Procedure
The MAX1978 EV kit is a fully assembled and tested
surface-mount board. Follow the steps below to verify
board operation. Do not turn on the power supply
until all connections are completed:
1) Place a shunt across pins 2-3 on JU1 to set the
frequency to 500kHz.
2) Place a shunt across JU2 to connect the thermal
loop to CTLI.
3) Place a shunt across pins 2-3 on JU4 to select the
potentiometer.
4) Place a shunt across pins 2-3 on JU3 to disable the
MAX1978 output.
5) Obtain TEC module specifications for absolute
maximum TEC voltage, absolute maximum cooling
current, and absolute maximum heating current. Set
these (or lower) limits at the MAX1978’s MAXV,
MAXIP (heating current), MAXIN (cooling current)
inputs. See Tables 1, 2, and 3 to select resistors, or
refer to the MAX1978 data sheet.
6) Connect the TEC module to OS1, OS2, THERM, and
GND. Typical connections for most modules:
• Module TEC+ to OS1
• Module TEC- to OS2
• Module thermistor to THERM
• Second module thermistor pin to GND
• Module case ground or shield to GND
Check module specifications before making con-
nections. For lowest noise, connect the thermistor
through shielded wire.
7) Connect the DVM to SET_POINT and GND.
8) Connect a 3.3V DC or 5V DC power supply with
sufficient power rating to VDD and GND.
9) Turn on the power supply.
Note: The MAX1978 output is not enabled yet.
10) Adjust R24 until the DVM reads 0.75V. This adjusts
the set point for approximately +25°C.
11) Move the DVM positive lead to THERM and verify a
voltage of approximately 0.75V. This corresponds
to an ambient temperature of +25°C at the TEC
module.
12) Enable the MAX1978 by moving the shunt on JU3
to the 1-2 position.
13) After enabling the MAX1978, verify that the THERM
voltage converges toward the set-point
voltage on R24 (set to 0.75V in Step 9) after approxi-
mately 30s. If the TEC is connected backward, the
THERM voltage moves away from 0.75V toward either
0V or 1.5V. If this occurs, shut down the MAX1978 and
reverse TEC+ and TEC- connections.
14) Once proper operation is verified, other tempera-
tures can be set with R24, the DAC, or an external
voltage applied to SET_POINT. (1V is approximately
+10°C; 0.5V is approximately +40°C. The slope is
approximately -14mV/°C for a typical NTC.)
Detailed Description
Voltage and Current-Limit Settings
The MAX1978 provides control of the maximum differ-
ential TEC voltage and the maximum positive and neg-
ative TEC currents.
The voltage on the MAXV pin of the MAX1978 sets the
maximum differential TEC voltage. Use the following
equations to set the voltage:
Maximum TEC voltage: V
TEC(MAX)
= 4 ✕ V
MAXV
The components installed on the MAX1978 EV kit set
V
MAXV
to 1V, for a maximum TEC voltage of 4V. See
Table 1 and refer to the MAX1978 data sheet for more
information.
The voltages on the MAXIP and MAXIN pins set the
maximum positive (heating) and negative (cooling)
currents through the TEC. Use the following equations
to set the currents:
Resistor values for R2 through R7 should be between
10kΩ and 100kΩ.
Maximum positive TEC current:
where R
SENSE
(R1) is 68mΩ.
