REV.

ADN8830

–7–

APPLICATION NOTES

Principle of Operation

The ADN8830 is a controller for a TEC and is used to set and

stabilize the temperature of the TEC. A voltage applied to the

input of the ADN8830 corresponds to a target temperature

setpoint. The appropriate current is then applied to the TEC

to pump heat either to or away from the object whose tem-

perature is being regulated. The temperature of the object is

measured by a thermistor and is fed back to the ADN8830 to

correct the loop and settle the TEC to the appropriate final

temperature. For best stability, the thermistor should be mounted

in close proximity to the object. In most laser diode modules,

the TEC and thermistor are already mounted in the unit and

are used to regulate the temperature of the laser diode.

A complete TEC controller solution requires:

• A precision input amplifier stage to accurately measure the

difference between the target and object temperatures.

• A compensation amplifier to optimize the stability and

temperature settling time.

• A high output current stage. Because of the high output

currents involved, a TEC controller should operate with

high efficiency to minimize the heat generated from

power dissipation.

In addition, an effective controller should operate down to 3.3 V

and have an indication of when the target temperature has been

reached. The ADN8830 accomplishes all of these requirements

with a minimum of external components. Figure 1 shows a

reference design for a typical application.

Temperature is monitored by connecting the measurement

thermistor to a precision amplifier, called the error amplifier,

with a simple resistor divider. This voltage is compared against

the temperature set input voltage, creating an error voltage that

is proportional to their difference. To maintain accurate wave-

length and power from the laser diode, this difference voltage

must be as accurate as possible. For this reason, self-correction

auto-zero amplifiers are used in the input stage of the ADN8830,

providing a maximum offset voltage of 250

μV over time and

temperature. This results in final temperature accuracy within

±0.01°C in typical applications, eliminating the ADN8830 as an

error source in the temperature control loop. A logic output is

provided at TEMPLOCK to indicate when the target temperature

has been reached.

The output of the error amplifier is then fed into a compensa-

tion amplifier. An external network consisting of a few resistors

and capacitors is connected around the compensation amplifier.

This network can be adjusted by the user to optimize the step

THERMFAULT

THERMIN

RTH

10k

@25 C

R2

7.68k

0.1%

VREF

C8

10 F

3.3V

VREF

TEMPLOCK

TEMPSET

R3

10k

0.1%

R4

7.68k

0.1%

VTEC

9

10

11

12

13

14

15

16

C9

10 F

R6

100k

R5

205k

C11

1 F

R7

1M

24

23

22

21

20

19

18

17

3.3V

ADN8830

C5

10nF

3.3V

TEC+

C7

10 F

Q3

FDW2520C-A

Q4

FDW2520C-B

C4

22 F

CDE ESRD

3.3V

Q2

FDW2520C-A

TEC–

C3

10 F

L1

4.7 H

COILCRAFT

DO3316-472

Q1

FDW2520C-B

32

31

30

29

28

27

26

25

C1

0.1 F

R1

150k

SYNCOUT

TEMPOUT

3.3V

C6

2.2nF

C10

330pF

3.3V

C12

3.3nF

C2

22 F

CDE ESRD

1

2

3

4

5

6

7

8

Figure 1. Typical Application Schematic

D