INA333-HT datasheet(16/24 Pages) TI

16 / 24 page

10kW

OPA333

±10mV

AdjustmentRange

100W

100 A

1/2REF200

100 A

1/2REF200

V+

V-

INA333

Ref

IN-

IN+

INA333

47kW

INA333

10kW

Microphone,

Hydrophone,

etc.

Thermocouple

INA333

Centertapprovides

biascurrentreturn.

SBOS514 – MARCH 2010

www.ti.com

INTERNAL OFFSET CORRECTION

Without a bias current path, the inputs will float to a

potential that exceeds the common-mode range of

The INA333 internal op amps use an auto-calibration

the INA333, and the input amplifiers will saturate. If

technique with a time-continuous 350-kHz op amp in

the differential source resistance is low, the bias

the signal path. The amplifier is zero-corrected every

current return path can be connected to one input

8 ms using a proprietary technique. Upon power-up,

(see the thermocouple example in Figure 36). With

the amplifier requires approximately 100 ms to

higher source impedance, using two equal resistors

achieve specified VOS accuracy. This design has no

provides a balanced input with possible advantages

aliasing or flicker noise.

of lower input offset voltage as a result of bias current

and better high-frequency common-mode rejection.

OFFSET TRIMMING

Most

applications

require

external

offset

adjustment; however, if necessary, adjustments can

be made by applying a voltage to the REF terminal.

Figure 35 shows an optional circuit for trimming the

output offset voltage. The voltage applied to REF

terminal is summed at the output. The op amp buffer

provides low impedance at the REF terminal to

preserve good common-mode rejection.

Figure 35. Optional Trimming of Output Offset

Figure 36. Providing an Input Common-Mode

Voltage

Current Path

NOISE PERFORMANCE

INPUT COMMON-MODE RANGE

The auto-calibration technique used by the INA333

results in reduced low frequency noise, typically only

The linear input voltage range of the input circuitry of

50 nV/

√Hz, (G = 100). The spectral noise density can

the INA333 is from approximately 0.1 V below the

be seen in detail in Figure 10. Low frequency noise of

positive supply voltage to 0.1 V above the negative

the INA333 is approximately 1 mVPP measured from

supply. As a differential input voltage causes the

0.1 Hz to 10 Hz, (G = 100).

output voltage to increase, however, the linear input

range is limited by the output voltage swing of

INPUT BIAS CURRENT RETURN PATH

amplifiers A1 and A2. Thus, the linear common-mode

input range is related to the output voltage of the

The input impedance of the INA333 is extremely

complete amplifier. This behavior also depends on

high—approximately 100 G

Ω. However, a path must

supply voltage—see Typical Characteristic curves

be provided for the input bias current of both inputs.

Typical Common-Mode Range vs Output Voltage

This input bias current is typically ±70 pA. High input

(Figure 22 to Figure 25).

impedance

means

that

this

input

bias

current

changes very little with varying input voltage.

Input overload conditions can produce an output

voltage that appears normal. For example, if an input

Input circuitry must provide a path for this input bias

current for proper operation. Figure 36 illustrates

various provisions for an input bias current path.

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