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19-2490; Rev 1; 2/07
Integrated Temperature
Controllers for Peltier Modules
General Description
The MAX1978/MAX1979 are the smallest, safest, most accurate complete single-chip temperature controllers for
Peltier thermoelectric cooler (TEC) modules. On-chip power
FETs and thermal control-loop circuitry minimize external components while maintaining high efficiency. Selectable
500kHz/1MHz switching frequency and a unique ripple-cancellation scheme optimize component size and efficiency while reducing noise. Switching speeds of internal
MOSFETs are optimized to reduce noise and EMI. An ultralow-drift chopper amplifier maintains ±0.001°C temperature stability. Output current, rather than voltage, is directly controlled to eliminate current surges. Individual heating and cooling current and voltage limits provide the highest level of
TEC protection.
The MAX1978 operates from a single supply and provides bipolar ±3A output by biasing the TEC between the outputs of two synchronous buck regulators. True bipolar operation controls temperature without “dead zones” or other nonlinearities at low load currents. The control system does not hunt when the set point is very close to the natural operating point, where only a small amount of heating or cooling is needed. An analog control signal precisely sets the TEC current. The MAX1979 provides unipolar output up to 6A.
A chopper-stabilized instrumentation amplifier and a highprecision integrator amplifier are supplied to create a proportional-integral (PI) or proportional-integral-derivative (PID) controller. The instrumentation amplifier can interface to an external NTC or PTC thermistor, thermocouple, or semiconductor temperature sensor. Analog outputs are provided to monitor TEC temperature and current. In addition, separate overtemperature and undertemperature outputs indicate when the TEC temperature is out of range. An on-chip voltage reference provides bias for a thermistor bridge.
The MAX1978/MAX1979 are available in a low-profile
48-lead thin QFN-EP package and is specified over the
-40°C to +85°C temperature range. The thermally enhanced QFN-EP package with exposed metal pad minimizes operating junction temperature. An evaluation kit is available to speed designs.
Applications
Fiber Optic Laser Modules
WDM, DWDM Laser-Diode Temperature Control
Fiber Optic Network Equipment
EDFA Optical Amplifiers
Telecom Fiber Interfaces
ATE
Typical Operating Circuit appears at end of data sheet.
Features
♦ Smallest, Safest, Most Accurate Complete
Single-Chip Controller
♦ On-Chip Power MOSFETS—No External FETs
♦ Circuit Footprint < 0.93in
2
♦ Circuit Height < 3mm
♦ Temperature Stability to 0.001°C
♦ Integrated Precision Integrator and Chopper
Stabilized Op Amps
♦ Accurate, Independent Heating and Cooling
Current Limits
♦ Eliminates Surges By Directly Controlling
TEC Current
♦ Adjustable Differential TEC Voltage Limit
♦ Low-Ripple and Low-Noise Design
♦ TEC Current Monitor
♦ Temperature Monitor
♦ Over- and Undertemperature Alarm
♦ Bipolar ±3A Output Current (MAX1978)
♦ Unipolar +6A Output Current (MAX1979)
Ordering Information
PART T EM P R A N G E PIN-PACKAGE PK G CO D E
MAX1978ETM - 40
° C to + 85° C 48 Thin QFN-EP*
T4877-6
MAX1979ETM - 40
° C to + 85° C 48 Thin QFN-EP*
T4877-6
*EP = Exposed paddle.
Pin Configuration
TOP VIEW
7
8
5
6
3
4
1
2
9
10
11
12
OS2
N.C.
PGND2
LX2
PGND2
LX2
PV
DD
2
N.C.
LX2
PV
DD
2
SHDN
OT
MAX1978
MAX1979
FREQ
N.C.
PGND1
LX1
PGND1
LX1
PV
DD
1
N.C.
LX1
PV
DD
1
GND
GND
32
31
30
29
36
35
34
33
28
27
26
25
QFN-EP
*ELECTRICALLY CONNECTED TO THE UNDERSIDE METAL SLUG.
NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Integrated Temperature
Controllers for Peltier Modules
ABSOLUTE MAXIMUM RATINGS
V
DD to GND ..............................................................-0.3V to +6V
SHDN, MAXV, MAXIP, MAXIN,
CTLI, OT, UT to GND............................................-0.3V to +6V
FREQ, COMP, OS1, OS2, CS, REF, ITEC, AIN+, AIN-,
AOUT, INT-, INTOUT, BFB+, BFB-, FB+, FB-,
DIFOUT to GND......................................-0.3V to (V
DD
+ 0.3V)
PV
DD
1, PV
DD
2 to V
DD
...........................................-0.3V to +0.3V
PV
DD
1, PV
DD
2 to GND...............................-0.3V to (V
DD
+ 0.3V)
PGND1, PGND2 to GND .......................................-0.3V to +0.3V
COMP, REF, ITEC, OT, UT, INTOUT, DIFOUT,
BFB-, BFB+, AOUT Short to GND .............................Indefinite
Peak LX Current (MAX1978) (Note 1).................................±4.5A
Peak LX Current (MAX1979) (Note 1)....................................+9A
Continuous Power Dissipation (T
A
= +70°C)
48-Lead Thin QFN-EP
(derate 26.3mW/°C above +70°C) (Note 2) .................2.105W
Operating Temperature Ranges
MAX1978ETM ..................................................-40°C to +85°C
MAX1979ETM ..................................................-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: LX has internal clamp diodes to PGND and PV
DD
. Applications that forward bias these diodes should not exceed the IC’s package power dissipation limits.
Note 2: Solder underside metal slug to PC board 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
(V
DD
= PV
DD
1 = PV
DD
2 =
SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T
A
unless otherwise noted. Typical values at T
A
= +25°C.)
