General Description
The MAX1968/MAX1969 are highly integrated and cost-
effective, high-efficiency, switch-mode drivers for Peltier
thermoelectric cooler (TEC) modules. Both devices uti-
lize direct current control to eliminate current surges in
the TEC. On-chip FETs minimize external components
while providing high efficiency. A 500kHz/1MHz switch-
ing frequency and a unique ripple cancellation scheme
reduce component size and noise.
The MAX1968 operates from a single supply and pro-
vides bipolar ±3A output by biasing the TEC between
the outputs of two synchronous buck regulators. Bipolar
operation allows for temperature control without “dead
zones” or other nonlinearities at low load currents. This
arrangement ensures that the control system does not
hunt when the set point is very close to the natural
operating point, requiring a small amount of heating or
cooling. An analog control signal precisely sets the TEC
current. The MAX1969 provides unipolar output up to
6A. Reliability is optimized with settable limits for both
TEC voltage and current, with independently set limits
for heating and cooling current. An analog output also
monitors TEC current.
The MAX1968/MAX1969 are available in a low-profile
28-pin TSSOP-EP package and is specified over the
-40°C to +85°C temperature range. The thermally-
enhanced TSSOP-EP package with exposed metal pad
minimizes operating junction temperature. An evalua-
tion 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
Biotech Lab Equipment
Features
oDirect Current Control Prevents TEC Current
Surges
oOn-Chip Power MOSFETs
oHigh-Efficiency Switch-Mode Design
oRipple Cancellation for Low Noise
oNo Dead-Zone or Hunting at Low-Output Current
oAdjustable TEC Voltage Limit
oSeparately Adjustable Heating and Cooling
Current Limits
oITEC Output Monitors TEC Current
o1% Accurate Voltage Reference
o500kHz/1MHz Switching Frequency
o±3A Output Current (MAX1968)
o6A Output Current (MAX1969)
oThermally Enhanced TSSOP-EP Package
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-2447; Rev 2; 2/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX1968EUI -40°C to +85°C 28 TSSOP-EP*
MAX1969EUI -40°C to +85°C 28 TSSOP-EP*
Typical Operating Circuit
PGND1
PGND2
CTLI
COMP
LX2 LX1
GND
VDD
MAX1968
PVDD1PV
DD2
OS1 CSOS2
TEC
3V TO
5.5V
TEC
CURRENT-
CONTROL
SIGNAL
Pin Configuration and Functional Diagram appear at end
of data sheet.
*
EP = Exposed pad.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1µF,
CCOMP = 0.1µF, LLX_ = 3.3µH, CCS = COS2 = 1µF, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = 0°C to +85°C, unless
otherwise noted. Typical values are at TA = +25°C.)
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.
VDD to GND..............................................................-0.3V to +6V
SHDN, MAXV, MAXIP, MAXIN, CTLI,
FREQ to GND .......................................................-0.3V to +6V
COMP, OS1, OS2, CS, REF,
ITEC to GND...........................................-0.3V to (VDD + 0.3V)
