advantageous for SHT4x, see Section 6| –

Table 2. Key electrical specifications of the SHT3x and SHT4x, where bold values highlight important differences. For further details, kindly refer to the SHT3x and SHT4x datasheets.

2.3 Timing Specifications

Parameter| Symbol| Conditions| Min| SHT3x
Typ.| Max| Min| SHT4x
Typ.| Max| Units
---|---|---|---|---|---|---|---|---|---
Power-up time| fpu| After hard reset,
VDD VPOR| | –| 17| –| tbd| 200| ms
Analog out settling
time| | For a step of
VDD 12| –| 0.3| | | tbd| | ms
Measurement interval| tMeasint| Heater disabled| | | | | 0.5| | s
Heater-on duration| tHeat| | –| –| –| 0| | 2| s

Table 3. Key timing specifications of the SHT3x and SHT4x, where bold values highlight important differences. For further details, kindly refer to the SHT3x and SHT4x datasheets.

Flagship SHT4x Feature: Built-In Heater

The SHT4x analog sensor incorporates an optional powerful on-chip heater on request, which can be used for selfdecontamination, e.g., in environments with solvents present, and periodical creep compensation in prolonged application in highest humidity. It provides an over-temperature up to about 60 °C and different heater powers (up to 200 mW) and durations (up to 2 s) can be selected. There is no dedicated command to turn off the heater since it has an internal timer after which it is switched off automatically. However, it is important to note that in case the active heater option is chosen by the user, the sensor will be continuously running periodic heating pulses in specific measurement intervals defined at factory level.

Package Differences

The SHT4x comes in a new open-cavity dual flat no lead (DFN) package design in order to enable additional features, such as conformal coating, protection cover, and filter membrane compatibility. In comparison to the SHT3x, the package is considerably smaller, enabling power efficient, accurate, and robust RH/T sensing with fast reaction times. Instead of featuring eight pins, the bottom side of the SHT4x DFN package exposes four metallic contacts, which are Ni/Pd/Au coated.

Figure 1, Figure 2.
Sensor opening| –| Top| Top|
Protection compatibility| –| Compatible with conformal coating,
Compatible with filter membranes| Compatible with conformal coating,
Compatible with filter membranes|
Pin Layout| –| 2 x 4 pins| 2 x 2 pins|
Necessity for fine-print PCB| –|  no| no|
Pin Assignment| –| | | Drawings not to scale
VDD: Supply voltage
SCL: Serial clock
SDA: Serial data bidirectional
VSS: Ground
R: no electrical function
Pin Size| mm| 0.25 x 0.35| 0.3 x 0.3|
Pin Pitch| mm| 0.5| 0.8|
Pin Material| –| Ni/Pd/Au coated Cu| Ni/Pd/Au coated Cu|
Housing Material| –| Epoxy housing| Epoxy housing|

Table 4. Key package differences between the SHT3x and SHT4x. For further details, kindly refer to the SHT3x and SHT4x datasheets

Figure 1. Dimensional drawing of the SHT3x including (units mm).

Figure 2. Dimensional drawing of SHT4x including package tolerances (units mm).

Communication and Signal Output

The start-up of the sensor and the conversion of the signal output have not undergone major changes, apart from the power-up/down levels reported in Table 2. In addition, all the voltage output characteristics have been maintained, only the names have been changed following the scheme reported in Table 5.

Table 5. New nomenclature of the SHT4x version and corresponding SHT3x version.

New Features and Design-in Advantages

The new SHT4x generation shows two main improvements in the analog output circuitry with respect to the previous SHT3x version. First, the new design introduces several enhancements (reference filtering, output buffer optimized bandwidth…) to improve the Power Supply Rejection Ratio (PSRR), which yields less noise on the output signals.
Second, the new design of the output buffers strongly increases the driving capability of resistive and capacitive loads (down to 1 kΩ and up to 100 nF respectively). Moreover, it is worth comparing the SHT4x sensor to the existing solutions available in the analog market. Table 6 reports some examples of Sensirion solutions and other SMD sensors.

| Haechitech
MXH1100| TE-ConnectivityHTU31V| Sensirion
SHT3x| Sensirion
SHT4x
---|---|---|---|---
Capacitive load up to| 400 pF| 5 nF| 5 nF| 100 nF

Table 6. Capacitive load comparison considering chip size analog sensors
In terms of design-in advantages, the new SHT4x improved PSRR and the higher output current allow major overall cost savings. In fact, any active filtering circuitry at the sensor’s output is no longer needed to improve PSRR or to drive long cables.
The following figures highlight the improvements just mentioned compared to the previous sensor generation. The first schematic (Figure 3) shows a standard application of the SHT3x in which loads are directly connected to the output pins. This configuration has two main limitations: the output signals are subject to significant noise and it cannot drive significant loads.

