INA330

8

SBOS260

www.ti.com

INA330 PIN 5

Pin 5 of the INA330 should be connected to V+ to ensure

proper operation.

COMPLETE TEMPERATURE CONTROLLER

See Figure 6 for a complete temperature control loop with a

TEC (thermoelectric cooler) for cooling and heating. PID

(proportional, integral, differential) control circuitry is shown

for loop compensation and stability.

The loop controls temperature to an adjustable set-point of

22.5

°C to 27.5°C. The nominal 10kΩ at 25°C thermistor

ranges from approximately 11.4k

Ω to 8.7kΩ over this range.

A 1V excitation voltage is applied to V1 and V2, producing a

nominal 100

µA current in the 10kΩ R

SET resistor. The ther-

The INA330 is designed and tested for amplifying 10k

Ω

thermistor signals used in the control of thermoelectric

coolers for optical networking applications. The simplified

schematic in Figure 5 shows the basic function of the

INA330. An excitation voltage is applied as V1 and V2.

Typically, these voltages are equal. They generate cur-

rents I1 and I2 in the thermistor and RSET resistor.

Auto-corrected current mirror circuitry around A1 and A2

produce an output current, IO, equal to the difference

A1

V+

Enable

Current Mirror

Current Mirror

I

2

I

2

I

2

R

SET

R

THERM

R

G

C

FILTER

V

O

V

2

V

1

I

2

I

O

I

1 – I2

I

O = I1 – I2

I

O

A3

A2

V

ADJUST

Current Mirror

Current Mirror

95

6

8

7

4

3

10

1

2

INA330

I

1

current I1 – I2. The gain is set by the value of RG. The

output voltage, VO, is the voltage resulting from IO flowing

through RG.

The INA330 uses internal charge pumps to create volt-

ages beyond the power-supply rails.

As a result, the

voltage on RG can actually swing 20mV below the nega-

tive power-supply rail, and 100mV beyond the positive

supply rail. An internal oscillator has a

frequency of

90kHz and accuracy of

±20%.

INSIDE THE INA330

FIGURE 5. INA330 Simplified Schematic.

mistor current is approximately 100

µA at 25°C, but will vary

above or below this value over the

±2.5°C set-point tempera-

ture range. The difference of these two currents flows in the

gain-set resistor, RG. This produces a voltage output of

approximately 0.9V/

°C.

The set-point temperature is adjusted with VADJ. Thus, the

voltage at VO is the sum of (IO)(RG) + VADJ. VADJ can be

manually adjusted or set with a Digital-to-Analog (D/A) con-

verter. Optionally, set-point temperature can be adjusted by

choosing a different fixed value resistor more closely ap-

proximating the value of RTHERM at the desired temperature.

The noninverting input of the integrator in the PID compen-

sation is connected to VBIAS. Thus, the feedback loop will

drive the heating or cooling of the TEC to force VO to equal

VBIAS. VADJ = 2.5V will produce a set-point temperature of