AVAILAB

LE MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
General Description Features
The MAX1978/MAX1979 are the smallest, safest, most o Smallest, Safest, Most Accurate Complete
accurate complete single-chip temperature controllers for Single-Chip Controller
Peltier thermoelectric cooler (TEC) modules. On-chip power o On-Chip Power MOSFETS—No External FETs
FETs and thermal control-loop circuitry minimize external o Circuit Footprint < 0.93in2
components while maintaining high efficiency. Selectable
500kHz/1MHz switching frequency and a unique ripple-can- o Circuit Height < 3mm
cellation scheme optimize component size and efficiency o Temperature Stability to 0.001°C
while reducing noise. Switching speeds of internal o Integrated Precision Integrator and Chopper
MOSFETs are optimized to reduce noise and EMI. An ultra- Stabilized Op Amps
low-drift chopper amplifier maintains ±0.001°C temperature
o Accurate, Independent Heating and Cooling
stability. Output current, rather than voltage, is directly con- Current Limits
trolled to eliminate current surges. Individual heating and
cooling current and voltage limits provide the highest level of o Eliminates Surges By Directly Controlling
TEC protection. TEC Current
The MAX1978 operates from a single supply and provides o Adjustable Differential TEC Voltage Limit
bipolar ±3A output by biasing the TEC between the outputs o Low-Ripple and Low-Noise Design
of two synchronous buck regulators. True bipolar operation o TEC Current Monitor
controls temperature without “dead zones” or other nonlin- o Temperature Monitor
earities at low load currents. The control system does not
hunt when the set point is very close to the natural operating o Over- and Undertemperature Alarm
point, where only a small amount of heating or cooling is o Bipolar ±3A Output Current (MAX1978)
needed. An analog control signal precisely sets the TEC o Unipolar +6A Output Current (MAX1979)
current. The MAX1979 provides unipolar output up to 6A.
A chopper-stabilized instrumentation amplifier and a high-
Ordering Information
precision integrator amplifier are supplied to create a pro- PART TEMP RANGE PIN-PACKAGE
portional-integral (PI) or proportional-integral-derivative (PID)
MAX1978ETM+ -40°C to +85°C 48 Thin QFN-EP*
controller. The instrumentation amplifier can interface to an
external NTC or PTC thermistor, thermocouple, or semicon- MAX1979ETM+ -40°C to +85°C 48 Thin QFN-EP*
ductor temperature sensor. Analog outputs are provided to *EP = Exposed pad.
monitor TEC temperature Functional Diagrams
and current. In addition, separate +Denotes a lead(Pb)-free/RoHS-compliant package.
overtemperature and undertemperature outputs indicate
when the TEC temperature is out of range. An on-chip volt-
Pin Configuration
age reference provides bias for a thermistor bridge.
MAXIN
MAXIP
COMP
MAXV

TOP VIEW
CTLI

GND
GND

ITEC
OS1

VDD
REF
CS

The MAX1978/MAX1979 are available in a low-profile

48
47
46
45
44
43
42
41
40
39
38
37

48-lead thin QFN-EP package and is specified over the

-40°C to +85°C temperature range. The thermally OS2 1 + 36 FREQ
enhanced QFN-EP package with exposed metal pad N.C. 2 35 N.C
PGND2 3 34 PGND1
minimizes operating junction temperature. An evaluation LX2 4 33 LX1
kit is available to speed designs. PGND2 5 32 PGND1
LX2 6 31 LX1
MAX1978
Applications PVDD2 7 MAX1979 30 PVDD1
N.C. 8 29 N.C.
Fiber Optic Laser Modules LX2 9 28 LX1
PVDD2 10 27 PVDD1
WDM, DWDM Laser-Diode Temperature Control SHDN 11 26 GND
Fiber Optic Network Equipment OT 12 25 GND
13
14
15
16
17
18
19
20
21
22
23
24

EDFA Optical Amplifiers

BFB-
UT
INTOUT
INT-
GND
DIFOUT
FB-
FB+

BFB+
AIN+
AIN-
AOUT

Telecom Fiber Interfaces

Pin Configurations appear at end of data sheet.
ATE
Functional Diagrams continued at end of data sheet. TQFN-EP
*ELECTRICALLY CONNECTED TO THE UNDERSIDE METAL SLUG.
UCSP is aOperating
Typical trademarkCircuit
of Maxim Integrated
appears Products,
at end of data Inc.
sheet. NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.

For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-2490; Rev 3; 3/10
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V Peak LX Current (MAX1978) (Note 1).................................±4.5A
SHDN, MAXV, MAXIP, MAXIN, Peak LX Current (MAX1979) (Note 1)....................................+9A
CTLI, OT, UT to GND............................................-0.3V to +6V Continuous Power Dissipation (TA = +70°C)
FREQ, COMP, OS1, OS2, CS, REF, ITEC, AIN+, AIN-, 48-Lead Thin QFN-EP
AOUT, INT-, INTOUT, BFB+, BFB-, FB+, FB-, (derate 26.3mW/°C above +70°C) (Note 2) .................2.105W
DIFOUT to GND......................................-0.3V to (VDD + 0.3V) Operating Temperature Ranges
PVDD1, PVDD2 to VDD ...........................................-0.3V to +0.3V MAX1978ETM ..................................................-40°C to +85°C
PVDD1, PVDD2 to GND...............................-0.3V to (VDD + 0.3V) MAX1979ETM ..................................................-40°C to +85°C
PGND1, PGND2 to GND .......................................-0.3V to +0.3V Maximum Junction Temperature .....................................+150°C
COMP, REF, ITEC, OT, UT, INTOUT, DIFOUT, Storage Temperature Range .............................-65°C to +150°C
BFB-, BFB+, AOUT Short to GND .............................Indefinite Lead Temperature (soldering, 10s) .................................+300°C
Note 1: LX has internal clamp diodes to PGND and PVDD. Applications that forward bias these diodes should not exceed the IC’s
package power dissipation limits.
Note 2: Solder underside metal slug to PCB ground plane.