= 0°C to +85°C,
PARAMETER
Input Supply Range
SYMBOL
V
DD
CONDITIONS MIN
3.0
TYP MAX
5.5
UNITS
V
Output Voltage Range
Maximum TEC Current
Reference Voltage
Reference Load Regulation
Current-Sense Threshold
NFET On-Resistance
PFET On-Resistance
NFET Leakage
V
OUT
I
TEC(MAX)
V
REF
∆V
REF
R
DS(ON-N)
R
DS(ON-P)
I
LEAK(N)
V
DD
= 5V, I
TEC
= 0 to ±3A,
V
OUT
= V
OS1
- V
OS2
(MAX1978)
V
DD
= 5V, I
TEC
= 0 to 6A,
V
OUT
= V
OS1
(MAX1979)
V
DD
= 3V, I
TEC
= 0 to ±3A,
V
OUT
= V
OS1
- V
OS2
(MAX1978)
V
DD
= 3V, I
TEC
= 0 to 6A,
V
OUT
= V
OS1
(MAX1979)
MAX1978
MAX1979
V
DD
= 3V to 5.5V, I
REF
= 150µA
V
DD
= 3V to 5.5V, I
REF
= +10µA to -1mA
V
MAXI_
= V
REF
V
OS1
< V
CS
V
MAXI_
= V
REF
/3
V
OS1
> V
CS
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
V
DD
= 5V, I = 0.5A
V
DD
= 3V, I = 0.5A
V
DD
= 5V, I = 0.5A
V
DD
= 3V, I = 0.5A
V
LX
= V
DD
= 5V, T
A
= +25
°C
V
LX
= V
DD
= 5V, T
A
= +85
°C
-4.3
-2.3
1.485
135
40
135
40
+4.3
4.3
+2.3
2.3
1.2
150
50
150
50
0.04
0.06
0.06
0.09
0.02
1
±3
6
1.500
1.515
5
160
60
160
60
0.07
0.08
0.10
0.12
10
V
A
V mV mV
Ω
Ω
µA
2 _______________________________________________________________________________________
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
DD
1 = PV
DD
2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T
A
= 0°C to +85°C, unless otherwise noted. Typical values at T
A
= +25°C.)
PARAMETER
PFET Leakage
No-Load Supply Current
Shutdown Supply Current
Thermal Shutdown
UVLO Threshold
Switching Frequency Internal
Oscillator
OS1, OS2, CS Input Current
SHDN, FREQ Input Current
SYMBOL
I
LEAK(P)
CONDITIONS
V
LX
= 0, T
A
= +25
°C
V
LX
= 0, T
A
= +85
°C
I
DD(NO
V
DD
= 5V
LOAD)
V
DD
= 3.3V
I
DD-SD
SHDN = GND, V
DD
T
S H U TD OWN
Hysteresis = 15
°C
= 5V (Note 3)
V
UVLO
V
DD
rising
V
DD
falling
FREQ = GND f
SW-INT
FREQ=V
DD
I
OS1
, I
OS2
,
I
CS
0 or V
DD
I
SHDN
,
I
FREQ
0 or V
DD
MIN
2.4
2.25
450
800
-100
-5
TYP
0.02
1
30
15
2
165
2.6
2.5
500
1000
MAX
10
50
30
3
2.8
2.75
650
1200
+100
+5
UNITS
µA mA mA
°C
V kHz
µA
µA
SHDN, FREQ Input Low Voltage
V
IL
V
DD
= 3V to 5.5V
0.25
×
V
DD
V
SHDN, FREQ Input High Voltage
V
IH
V
DD
= 3V to 5.5V
0.75
×
V
DD
V
MAXV Threshold Accuracy
MAXV, MAXIP, MAXIN
Input Bias Current
CTLI Gain
CTLI Input Resistance
Error Amp Transconductance
ITEC Accuracy
ITEC Load Regulation
V
MAXV
= V
REF
✕ 0.67,
V
OS1
to V
OS2
= ±4V, V
DD
= 5V
V
MAXV
= V
REF
✕ 0.33,
V
OS1
to V
OS2
= ±2V, V
DD
= 3V
I
MAXV-BIAS
,
I
MAXI_-BIAS
A
CTLI
R
CTLI g m
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
V
CTLI
= 0.5V to 2.5V (Note 4)
1M
Ω terminated at REF
∆V
ITEC
V
OS1
to V
CS
= +100mV or -100mV
V
OS1
to V
CS
= +100mV or -100mV,
I
ITEC
= ±10µA
-1
-2
-0.1
9.5
0.5
50
-10
-0.1
10
1.0
100
+1
+2
+0.1
10.5
2.0
175
+10
+0.1
%
µA
V/V
M
Ω
µS
%
%
Instrumentation Amp Input Bias
Current
Instrumentation Amp Offset
Voltage
Instrumentation Amp Offset-
Voltage Drift with Temperature
Instrumentation Amp Preset
Gain
I
DIF-BIAS
V
DIF-OS
A
DIF
V
DD
= 3V to 5.5V
V
DD
= 3V to 5.5V
R
LOAD
= 10k
Ω to REF
-10
-200
45
0
+20
0.1
50
+10
+200
55 nA
µV
µV/°C
V/V
_______________________________________________________________________________________ 3
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
DD
1 = PV
DD
2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T
A
= 0°C to +85°C, unless otherwise noted. Typical values at T
A
= +25°C.)
