ADN8830
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
SYNCOUT
TEMPOUT
C1
0.1 F
R1
150k
3.3V
L1
4.7 H
COILCRAFT
DO3316-472
TEC–
C2
22 F
CDE ESRD
Q1
FDW2520C-B
32
THERMFAULT
THERMIN
RTH
10k
@25 C
1
31
30
29
28
27
26
25
24
R2
7.68k
0.1%
VREF
2
23
3
3.3V
TEMPSET
22
Q2
FDW2520C-A
R3
10k
0.1%
R4
7.68k
0.1%
4
21
ADN8830
5
20
C3
10 F
C4
22 F
CDE ESRD
3.3V
TEMPLOCK
6
19
3.3V
VREF
7
18
C5
10nF
3.3V
C8
10 F
8
9
10
11
12
R5
205k
C11
1 F
13
C9
10 F
R6
100k
C10
330pF
14
15
17
16
3.3V
C7
10 F
Q3
FDW2520C-A
C6
2.2nF
TEC+
VTEC
Q4
FDW2520C-B
C12
3.3nF
R7
1M
Figure 1. Typical Application Schematic
REV. C
–7–
AD [ ANALOG DEVICES ]