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = V SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0°C to +85°C,
unless otherwise noted. Typical values at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Input Supply Range VDD 3.0 5.5 V
VDD = 5V, ITEC = 0 to ±3A,
-4.3 +4.3
VOUT = VOS1 - VOS2 (MAX1978)
VDD = 5V, ITEC = 0 to 6A,
4.3
VOUT = VOS1 (MAX1979)
Output Voltage Range VOUT V
VDD = 3V, ITEC = 0 to ±3A,
-2.3 +2.3
VOUT = VOS1 - VOS2 (MAX1978)
VDD = 3V, ITEC = 0 to 6A,
2.3
VOUT = VOS1 (MAX1979)
MAX1978 ±3
Maximum TEC Current ITEC(MAX) A
MAX1979 6
Reference Voltage VREF VDD = 3V to 5.5V, IREF = 150µA 1.485 1.500 1.515 V
Reference Load Regulation ∆VREF VDD = 3V to 5.5V, IREF = +10µA to -1mA 1.2 5 mV
VMAXI_ = VREF 135 150 160
VOS1 < VCS
VMAXI_ = VREF/3 40 50 60
Current-Sense Threshold mV
VMAXI_ = VREF 135 150 160
VOS1 > VCS
VMAXI_ = VREF/3 40 50 60
VDD = 5V, I = 0.5A 0.04 0.07
NFET On-Resistance RDS(ON-N) Ω
VDD = 3V, I = 0.5A 0.06 0.08
VDD = 5V, I = 0.5A 0.06 0.10
PFET On-Resistance RDS(ON-P) Ω
VDD = 3V, I = 0.5A 0.09 0.12
VLX = VDD = 5V, TA = +25°C 0.02 10
NFET Leakage ILEAK(N) µA
VLX = VDD = 5V, TA = +85°C 1

2 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = V SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0°C to +85°C,
unless otherwise noted. Typical values at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VLX = 0, TA = +25°C 0.02 10
PFET Leakage ILEAK(P) µA
VLX = 0, TA = +85°C 1
IDD(NO VDD = 5V 30 50
No-Load Supply Current mA
LOAD) VDD = 3.3V 15 30
Shutdown Supply Current IDD-SD SHDN = GND, VDD = 5V (Note 3) 2 3 mA
Thermal Shutdown TSHUTDOWN Hysteresis = 15°C 165 °C
VDD rising 2.4 2.6 2.8
UVLO Threshold VUVLO V
VDD falling 2.25 2.5 2.75
Switching Frequency Internal FREQ = GND 450 500 650
fSW-INT kHz
Oscillator FREQ=VDD 800 1000 1200
IOS1, IOS2,
OS1, OS2, CS Input Current 0 or VDD -100 +100 µA
ICS
ISHDN,
SHDN, FREQ Input Current 0 or VDD -5 +5 µA
IFREQ
0.25 ×
SHDN, FREQ Input Low Voltage VIL VDD = 3V to 5.5V V
VDD
0.75 ×
SHDN, FREQ Input High Voltage VIH VDD = 3V to 5.5V V
VDD
VMAXV = VREF ✕ 0.67,
-1 +1
VOS1 to VOS2 = ±4V, VDD = 5V
MAXV Threshold Accuracy %
VMAXV = VREF ✕ 0.33,
-2 +2
VOS1 to VOS2 = ±2V, VDD = 3V
MAXV, MAXIP, MAXIN IMAXV-BIAS,
VMAXV = VMAXI_ = 0.1V or 1.5V -0.1 +0.1 µA
Input Bias Current IMAXI_-BIAS
CTLI Gain ACTLI VCTLI = 0.5V to 2.5V (Note 4) 9.5 10 10.5 V/V
CTLI Input Resistance RCTLI 1MΩ terminated at REF 0.5 1.0 2.0 MΩ
Error Amp Transconductance gm 50 100 175 µS
ITEC Accuracy VOS1 to VCS = +100mV or -100mV -10 +10 %
VOS1 to VCS = +100mV or -100mV,
ITEC Load Regulation ∆VITEC -0.1 +0.1 %
IITEC = ±10µA
Instrumentation Amp Input Bias
IDIF-BIAS -10 0 +10 nA
Current
Instrumentation Amp Offset
VDIF-OS VDD = 3V to 5.5V -200 +20 +200 µV
Voltage
Instrumentation Amp Offset-
VDD = 3V to 5.5V 0.1 µV/°C
Voltage Drift with Temperature
Instrumentation Amp Preset
ADIF RLOAD = 10kΩ to REF 45 50 55 V/V
Gain

Maxim Integrated 3
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = V SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0°C to +85°C,
unless otherwise noted. Typical values at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Integrator Amp Open-Loop Gain AOL-INT RLOAD = 10kΩ to REF 120 dB
Integrator Amp CMRR CMRRINT 100 dB
Integrator Amp Input Bias Current IINT-BIAS VDD = 3V to 5.5V 1 nA
Integrator Amp Voltage Offset VINT-OS VDD = 3V to 5.5V -3 +0.1 +3 mV
Integrator Amp Gain Bandwidth GBWINT 100 kHz
Undedicated Chopper Amp
AOL-AIN RLOAD = 10kΩ to REF 120 dB
Open-Loop Gain
Undedicated Chopper Amp
CMRRAIN 85 dB
CMRR
Undedicated Chopper Amp Input
IAIN-BIAS VDD = 3V to 5.5V -10 0 +10 nA
Bias Current
Undedicated Chopper Amp
VAIN-OS VDD = 3V to 5.5V -200 +10 +200 µV
Offset Voltage
Undedicated Chopper Amp Gain
GBWAIN 100 kHz
Bandwidth
Undedicated Chopper Amp
VRIPPLE A=5 20 mV
Output Ripple
BFB_ Buffer Error CLOAD < 100pF -200 0 +200 µV
UT and OT Leakage Current ILEAK V UT = V OT = 5.5V 1 µA
UT and OT Output Low Voltage VOL Sinking 4mA 50 150 mV
UT Trip Threshold FB+ - FB- (see Typical Application Circuit) -20 mV
OT Trip Threshold FB+ - FB- (see Typical Application Circuit) 20 mV