PVDD1, PVDD2 to GND ...............................-0.3V to (VDD + 0.3V)
PVDD1, PVDD2 to VDD ..................................................-0.3V to +0.3V
PGND1, PGND2 to GND .......................................-0.3V to +0.3V
COMP, REF, ITEC Short to GND ...................................Indefinite
Peak LX Current (MAX1968) (Note 1).................................±4.5A
Peak LX Current (MAX1969) (Note 1)....................................+9A
Continuous Power Dissipation (TA= +70°C)
28-Pin TSSOP-EP (derate 23.8mW/°C above +70°C).....1.9W
Operating Temperature Range ...........................-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering 10s) ..................................+300°C
PARAMETER
SYMBOL
CONDITIONS MIN TYP MAX UNITS
Input Supply Range VDD 3.0 5.5 V
VDD = 5V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968) -4.3 +4.3
VDD = 5V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969) 4.3
VDD = 3V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968) -2.3 +2.3
Output Voltage Range
VOUT
VDD = 3V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969) 2.3
V
MAX1968 ±3
Maximum TEC
Current
ITEC
(
MAX
)
MAX1969 6 A
Reference Voltage VREF VDD = 3V to 5.5V, IREF = 150µA 1.485 1.500 1.515 V
Reference Load
Regulation ΔVREF VDD = 3V to 5.5V, IREF = +10µA to -1mA 1.2 5 mV
VMAXI_ = VREF 140 150 160
VOS1 < VCS
VMAXI_ = VREF/3
40 50 60
VMAXI_ = VREF 140 150 160
Current-Sense
Threshold Accuracy
VOS1 > VCS
VMAXI_ = VREF/3
40 50 60
mV
Switch-Fault Reset
Voltage 50 150 250 mV
VDD = 5V, I = 0.5A 0.04 0.07
NFET On-Resistance
RDS
(
ON-N
)
VDD = 3V, I = 0.5A 0.06 0.08 Ω
VDD = 5V, I = 0.5A 0.06 0.10
PFET On-Resistance
RDS
(
ON-P
)
VDD = 3V, I = 0.5A 0.09 0.12 Ω
VLX = VDD = 5V, TA = +25°C 0.02 10
NFET Leakage
ILEAK
(
N
)
VLX = VDD = 5V, TA = +85°C 1 µA
Note 1: LX has internal clamp diodes to PGND and PVDD_. Applications that forward bias these diodes should take care not to
exceed the IC’s package power dissipation limits.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1µF,
CCOMP = 0.01µF, LLX_ = 3.3µH, CCS = COS2 = 1µF, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = 0°C to +85°C, unless
otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS MIN TYP MAX UNITS
VLX = 0, TA = +25°C 0.02 10
VLX = 0, TA = +85°C 1
PFET Leakage
ILEAK
(
P
)
µA
VDD = 5V 32 100
No Load Supply
Current
IDD
(
NO LOAD
)
VDD = 3.3V 20 30 mA
Shutdown Supply
Current IDD-SD VDD = 5V (Note 2) 2 3 mA
Thermal Shutdown
TSHUTDOWN
Hysteresis = 15°C +165 °C
VDD rising 2.4 2.6 2.8
UVLO Threshold VUVLO VDD falling 2.25 2.5 2.75 V
Switching Frequency
Internal Oscillator fSW-INT FREQ = GND 400 550 650 kHz
OS1, OS2, CS Input
Current
IOS1,
IOS2, ICS
0 or VDD -100 +100 µA
SHDN, FREQ Input
Current
ISHDN,
IFREQ 0 or VDD -5 +5 µA
SHDN, FREQ Input
Low Voltage VIL VDD = 3V to 5.5V VDD x
0.25 V
SHDN, FREQ Input
High Voltage VIH VDD = 3V to 5.5V VDD x
0.75 V
VMAXV = VREF x 0.67, VOS1 to VOS2 =
±4V, VDD = 5V -2 +2 %
MAXV Threshold
Accuracy VMAXV = VREF x 0.33, VOS1 to VOS2 =
±2V, VDD = 3V -2 +2 %
