INA330

7

SBOS260

www.ti.com

loop can be accomplished by simply reversing the connec-

tions to the TEC, or by creating the desired polarity in the

intervening control circuitry. If differing values of V1 and V2

are used, resistor values should be chosen to maintain

balanced currents, I1 and I2. Likewise, if a lower value of RSET

is used, the excitation voltage must be lowered to keep I1 and

I2 at or below 125µA.

CFILTER is calculated by:

C

R

kHz

FILTER

G

=

(

)

1

21 6

π

.

NOISE PERFORMANCE

Temperature control loops require low noise over a small

bandwidth, typically 10Hz, or less. The INA330’s internal

auto-correction circuitry eliminates virtually all 1/f noise (noise

that increases at low frequency). The peak-to-peak voltage

noise due to IERROR, RTHERM, RSET, and the buffers at 0.01Hz

to 10Hz results in a 0.0001

°C contribution.

OUTPUT

The INA330 output (pin 8) is capable of swinging to within

10mV of the power-supply rails. It is able to achieve rail-to-

rail output performance while sinking or sourcing 12.5

µA.

VADJUST can be used to create an offset voltage around which

the output can be centered.

ENABLE FUNCTION

The INA330 is enabled by applying a logic HIGH voltage

level to the Enable pin. Conversely, a logic LOW voltage

level will disable the amplifier, reducing its supply current

from 2.6mA to typically 2

µA. This pin should be connected to

a valid HIGH or LOW voltage or driven, not left open circuit.

Applications not requiring disable can connect pin 6 directly

to V+. The Enable pin can be modeled as a CMOS input

gate, as shown in Figure 4.

SELECTING COMPONENTS

RSET is the primary “reference” for the temperature control

loop. Its absolute resistance controls the set-point tempera-

ture. Again, its initial accuracy can be calibrated, but its

stability is crucial. Therefore, a high-quality, low-temperature

coefficient type must be used.

A 25ppm/

°C precision resistor changes 0.15% from –40°C to

+85

°C. This will produce a 0.03°C change in set-point tem-

perature. This error is approximately three-times larger than

that produced by the INA330.

The transfer function for the configuration shown in Figure 3 is:

VV

R

I

I

O

ADJ

G

=+

(

)

12

–

or

VV

R

V

R

V

R

O

ADJ

G

THERM

SET

=+









12

–

With V1 = V2 = VEXCITE,

VV

V

R

RR

O

ADJ

EXCITE

G

THERM

SET

=+









11

–

2

3

10

1

95

4

V+

V

2

V

EXCITE

1V

V

1

6

Enable

High = On

Low = Off

8

7

I

1

I

2

R

SET

10k

Ω

R

G

200k

Ω

Thermistor

R

THERM = 10kΩ

C

FILTER

500pF

I

O = I1 – I2

V

O

V

ADJUST = +2.5V

FIGURE 3. Basic Configuration for the INA330.

V+

Enable

6

2

µA

FIGURE 4. Enable Pin Model.

Nominal values should use RSET = RTHERM = 10kΩ at the

designed control temperature. Values less than 2k

Ω can

cause the voltage excitation buffers to become unstable. The

buffer connected to pin 10 is characterized and tested to

supply the changing current in the thermistor. The thermistor

should not be connected to pin 1. An inversion of the control