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.

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

10kΩ

118kΩ

1kΩ

0.1µF

3.3µH

60µF

VDD

TEC

NC

NC

NC = NO CONNECT

Figure 12. Typical Application Circuit 1