Figure 3. Standard schematic for the SHT3x. Load is directly connected to the sensor, but there is large noise at the output.

To improve these limitations, some additional components may be introduced between the SHT3x sensor and the load, as shown in Figure 4. In this example, the first external stage is a passive RC filter to reduce the noise while the second external stage is an OpAmp (Operational Amplifier) to increase the driving capability. If this solution improves the overall performance, it also significantly increases the total production costs.

Figure 4. Possible improved schematic for the SHT3x. This solution allows greater drive capability and reduces output noise.
However, it considerably increases the overall costs of the final product.
On the other hand, the implementation of the new SHT4xI sensor brings evident design-in advantages and improves performances as well. Thanks to the new chip design, significant loads can now be connected directly to the output pins while no additional noise-filtering stage is needed. This dramatically simplifies the final product, as reported in Figure 5, and results in significant cost saving.

Figure 5. Standard schematic for the new SHT4xI analog sensor. Significant loads can be directly connected to the sensor and the output signals have negligible noise.

Quality and Material Contents

Qualification of the SHT3x and SHT4x is performed based on the JEDEC JESD47 qualification test method. W devices are fully RoHS and REACH compliant, the SHT4x is also WEEE compliant.

Further Information

This transition guide aims at providing an overview of the key differences between the SHT3x and the SHT4x, yet it might not be fully inclusive. For further reading on the SHT4x specifications, communication, operation, and application, please consult the dedicated SHT3x and SHT4x documents provided on the Sensirion webpage www.sensirion.com. In case you are in need of specific details, or would like to request assistance in transitioning from the SHT3x to the SHT4x or any other Sensirion product, please consult us directly at www.sensirion.com/en/about- us/contact/.

Revision History

Important Notices
Warning, Personal Injury
Do not use this product as safety or emergency stop devices or in any other application where failure of the product could resultin personal injury. Do not use this product for applications other than its intended and authorized use. Before installing, handlingusing or servicing this product, please consult the data sheet and application notes. Failure to comply with these instructionscould result in death or serious injury.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify andhold harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if SENSIRION shall be allegedly negligent with respect to the design or the manufacture of the product.ESD Precautions The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD-induced damage and/ordegradation, take customary and statutory ESD precautions when handling this product. See application note “ESD, Latchup and EMC” fomore information.

Warranty
SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of delivery that thisproduct shall be of the quality, material and workmanship defined in SENSIRION’s published specifications of the product. Within such period, if proven to be defective, SENSIRION shall repair and/or replace this product, in SENSIRION’s discretion, free of charge to the Buyerprovided that:
• notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;
• such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design, material, orworkmanship;
• the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; and
• the warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period.
This warranty does not apply to any equipment which has not been installed and used within the specifications recommended by SENSIRIONfor the intended and proper use of the equipment. EXCEPT FOR THE WARRANTIES EXPRESSLY SET FORTH HEREIN, SENSIRIONMAKES NO WARRANTIES, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT. ANY AND ALL WARRANTIES,INCLUDING WITHOUT LIMITATION, WARRANTIES OF  ERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, AREEXPRESSLY EXCLUDED AND DECLINED.
SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper use of the goods. SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated or storednot in accordance with the technical specifications.
SENSIRION does not assume any liability arising out of any application or use of any product or circuit and specifically disclaims any and allliability, including without limitation consequential or incidental damages. All operating parameters, including without limitation recommendedparameters, must be validated for each customer’s applications by customer’s technical experts. Recommended parameters can and do vary in different applications.
SENSIRION reserves the right, without further notice, (i) to change the product specifications and/or the information in this document and (iito improve reliability, functions and design of this product.
Copyright
© 2022, by SENSIRION. CMOSens® is a trademark of Sensirion. All rights reserved

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References

• Smart sensor solutions
• Smart sensor solutions
• Smart sensor solutions
• Smart sensor solutions
• Smart sensor solutions
• Smart sensor solutions
• Humidity

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