Low-Power VOC Smart Sensing Module
Description
IDT’s SMOD707 is a complete smart sensing solution for general
volatile organic compounds (VOCs). The module, consisting of
the SMOD smart sensing platform combined with IDT’s SGAS707
VOC sensor, provides an indication of total VOCs measured both
as resistance and as a linear response proportional to the
concentration of a representative VOC calibration gas (ethanol).
The SMOD707 communicates with an external controller or a
data logger through a USB interface, and it can be supplied with
an I
2
C or UART interface via special order.
The SGAS707 sensor can be supplied separately from the
SMOD707 Smart Sensing Module. See the
SGAS707 Datasheet
for more information.
Figure 1. SMOD707 Smart Sensing Module
SMOD707
Datasheet
Features
High-sensitivity, non-specific detection of a wide range of
VOCs
Sensor operating parameters can be tailored to specific VOC
measurement applications
Targeted toward OEM system integration and peripheral
device applications
Typical Applications
General indoor air quality
Solvent levels in manufacturing environments
Typical Module Response
Figure 2 shows the typical response and selectivity of the SMOD707 module for detecting several applied VOC and non-VOC gases operated
in clean, dry air.
Figure 2.
Typical Response and Selectivity of the SMOD707 vs. Common VOC Gases
Sensor resistance (ohms)
Air
1.0E+07
Ethanol
Isobutylene
Acetone
1.0E+06
Formaldehyde
Toluene
1.0E+05
1
10
100
Octane
Xylenes
Concentration (ppm)
© 2017 Integrated Device Technology, Inc.
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July 21, 2017
SMOD707 Datasheet
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the SMOD707. These ratings, which are standard values for IDT
commercially rated parts, are stress ratings only. Functional operation of the device at these or any other conditions above those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can affect
product reliability. Electrical parameters are guaranteed only over the recommended operating temperature range.
Table 1.
SMOD707 Absolute Maximum Ratings
Symbol
V
IN
Parameter
Supply Voltage (referenced to ground)
Digital Inputs and Output Voltage Level
Electrostatic Discharge (MIl-STD-883)
Conditions
Minimum
-0.5
2000
0
-65
Maximum
12
3.8
50
150
Units
V
V
V
°C
°C
T
AMB
T
STOR
Ambient Operating Temperature
Storage Temperature
Recommended Operating Conditions
Table 2.
Recommended Operating Conditions
Symbol
V
IN
T
AMB
RH
Parameter
Supply Voltage (referenced to ground)
Ambient Operating Temperature
Ambient Relative Humidity – Non-condensing
Minimum
0
0
Typical
5
Maximum
50
95
Units
V
°C
%
DC Electrical Characteristics
Table 3.
DC Electrical Characteristics
Symbol
V
IN
V
IN,RIPPLE
I
IN
V
HTR
I
HTR
V
SEN
Parameter
Input Voltage
Input Voltage Ripple
Input Supply Current
Heater Drive Voltage
Heater Drive Current
Sensor Drive Voltage
Conditions
I
HTR
= 114mA
I
HTR
= 114mA
Minimum
4.5
Typical
5
125
3.5
114
Maximum
12
100
140
3.85
125
3.0
Units
V
mV
PP
mA
V
mA
V
© 2017 Integrated Device Technology, Inc.
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July 21, 2017
SMOD707 Datasheet
Interface Characteristics
The SMOD707 utilizes a USB communication interface that conforms to the USB 2.0 standard.
Connector Assignments
Refer to Figure 3 for the location of the connectors described in the following tables.
Figure 3.
Connector Locations on the SMOD707
Pin 1
Pin 2
Power Supply
Terminal (J2)
Pins 1 2 3 4 5
USB Connector (J3)
Table 3.
Pin Assignments: 2-Post Screw Terminal for Input Power (J2)
Pin Number
1
2
Table 4.
Description
Power ground
V
IN
Pin Assignments: Mini-B Connector for USB Communications (J3)
Pin Number
1
2
3
4
5
Description
VBUS
D+
D-
No connection
USB ground
© 2017 Integrated Device Technology, Inc.
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July 21, 2017
SMOD707 Datasheet
The SGAS707 VOC sensor is housed in a TO-39 package. Figure 4 shows the combined TO-39/46 sensor socket (SEN1) on the module.
The SGAS707 sensor utilizes pins 1, 2, 3, and 4 (pins 5-7 are unused). Figure 4 provides the definitions of the pins.
Figure 4.
Top View SEN1 Sensor Socket
1
7
4
3
Table 5.
Pin Assignments: TO-39 Sensor Socket for SGAS707 (SEN1)
5
6
2
Pin Number
1 (clockwise from tab)
2, 5
3, 6
4, 7
Description
Heater +
Sensor +
Heater -
Sensor -
© 2017 Integrated Device Technology, Inc.
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July 21, 2017
SMOD707 Datasheet
Principles of Operation
The SMOD707 module consists of a combination of the SMOD smart sensing platform and a SGAS707 VOC sensor. The SMOD smart
sensing platform is a general purpose microcontrolled device with a broad array of capabilities that can be applied in gas sensing
applications. As in other SMOD7xx devices, the SMOD707 selects a subset of measurement and control capabilities from a larger set and
adds application-specific settings/capability, such as default sensor operation parameters, and calibration and analysis algorithms appropriate
for the gas sensor utilized in the module.
Figure 5.
SMOD707 Block Diagram
Microcontroller
I
2
C
PWM
Comm
ADC
Port
Drive
External
Controller
USB
UART
MOS
FTDI
Memory
Power Requirements
The SMOD707 utilizes an SGAS707 ceramic sensor that requires a nominal heater drive of 3.5V at 114mA. The input power to the module
can be sourced from one of the following:
4.5V to 12V DC power supply connected directly to J2
USB +5V supply
External commands (described below) support operation of the sensor heater at voltages other than 3.5V. Power supplied to the module does
not require regulation, but the supply should have a ripple of less than 0.1V under load.
External Communication
The SMOD707 communicates with external devices via a USB connection at J3 (Mini-B connector). The SMOD707 conforms to the USB 2.0
specification (full speed). The communication protocol used for sending commands to and receiving responses from the SMOD707 is
described in the “Communication Protocol” section.
Sensor Operating Conditions
The SMOD707 operates the SGAS707 sensor in isothermal mode at a constant voltage defaulting to 3.5V. This corresponds to a nominal
heater current of 114mA and a heater power of 400mW. The heater voltage is regulated via a feedback measurement so that the voltage set-
point is maintained under changing environmental conditions. The heater voltage set-point can be altered via the
HVw
command described in
the “Command Summary” section.
Sensor measurements are performed by default once every second; this rate may be changed to any value between 1 and 60 seconds using
the
PDw
command.
© 2017 Integrated Device Technology, Inc.
5
Sensor
Heater
July 21, 2017
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