PARAMETER
Integrator Amp Open-Loop Gain
Integrator Amp Gain Bandwidth
SYMBOL CONDITIONS
A
OL-INT
R
LOAD
= 10k
Ω to REF
Integrator Amp CMRR CMRR
INT
Integrator Amp Input Bias Current I
INT-BIAS
V
DD
= 3V to 5.5V
Integrator Amp Voltage Offset V
INT-OS
GBW
INT
V
DD
= 3V to 5.5V
Undedicated Chopper Amp
Open-Loop Gain
A
OL-AIN
R
LOAD
= 10k
Ω to REF
Undedicated Chopper Amp
CMRR
CMRR
AIN
Undedicated Chopper Amp Input
Bias Current
Undedicated Chopper Amp
Offset Voltage
I
AIN-BIAS
V
AIN-OS
V
V
DD
DD
= 3V to 5.5V
= 3V to 5.5V
Undedicated Chopper Amp Gain
Bandwidth
Undedicated Chopper Amp
Output Ripple
BFB_ Buffer Error
UT and OT Leakage Current
UT and OT Output Low Voltage
UT Trip Threshold
OT Trip Threshold
GBW
V
I
RIPPLE
LEAK
V
AIN
OL
A = 5
MIN
-3
-10
-200
TYP
120
100
+0.1
100
120
85
0
+10
100
20
MAX
1
+3
+10
+200
C
L OA D
< 100p F -200 0 +200
V
UT
= V
OT
= 5.5V 1
Sinking 4mA
FB+ - FB- (see Typical Application Circuit)
FB+ - FB- (see Typical Application Circuit)
50
-20
20
150
µV
µA mV mV mV
UNITS
dB dB nA mV kHz dB dB nA
µV kHz mV
4 _______________________________________________________________________________________
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS
(V
DD
= PV
DD
1 = PV
DD
2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T
A
= -40°C to +85°C, unless otherwise noted.) (Note 5)
PARAMETER
Input Supply Range
Output Voltage Range
Maximum TEC Current
Reference Voltage
Reference Load Regulation
Current-Sense Threshold
No-Load Supply Current
Shutdown Supply Current
UVLO Threshold
Switching Frequency Internal
Oscillator
OS1, OS2, CS Input Current
SHDN, FREQ Input Current
SYMBOL CONDITIONS
V
DD
V
DD
= 5V, I
TEC
= 0 to ±3A,
V
OUT
= V
OS1
-V
OS2
(MAX1978)
I
I
I f
DD(NO
LOAD)
DD-SD
V
V
OUT
TEC(MAX)
V
∆V
REF
REF
UVLO
SW-INT
V
DD
= 5V, I
TEC
= 0 to 6A,
V
OUT
= V
OS1
(MAX1979)
V
DD
= 3V, I
TEC
= 0 to ±3A,
V
OUT
= V
OS1
- V
OS2
(MAX1978)
V
DD
= 3V, I
TEC
= 0 to 6A,
V
OUT
= V
OS1
(MAX1979)
MAX1978
MAX1979
V
DD
= 3V to 5.5V, I
REF
= 150µA
V
DD
= 3V to 5.5V,
I
REF
= 10µA to -1mA
V
V
OS1
OS1
< V
> V
CS
CS
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
V
DD
= 5V
V
DD
= 3.3V
SHDN = GND, V
DD
= 5V (Note 3)
V
DD
rising
V
DD
falling
FREQ = GND
FREQ = V
DD
I
OS1
, I
OS2
,
I
CS
I
SHDN
,
I
F REQ
0 or V
DD
0 or V
DD
MIN
3
-4.3
-2.3
1.475
135
40
135
40
2.4
2.25
450
800
-100
-5
MAX UNITS
5.5
V
+4.3
4.3
+2.3
2.3
±3
6
1.515
5
160
60
160
60
50
30
3
2.8
2.75
650
1200
+100
+5
V
A
V mV mV mA mA
V kHz
µA
µA
SHDN, FREQ Input Low Voltage
V
IL
V
DD
= 3V to 5.5V
0.25 ✕
V
DD
V
SHDN, FREQ Input High Voltage
V
IH
V
DD
= 3V to 5.5V
0.75 ✕
V
DD
V
_______________________________________________________________________________________ 5
Integrated Temperature
Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
DD
1 = PV
DD
2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T
A
= -40°C to +85°C, unless otherwise noted.) (Note 5)
PARAMETER MIN MAX UNITS
MAXV Threshold Accuracy
MAXV, MAXIP, MAXIN
Input Bias Current
CTLI Gain
CTLI Input Resistance
Error Amp Transconductance
SYMBOL CONDITIONS
V
MAXV
= V
REF
✕ 0.67,
V
OS1
to V
OS2
= ±4V, V
DD
= 5V
V
MAXV
= V
REF
✕
0.33, V
OS1
to V
OS2
= ±2V,
V
DD
= 3V
I
MAXV-BIAS
,
I
MAXI_-BIAS
A
CTLI
R
CTLI g m
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
V
CTLI
= 0.5V to 2.5V (Note 4)
1M
Ω terminated at REF
-1
-2
-0.1
9.5
0.5
50
+1
+2
+0.1
10.5
2.0
175
%
µA
V/V
M
Ω
µS
ITEC Accuracy V
OS1
to V
CS
= +100mV or -100mV -10 +10 %
ITEC Load Regulation
∆V
ITEC
V
OS1
to V
CS
= +100mV or
-100mV, I
ITEC
= ±10µA
-0.125
+0.125
Instrumentation Amp
Input Bias Current
Instrumentation Amp
Offset Voltage
I
DIF-BIAS
V
DIF-OS
V
DD
= 3V to 5.5V
-10
-200
+10
+200
Instrumentation Amp
Preset Gain
Integrator Amp Input Bias Current I
INT-BIAS
V
DD
= 3V to 5.5V
Integrator Amp Voltage Offset V
INT-OS
V
DD
= 3V to 5.5V
Undedicated Chopper Amp Input
Bias Current
I
A
DIF
AIN-BIAS
R
V
LOAD
DD
= 10k
Ω to REF
= 3V to 5.5V
Undedicated Chopper Amp
Offset Voltage
BFB_ Buffer Error
UT and OT Leakage Current
UT and OT Output Low Voltage
V
I
AIN-OS
LEAK
V
OL
V
C
V
DD
LOAD
UT
= 3V to 5.5V
< 100pF
= V
OT
Sinking 4mA
45
-3
-10
-200
-200
55
1
+3
+10
+200
+200
= 5.5V 1
150
% nA
µV
V/V nA mV nA
µV
µV
µA mV
Note 3: Includes power FET leakage.
Note 4: CTLI gain is defined as:
A
CTLI
=
(
(
V
CTLI
−
V
REF
V
OSI
−
V
CS
)
)
Note 5: Specifications to -40°C are guaranteed by design, not production tested.
