PRELIMINARY TECHNICAL DATA

ADN8831

Rev. C | Page 9 of 11

THEORY OF OPERATION

Introduction

The ADN831 is a thermoelectric cooler (TEC) controller used

to set and stabilize the temperature of the TEC. A voltage

applied to the input of the ADN8831 corresponds to a target

temperature set-point. Using a thermistor to monitor the

current temperature of the target object, the ADN8831 applies

the appropriate current to the TEC to pump heat either towards

or away from the target object until the set-point temperature is

reached.

Self correcting auto-zero amplifiers (chop1 and chop2) are used

in the input and compesation stages of the aDN8831 to provide

a maximum offset voltage of 100uV over time and temperature.

This results in a final temperature accuracy of 0.01C in typical

applications, eliminating the ADN8831 as an error source in the

temperature control loop.

The TEC is driven differentially using an H-bridge

configuration. The ADN8831 drives external transistors that are

used to provide the current to the TEC. The maximum voltage

across the TEC and current flowing through the TEC can be set

using the VLIM and ILIM pins. Additional details are provided

in the Setting Voltage and Current Limits section.

One side of the H-bridge uses a switched output, while the

other is linear. This proprietary configuration allows the

ADN8831 to provide efficiency of >90%, while minimizing

external filtering component count. The ADN8831 requires

only one inductor and one capacitor to filter the switching

frequency of the switched output. For most applications, a

4.7uH inductor, a 22uF capacitor and a switching frequency of

1MHz maintains less than 0.5% worst-case output voltage ripple

across the TEC.

The switched output is controlled by the ADN8831’s oscillator.

A single resistor on the FREQ pin (pin #13) sets the switching

frequency from 100kHz to 1MHz. The clock output is available

at the SYNCO pin (pin #15). Connecting SYNCO to the SYNI

pin of another ADN8831 allows multiple ADN8831s to be

driven using a single clock.

The clock phase can be changed using a simple resistor divider

at the PHASE pin )pin #10). Phase adjustment allows two or

more ADN8831 devices to operate from the same clock

frequency and not have all outputs switch simultaneously,

which could create excessive power supply ripple. Details of

how to adjust the clock frequency and phase are provided in the

Setting the Frequency section.

The logic output of the TEMPGD pin (pin #11) indicates when

the target temperature is reached. Shutdown, standby, and true

current-sensing are also provided by the ADN8831 to protect

from catastrophic system failures that could damage the TEC.