INA170EASLASH2K5 datasheet(7/15 Pages) TI1

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INA170

SBOS193D

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currents by minimizing the effects of offset, while low values

of RS minimize voltage loss in the supply line. For most

applications, best performance is attained with an RS value

that provides a full-scale shunt voltage of 50mV to 100mV.

Maximum input voltage for accurate measurements is 500mV.

RL is chosen to provide the desired full-scale output voltage.

The output impedance of the INA170 Out terminal is very

high which permits using values of RL up to 100kΩ with

excellent accuracy. The input impedance of any additional

circuitry at the output should be much higher than the value

of RL to avoid degrading accuracy.

Some Analog-to-Digital (A/D) converters have input imped-

ances that will significantly affect measurement gain. The

input impedance of the A/D converter can be included as

part of the effective RL if its input can be modeled as a

resistor to ground. Alternatively, an op-amp can be used to

buffer the A/D converter input, as shown in Figure 2. See

Figure 1 for recommended values of RL.

OUTPUT VOLTAGE RANGE

The output of the INA170 is a current, which is converted to

a voltage by the load resistor, RL. The output current remains

accurate within the compliance voltage range of the output

circuitry. The shunt voltage and the input common-mode

and power supply voltages limit the maximum possible

output swing. The maximum output voltage compliance is

limited by the lower of the two equations below:

Vout max = (V+) – 0.7V – (VIN

+ – V

– )(5)

Vout max = VIN

– – 0.5V

(6)

(whichever is lower)

BANDWIDTH

Measurement bandwidth is affected by the value of the load

resistor, RL. High gain produced by high values of RL will

yield a narrower measurement bandwidth (see Typical Char-

acteristic Curves). For widest possible bandwidth, keep the

capacitive load on the output to a minimum.

If bandwidth limiting (filtering) is desired, a capacitor can be

added to the output, as shown in Figure 3. This will not

cause instability.

APPLICATIONS

The INA170 is designed for current shunt measurement

circuits as shown in Figure 1, but its basic function is useful

in a wide range of circuitry. A creative engineer will find

many unforeseen uses in measurement and level shifting

circuits.

FIGURE 4. Offsetting the Output Voltage.

FIGURE 2. Buffering Output to Drive A/D Converter.

FIGURE 3. Output Filter.

OPA340

INA170

Buffer of amp drives A/D converter

without affecting gain.

INA170

–3dB =

πR

LCL

–3dB

REF

Gain Set by R

Output Offset Current =

REF

Output Offset Voltage =

• R

REF

INA170

INA170EA/2K5 Datasheet(PDF) 7 Page - Texas Instruments

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