Datasheet

Detailed Description
Power Stage
The power stage of the MAX1978/MAX1979
thermoelectric cooler (TEC) temperature controllers
consists of two switching buck regulators that operate
together to directly control TEC current. This configura-
tion creates a differential voltage across the TEC, allow-
ing bidirectional TEC current for controlled cooling and
heating. Controlled cooling and heating allow accurate
TEC temperature control within the tight tolerances of
laser driver specifications.
The voltage at CTLI directly sets the TEC current. The
internal thermal-control loop drives CTLI to regulate
TEC temperature. The on-chip thermal-control circuitry
can be configured to achieve temperature control sta-
bility of 0.001°C. Figure 1 shows a typical TEC thermal-
control circuit.
Ripple Cancellation
Switching regulators like those used in the
MAX1978/MAX1979 inherently create ripple voltage on
each common-mode output. The regulators in the
MAX1978 switch in phase and provide complementary
in-phase duty cycles, so ripple waveforms at the differ-
ential TEC output are greatly reduced. This feature sup-
presses ripple currents and electrical noise at the TEC
to prevent interference with the laser diode while mini-
mizing output capacitor filter size.
Integrated Temperature
Controllers for Peltier Modules
TEC
MAX1978
10µF
0.01µF
V
DD
V
DD SHDN
PV
DD
1PV
DD
2
REF
REF MAXV MAXIN MAXIP
UNDERTEMP
ALARM
COMP
OVERTEMP
ALARM
DC CURRENT
MONITOR
REF
ITEC
BFB-
AIN-
AIN+
CTLI
FREQ
GND PGND2 PGND1 INTOUT INT- DIFOUT FB+
FB-
LX2
OS2
OS1
CS
LX1
AOUT
20kΩ
1%
69.8kΩ
1%
105kΩ
1%
1µF
THERMISTOR
VOLTAGE
MONITOR
80.6kΩ
100kΩ
100kΩ
0.068Ω
10kΩ
1µF
3µH
3µH
4.7µF
1µF
20kΩ
1MΩ
10µF
0.047µF
0.47µF
REF
THERMAL
FEEDBACK
UT
OT
10µF 10µF 1µF
Figure 1. MAX1978 Typical Application Circuit. Circuit is configured for both cooling and heating the NTC thermistor. Current flowing
from OS2 and OS1 is cooling.
MAX1978/MAX1979
12
Maxim Integrated