4 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = V SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
Input Supply Range VDD 3 5.5 V
VDD = 5V, ITEC = 0 to ±3A,
-4.3 +4.3
VOUT = VOS1 -VOS2 (MAX1978)
VDD = 5V, ITEC = 0 to 6A,
4.3
VOUT = VOS1 (MAX1979)
Output Voltage Range VOUT V
VDD = 3V, ITEC = 0 to ±3A,
-2.3 +2.3
VOUT = VOS1 - VOS2 (MAX1978)
VDD = 3V, ITEC = 0 to 6A,
2.3
VOUT = VOS1 (MAX1979)
MAX1978 ±3
Maximum TEC Current ITEC(MAX) A
MAX1979 6
Reference Voltage VREF VDD = 3V to 5.5V, IREF = 150µA 1.475 1.515 V
VDD = 3V to 5.5V,
Reference Load Regulation ∆VREF 5 mV
IREF = 10µA to -1mA
VMAXI_ = VREF 135 160
VOS1 < VCS
VMAXI_ = VREF/3 40 60
Current-Sense Threshold mV
VMAXI_ = VREF 135 160
VOS1 > VCS
VMAXI_ = VREF/3 40 60
IDD(NO VDD = 5V 50
No-Load Supply Current mA
LOAD) VDD = 3.3V 30
Shutdown Supply Current IDD-SD SHDN = GND, VDD = 5V (Note 3) 3 mA
VDD rising 2.4 2.8
UVLO Threshold VUVLO V
VDD falling 2.25 2.75
Switching Frequency Internal FREQ = GND 450 650
fSW-INT kHz
Oscillator FREQ = VDD 800 1200
IOS1, IOS2,
OS1, OS2, CS Input Current 0 or VDD -100 +100 µA
ICS
I SHDN,
SHDN, FREQ Input Current 0 or VDD -5 +5 µA
I FREQ
0.25 ✕
SHDN, FREQ Input Low Voltage VIL VDD = 3V to 5.5V V
VDD
0.75 ✕
SHDN, FREQ Input High Voltage VIH VDD = 3V to 5.5V V
VDD

Maxim Integrated 5
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = V SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
✕
VMAXV = VREF 0.67,
-1 +1
VOS1 to VOS2 = ±4V, VDD = 5V
MAXV Threshold Accuracy %
VMAXV = VREF ✕ 0.33, VOS1 to VOS2 = ±2V,
-2 +2
VDD = 3V
MAXV, MAXIP, MAXIN IMAXV-BIAS,
VMAXV = VMAXI_ = 0.1V or 1.5V -0.1 +0.1 µA
Input Bias Current IMAXI_-BIAS
CTLI Gain ACTLI VCTLI = 0.5V to 2.5V (Note 4) 9.5 10.5 V/V
CTLI Input Resistance RCTLI 1MΩ terminated at REF 0.5 2.0 MΩ
Error Amp Transconductance gm 50 175 µS

ITEC Accuracy VOS1 to VCS = +100mV or -100mV -10 +10 %

VOS1 to VCS = +100mV or

ITEC Load Regulation ∆VITEC -0.125 +0.125 %
-100mV, IITEC = ±10µA
Instrumentation Amp
IDIF-BIAS -10 +10 nA
Input Bias Current
Instrumentation Amp
VDIF-OS VDD = 3V to 5.5V -200 +200 µV
Offset Voltage
Instrumentation Amp
ADIF RLOAD = 10kΩ to REF 45 55 V/V
Preset Gain
Integrator Amp Input Bias Current IINT-BIAS VDD = 3V to 5.5V 1 nA
Integrator Amp Voltage Offset VINT-OS VDD = 3V to 5.5V -3 +3 mV
Undedicated Chopper Amp Input
IAIN-BIAS VDD = 3V to 5.5V -10 +10 nA
Bias Current
Undedicated Chopper Amp
VAIN-OS VDD = 3V to 5.5V -200 +200 µV
Offset Voltage
BFB_ Buffer Error CLOAD < 100pF -200 +200 µV
UT and OT Leakage Current ILEAK V UT = V OT = 5.5V 1 µA
UT and OT Output Low Voltage VOL Sinking 4mA 150 mV

Note 3: Includes power FET leakage.

Note 4: CTLI gain is defined as:

A CTLI = (VCTLI −VREF )

(VOSI −VCS )
Note 5: Specifications to -40°C are guaranteed by design, not production tested.

6 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. TEC CURRENT EFFICIENCY vs. TEC CURRENT OUTPUT-VOLTAGE

VDD = 5V VDD = 3.3V RIPPLE WAVEFORMS
90 80

MAX1978 toc02

MAX1978 toc03
MAX1978 toc01

VOS2
80 70 100mV/div
70 AC-COUPLED
60
EFFICIENCY (%)

60
EFFICIENCY (%)

50
50 VOS1
40 100mV/div
40 AC-COUPLED
30
30
20 VOS1 - VOS1
20 RTEC = 0.855Ω
RTEC = 1.1Ω 50mV/div
10 10

0 0
0 0.5 1.0 1.5 2.0 2.5 0 0.5 1.0 1.5 2.0 2.5 400ns/div
TEC CURRENT (A) TEC CURRENT (A)

INPUT SUPPLY RIPPLE TEC CURRENT vs. CTLI VOLTAGE ZERO-CROSSING TEC CURRENT
MAX1978 toc04

MAX1978 toc05

MAX1978 toc06
VCTLI
200mV/div
1.5V
VCTLI
1V/div
VDD
20mV/div -0V
ITEC
AC-COUPLED
-0A ITEC 500mA/div 0A
2A/div

200ns/div 20ms/div 1ms/div

SWITCHING FREQUENCY
VITEC vs. TEC CURRENT TEC CURRENT vs. TEMPERATURE vs. TEMPERATURE
3.0 1.010 508
MAX1978 toc07

MAX1978 toc08

MAX1978 toc09

506
2.5
SWITCHING FREQUENCY (kHz)

