How the INA333 Amplifies Small Sensor Signals

FREE-SKY (HK) ELECTRONICS CO.,LIMITED / 06-15 15:37

The INA333 instrumentation amplifier IC is designed for accurate measurement of very small differential signals. This article explains the INA333 main features, pin functions, equivalent parts, working principle, proper usage, real-world applications, and comparison with other instrumentation amplifiers.

Catalog

1. INA333 Instrumentation Amplifier IC

2. Equivalent for INA333 IC

3. INA333 Key Features and Specifications

4. INA333 Pin Configuration and Functions

5. How the INA333 IC Works

6. How to Utilized INA333 IC

7. Real-World Applications of the INA333

8. INA333 vs Other Instrumentation Amplifiers

9. Mechanical Dimensions of INA333

10. Manufacturer

INA333 Instrumentation Amplifier IC

The AD623

• INA188

INA333 Key Features and Specifications

Parameter	INA333 Specification
Device Type	Precision Instrumentation Amplifier
Supply Voltage Range	1.8 V to 5.5 V
Absolute Maximum Supply Voltage	7 V
Gain Range	1 to 1000
Gain Formula	G = 1 + (100 kΩ / RG)
Input Offset Voltage	25 μV (Max), G ≥ 100
Offset Voltage Drift	0.1 μV/°C, G ≥ 100
Input Noise Density	50 nV/√Hz, G ≥ 100
Common-Mode Rejection Ratio (CMRR)	100 dB (Min), G ≥ 10
Input Bias Current	200 pA (Max)
Quiescent Current	50 μA (Typical)
Input Voltage Range	(V−) + 0.1 V to (V+) − 0.1 V
Output Voltage Range	(V−) + 0.05 V to (V+) − 0.05 V
RFI Filtering	Integrated RFI Filtered Inputs
Operating Temperature Range	−40°C to +125°C
Storage Temperature Range	−65°C to +150°C
Junction Temperature	+150°C (Max)
Human Body Model (HBM) ESD Rating	±4000 V
Charged Device Model (CDM) ESD Rating	±1000 V
Machine Model (MM) ESD Rating	±200 V
Package Options	8-Pin VSSOP, 8-Pin WSON
Junction-to-Ambient Thermal Resistance (VSSOP)	169.5 °C/W
Junction-to-Ambient Thermal Resistance (WSON)	60 °C/W
Low-Power Operation	Yes
Precision Performance	High Accuracy, Low Drift, Low Noise

INA333 Pin Configuration and Functions

Pin No.	Pin Name	I/O	Function
1	RG	—	Gain-setting pin. Connect a gain resistor between Pins 1 and 8 to set the amplifier gain above 1.
2	VIN−	Input	Inverting (negative) differential input signal.
3	VIN+	Input	Non-inverting (positive) differential input signal.
4	V−	Power	Negative power supply connection.
5	REF	Input	Reference voltage input that sets the output reference level. Typically connected to ground in single-supply systems.
6	VOUT	Output	Amplified output signal.
7	V+	Power	Positive power supply connection.
8	RG	—	Gain-setting pin. Connect a gain resistor between Pins 1 and 8 to configure the desired gain.

How the INA333 IC Works

The INA333 uses a three-op-amp instrumentation amplifier architecture to accurately amplify small differential signals while rejecting unwanted noise. As shown in the diagram, the input signals enter through VIN+ and VIN−, where integrated RFI-filtered inputs help reduce radio-frequency interference before amplification.

The first stage consists of amplifiers A1 and A2, which amplify the differential voltage between the two input signals. The gain is determined by the external resistor RG connected between Pins 1 and 8. A smaller RG value produces a higher gain according to the equation G = 1 + (100 kΩ / RG).

The amplified signals are then sent to amplifier A3, which acts as a differential amplifier. This stage subtracts the two amplified signals, rejects common-mode noise, and produces a precise output voltage at VOUT. The REF pin allows the output voltage level to be shifted when required, while V+ and V− provide the power supply for the device.