MAXV, MAXIP, MAXIN
Input Bias Current
IMAXV-BIAS,
IMAXI_-BIAS
VMAXV = VMAXI_ = 0.1V or 1.5V -0.1 +0.1 µA
CTLI Gain Accuracy ACTLI VCTLI = 0.5V to 2.5V (Note 3) 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 gm50 100 175 µA/V
ITEC Accuracy VOS1 to VCS = +100mV or -100mV -10 +10 %
ITEC Load Regulation
ΔVITEC VOS1 to VCS = +100mV or -100mV,
IITEC = ±10µA -0.1 +0.1 %
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1µF,
CCOMP = 0.1µF, LLX_ = 3.3µH, CCS = COS2 = 1µF, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = -40°C to +85°C, unless
otherwise noted.) (Note 4)
PARAMETER
SYMBOL
CONDITIONS MIN TYP MAX UNITS
Input Supply Range VDD 3.0 5.5 V
VDD = 5V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968) -4.3 +4.3
VDD = 5V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969) 4.3
VDD = 3V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968) -2.3 +2.3
Output Voltage Range
VOUT
VDD = 3V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969) 2.3
V
MAX1968 ±3
Maximum TEC
Current
ITEC
(
MAX
)
MAX1969 6 A
Reference Voltage VREF VDD = 3V to 5.5V, IREF = 150µA 1.475 1.515 V
Reference Load
Regulation ΔVREF VDD = 3V to 5.5V, IREF = +10µA to -1mA 5 mV
VMAXI_ = VREF 135 165
VOS1 < VCS
VMAXI_ = VREF / 3
35 65
VMAXI_ = VREF 135 165
Current-Sense
Threshold Accuracy
VOS1 > VCS
VMAXI_ = VREF / 3
35 65
mV
Switch-Fault Reset
Voltage 50 250 mV
VDD = 5V, I = 0.5A 0.07
NFET On-Resistance
RDS
(
ON-N
)
VDD = 3V, I = 0.5A 0.08 Ω
VDD = 5V, I = 0.5A 0.07
PFET On-Resistance
RDS
(
ON-P
)
VDD = 3V, I = 0.5A 0.12 Ω
VLX = VDD = 5V, TA = +25°C10
NFET Leakage
ILEAK
(
N
)
VLX = VDD = 5V, TA = -40°C10
µA
VLX = 0, TA = +25°C10
PFET Leakage
ILEAK
(
P
)
VLX = 0, TA = -40°C10
µA
VDD = 5V 100
No Load Supply
Current
IDD(NO
LOAD) VDD = 3.3V 30 mA
Shutdown Supply
Current IDD-SD SHDN = GND, VDD = 5V (Note 2) 3 mA
VDD rising 2.4 2.8
UVLO Threshold VUVLO VDD falling 2.25 2.75 V
Switching-Frequency
Internal Oscillator
fSW-INT
FREQ = GND 400 650 kHz
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, PGND1 = PGND2 = FREQ = GND, CTLI = MAXV = MAXIP = MAXIN = REF, CREF = 1µF,
CCOMP = 0.01µF, LLX_ = 3.3µH, CCS = COS2 = 1µF, ITEC < 3ARMS (MAX1968), ITEC < 6ARMS (MAX1969), TA = -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
SYMBOL
CONDITIONS MIN TYP MAX UNITS
OS1, OS2, CS Input
Current
IOS1,
IOS2, ICS
0 or VDD -100 +100 µA
SHDN, FREQ Input
Current
ISHDN,
IFREQ 0 or VDD -5 +5 µA
SHDN, FREQ Input
Low Voltage VIL VDD = 3V to 5.5V VDD x
0.25
SHDN, FREQ Input
High Voltage VIH VDD = 3V to 5.5V VDD x
0.75
V
VMAXV = VREF x 0.67, VOS1 to VOS2 =
±4V, VDD = 5V
MAXV Threshold
Accuracy VMAXV = VREF x 0.33, VOS1 to VOS2 =
±2V, VDD = 3V
-2 +2 %
MAXV, MAXIP, MAXIN
Input Bias Current
IMAXV-BIAS,
IMAXI_-BIAS
VMAXV = VMAXI_ = 0.1V or 1.5V -0.1 +0.1 µA
CTLI Gain Accuracy ACTLI VCTLI = 0.5V to 2.5V (Note 3) 9.5 10.5 V/V
RCTLI 1MΩ terminated at REF 0.5 2.0 MΩ
Error-Amp
Transconductance gm50 175 µA/V
ITEC Accuracy VOS1 to VCS = +100mV or -100mV -10 +10 %
Note 2: Includes power FET leakage.