1.005 504
2.0
502
VITEC (V)

ITEC (A)

1.5 1.000 500

498
1.0
0.995 496
0.5 ITEC = 1A VCTLI = 1.5V
494 RTEC = 1Ω
RSENSE = 0.68Ω
0 0.990 492
-3 -2 -1 0 1 2 3 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80
TEC CURRENT (A) TEMPERATURE (°C) TEMPERATURE (°C)

Maxim Integrated 7
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)

SWITCHING FREQUENCY CHANGE REFERENCE VOLTAGE CHANGE REFERENCE VOLTAGE CHANGE

vs. INPUT SUPPLY vs. INPUT SUPPLY vs. TEMPERATURE
10 1.0 3

MAX1978 toc11

MAX1978 toc12
MAX1978 toc10
SWITCHING FREQUENCY CHANGE (kHz)

5 0.5
REFERENCE VOLTAGE CHANGE (mV)

REFERENCE VOLTAGE CHANGE (mV)

2
0 0
1
-5
-0.5
-10 0
-1.0
-15 -1
-1.5
-20
-2
-2.0
-25
-2.5 -3
-30
-35 -3.0 -4
3.0 3.5 4.0 4.5 5.0 5.5 3.0 3.5 4.0 4.5 5.0 5.5 -40 -20 0 20 40 60 80
VDD (V) VDD (V) TEMPERATURE (°C)

ATO VOLTAGE
REFERENCE LOAD REGULATION vs. THERMISTOR TEMPERATURE STARTUP AND SHUTDOWN WAVEFORMS
0.6 4.5
MAX1978 toc13

MAX1978 toc15
MAX1978 toc14

0.4 4.0 NTC, 10kΩ THERMISTOR VSHDN

REFERENCE VOLTAGE CHANGE (mV)

CIRCUIT IN FIGURES 1 AND 2 5V/div

0.2 3.5
ATO VOLTAGE (V)

3.0
0
2.5
-0.2
ITEC
2.0
-0.4 500mA/div
1.5
-0.6 SINK SOURCE
1.0
-0.8 IDD
0.5
200mA/div
-1.0 0
-0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 -10 0 10 20 30 40 50 60 100µs/div
REFERENCE LOAD CURRENT (mA) THERMISTOR TEMPERATURE (°C)

THERMAL STABILITY,
CTLI STEP RESPONSE INPUT SUPPLY STEP RESPONSE COOLING MODE
MAX1978 toc17

MAX1978 toc18
MAX1978 toc16

VCTLI VDD
1V/div 2V/div
1.5V

TEMPERATURE
0V 0.001°C/div
ITEC ITEC
1A/div 20mA/div
0A
1A
ITEC = +25°C
TA = +45°C

1ms/div 10ms/div 4s/div

8 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)

THERMAL STABILITY, THERMAL STABILITY, TEMPERATURE ERROR

ROOM TEMPERATURE HEATING MODE vs. AMBIENT TEMPERATURE
0.03

MAX1978 toc20
MAX1978 toc19

MAX1978 toc21
0.02

TEMPERATURE ERROR (°C)

0.01
MPERATURE TEMPERATURE
0.001°C/div 0.001°C/div
0

-0.01

ITEC = +25°C TTEC = +25°C

TA = +25°C TA = +5°C -0.02

-0.03
4s/div 4s/div -20 -10 0 10 20 30 40 50
AMBIENT TEMPERATURE (°C)

Pin Description
PIN NAME FUNCTION
Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power
1 OS2
output.
2, 8, 29,
N.C. Not Internally Connected
35
Power Ground 2. Internal synchronous rectifier ground connections. Connect all PGND pins together at
3, 5 PGND2
power ground plane.
4, 6, 9 LX2 Inductor 2 Connection. Connect all LX2 pins together. Connect LX2 to LX1 when using the MAX1979.
Power 2 Inputs. Must be same voltage as VDD. Connect all PVDD2 inputs together at the VDD power plane.
7, 10 PVDD2
Bypass to PGND2 with a 10µF ceramic capacitor.
11 SHDN Shutdown Control Input. Active-low shutdown control.
Over-Temperature Alarm. Open-drain output pulls low if temperature feedback rises 20mV
12 OT
(typically +1.5°C) above the set-point voltage.
Under-Temperature Alarm. Open-drain output pulls low if temperature feedback falls 20mV
13 UT
(typically +1.5°C) below the set-point voltage.
14 INTOUT Integrator Amp Output. Normally connected to CTLI.
15 INT- Integrator Amp Inverting Input. Normally connected to DIFOUT through thermal-compensation network.
16, 25,
GND Analog Ground. Connect all GND pins to analog ground plane.
26, 42, 43
17 DIFOUT Chopper-Stabilized Instrumentation Amp Output. Differential gain is 50 ✕ (FB+ - FB-).
18 FB- Chopper-Stabilized Instrumentation Amp Inverting Input. Connect to thermistor bridge.
19 FB+ Chopper-Stabilized Instrumentation Amp Noninverting Input. Connect to thermistor bridge.
20 BFB- Chopper-Stabilized Buffered FB- Output. Used to monitor thermistor bridge voltage.
21 BFB+ Chopper-Stabilized Buffered FB+ Output. Used to monitor thermistor bridge voltage.
22 AIN+ Undedicated Chopper-Stabilized Amplifier Noninverting Input

