INA188IDR datasheet(24/41 Pages) TI2

24 / 41 page

INA188

VIN-

VIN+

VOUT

REF

5 V

INA188

VIN-

VIN+

VOUT

REF

5 V

REF3225

2.5 V

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

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

INA188

SBOS632 – SEPTEMBER 2015

www.ti.com

Product Folder Links: INA188

Submit Documentation Feedback

Device Functional Modes (continued)

7.4.4 Driving the Reference Pin

The output voltage of the INA188 is developed with respect to the voltage on the reference pin. Often, the

reference pin (pin 5) is connected to the low-impedance system ground in dual-supply operation. In single-supply

operation, offsetting the output signal to a precise mid-supply level (for example, 2.5 V in a 5-V supply

environment) can be useful. To accomplish this, a voltage source can be tied to the REF pin to level-shift the

output so that the INA188 can drive a single-supply analog-to-digital converter (ADC).

For best performance, keep the source impedance to the REF pin below 5

Ω. As illustrated in the Functional

Block Diagram section, the reference pin is internally connected to a 20-k

Ω resistor. Additional impedance at the

REF pin adds to this 20-k

Ω resistor. The imbalance in the resistor ratios results in degraded common-mode

rejection ratio (CMRR).

Figure 53 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 a space-saving SC70 and an even smaller chip-scale package. The REF3225 is a precision

reference in a small SOT23-6 package.

Figure 53. Options for Low-Impedance Level Shifting

INA188IDR Datasheet(PDF) 24 Page - Texas Instruments