6 _______________________________________________________________________________________
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics
(V
DD
= 5V, V
CTLI
= 1V, V
FREQ
= GND, RTEC = 1
Ω, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
50
40
30
20
10
0
0
90
80
70
60
EFFICIENCY vs. TEC CURRENT
V
DD
= 5V
R
TEC
= 1.1
Ω
0.5
1.0
1.5
TEC CURRENT (A)
2.0
2.5
80
70
60
50
40
30
20
10
0
0
EFFICIENCY vs. TEC CURRENT
V
DD
= 3.3V
R
TEC
= 0.855
Ω
0.5
1.0
1.5
TEC CURRENT (A)
2.0
2.5
V
OS2
100mV/div
AC-COUPLED
V
OS1
100mV/div
AC-COUPLED
V
OS1
- V
OS1
50mV/div
OUTPUT-VOLTAGE
RIPPLE WAVEFORMS
400ns/div
INPUT SUPPLY RIPPLE
V
DD
20mV/div
AC-COUPLED
TEC CURRENT vs. CTLI VOLTAGE
V
CTLI
200mV/div
-0V
-0A
V
CTLI
1V/div
I
TEC
2A/div
I
TEC
500mA/div
ZERO-CROSSING TEC CURRENT
1.5V
0A
200ns/div
20ms/div 1ms/div
V
ITEC
vs. TEC CURRENT
1.0
0.5
0
-3
3.0
2.5
2.0
1.5
-2 -1 0 1
TEC CURRENT (A)
2 3
1.010
1.005
1.000
TEC CURRENT vs. TEMPERATURE
0.995
0.990
-40 -20 0 20
I
TEC
R
= 1A
SENSE
= 0.68
Ω
40
TEMPERATURE (
°C)
60 80
SWITCHING FREQUENCY vs. TEMPERATURE
508
506
504
502
500
498
496
494
492
-40
V
CTLI
R
TEC
= 1.5V
= 1
Ω
-20 0 20 40
TEMPERATURE (
°C)
60 80
_______________________________________________________________________________________
7
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics (continued)
(V
DD
= 5V, V
CTLI
= 1V, V
FREQ
= GND, RTEC = 1
Ω, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
0
-5
-10
-15
-20
10
5
-25
-30
-35
3.0
SWITCHING FREQUENCY CHANGE vs. INPUT SUPPLY
3.5
4.0
V
DD
(V)
4.5
5.0
5.5
REFERENCE LOAD REGULATION
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
SINK SOURCE
-1.0
-0.4
-0.2
0 0.2
0.4
0.6
REFERENCE LOAD CURRENT (mA)
0.8
1.0
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
3.0
REFERENCE VOLTAGE CHANGE vs. INPUT SUPPLY
3.5
4.0
V
DD
(V)
4.5
5.0
5.5
ATO VOLTAGE vs. THERMISTOR TEMPERATURE
2.0
1.5
1.0
0.5
0
-10
4.5
4.0
3.5
3.0
2.5
NTC, 10k
Ω THERMISTOR
CIRCUIT IN FIGURES 1 AND 2
0 10 20 30 40
THERMISTOR TEMPERATURE (
°C)
50 60
REFERENCE VOLTAGE CHANGE vs. TEMPERATURE
3
2
1
0
-1
-2
-3
-4
-40 -20 0 20 40
TEMPERATURE (
°C)
60 80
V
SHDN
5V/div
STARTUP AND SHUTDOWN WAVEFORMS
I
TEC
500mA/div
I
DD
200mA/div
100
µs/div
CTLI STEP RESPONSE INPUT SUPPLY STEP RESPONSE
THERMAL STABILITY,
COOLING MODE
V
CTLI
1V/div
1.5V
V
DD
2V/div
0V
TEMPERATURE
0.001
°C/div
I
TEC
1A/div
0A
I
TEC
20mA/div
1A
I
T
TEC
A
= +25
°C
= +45
°C
1ms/div 10ms/div
8 _______________________________________________________________________________________
4s/div
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Characteristics (continued)
(V
DD
= 5V, V
CTLI
= 1V, V
FREQ
= GND, RTEC = 1
Ω, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
THERMAL STABILITY,
ROOM TEMPERATURE
THERMAL STABILITY,
HEATING MODE
TEMPERATURE ERROR vs. AMBIENT TEMPERATURE
0.03
0.02
0.01
TEMPERATURE
0.001
°C/div
TEMPERATURE
0.001
°C/div
0
-0.01
I
T
TEC
A
= +25
°C
= +25
°C
T
T
TEC
A
= +25
°C
= +5
°C
-0.02
4s/div 4s/div
-0.03
-20 -10 0 10 20 30 40
AMBIENT TEMPERATURE (
°C)
50
Pin Description
PIN
1
NAME
OS2
FUNCTION
Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power output.
2, 8, 29,
35
N.C.
Not Internally Connected
3, 5
4, 6, 9
7, 10
11
12
13
PGND2
Power Ground 2. Internal synchronous rectifier ground connections. Connect all PGND pins together at power ground plane.
Inductor 2 Connection. Connect all LX2 pins together. Connect LX2 to LX1 when using the MAX1979.
LX2
PV
DD
2
Power 2 Inputs. Must be same voltage as V
DD
. Connect all PV
DD
2 inputs together at the V
DD
power plane.
Bypass to PGND2 with a 10µF ceramic capacitor.
SHDN
Shutdown Control Input. Active-low shutdown control.
OT
Over-Temperature Alarm. Open-drain output pulls low if temperature feedback rises 20mV
(typically +1.5°C) above the set-point voltage.
UT
Under-Temperature Alarm. Open-drain output pulls low if temperature feedback falls 20mV
(typically +1.5°C) below the set-point voltage.
INTOUT Integrator Amp Output. Normally connected to CTLI.
INTIntegrator Amp Inverting Input. Normally connected to DIFOUT through thermal-compensation network.
14
15
16, 25,
26, 42, 43
17
18
19
20
21
22
GND Analog Ground. Connect all GND pins to analog ground plane.
DIFOUT Chopper-Stabilized Instrumentation Amp Output. Differential gain is 50 ✕ (FB+ - FB-).