How to Utilized INA333 IC

The INA333 can be used as a precision amplifier for small sensor signals. In this circuit, Pin 7 is connected to the +5 V supply, while Pin 4 is connected to ground. A 0.1 μF bypass capacitor is placed near the supply pin to reduce power noise and help keep the circuit stable.

The input signal is connected to VIN+ and VIN−, and the gain is set by resistor R1 between Pins 1 and 8. With a 500 Ω gain resistor, the gain is about 201 using the formula G = 1 + (100 kΩ / RG). The REF pin is connected to ground, so the output is referenced to 0 V. The amplified signal is taken from Pin 6 and can be sent to an ADC, microcontroller, or measurement circuit.

Real-World Applications of the INA333

Electronic Weighing Scales

The INA333 is commonly used in electronic weighing scales to amplify the very small voltage signals from load cells. Its low offset voltage and high accuracy help produce stable and precise weight readings, even when measuring small load changes.

Medical Monitoring Equipment

Medical devices often measure weak biological signals that need accurate amplification. The INA333 helps improve signal quality by amplifying low-level signals while reducing unwanted electrical noise.

Industrial, Data Acquisition, and Environmental Measurement Systems

The INA333 is useful in industrial monitoring, data acquisition systems, and environmental sensing equipment. It amplifies small sensor outputs from pressure, force, temperature, and other measurement devices before the signals are processed by an ADC, controller, or recording system.

Portable and Battery-Powered Test Instruments

Because of its low power consumption, the INA333 is suitable for handheld meters, portable test tools, and battery-powered sensor systems. It helps extend battery life while still providing accurate amplification for small signals.

INA333 vs Other Instrumentation Amplifiers

Specification	INA333	INA317	AD623	AD8226	INA826	AD620
Manufacturer	Texas Instruments	Texas Instruments	Analog Devices	Analog Devices	Texas Instruments	Analog Devices
Supply Voltage Range	1.8 V to 5.5 V	1.8 V to 5.5 V	3 V to 12 V	2.2 V to 36 V	2.7 V to 36 V	±2.3 V to ±18 V
Quiescent Current	50 μA	50 μA	550 μA	350 μA	200 μA	1.3 mA
Input Offset Voltage (Max)	25 μV	25 μV	200 μV	35 μV	125 μV	50 μV
Offset Drift	0.1 μV/°C	0.1 μV/°C	2 μV/°C	0.3 μV/°C	0.4 μV/°C	0.6 μV/°C
Input Bias Current	200 pA	200 pA	25 nA	300 pA	5 nA	1 nA
CMRR (Min)	100 dB	100 dB	90 dB	100 dB	100 dB	100 dB
Input Noise Density	50 nV/√Hz	50 nV/√Hz	35 nV/√Hz	22 nV/√Hz	28 nV/√Hz	9 nV/√Hz
Gain Range	1 to 1000	1 to 1000	1 to 1000	1 to 1000	1 to 10,000	1 to 10,000
Gain Set Method	Single Resistor	Single Resistor	Single Resistor	Single Resistor	Single Resistor	Single Resistor
Rail-to-Rail Output	Yes	Yes	Near Rail-to-Rail	Yes	No	No
Operating Temperature	-40°C to +125°C	-40°C to +125°C	-40°C to +85°C	-40°C to +125°C	-40°C to +125°C	-40°C to +85°C
Package Options	VSSOP, WSON	VSSOP, WSON	SOIC, MSOP	MSOP	SOIC, VSSOP	DIP, SOIC
Main Strength	Ultra-Low Power	Direct Replacement	Low Cost	Low Noise	Wide Supply Range	High Precision

Mechanical Dimensions of INA333

Manufacturer

Texas Instruments is a leading analog IC manufacturer. It has strong experience in making precision amplifiers like the INA333. The company uses advanced semiconductor processes, automated wafer fabrication, and strict testing systems. These help the INA333 achieve low offset voltage, low drift, low noise, and stable performance. Texas Instruments also uses quality control and reliability testing to support operation across a wide temperature range. Its global manufacturing network helps ensure consistent supply and product quality.