Maxim Integrated 9
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Pin Description (continued)
PIN NAME FUNCTION
23 AIN- Undedicated Chopper-Stabilized Amplifier Inverting Input
24 AOUT Undedicated Chopper-Stabilized Amplifier Output
Power 1 Inputs. Must be same voltage as VDD. Connect all PVDD1 inputs together at the VDD power plane.
27, 30 PVDD1
Bypass to PGND1 with a 10µF ceramic capacitor.
28, 31, 33 LX1 Inductor 1 Connection. Connect all LX1 pins together. Connect LX1 to LX2 when using the MAX1979.
Power Ground 1. Internal synchronous-rectifier ground connections. Connect all PGND pins together at
32, 34 PGND1
power ground plane.
36 FREQ Switching-Frequency Select. Low = 500kHz, high = 1MHz.
TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC current-
37 ITEC
sense resistor. VITEC = 1.50V + (VOS1 - VCS) ✕ 8.
38 COMP Current-Control Loop Compensation. For most designs, connect a 10nF capacitor from COMP to GND.
39 MAXIP Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV/RSENSE.
Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit -150mV /
40 MAXIN
RSENSE. Connect MAXIN to MAXIP when using the MAX1979.
Maximum Bipolar TEC Voltage. Connect an external resistive divider from REF to GND to set the maximum
41 MAXV
voltage across the TEC. The maximum TEC voltage is 4 ✕ VMAXV.
44 VDD Analog Supply Voltage Input. Bypass to GND with a 10µF ceramic capacitor.
TEC Current-Control Input. Sets differential current into the TEC. Center point is 1.50V (no TEC current).
45 CTLI Connect to INTOUT when using the thermal control loop. ITEC = (VOS1 - VCS)/RSENSE = (VCTLI - 1.50)/(10 ✕
RSENSE). When (VCLTI - VREF) > 0, VOS2 > VOS1 > VCS.
46 REF 1.5V Reference Voltage Output. Bypass REF to GND with a 1µF ceramic capacitor.
Current-Sense Input. The current through the TEC is monitored between CS and OS1. The maximum TEC
47 CS
current is given by 150mV/RSENSE and is bipolar for the MAX1978. The MAX1979 TEC current is unipolar.
Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power
48 OS1
output.
— EP Exposed Pad. Solder evenly to the PCB ground plane to maximize thermal performance.

10 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Functional Diagram
ON

OFF

SHDN FREQ
VDD 3V TO 5.5V
REF 1.5V
REFERENCE PVDD1

MAXV MAX VTEC =

VMAXV x 4
LX1

MAXIP MAX ITEC = (VMAXIP/

VREF) x (0.15V/RSENSE)
PGND1
PWM CONTROL AND GATE DRIVE

MAX ITEC = (VMAXIN/

VREF) x (0.15V/RSENSE)
MAXIN
CS

RSENSE

CS OS1

ITEC OS1 OS2

REF
PVDD2
CTLI
VDD
COMP

LX2

GND MAX1978

OT
50R PGND2
REF + 1V

R
UT
REF
50R
REF - 1V R

REF BFB-

BFB+
INTOUT INT- AIN- AOUT AIN+ DIFOUT FB+ FB-

Maxim Integrated 11
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Detailed Description TEC temperature. The on-chip thermal-control circuitry
can be configured to achieve temperature control sta-
Power Stage bility of 0.001°C. Figure 1 shows a typical TEC thermal-
The power stage of the MAX1978/MAX1979 control circuit.
thermoelectric cooler (TEC) temperature controllers
consists of two switching buck regulators that operate Ripple Cancellation
together to directly control TEC current. This configura- Switching regulators like those used in the
tion creates a differential voltage across the TEC, allow- MAX1978/MAX1979 inherently create ripple voltage on
ing bidirectional TEC current for controlled cooling and each common-mode output. The regulators in the
heating. Controlled cooling and heating allow accurate MAX1978 switch in phase and provide complementary
TEC temperature control within the tight tolerances of in-phase duty cycles, so ripple waveforms at the differ-
laser driver specifications. ential TEC output are greatly reduced. This feature sup-
presses ripple currents and electrical noise at the TEC
The voltage at CTLI directly sets the TEC current. The
to prevent interference with the laser diode while mini-
internal thermal-control loop drives CTLI to regulate
mizing output capacitor filter size.

VDD REF

10µF 10µF 1µF

10µF

0.01µF
VDD SHDN PVDD1 PVDD2 REF MAXV MAXIN MAXIP
3µH
COMP LX1
UNDERTEMP
UT CS 1µF
ALARM
OVERTEMP 0.068Ω
OT
ALARM
DC CURRENT OS1
ITEC
MONITOR
20kΩ 4.7µF
1% MAX1978 TEC
BFB-
80.6kΩ
1µF AIN- OS2
THERMISTOR
VOLTAGE AOUT 3µH
MONITOR LX2
1µF
REF AIN+
69.8kΩ THERMAL
CTLI REF FEEDBACK
1% 105kΩ
1% FREQ FB-
GND PGND2 PGND1 INTOUT INT- DIFOUT FB+

10kΩ
100kΩ

100kΩ 10µF 0.47µF 20kΩ

0.047µF 1MΩ

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.

