Datasheet

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
MAXIP 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
voltage across the TEC is four times V
MAXV
and can be
positive or negative.
|V
OS1
- V
OS2
| = 4  V
MAXV
Use resistors from 10kΩ to 100kΩ to form a voltage-
divider to set V
MAXV
.
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-
trol circuit C
INTOUT
. For the purposes of the following
equations, it is assumed that positive TEC current is
heating.
The transfer function relating current through the TEC
(I
TEC
) and V
CTLI
is given by:
I
TEC
= (V
CTLI
- V
REF
) / (10  R
SENSE
)
where V
REF
is 1.50V
and I
TEC
= (V
OS1
- V
CS
) / R
SENSE
V
CTLI
is centered around REF (1.50V). I
TEC
is zero when
V
CTLI
= 1.50V. When V
CTLI
> 1.50V, the MAX1978 is heat-
ing. Current flow is from OS2 to OS1. The voltages are:
V
OS2
> V
OS1
> V
CS
when V
CTLI
< 1.50V, current flows from OS1 to OS2:
V
OS2
< V
OS1
< V
CS
Integrated Temperature
Controllers for Peltier Modules
C3
C2
C1
R3
R2
DIFOUT
INTOUT
REF
INT-
R1
Figure 4. Proportional Integral Derivative Controller
MAX1978
MAX1979
FB-
REF
FB+
C
REF
V
SETPOINT
V
THERMISTOR
MAX1978
MAX1979
FB-
REF
FB+
C
REF
V
SETPOINT
V
THERMISTOR
DAC
DIGITAL
INPUT
Figure 5. The Set Point can be Derived from a Potentiometer
or a DAC
MAX1978/MAX1979
16
Maxim Integrated