Data Sheet ADN8831
Rev. A | Page 11 of 20
THEORY OF OPERATION
The ADN8831 is a single chip TEC controller that sets and
stabilizes a TEC temperature. A voltage applied to the input
of the ADN8831 corresponds to a target TEC temperature
setpoint (TEMPSET). By controlling an external FET H-bridge,
the appropriate current is then applied to the TEC to pump
heat either to or away from an object attached to the TEC.
The objective temperature is measured with a thermal sensor
attached to the TEC and the sensed temperature (voltage) is
fed back to the ADN8831 to complete a closed thermal control
loop of the TEC. For best stability, the thermal sensor is to be
closed to the object. In most laser diode modules, a TEC and a
NTC thermistor are already mounted in the same package to
regulate the laser diode temperature.
The ADN8831 integrates two self-correcting, auto-zero amplifiers
(Chop1 and Chop2). The Chop1 amplifier usually takes a thermal
sensor input and converts or regulates the input to a linear
voltage output. The OUT1 (Pin 4) voltage is proportional to the
object temperature. The OUT1 (Pin 4) voltage is fed into the
compensation amplifier (Chop2) and compared with a tempera-
ture setpoint voltage, creating an error voltage that is proportional
to the difference. When using the Chop2 amplifier, a PID
network is recommended, as shown in Figure 12.
Adjusting the PID network optimizes the step response of
the TEC control loop. A compromised settling time and the
maximum current ringing become available when this is done.
Details of how to adjust the compensation network are in the
PID Compensation Amplifier (CHOP2) section. The TEC is
differentially driven in an H-bridge configuration. The ADN8831
drives external MOSFET transistors to provide the TEC current.
To further improve the power efficiency of the system, one side
of the H-bridge uses a PWM driver. Only one inductor and one
capacitor are required to filter out the switching frequency. The
other side of the H-bridge uses linear output without requiring
any additional circuitry. This proprietary configuration allows
the ADN8831 to provide efficiency of >90%. For most applica-
tions, a 4.7 μH inductor, a 22 μF capacitor, and a switching
frequency of 1 MHz, maintain less than 0.5% worst-case output
voltage ripple across a TEC.
The maximum voltage across the TEC and current flowing
through the TEC is to be set using the VLIM (Pin 31) and
ILIMC (Pin 1)/ILIMH (Pin 32). Additional details are in the
Maximum TEC Voltage Limit section and the Maximum TEC
Current Limit section.
04663-012
PGND
AGND
TMPGD
ITEC
VTEC
IN1N
IN2P
OUT1
IN1P
ILIMH
ILIMC
VLIM
AVDD
VREF
PVDD
5Ω
LPGATE
LFB
LNGATE
CS
COMPSW
SFB
COMPOSC
SPGATE
SYNCI/SD
SW
SYNCO
PHASE
FREQ
SS/SB
SNGATE
TEMP GOOD INDICATOR
TEC CURRENT OUTPUT
TEC VOLTAGE OUTPUT
TEMPERATURE SET INPUT
30.1kΩ
10µF
27nF
THERMISTOR
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
17.8kΩ
8.2kΩ
8.2kΩ
IN2N
OUT2
7.68kΩ
17.8kΩ
0.1µF
0.1µF 0.1µF
VDD
3.0V TO 5.5V
0.1µF
40µF
R
SENSE
10kΩ
118kΩ
1kΩ
0.1µF
3.3µH
60µF
VDD
TEC
NC
NC
NC = NO CONNECT
Figure 12. Typical Application Circuit 1