Note 3: CTLI Gain is defined as:
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
AVV
VV
CTLI CTLI REF
OS CS
=−
−
()
1
ITEC vs. TEMPERATURE
MAX1968 toc09
TEMPERATURE (°C)
TEC CURRENT (A)
806020 400-20
0.996
0.998
1.000
1.002
1.004
1.006
1.008
1.010
1.012
1.014
0.994
-40
FREQ = 500kHz
VCTLI = 1.9V
RTEC = 1Ω
VITEC vs. TEC CURRENT
MAX1968 toc08
TEC CURRENT (A)
VITEC (V)
1
-1
0.5
1.0
1.5
2.0
2.5
3.0
0
-3 3
ZERO-CROSSING TEC CURRENT
vs. CTLI VOLTAGE
MAX1968 toc07
1ms/div
ITEC
500mA/div
1.5V
0A
VCTLI
100mV/div
TEC CURRENT vs. CTLI VOLTAGE
MAX1968 toc06
20ms/div
ITEC
1A/div
0V
0A
VCTLI
1V/div
TEC CURRENT RIPPLE
MAX1968 toc05
400ns/div
ITEC
2mA/div
DC CURRENT = 1A
VDD RIPPLE
MAX1968 toc04
200ns/div
VDD
100mV/div
AC-COUPLED
OUTPUT VOLTAGE RIPPLE
MAX1968 toc03
400ns/div
VOS2
100mV/div
AC-COUPLED
VOS1
100mV/div
AC-COUPLED
EFFICIENCY vs. TEC CURRENT
VDD = 3.3V
MAX1968 toc02
TEC CURRENT (A)
EFFICIENCY (%)
21
10
20
30
40
50
60
70
80
90
0
03
FREQ = 500kHz
RLOAD = 0.85Ω
EFFICIENCY vs. TEC CURRENT
VDD = 5V
MAX1968 toc01
TEC CURRENT (A)
EFFICIENCY (%)
21
10
20
30
40
50
60
70
80
90
0
03
FREQ = 500kHz
RLOAD = 1Ω
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
6 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
VDD STEP RESPONSE
MAX1968 toc18
10ms/div
1A
0V
ITEC
20mA/div
VDD
2V/div
CTLI STEP RESPONSE
MAX1968 toc17
1ms/div
ITEC
2A/div
1.5V
0A
VCTLI
1V/div
STARTUP AND SHUTDOWN WAVEFORMS
MAX1968 toc16
2ms/div
0V
0A
0A
ITEC
500mA/div
VCTLI = 2V
IDD
200mA/div
VSHDN
5V/div
REFERENCE LOAD REGULATION
VDD = 5V
LOAD CURRENT (mA)
REFERENCE VOLTAGE CHANGE (mV)
0.80.60.2 0.40-0.2
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-0.4 1.0
SINK SOURCE
MAX1968 toc15
REFERENCE LOAD REGULATION
VDD = 3.3V
MAX1968 toc14
LOAD CURRENT (mA)
REFERENCE VOLTAGE CHANGE (mV)
0.80.60.2 0.40-0.2
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-1.4
-0.4 1.0
SINK SOURCE
REFERENCE VOLTAGE CHANGE
vs. TEMPERATURE
MAX1968 toc13
TEMPERATURE (°C)
REFERENCE VOLTAGE CHANGE (mV)
804020-20
-4
-2
-1
0
1
2
-5
-40
-3
060
REFERENCE VOLTAGE CHANGE
vs. VDD
MAX1968 toc12
VDD (V)
REFERENCE VOLTAGE CHANGE (mV)
5.04.54.03.5
-3.0
-2.5
-1.5
-1.0
0
0.5
1.0
-3.5
3.0 5.5
-2.0
-0.5
SWITCHING FREQUENCY CHANGE
vs. VDD
MAX1968 toc11
VDD (V)
SWITCHING FREQUENCY CHANGE (kHz)
5.04.54.03.5
5
10
15
20
25
30
35
0
3.0 5.5
FREQ = 500kHz
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX1968 toc10
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
806020 400-20
470
490
510
530
550
570
590
610
630
650
450
-40
FREQ = 500kHz
VCTLI = 1.5V
RTEC = 1Ω
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
THERMAL STABILITY, ROOM TEMPERATURE
MAX1968 toc21
4s/div
TEMPERATURE
0.001°C/div
TTEC = +25°C
TA = +25°C
THERMAL STABILITY, COOLING
MAX1968 toc20
4s/div
TEMPERATURE
0.001°C/div
TTEC = +25°C
TA = +45°C
THERMAL STABILITY, HEATING
MAX1968 toc19
4s/div
TEMPERATURE
0.001°C/div
TTEC = +25°C
TA = +5°C
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
_______________________________________________________________________________________ 9
Pin Description
PIN NAME FUNCTION
1VDD Analog Supply Voltage Input
2GND Analog Ground
3CTLI
TEC Current Control Input. Sets differential current into the TEC. Center point is 1.50V (no TEC current).
