OPA330

+5 V

+5 V

R

G

INA827

V

IN-

V

IN+

REF

V

OUT

+5 V

a) Level shifting using the OPA330 as a low-impedance buffer

b) Level shifting using the low-impedance output of the REF3225

+5 V

+5 V

R

G

INA827

V

IN-

V

IN+

REF

V

OUT

REF3225

+2.5 V

INA827

www.ti.com

SBOS631 – JUNE 2012

REFERENCE TERMINAL

The INA827 output voltage is developed with respect to the voltage on the reference terminal. Often, in dual-

supply operation, the reference pin (pin 6) is connected to the low-impedance system ground. Offsetting the

output signal to a precise mid-supply level (for example, 2.5 V in a 5-V supply environment) can be useful in

single-supply operation. The signal can be shifted by applying a voltage to the device REF pin, which can be

useful when driving a single-supply ADC.

For best performance, any source impedance to the REF terminal should be kept below 5

Ω. Referring to

Figure 54, the reference resistor is at one end of a 50-k

Ω resistor. Additional impedance at the REF pin adds to

this 50-k

Ω resistor. The imbalance in resistor ratios results in degraded common-mode rejection ratio (CMRR).

Figure 58 shows two different methods of driving the reference pin with low impedance. The OPA330 is a low-

power, chopper-stabilized amplifier and therefore offers excellent stability over temperature. The OPA330 is

available in the space-saving SC70 and even smaller chip-scale package. The REF3225 is a precision reference

in a small SOT23-6 package.

Figure 58. Options for Low-Impedance Level Shifting

DYNAMIC PERFORMANCE

Figure 19 illustrates that, despite having low quiescent current of only 200 µA, the INA827 achieves much wider

bandwidth than other instrumentation amplifiers (INAs) in its class. This achievement is a result of using TI’s

proprietary high-speed precision bipolar process technology. The current-feedback topology provides the INA827

with wide bandwidth even at high gains. Settling time also remains excellent at high gain because of a 1.5-V/µs

high slew rate.

Copyright © 2012, Texas Instruments Incorporated

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