FBChopper-Stabilized Instrumentation Amp Inverting Input. Connect to thermistor bridge.
FB+ Chopper-Stabilized Instrumentation Amp Noninverting Input. Connect to thermistor bridge.
BFBChopper-Stabilized Buffered FB- Output. Used to monitor thermistor bridge voltage.
BFB+ Chopper-Stabilized Buffered FB+ Output. Used to monitor thermistor bridge voltage.
AIN+ Undedicated Chopper-Stabilized Amplifier Noninverting Input
_______________________________________________________________________________________ 9
Integrated Temperature
Controllers for Peltier Modules
Pin Description (continued)
PIN
23
24
27, 30
28, 31, 33
32, 34
36
37
38
39
40
41
44
45
46
47
48
EP
NAME FUNCTION
AINUndedicated Chopper-Stabilized Amplifier Inverting Input
AOUT Undedicated Chopper-Stabilized Amplifier Output
PV
DD
LX1
1
Power 1 Inputs. Must be same voltage as V
DD
. Connect all PV
DD
1 inputs together at the V
DD
power plane.
Bypass to PGND1 with a 10µF ceramic capacitor.
Inductor 1 Connection. Connect all LX1 pins together. Connect LX1 to LX2 when using the MAX1979.
PGND1
Power Ground 1. Internal synchronous-rectifier ground connections. Connect all PGND pins together at power ground plane.
FREQ Switching-Frequency Select. Low = 500kHz, high = 1MHz.
ITEC
MAXIN
TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC currentsense resistor. V
ITEC
= 1.50V + (V
OS1
- V
CS
) ✕ 8.
COMP Current-Control Loop Compensation. For most designs, connect a 10nF capacitor from COMP to GND.
MAXIP Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV / R
SENSE
.
Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit
-150mV / R
SENSE
. Connect MAXIN to GND when using the MAX1979.
MAXV
Maximum Bipolar TEC Voltage. Connect an external resistive divider from REF to GND to set the maximum voltage across the TEC. The maximum TEC voltage is 4 ✕ V
MAXV
.
V
DD
Analog Supply Voltage Input. Bypass to GND with a 10µF ceramic capacitor.
CTLI
TEC Current-Control Input. Sets differential current into the TEC. Center point is 1.50V (no TEC current).
Connect to INTOUT when using the thermal control loop. I
TEC
= (V
OS1
- V
CS
) / R
SENSE
= (V
CTLI
- 1.50) / (10 ✕
R
SENSE
). When (V
CLTI
- V
REF
) > 0, V
OS2
> V
OS1
> V
CS
.
REF 1.5V Reference Voltage Output. Bypass REF to GND with a 1µF ceramic capacitor.
CS
Current-Sense Input. The current through the TEC is monitored between CS and OS1. The maximum TEC current is given by 150mV / R
SENSE
and is bipolar for the MAX1978. The MAX1979 TEC current is unipolar.
OS1
EP
Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power output.
Exposed Paddle. Solder evenly to the PCB ground plane to maximize thermal performance.
10 ______________________________________________________________________________________
REF
1.5V
REFERENCE
OFF
ON
SHDN
Integrated Temperature
Controllers for Peltier Modules
Functional Diagram
FREQ
V
DD
PV
DD
1
3V TO 5.5V
MAXV MAX V
TEC
V
MAXV
=
x 4
LX1
MAXIP
MAXIN
MAX I
TEC
= (V
MAXIP
/
V
REF
) x (0.15V/R
SENSE
)
MAX I
TEC
= (V
MAXIN
/
V
REF
) x (0.15V/R
SENSE
)
PGND1
CS
ITEC
CTLI
COMP
GND
OT
UT
MAX1978
CS
OS1
REF
REF + 1V
50R
PGND2
R
50R
R
REF
REF - 1V
REF
INTOUT INTAINAOUT AIN+ DIFOUT FB+ FB-
BFB-
BFB+
OS1
OS2
PV
DD
2
LX2
V
DD
R
SENSE
______________________________________________________________________________________ 11
Integrated Temperature
Controllers for Peltier Modules
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 configuration creates a differential voltage across the TEC, allowing 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 stability of 0.001°C. Figure 1 shows a typical TEC thermalcontrol 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 differential TEC output are greatly reduced. This feature suppresses ripple currents and electrical noise at the TEC to prevent interference with the laser diode while minimizing output capacitor filter size.
V
DD
REF
10
µF
10
µF
1
µF
10
µF
THERMISTOR
VOLTAGE
MONITOR
80.6k
Ω
REF
69.8k
Ω
1%
UNDERTEMP
ALARM
OVERTEMP
ALARM
DC CURRENT
MONITOR
1
µF
105k
Ω
1%
0.01
µF
20k
Ω
1%
V
DD
COMP
UT
SHDN
PV
DD
1 PV
DD
2
OT
ITEC
MAX1978
REF MAXV MAXIN MAXIP
LX1
CS
OS1
BFB-
AIN-
AOUT
OS2
LX2
AIN+
CTLI
FREQ
GND PGND2 PGND1 INTOUT INT-
FB-
DIFOUT FB+
4.7
µF
3
µH
3
µH
TEC
0.068
Ω
1
µF
REF
10k
Ω
100k
Ω
100k
Ω 10
µF
0.47
µF
20k
Ω
0.047
µF
1M
Ω
1
µF
THERMAL
FEEDBACK
Figure 1. MAX1978 Typical Application Circuit
12 ______________________________________________________________________________________
Switching Frequency
FREQ sets the switching frequency of the internal oscillator. The oscillator frequency is 500kHz when FREQ =
GND. The oscillator frequency is 1MHz when FREQ =
V
DD
. The 1MHz setting allows minimum inductor and filter-capacitor values. Efficiency is optimized with the
500kHz setting.
Voltage and Current-Limit Settings
The MAX1978 and MAX1979 provide settings to limit the maximum differential TEC voltage. Applying a voltage to MAXV limits the maximum voltage across the
TEC to ±(4 ✕ V
MAXV
).
