The MAX1979 controls the TEC current in only one

direction (unipolar). Set the maximum unipolar TEC cur-

rent by applying a voltage to MAXIP. Connect MAXIN to

GND when using the MAX1979. The equation for set-

ting MAXIP is the same for the MAX1978 and

MAX1979. Do not exceed the positive or negative cur-

rent-limit specifications on the TEC. Refer to the TEC

manufacturer’s data sheet for these limits.

Setting Max TEC Voltage

Apply a voltage to MAXV to control the maximum differ-

ential TEC voltage. MAXV can vary from 0 to REF. The

positive or negative.

Use resistors from 10k

Ω to 100kΩ to form a voltage-

Thermal-Control Loop

The MAX1978/MAX1979 provide all the necessary

amplifiers needed to create a thermal-control loop.

Typically, the chopper-stabilized instrumentation ampli-

fier generates an error signal and the integrator amplifi-

er is used to create a PID controller. Figure 4 shows an

example of a simple PID implementation. The error sig-

nal needed to control the loop is generated from the

difference between the set point and the thermistor

voltage. The desired set-point voltage can be derived

from a potentiometer, DAC, or other voltage source.

Figure 5 details the required connections. Connect the

output of the PID controller to CTLI. For details, see the

Applications Information section.

Control Inputs/Outputs

TEC Current Control

The voltage at CTLI directly sets the TEC current. CTLI

typically is driven from the output of a temperature-con-

equations, it is assumed that positive TEC current is

heating.

The transfer function relating current through the TEC

ing. Current flow is from OS2 to OS1. The voltages are:

Integrated Temperature

Controllers for Peltier Modules

16

______________________________________________________________________________________

C3

C2

C1

R3

R2

DIFOUT

INTOUT

REF

INT-

R1

Figure 4. Proportional Integral Derivative Controller

MAX1978

MAX1979

FB-

REF

FB+

MAX1978

MAX1979

FB-

REF

FB+

DAC

DIGITAL

INPUT

Figure 5. The Set Point can be Derived from a Potentiometer

or a DAC