|
 |
acquisitionZONE Products for the week of July 28, 2008
Texas Instruments Says…
INA333: Low Power Zero-Drift Instrumentation Amplifier For Precision Applications
Device improves accuracy and extends battery life in portables
Providing an unmatched combination of precision, low power and low supply voltage, Texas Instruments Incorporated (TI) introduced the industry's lowest power zero-drift instrumentation amplifier. The device features the lowest quiescent current and lowest input bias current versus the nearest competition, as well as an impressive power-to-noise ratio, very low offset voltage/drift and 1.8 V operation. Consequently, the INA333 improves accuracy and stability while extending battery life in a variety of precision, low-power applications such as portable medical, handheld instrumentation, weigh scales and data acquisition.
"Customers are consistently demanding higher precision combined with lower power and lower operating voltages in order to increase the performance and value of their sensor signal acquisition systems," said Art George, senior vice president of TI's High-Performance Analog business unit. "The INA333 leverages our expertise in analog signal conditioning to deliver a new standard for precision, low-power instrumentation amplifiers and enable our customers to gain a competitive advantage in the market."
The INA333 utilizes TI's zero-drift technology, which incorporates a proprietary switched-capacitor notch filter to eliminate chopping noise and provide very low input voltage noise of 50 nV/rtHz. The device features a versatile three op amp architecture to simplify design and reduce board space.
EN-Genius Says…
The INA333 uses a classic three-op-amp architecture with the overall gain set with a single external resistor over a range of 1 V/V to 1000 V/V using the industry standard gain equation of G = 1 + (100 kΩ ÷ RG). It uses TI’s proprietary zero-drift technology.
Where TI has taken the INA333 is to keep the part in the precision zone, but to attend very closely to the quiescent current. This is the first TI instrumentation amplifier to offer operation down to 1.8 V (or ±0.9 V) with a quiescent of a remarkably low typical 50 µA (75 µA max). The only other 1.8 V zero-drift IA that I could find was the AD8553 which has a typical quiescent of 1.3 mA, while Linear and Maxim offer parts only down to 2.7 V.
At the same time TI has managed to better the input offset by a factor of five over its previous best with ±0.1 µV/ºC. They have also thrown in RFI filtering in the input legs of the differential op amps which should help in dramatically reducing additional dc offsets caused by rectification of small RFI signals.
CMRR is among the best with typical numbers of 90 dB at a gain of 1 V/V going up to 115 dB with gains of 100 V/V and higher (both out to 100 Hz). -3 dB bandwidths are 150 kHz at a gain of 1 V/V and then ratiometric with 35 kHz, 3.5 kHz and 350 Hz at gains of 10/100/1000 V/V, respectively. Slew rates are, of course, low at 0.16 V/µs at unity gain and 0.05 V/µs at a gain of 100.
Input voltage noise is a typical 50 nV/rtHz up to 1 kHz, extremely good numbers for the auto-calibration technique in use. Spectral noise density is about 1 µVpp from 0.1 Hz to 10 Hz at a gain of 100 V/V. Auto-calibration for zero-correction takes place every 8 µs and TI claims no aliasing or flicker noise.
As with all single-resistor-set gained IAs care should be taken with how that resistor is selected and loaded on to the PCB, particularly with the low value resistors needed for higher gains (100 Ω, for example, for a gain of 1000 V/V. A reference input allows trimming of the output offset voltage if that is needed.
The range of applications for precision instrumentation amplifiers is endless, literally endless. From the ECG circuit suggestion in the data sheet TI is obviously preferring to target multi-channel applications (with lots of OPA333s thrown in as well!), and I don’t blame them. Portable is obviously the big beneficiary of the INA333, but there is nothing compromised in the specifications that are achieved so it is certainly not limited to just portable. My only complaint would be that I think the part has been priced rather low in a field where there is no current opposition. The part will do extraordinarily well.
The INA333 is in production in MSOP-8 and will also be available in DFN-8 in Q4 of 2008. Pricing is $1.80 in 1000-piece lots.
Data Sheet
|
|
|
|
|