The current is given by:
ITEC = (VOS1
- VCS) / RSENSE = (VCTLI - 1.50) / (10 x RSENSE). When (VCTLI - VREF) > 0, VOS2
> VOS1
> VCS.
4REF 1.50V Reference Output. Bypass REF to GND with a 1µF ceramic capacitor.
5, 7 PGND2 Power Ground 2. Internal synchronous rectifier ground connections. Connect all PGND pins together at
power ground plane.
6, 8, 10 LX2 Inductor Connection. Connect all LX2 pins together. For MAX1969, connect LX1 and LX2 pins together.
9, 11 PVDD2Power 2 Inputs. Must be same voltage as VDD. Connect all PVDD2 inputs together at the VDD power plane.
12 FREQ Switching Frequency Select. High = 1MHz, Low = 500kHz.
13 ITEC TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC current-
sense resistor. VITEC = 1.50V + (VOS1 - VCS) x 8.
14 OS2 Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power
output. For MAX1969, connect OS2 to GND.
15 OS1 Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power
output.
16 CS Current-Sense Input. The current through the TEC is monitored between CS and OS1. The maximum TEC
current is given by 150mV / RSENSE and is bipolar.
17 SHDN Shutdown Control Input. Active-low shutdown control.
18, 20 PVDD1Power 1 Inputs. Must be same voltage as VDD. Connect all PVDD1 inputs together at the VDD power plane.
19, 21, 23 LX1 Inductor Connection. Connect all LX1 pins together. For MAX1969, connect all LX1 and LX2 pins together.
22, 24 PGND1 Power Ground 1. Internal synchronous rectifier ground connections. Connect all PGND pins together at
power ground plane.
25 COMP Current Control-Loop Compensation. For most designs connect a 0.01µF capacitor from COMP to GND.
26 MAXIN Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit
-150mV / RSENSE. For MAX1969, connect MAXIN to MAXIP.
27 MAXIP M axi m um P osi ti ve TE C C ur r ent. C onnect M AX IP to RE F to set d efaul t p osi ti ve cur r ent l i m i t + 150m V / RS E N S E
.
(See the Setting Max Positive and Negative TEC Current section).
28 MAXV Maximum Bipolar TEC Voltage. Connect an external resistive-divider from REF to GND to set the maximum
voltage. The maximum TEC voltage is 4 x VMAXV.
—EP
Exposed Pad. Internally connected to GND. Connect to a large ground plane to maximize thermal
performance.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
10 ______________________________________________________________________________________
Functional Diagram
MAX VTEC =
VMAXV ✕ 4
GND
COMP
CTLI
ITEC
MAXIP
FREQ
PWM CONTROL
AND
GATE CONTROL
MAXIN
VDD
PVDD1
PVDD2
RSENSE
PGND1
PGND2
MAXV
REF
MAX1968
SHDN
MAX ITEC =
(VMAXIP / VREF) ✕
(0.15V / RSENSE)
MAX ITEC =
-(VMAXIN / VREF) ✕
(0.15V / RSENSE)
REF
OS1
OS2
CS
LX1
LX2
ON
OFF
3V TO
5.5V
VDD
OS1
REF
CS
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
______________________________________________________________________________________ 11
Detailed Description
The MAX1968/MAX1969 TEC drivers consist of two
switching buck regulators that operate together to
directly control TEC current. This configuration creates
a differential voltage across the TEC, allowing bidirec-
tional 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. An external thermal-control loop is typ-
ically used to drive CTLI. Figures 1 and 2 show exam-
ples of thermal control-loop circuits.
Ripple Cancellation
Switching regulators like those used in the
MAX1968/MAX1969 inherently create ripple voltage on
the output. The regulators in the MAX1968 switch in
phase and provide complementary in-phase duty cycles
so ripple waveforms at the TEC are greatly reduced. This
feature suppresses ripple currents and electrical noise at
the TEC to prevent interference with the laser diode.