12 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Switching Frequency derived from, and is synchronized to, the switching fre-
FREQ sets the switching frequency of the internal oscil- quency of the power stage.
lator. The oscillator frequency is 500kHz when FREQ =
GND. The oscillator frequency is 1MHz when FREQ = Integrator Amplifier
VDD. The 1MHz setting allows minimum inductor and fil- An on-chip integrator amplifier is provided on the
ter-capacitor values. Efficiency is optimized with the MAX1978/MAX1979. The noninverting terminal of the
500kHz setting. amplifier is connected internally to REF. Connect an
appropriate network of resistors and capacitors between
Voltage and Current-Limit Settings DIFOUT and INT-, and connect INTOUT to CTLI for typi-
The MAX1978 and MAX1979 provide settings to limit cal operation. CTLI directly controls the TEC current
the maximum differential TEC voltage. Applying a volt- magnitude and polarity. The thermal-control-loop dynam-
age to MAXV limits the maximum voltage across the ics are set by the integrator input and feedback compo-
TEC to ±(4  VMAXV). nents. See the Applications Information section for
The MAX1978 also limits the maximum positive and details on thermal-loop compensation.
negative TEC current. The voltages applied to MAXIP Current Monitor Output
and MAXIN independently set the maximum positive ITEC provides a voltage output proportional to the TEC
and negative output current limits. The MAX1979 con- current, ITEC (see the Functional Diagram):
trols TEC current in only one direction, so the maximum
current is set only with MAXIP. MAXIN must be con-
nected to MAXIP when using the MAX1979. VITEC = 1.5V + 8  (VOS1 - VCS)
Chopper-Stabilized Instrumentation
Amplifier Over- and Under-Temperature Alarms
The MAX1978 and MAX1979 include a chopped input The MAX1978/MAX1979 provide open-drain status out-
instrumentation amplifier with a fixed gain of 50. An puts that alert a microcontroller when the TEC tempera-
external thermal sensor, typically a thermistor, is con- ture is over or under the set-point temperature. OT and
nected to one of the amp’s inputs. The other input is UT pull low when V(FB1+ - FB-) is more than 20mV. For a
connected to a voltage that represents the temperature typical thermistor connection, this translates to approxi-
set point. This set point can be derived from a resistor- mately 1.5°C error.
divider network or DAC. The included instrumentation
amplifier provides low offset drift needed to prevent Reference Output
temperature set-point drift with ambient temperature The MAX1978/MAX1979 include an on-chip 1.5V volt-
changes. Temperature stability of 0.001°C can be age reference accurate to 1% over temperature.
achieved over a 0°C to +50°C ambient temperarure Bypass REF with 1µF to GND. REF can be used to bias
range by using the amplifier as in Figure 1. DIFOUT is an external thermistor for temperature sensing as
the instrumentation amplifier output and is proportional shown in Figures 1 and 2. Note that the 1% accuracy of
to 50 times the difference between the set-point tem- REF does not limit the temperature stability achievable
perature and the TEC temperature. This difference is with the MAX1978/MAX1979. This is because the ther-
commonly referred to as the “error signal”. For best mistor and set-point bridge legs are intended to be dri-
temperature stability, derive the set-point voltage from ven ratiometrically by the same reference source (REF).
the same reference that drives the thermistor (usually Variations in the bridge-drive voltage then cancel out
the MAX1978/MAX1979 REF output). This is called a and do not generate errors. Consequently, 0.001°C sta-
“ratiometric” or “bridge” connection. The bridge con- ble temperature control is achievable with the
nection optimizes stability by eliminating REF drift as an MAX1978/MAX1979 reference.
error source. Errors at REF are nullified because they An external source can be used to bias the thermistor
affect the thermistor and set point equally. bridge. For best accuracy, the common-mode voltage
The instrumentation amplifier utilizes a chopped input applied to FB+ and FB- should be kept between 0.5V
scheme to minimize input offset voltage and drift. This and 1V, however the input range can be extended from
generates output ripple at DIFOUT that is equal to the 0.2V to VDD / 2 if some shift in instrumentation amp offset
chop frequency. The DIFOUT peak-to-peak ripple (approximately -50µV/V) can be tolerated. This shift
amplitude is typically 100mV but has no effect on tem- remains constant with temperature and does not con-
perature stability. DIFOUT ripple is filtered by the inte- tribute to set-point drift.
grator in the following stage. The chopper frequency is

Maxim Integrated 13
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
VDD REF

10µF 10µF 1µF

10µF

0.01µF
VDD SHDN PVDD1 PVDD2 REF MAXV MAXIN MAXIP
COMP LX1 3µH
UNDERTEMP LX2
UT
ALARM CS 1µF
OVERTEMP
OT 0.03Ω
ALARM
DC CURRENT
ITEC OS1
MONITOR
20kΩ
1% MAX1979 4.7µF
TEC
BFB-
80.6kΩ
1µF AIN-
THERMISTOR OS2
VOLTAGE AOUT
MONITOR

REF AIN+
69.8kΩ THERMAL
CTLI FB- REF FEEDBACK
1% 105kΩ
1% FREQ FB+
GND PGND2 PGND1 INTOUT INT- DIFOUT

10kΩ

10µF 0.47µF 100kΩ

100kΩ 20kΩ

0.047µF 1MΩ

Figure 2. MAX1979 Typical Application Circuit. MAXIN sets the maximum TEC current circuit configured for cooling with NTC ther-
mistor. Current always flow from CS and OS2.

Buffered Outputs, BFB+ and BFB- ted but is intended to provide a temperature-propor-
BFB+ and BFB- output a buffered version of the voltage tional analog output. The thermistor voltage typically is
that appears on FB+ and FB-, respectively. The buffers connected to the undedicated chopper amplifier
are typically used in conjunction with the undedicated through the included buffers BFB+ and BFB-. Figure 3
chopper amplifier to create a monitor for the thermistor shows how to configure the undedicated amplifier as a
voltage/TEC temperature (Figures 1 and 2). These thermistor voltage monitor. The output voltage at AOUT
buffers are unity-gain chopper amplifiers and exhibit is not precisely linear, because the thermistor is not lin-
output ripple. Each output can be either integrated or ear. AOUT is also chopper stabilized and exhibits out-
filtered to remove the ripple content if necessary. put ripple and can be either integrated or filtered to
remove the ripple content if necessary.
Undedicated Chopper-Stabilized Amplifier
In addition to the chopper amplifiers at DIFOUT and
BFB_, the MAX1978/MAX1979 include an additional
chopper amplifier at AOUT. This amplifier is uncommit-

