INA330 datasheet(11/17 Pages) TI2

11 / 17 page

INA330

SBOS260

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FIGURE 10. Digitally Compensated Loop.

FIGURE 11. Traditional Bridge Circuit.

DIGITALLY COMPENSATED LOOP

The PID compensation can be replaced with a microcontroller

or DSP, as shown in Figure 10. An Analog-to-Digital (A/D)

converter would be used to digitize the output of the INA330.

The analog PID provides sufficient filtering inherently, and,

therefore requires no additional filtering. The digital control

loop shown in Figure 10 does not provide this inherent

filtering, requiring additional output filtering (RO and CO) as

shown to avoid sampling the internal chopping noise of the

INA330 and the A/D converter input and affecting accuracy.

High-frequency noise is created by internal auto-correction

circuitry and is highly dependent on the filter characteristics

chosen. “Spurs” occur at approximately 90kHz and its har-

monics which is reduced by additional filtering at or below

1kHz. This may be the dominant source of noise visible when

viewing the output on an oscilloscope. Low cutoff frequency

filters will provide lowest noise.

TRADITIONAL BRIDGE CIRCUIT

The traditional bridge circuit (Figure 11) uses three matched

resistors and a thermistor to detect temperature changes.

The INA326 and INA327 instrumentation amplifiers are well

suited to a bridge implementation for thermistor measure-

ment.

INA330

DSP

Loop Compensation

is performed in DSP.

TEC

+5V

Enable

+5V

SET

10k

Ω

200k

Ω

THERM

FILTER

500pF

ADJ

0V to 5V

D/A

Converter

Temp

Adjust

Ref

100

Ω

µF

A/D

Converter

D/A

Converter

+1V

Ω

10k

Ω(2)

10k

Ω(1)

10k

Ω(1)

✻ 10k

Ω at set-point

temperature.

✻

NOTES: (1) Requires ratio matching tracking.

(2) Requires absolute accuracy and stability.

EXCITE

PID CONTROLLER

INA326

+5V

100k

Ω

REF

2.5V

1nF

ADJ

D/A

Converter

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