The MAX1978 also limits the maximum positive and negative TEC current. The voltages applied to MAXIP and MAXIN independently set the maximum positive and negative output current limits. The MAX1979 controls TEC current in only one direction, so the maximum current is set only with MAXIP. MAXIN must be connected to GND when using the MAX1979.
Chopper-Stabilized Instrumentation
Amplifier
The MAX1978 and MAX1979 include a chopped input instrumentation amplifier with a fixed gain of 50. An external thermal sensor, typically a thermistor, is connected to one of the amp’s inputs. The other input is connected to a voltage that represents the temperature set point. This set point can be derived from a resistordivider network or DAC. The included instrumentation amplifier provides low offset drift needed to prevent temperature set-point drift with ambient temperature changes. Temperature stability of 0.001°C can be achieved over a 0°C to +50°C ambient temperarure range by using the amplifier as in Figure 1. DIFOUT is the instrumentation amplifier output and is proportional to 50 times the difference between the set-point temperature and the TEC temperature. This difference is commonly referred to as the “error signal”. For best temperature stability, derive the set-point voltage from the same reference that drives the thermistor (usually the MAX1978/MAX1979 REF output). This is called a
“ratiometric” or “bridge” connection. The bridge connection optimizes stability by eliminating REF drift as an error source. Errors at REF are nullified because they affect the thermistor and set point equally.
The instrumentation amplifier utilizes a chopped input scheme to minimize input offset voltage and drift. This generates output ripple at DIFOUT that is equal to the chop frequency. The DIFOUT peak-to-peak ripple amplitude is typically 100mV but has no effect on temperature stability. DIFOUT ripple is filtered by the integrator in the following stage. The chopper frequency is
Integrated Temperature
Controllers for Peltier Modules
derived from, and is synchronized to, the switching frequency of the power stage.
Integrator Amplifier
An on-chip integrator amplifier is provided on the
MAX1978/MAX1979. The noninverting terminal of the amplifier is connected internally to REF. Connect an appropriate network of resistors and capacitors between
DIFOUT and INT-, and connect INTOUT to CTLI for typical operation. CTLI directly controls the TEC current magnitude and polarity. The thermal-control-loop dynamics are set by the integrator input and feedback components. See the Applications Information section for details on thermal-loop compensation.
Current Monitor Output
ITEC provides a voltage output proportional to the TEC current, ITEC (see the Functional Diagram):
V
ITEC
= 1.5V + 8 ✕ (V
OS1
- V
CS
)
Over- and Under-Temperature Alarms
The MAX1978/MAX1979 provide open-drain status outputs that alert a microcontroller when the TEC temperature is over or under the set-point temperature. OT and
UT pull low when V
(FB1+ - FB-) is more than 20mV. For a typical thermistor connection, this translates to approximately 1.5°C error.
Reference Output
The MAX1978/MAX1979 include an on-chip 1.5V voltage reference accurate to 1% over temperature.
Bypass REF with 1µF to GND. REF can be used to bias an external thermistor for temperature sensing as shown in Figures 1 and 2. Note that the 1% accuracy of
REF does not limit the temperature stability achievable with the MAX1978/MAX1979. This is because the thermistor and set-point bridge legs are intended to be driven ratiometrically by the same reference source (REF).
Variations in the bridge-drive voltage then cancel out and do not generate errors. Consequently, 0.001°C stable temperature control is achievable with the
MAX1978/MAX1979 reference.
An external source can be used to bias the thermistor bridge. For best accuracy, the common-mode voltage applied to FB+ and FB- should be kept between 0.5V
and 1V, however the input range can be extended from
0.2V to V
DD
/ 2 if some shift in instrumentation amp offset
(approximately -50µV/V) can be tolerated. This shift remains constant with temperature and does not contribute to set-point drift.
______________________________________________________________________________________ 13
Integrated Temperature
Controllers for Peltier Modules
V
DD
REF
10
µF
10
µF
1
µF
10
µF
THERMISTOR
VOLTAGE
MONITOR
80.6k
Ω
REF
69.8k
Ω
1%
UNDERTEMP
ALARM
OVERTEMP
ALARM
DC CURRENT
MONITOR
1
µF
0.01
µF
20k
Ω
1%
V
DD
COMP
UT
SHDN
PV
DD
1 PV
DD
2
OT
ITEC
MAX1979
REF MAXV MAXIN MAXIP
LX1
LX2
CS
OS1
BFB-
AIN-
AOUT
OS2
4.7
µF
3
µH
105k
Ω
1%
AIN+
CTLI
FREQ
GND PGND2 PGND1 INTOUT INTDIFOUT
FB-
FB+
TEC
0.03
Ω
REF
10k
Ω
100k
Ω 10
µF
0.47
µF
20k
Ω
100k
Ω
0.047
µF
1M
Ω
1
µF
THERMAL
FEEDBACK
Figure 2. MAX1979 Typical Application Circuit
Buffered Outputs, BFB+ and BFB-
BFB+ and BFB- output a buffered version of the voltage that appears on FB+ and FB-, respectively. The buffers are typically used in conjunction with the undedicated chopper amplifier to create a monitor for the thermistor voltage/TEC temperature (Figures 1 and 2). These buffers are unity-gain chopper amplifiers and exhibit output ripple. Each output 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 uncommitted but is intended to provide a temperature-proportional analog output. The thermistor voltage typically is connected to the undedicated chopper amplifier through the included buffers BFB+ and BFB-. Figure 3 shows how to configure the undedicated amplifier as a thermistor voltage monitor. The output voltage at AOUT is not precisely linear, because the thermistor is not linear. AOUT is also chopper stabilized and exhibits output ripple and can be either integrated or filtered to remove the ripple content if necessary.