14 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
22µF to 100µF ceramic capacitor between the V DD
REF power plane and power ground. Insufficient supply
bypassing can result in supply bounce and degraded
69.8kΩ accuracy.
1%
AIN+ Compensation Capacitor
Include a compensation capacitor to ensure current-
105kΩ
AOUT 1%
power control-loop stability. Select the capacitor so that
the unity-gain bandwidth of the current-control loop is
less than or equal to 10% the resonant frequency of the
80.6kΩ output filter:
1µF
1%
⎛g ⎞ ⎛ 24 × RSENSE ⎞
AIN- CCOMP ≥ ⎜ m ⎟ × ⎜ ⎟
REF ⎝ fBW ⎠ ⎝ 2π × (RSENSE + RTEC ) ⎠
20kΩ
MAX1978 1% where:
MAX1979 BFB-
10kΩ fBW = unity-gain bandwidth frequency
gm = loop transconductance, typically 100µA/V
x50
FB- CCOMP = value of the compensation capacitor
VSETPOINT RTEC = TEC series resistance
FB+ RSENSE = sense resistor
Setting Voltage and Current Limits
Consider TEC parameters to guarantee a robust
Figure 3. Thermistor Voltage Monitor design. These parameters include maximum positive
current, maximum negative current, and the maximum
Design Procedure voltage allowed across the TEC. These limits should be
used to set MAXIP, MAXIN, and MAXV voltages.
Inductor Selection
Small surface-mount inductors are ideal for use with the Setting Max Positive and Negative TEC Current
MAX1978/MAX1979. Select the output inductors so that MAXIP and MAXIN set the maximum positive and nega-
the LC resonant frequency of the inductance and the tive TEC currents, respectively. The default current limit
output capacitance is less than 1/5 the selected switch- is ±150mV / RSENSE when MAXIP and MAXIN are con-
ing frequency. For example, 3.0µH and 1µF have a res- nected to REF. To set maximum limits other than the
onance at 92kHz, which is adequate for 500kHz defaults, connect a resistor-divider from REF to GND to
operation. set VMAXI_. Use resistors in the 10kΩ to 100kΩ range.
VMAXI_ is related to ITEC by the following equations:

1
f LC= VMAXIP = 10 (ITECP(MAX)  RSENSE)
¡ 2π LC
VMAXIN = 10 (ITECN(MAX)  RSENSE)
where:
fLC = resonant frequency of output filter. where ITECP(MAX) is the maximum positive TEC current
and ITECN(MAX) is the maximum negative TEC current.
Capacitor Selection
Positive TEC current occurs when CS is less than OS1:
Filter Capacitors
Decouple each power-supply input (VDD, PVDD1, and
PVDD2) with a 10µF ceramic capacitor close to the sup- ITEC  RSENSE = CS - OS1 when ITEC < 0.
ply pins. If long supply lines separate the source sup- ITEC  RSENSE = OS1 - CS when ITEC > 0.
ply from the MAX1978/MAX1979, or if the source
supply has high output impedance, place an additional

Maxim Integrated 15
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
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 FB-
MAXIP when using the MAX1979. The equation for set- REF
ting MAXIP is the same for the MAX1978 and
CREF
MAX1979. Do not exceed the positive or negative cur- MAX1978
rent-limit specifications on the TEC. Refer to the TEC MAX1979
manufacturer’s data sheet for these limits. FB+ VTHERMISTOR
VSETPOINT
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 VMAXV and can be
positive or negative.
FB-
REF
|VOS1 - VOS2| = 4  VMAXV
VTHERMISTOR
CREF
MAX1978
Use resistors from 10kΩ to 100kΩ to form a voltage- MAX1979
divider to set VMAXV. FB+ DAC DIGITAL
VSETPOINT INPUT
Thermal-Control Loop
The MAX1978/MAX1979 provide all the necessary
amplifiers needed to create a thermal-control loop.
Typically, the chopper-stabilized instrumentation ampli-
Figure 5. The Set Point can be Derived from a Potentiometer
fier generates an error signal and the integrator amplifi- or a DAC
er is used to create a PID controller. Figure 4 shows an Control Inputs/Outputs
example of a simple PID implementation. The error sig-
nal needed to control the loop is generated from the TEC Current Control
difference between the set point and the thermistor The voltage at CTLI directly sets the TEC current. CTLI
voltage. The desired set-point voltage can be derived typically is driven from the output of a temperature-con-
from a potentiometer, DAC, or other voltage source. trol circuit CINTOUT. For the purposes of the following
Figure 5 details the required connections. Connect the equations, it is assumed that positive TEC current is
output of the PID controller to CTLI. For details, see the heating.
Applications Information section.
The transfer function relating current through the TEC
(ITEC) and VCTLI is given by:
C3

ITEC = (VCTLI - VREF) / (10  RSENSE)

where VREF is 1.50V

C1 R1 R3 C2
and ITEC = (VOS1 - VCS) / RSENSE
INT- VCTLI is centered around REF (1.50V). ITEC is zero when
VCTLI = 1.50V. When VCTLI > 1.50V, the MAX1978 is heat-
ing. Current flow is from OS2 to OS1. The voltages are:
DIFOUT INTOUT
R2

VOS2 > VOS1 > VCS

REF when VCTLI < 1.50V, current flows from OS1 to OS2:
VOS2 < VOS1 < VCS
Figure 4. Proportional Integral Derivative Controller

