INA333-HT datasheet(17/24 Pages) TI

17 / 24 page

300W

+3V

150W

(1)

- D

2V+ V

INA333

Ref

1.5V

www.ti.com

SBOS514 – MARCH 2010

overload condition drives both input amplifiers to the

respective positive output swing limit, the difference

voltage measured by the output amplifier is near

zero. The output of the INA333 is near 0 V even

though both inputs are overloaded.

OPERATING VOLTAGE

The INA333 operates over a power-supply range of

+1.8 V to +5.5 V (±0.9 V to ±2.75 V). Supply voltages

higher

than

(absolute

maximum)

can

permanently damage the device. Parameters that

vary over supply voltage or temperature are shown in

(1) R1 creates proper common-mode voltage, only for low-voltage

the Typical Characteristics section of this data sheet.

operation—see the Single-Supply Operation section.

Figure 37. Single-Supply Bridge Amplifier

LOW VOLTAGE OPERATION

The INA333 can be operated on power supplies as

INPUT PROTECTION

low as ±0.9 V. Most parameters vary only slightly

throughout this supply voltage range—see the Typical

The input terminals of the INA333 are protected with

Characteristics section. Operation at very low supply

internal diodes connected to the power-supply rails.

voltage requires careful attention to assure that the

These diodes clamp the applied signal to prevent it

input voltages remain within the linear range. Voltage

from damaging the input circuitry. If the input signal

swing requirements of internal nodes limit the input

voltage can exceed the power supplies by more than

common-mode range with low power-supply voltage.

0.3 V, the input signal current should be limited to

The

Typical

Characteristic

curves

Typical

less than 10 mA to protect the internal clamp diodes.

Common-Mode Range vs Output Voltage (Figure 22

This current limiting can generally be done with a

to Figure 25) show the range of linear operation for

series input resistor. Some signal sources are

various supply voltages and gains.

inherently current-limited and do not require limiting

resistors.

SINGLE-SUPPLY OPERATION

GENERAL LAYOUT GUIDELINES

The INA333 can be used on single power supplies of

+1.8 V to +5.5 V. Figure 37 illustrates a basic

Attention

good

layout

practices

always

single-supply circuit. The output REF terminal is

recommended.

Keep

traces

short

and,

when

connected to mid-supply. Zero differential input

possible, use a printed circuit board (PCB) ground

voltage demands an output voltage of mid-supply.

plane with surface-mount components placed as

Actual

output

voltage

swing

limited

close to the device pins as possible. Place a 0.1-mF

approximately 50 mV above ground, when the load is

bypass capacitor closely across the supply pins.

referred

ground

shown.

The

typical

These guidelines should be applied throughout the

characteristic curve Output Voltage Swing vs Output

analog circuit to improve performance and provide

Current (Figure 31) shows how the output voltage

benefits

such

reducing

the

swing varies with output current.

electromagnetic-interference (EMI) susceptibility.

With single-supply operation, VIN+ and VIN– must both

Instrumentation amplifiers vary in the susceptibility to

be 0.1V above ground for linear operation. For

radio-frequency interference (RFI). RFI can generally

instance, the inverting input cannot be connected to

be identified as a variation in offset voltage or dc

ground to measure a voltage connected to the

signal levels with changes in the interfering RF signal.

noninverting input.

The INA333 has been specifically designed to

minimize

susceptibility

RFI

incorporating

illustrate

the

issues

affecting

low

voltage

passive RC filters with an 8-MHz corner frequency at

operation, consider the circuit in Figure 37. It shows

the VIN+ and VIN– inputs. As a result, the INA333

the INA333 operating from a single 3-V supply. A

demonstrates remarkably low sensitivity compared to

resistor in series with the low side of the bridge

previous generation devices. Strong RF fields may

assures that the bridge output voltage is within the

continue to cause varying offset levels, however, and

common-mode range of the amplifier inputs.

may require additional shielding.

APPLICATION IDEAS

Additional application ideas are shown in Figure 38 to

Figure 41.

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