14 ______________________________________________________________________________________
x50
MAX1978
MAX1979
AIN+
AOUT
AIN-
BFB-
FB-
FB+
REF
69.8k
Ω
1%
105k
Ω
1%
80.6k
Ω
1%
20k
Ω
1%
V
SETPOINT
Integrated Temperature
Controllers for Peltier Modules
1
µF
REF
10k
Ω
Figure 3. Thermistor Voltage Monitor
Design Procedure
Inductor Selection
Small surface-mount inductors are ideal for use with the
MAX1978/MAX1979. Select the output inductors so that the LC resonant frequency of the inductance and the output capacitance is less than 1/5 the selected switching frequency. For example, 3.0µH and 1µF have a resonance at 92kHz, which is adequate for 500kHz operation.
22µF to 100µF ceramic capacitor between the V
DD power plane and power ground. Insufficient supply bypassing can result in supply bounce and degraded accuracy.
Compensation Capacitor
Include a compensation capacitor to ensure currentpower 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 output filter:
C
COMP
≥
g m
f
BW
×
2
×
24
R
×
R
SENSE
SENSE
+
R
TEC
)
where: f
BW
= unity-gain bandwidth frequency g m
= loop transconductance, typically 100µA/V
C
COMP
= value of the compensation capacitor
R
TEC
= TEC series resistance
R
SENSE
= sense resistor
Setting Voltage and Current Limits
Consider TEC parameters to guarantee a robust design. These parameters include maximum positive current, maximum negative current, and the maximum voltage allowed across the TEC. These limits should be used to set MAXIP, MAXIN, and MAXV voltages.
Setting Max Positive and Negative TEC Current
MAXIP and MAXIN set the maximum positive and negative TEC currents, respectively. The default current limit is ±150mV / R
SENSE when MAXIP and MAXIN are connected to REF. To set maximum limits other than the defaults, connect a resistor-divider from REF to GND to set V
MAXI_
. Use resistors in the 10k
Ω to 100kΩ range.
V
MAXI_ is related to ITEC by the following equations:
¡ f
LC
=
2
π
1
LC where: f
LC
= resonant frequency of output filter.
Capacitor Selection
Filter Capacitors
Decouple each power-supply input (V
DD
, PV
DD
1, and
PV
DD
2) with a 10µF ceramic capacitor close to the supply pins. If long supply lines separate the source supply from the MAX1978/MAX1979, or if the source supply has high output impedance, place an additional
V
MAXIP
= 10 (I
TECP(MAX)
✕ R
SENSE
)
V
MAXIN
= 10 (I
TECN(MAX)
✕ R
SENSE
) where I
TECP(MAX) is the maximum positive TEC current and I
TECN(MAX) is the maximum negative TEC current.
Positive TEC current occurs when CS is less than OS1:
I
TEC
✕ R
SENSE
= CS - OS1 when I
TEC
< 0.
I
TEC
✕
R
SENSE
= OS1 - CS when I
TEC
> 0.
______________________________________________________________________________________ 15
Integrated Temperature
Controllers for Peltier Modules
The MAX1979 controls the TEC current in only one direction (unipolar). Set the maximum unipolar TEC current by applying a voltage to MAXIP. Connect MAXIN to
GND when using the MAX1979. The equation for setting MAXIP is the same for the MAX1978 and
MAX1979. Do not exceed the positive or negative current-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 differential 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.
FB-
REF
MAX1978
MAX1979
FB+
C
REF
V
SETPOINT
V
THERMISTOR
|V
OS1
- V
OS2
| = 4
✕
V
MAXV
Use resistors from 10k
Ω to 100kΩ to form a voltagedivider 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 amplifier generates an error signal and the integrator amplifier is used to create a PID controller. Figure 4 shows an example of a simple PID implementation. The error signal 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.
FB-
REF
C
REF
MAX1978
MAX1979
FB+
V
SETPOINT
DAC
DIGITAL
INPUT
V
THERMISTOR
Figure 5. The Set Point can be Derived from a Potentiometer or a DAC
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-control circuit C
INTOUT
. For the purposes of the following equations, it is assumed that positive TEC current is heating.
C3
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
)
C1
R1
INT-
R3
C2 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 heating. Current flow is from OS2 to OS1. The voltages are:
DIFOUT
R2
INTOUT
V
OS2
> V
OS1
> V
CS
REF
Figure 4. Proportional Integral Derivative Controller
when V
CTLI
< 1.50V, current flows from OS1 to OS2:
V
OS2
< V
OS1
< V
CS
16 ______________________________________________________________________________________
Integrated Temperature
Controllers for Peltier Modules
Shutdown Control
Drive SHDN low to place the MAX1978/MAX1979 in a power-saving shutdown mode. When the MAX1978/
MAX1979 are in shutdown, the TEC is off (V
OS1 and
V
OS2 decay to GND) and input supply current lowers to
2mA (typ).
ITEC Output
ITEC is a status output that provides a voltage proportional to the actual TEC current. ITEC = REF when TEC current is zero. The transfer function for the ITEC output:
V
ITEC
= 1.50 + 8 ✕ (V
OS1
- V
CS
)
Use ITEC to monitor the cooling or heating current through the TEC. The maximum capacitance that ITEC can drive is 100pF.
Applications Information
The MAX1978/MAX1979 drive a thermoelectric cooler inside a thermal-control loop. TEC drive polarity and power are regulated to maintain a stable control temperature based on temperature information read from a thermistor, or from other temperature-measuring devices. Carefully selected external components can achieve 0.001°C temperature stability. The MAX1978/
MAX1979 provide precision amplifiers and an integrator amplifier to implement the thermal-control loop
(Figures 1 and 2).
Connecting and Compensating the
Thermal-Control Loop
Typically, the thermal loop consists of an error amplifier and proportional integral derivative controller (PID)
(Figure 4). The thermal response of the TEC module must be understood before compensating the thermal loop. In particular, TECs generally have stronger heating capacity than cooling capacity because of the effects of waste heat. Consider this point when analyzing the TEC response.
Analysis of the TEC using a signal analyzer can ease compensation calculations. Most TECs can be crudely modeled as a two-pole system. The second pole potentially creates an oscillatory condition because of the associated 180° phase shift. A dominant pole compensation scheme is not practical because the crossover frequency (the point of the Bode plot where the gain is zero dB) must be below the TEC’s first pole, often as low as 0.02Hz. This requires an excessively large integrator capacitor and results in slow loop-transient response. A better approach is to use a PID controller, where two additional zeros are used to cancel the TEC and integrator poles. Adequate phase margin can be achieved near the frequency of the TEC’s second pole when using a PID controller. The following is an example of the compensation procedure using a PID controller.