16 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Shutdown Control grator capacitor and results in slow loop-transient
Drive SHDN low to place the MAX1978/MAX1979 in a response. A better approach is to use a PID controller,
power-saving shutdown mode. When the MAX1978/ where two additional zeros are used to cancel the TEC
MAX1979 are in shutdown, the TEC is off (VOS1 and and integrator poles. Adequate phase margin can be
VOS2 decay to GND) and input supply current lowers to achieved near the frequency of the TEC’s second pole
2mA (typ). when using a PID controller. The following is an exam-
ple of the compensation procedure using a PID con-
ITEC Output troller.
ITEC is a status output that provides a voltage propor-
tional to the actual TEC current. ITEC = REF when TEC Figure 6 details a two-pole transfer function of a typical
current is zero. The transfer function for the ITEC output: TEC module. This Bode plot can be generated with a
signal analyzer driving the CTLI input of the
MAX1978/MAX1979, while plotting the thermistor volt-
VITEC = 1.50 + 8  (VOS1 - VCS) age from the module. For the example module, the two
poles are at 0.02Hz and 1Hz.
Use ITEC to monitor the cooling or heating current The first step in compensating the control loop involves
through the TEC. The maximum capacitance that ITEC selecting components R3 and C2 for highest DC gain.
can drive is 100pF. Film capacitors provide the lowest leakage but can be
large. Ceramic capacitors are a good compromise
Applications Information between low leakage and small size. Tantalum and
The MAX1978/MAX1979 drive a thermoelectric cooler electrolytic capacitors have the highest leakage and
inside a thermal-control loop. TEC drive polarity and generally are not suitable for this application. The inte-
power are regulated to maintain a stable control tem- grating capacitor, C2, and R3 (Figure 4) set the first
perature based on temperature information read from a zero (fz1). The specific application dictates where the
thermistor, or from other temperature-measuring first zero should be set. Choosing a very low frequency
devices. Carefully selected external components can results in a very large value capacitor. Set the first zero
achieve 0.001°C temperature stability. The MAX1978/ frequency to no more than 8 times the frequency of the
MAX1979 provide precision amplifiers and an integra- lowest TEC pole. Setting the frequency more than 8
tor amplifier to implement the thermal-control loop times the lowest pole results in the phase falling below
(Figures 1 and 2). -135° and may cause instability in the system. For this
example, C2 = 10µF. Resistor R3 then sets the zero at
Connecting and Compensating the 0.16Hz using the following equation:
Thermal-Control Loop
Typically, the thermal loop consists of an error amplifier 1
and proportional integral derivative controller (PID) fz1 =
2π × C2 × R3
(Figure 4). The thermal response of the TEC module
must be understood before compensating the thermal This yields a value of R3 = 99.47kΩ. For our example,
loop. In particular, TECs generally have stronger heat- use 100kΩ.
ing capacity than cooling capacity because of the
Next, adjust the gain for a crossover frequency for max-
effects of waste heat. Consider this point when analyz-
imum phase margin near the TEC’s second pole. From
ing the TEC response.
Figure 6, the TEC bode plot, approximately 30dB of
Analysis of the TEC using a signal analyzer can ease gain is needed to move the 0dB crossover point up to
compensation calculations. Most TECs can be crudely 1.5Hz. The error amplifier provides a fixed gain of 50,
modeled as a two-pole system. The second pole poten- or approximately 34dB. Therefore, the integrator needs
tially creates an oscillatory condition because of the to provide -4dB of gain at 1.5Hz. C1 and R3 set the
associated 180° phase shift. A dominant pole compen- gain at the crossover frequency.
sation scheme is not practical because the crossover
frequency (the point of the Bode plot where the gain is A
C1 =
zero dB) must be below the TEC’s first pole, often as 1
+ 2π × R3 × fC
low as 0.02Hz. This requires an excessively large inte- C2

Maxim Integrated 17
MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
where: Choose fp1 = 15Hz, find R1 using the following equation:
A = The gain needed to move the 0dB crossover point 1
up to the desired frequency. In this case, A = -4dB = fp1 =
2π × C1× R1
0.6.
fC = The desired crossover frequency, 1.5Hz in this Resistor R1 is found to be 22kΩ, use 20kΩ
example. The final step is to terminate the first zero by setting the
C1 is found to be 0.58µF; use 0.47µF. rolloff frequency with a second pole, fp2. A good
Next, the second TEC pole must be cancelled by choice is 2 times fp1.
adding a zero. Canceling the second TEC pole pro- Choose fp2 = 30Hz, find C3 using the following equation:
vides maximum phase margin by adding positive
phase to the circuit. Setting a second zero (fz2) to at 1
least 1/5 the crossover frequency (1.5Hz/5 = 0.3Hz), fp2 =
2π × C3 × R3
and a pole (fp1) to 5 times the crossover frequency or
higher (5 × 1.5Hz = 7.5Hz) ensures good phase margin, where C3 is found to be 0.05µF, use 0.047µF.
while allowing for variation in the location of the TEC’s
second pole. Set the zero fz2 to 0.3Hz and calculate R2: Figure 7 displays the compensated gain and phase
1 plots for the above example.
fz2 = The example given is a good place to start when com-
2π × C1× R2
pensating the thermal loop. Different TEC modules
where fz2 is the second zero. require individual testing to find their optimal compen-
sation scheme. Other compensation schemes can be
R2 is calculated to be 1.1MΩ; use 1MΩ. used. The above procedure should provide good
Now pole fp1 is added at least 5 times the crossover results for the majority of optical modules.
frequency to terminate zero fz2.

COMPENSATED
TEC GAIN AND PHASE TEC GAIN AND PHASE
40 90 80 90
30 70
20 45 60
50 45
10
40
PHASE (DEGREES)

0 0 30

PHASE (DEGREES)
0
20
GAIN (dB)

-10
GAIN (dB)

10
-20 -45 -45
0
-30 -10
-40 -90 -20
-30 -90
-50 -40
-60 -135 -50 -135
-70 -60
-70
-80 -180 -80 -180
0.001 0.01 0.1 1 10 100 0.001 0.01 0.1 1 10 100
FREQUENCY (Hz) FREQUENCY (Hz)

Figure 6. Bode Plot of a Generic TEC Module Figure 7. Compensated Thermal-Control Loop Using the TEC
Module in Figure 6

18 Maxim Integrated
 MAX1978/MAX1979
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Circuit

INPUT VDD
LX1
3V TO 5.5V PVDD-

PGND1

ON CS
SHDN
OFF

OVERTEMP ALARM OT
OS1
UNDERTEMP ALARM UT ITEC = ±3A
OS2 TEC
MAX1978
BFB- LX2

PGND2

AIN- REF

TEMP MONITOR AOUT

FB+
TEC CURRENT MONITOR ITEC

AIN+
NTC
VOLTAGE LIMIT MAXV

HEATING CURRENT LIMIT MAXIP FB-

COOLING CURRENT LIMIT MAXIN DAC

OPTIONAL DAC
REF

Chip Information Package Information

TRANSISTOR COUNT: 6023 For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in
PROCESS: BiCMOS the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
48 TQFN-EP T4877+6 21-0144

Maxim Integrated 19
MAX1978/MAX1979
Integrated Temperature Controller for
Peltier Modules
Revision History

REVISION REVISION PAGES

DESCRIPTION
NUMBER DATE CHANGED
0 7/02 Initial release —
1 2/07 Updated the Ordering Information, Pin Description, and Package Information. 1, 9, 10, 19, 20, 21
Revised the Pin Description and the Setting Max Positive and Negative TEC
2 1/10 10, 16
Current section.
Revised the Figure 1 and 2 captions, and the Voltage and Current-Limit Settings
3 3/10 12–14
section.

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical
Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
20 Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.