Figure 6 details a two-pole transfer function of a typical
TEC module. This Bode plot can be generated with a signal analyzer driving the CTLI input of the
MAX1978/MAX1979, while plotting the thermistor voltage from the module. For the example module, the two poles are at 0.02Hz and 1Hz.
The first step in compensating the control loop involves selecting components R3 and C2 for highest DC gain.
Film capacitors provide the lowest leakage but can be large. Ceramic capacitors are a good compromise between low leakage and small size. Tantalum and electrolytic capacitors have the highest leakage and generally are not suitable for this application. The integrating capacitor, C2, and R3 (Figure 4) set the first zero (fz1). The specific application dictates where the first zero should be set. Choosing a very low frequency results in a very large value capacitor. Set the first zero frequency to no more than 8 times the frequency of the lowest TEC pole. Setting the frequency more than 8 times the lowest pole results in the phase falling below
-135° and may cause instability in the system. For this example, C2 = 10µF. Resistor R3 then sets the zero at
0.16Hz using the following equation: fz 1
=
1
2
π ×
C 2
×
R 3
This yields a value of R3 = 99.47k
Ω. For our example, use 100k
Ω.
Next, adjust the gain for a crossover frequency for maximum phase margin near the TEC’s second pole. From
Figure 6, the TEC bode plot, approximately 30dB of gain is needed to move the 0dB crossover point up to
1.5Hz. The error amplifier provides a fixed gain of 50, or approximately 34dB. Therefore, the integrator needs to provide -4dB of gain at 1.5Hz. C1 and R3 set the gain at the crossover frequency.
C 1
=
A
1
C 2
+
2
π ×
R 3
× f
C
______________________________________________________________________________________ 17
Integrated Temperature
Controllers for Peltier Modules
where:
A = The gain needed to move the 0dB crossover point up to the desired frequency. In this case, A = -4dB =
0.6.
f
C
= The desired crossover frequency, 1.5Hz in this example.
C1 is found to be 0.58µF; use 0.47µF.
Next, the second TEC pole must be cancelled by adding a zero. Canceling the second TEC pole provides maximum phase margin by adding positive phase to the circuit. Setting a second zero (fz2) to at least 1/5 the crossover frequency (1.5Hz/5 = 0.3Hz), and a pole (fp1) to 5 times the crossover frequency or higher (5
× 1.5Hz = 7.5Hz) ensures good phase margin, while allowing for variation in the location of the TEC’s second pole. Set the zero fz2 to 0.3Hz and calculate R2: fz 2
=
1
2
π ×
C 1
×
R 2 where fz2 is the second zero.
R2 is calculated to be 1.1M
Ω; use 1MΩ.
Now pole fp1 is added at least 5 times the crossover frequency to terminate zero fz2.
Choose fp1 = 15Hz, find R1 using the following equation: fp 1
=
1
2
π ×
C 1
×
R 1
Resistor R1 is found to be 22k
Ω, use 20kΩ
The final step is to terminate the first zero by setting the rolloff frequency with a second pole, fp2. A good choice is 2 times fp1.
Choose fp2 = 30Hz, find C3 using the following equation: fp 2
=
1
2
π ×
C 3
×
R 3 where C3 is found to be 0.05µF, use 0.047µF.
Figure 7 displays the compensated gain and phase plots for the above example.
The example given is a good place to start when compensating the thermal loop. Different TEC modules require individual testing to find their optimal compensation scheme. Other compensation schemes can be used. The above procedure should provide good results for the majority of optical modules.
TEC GAIN AND PHASE
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
0.001
0.01
0.1
1
FREQUENCY (Hz)
10
Figure 6. Bode Plot of a Generic TEC Module
90
45
-135
100
-180
0
-45
-90
COMPENSATED
TEC GAIN AND PHASE
50
40
30
20
10
0
-10
80
70
60
-20
-30
-40
-50
-60
-70
-80
0.001
90
45
0
-45
-90
-135
0.01
0.1
1
FREQUENCY (Hz)
10 100
-180
Figure 7. Compensated Thermal-Control Loop Using the TEC
Module in Figure 6
18 ______________________________________________________________________________________
INPUT
3V TO 5.5V
ON
OFF
OVERTEMP ALARM
UNDERTEMP ALARM
TEMP MONITOR
TEC CURRENT MONITOR
VOLTAGE LIMIT
HEATING CURRENT LIMIT
COOLING CURRENT LIMIT
AOUT
ITEC
AIN+
MAXV
MAXIP
MAXIN
REF
Integrated Temperature
Controllers for Peltier Modules
Typical Operating Circuit
V
DD
PV
DD-
SHDN
OT
UT
BFB-
LX1
PGND1
CS
MAX1978
OS1
OS2
LX2
PGND2
TEC
I
TEC
=
±3A
AIN-
REF
FB+
FB-
NTC
OPTIONAL DAC
DAC
TRANSISTOR COUNT: 6023
PROCESS: BiCMOS
Chip Information Revision History
Pages changed at Rev 1: 1, 9, 10, 19, 20, 21
______________________________________________________________________________________ 19
Integrated Temperature Controller for
Peltier Modules
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
D
D/2
E/2
E
DETAIL A
(NE-1) X e e k e
(ND-1) X e
D2/2
CL
D2 b
L1
L
DETAIL B
L k
CL
CL
E2
E2/2
L e
A1 A2
A
CL e
L
PACKAGE OUTLINE
32, 44, 48, 56L THIN QFN, 7x7x0.8mm
21-0144 E
1
2
20 ______________________________________________________________________________________
Integrated Temperature Controller for
Peltier Modules
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE
32, 44, 48, 56L THIN QFN, 7x7x0.8mm
21-0144 E
2
2
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
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