Switching Frequency
FREQ sets the switching frequency of the internal oscil-
lator. With FREQ = GND, the oscillator frequency is set
to 500kHz. The oscillator frequency is 1MHz when
FREQ = VDD.
Voltage and Current-Limit Settings
Both the MAX1968 and MAX1969 provide control of the
maximum differential TEC voltage. Applying a voltage
to MAXV limits the maximum voltage across the TEC.
The MAX1968 provides control of the maximum positive
and negative TEC current. The voltage at MAXIP and
MAXIN sets the maximum positive and negative current
through the TEC. These current limits can be indepen-
dently controlled. The MAX1969 only controls TEC cur-
rent in one direction. The maximum TEC current is
controlled by MAXIP. Connect MAXIN to GND when
using the MAX1969.
Current Monitor Output
ITEC provides a voltage output proportional to the TEC
current (ITEC). See the Functional Diagram for more
detail:
VITEC = 1.5V + 8 x (VOS1 - VCS)
Reference Output
The MAX1968/MAX1969 include an on-chip voltage ref-
erence. The 1.50V reference is accurate to 1% over
temperature. Bypass REF with 1µF to GND. REF may
be used to bias an external thermistor for temperature
sensing as shown in Figures 1 and 2.
Design Procedure
Inductor Selection
Small surface-mount inductors are ideal for use with the
MAX1968/MAX1969. 3.3µH inductors are suitable for
most applications. Select the output inductors so that
the LC resonant frequency of the inductance and the
output capacitance is less than 1/5 the selected switch-
ing frequency. For example, 3.3µH and 1µF have a res-
onance at 87.6kHz, which is adequate for 500kHz
operation
where:
f = resonant frequency of output filter.
Capacitor Selection
Filter Capacitors
Decouple each power-supply input (VDD, PVDD1,
PVDD2) with a 1µF ceramic capacitor close to the supply
pins. In some applications with long distances between
the source supply and the MAX1968/MAX1969, addition-
al bypassing may be needed to stabilize the input sup-
ply. In such cases, a low-ESR electrolytic capacitor of
100µF or more at VDD is usually sufficient.
Compensation Capacitor
A compensation capacitor is needed to ensure current
control-loop stability. Select the capacitor so that the
unity-gain bandwidth of the current control loop is less
than or equal to 1/12th the resonant frequency of the out-
put filter:
where:
fBW = loop unity gain bandwidth
gm= loop transconductance, typically 100µA/V
CCOMP = value of the compensation capacitor
RTEC = TEC series resistance
RSENSE = sense resistor
Cg
f
R
RR
For MAX
Cg
f
R
RR
For MAX
COMP m
BW
SENSE
SENSE TEC
COMP m
BW
SENSE
SENSE TEC
≥⎛
⎝
⎜⎞
⎠
⎟××
×+
⎛
⎝
⎜⎞
⎠
⎟
≥⎛
⎝
⎜⎞
⎠
⎟××
×+
⎛
⎝
⎜⎞
⎠
⎟
24
21968
12
21969
π
π
()
()
()
()
f
LC
=1
2π
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
12 ______________________________________________________________________________________
Setting Voltage and Current Limits
Certain TEC parameters must be considered to guaran-
tee a robust design. These include maximum positive
current, maximum negative current, and the maximum
voltage allowed across the TEC. These limits should be
used to set the MAXIP, MAXIN, and MAXV voltages.
Setting Max Positive and
Negative TEC Current
MAXIP and MAXIN set the maximum positive and nega-
tive TEC currents, respectively. The default current limit
is ±150mV / RSENSE when MAXIP and MAXIN are con-
nected to REF. To set maximum limits other than the
defaults, connect a resistor-divider from REF to GND to
set VMAXI_. Use resistors in the 10kΩto 100kΩrange.
VMAXI_ is related to ITEC by the following equations:
VMAXIP = 10(ITECP(MAX) x RSENSE)
VMAXIN = 10(ITECN(MAX) x RSENSE)
where ITECP(MAX) is the maximum positive TEC current
and ITECN(MAX) is the negative maximum TEC current.
Positive TEC current occurs when CS is less than OS1:
ITEC x RSENSE = VOS1 -V
CS
when ITEC > 0.
ITEC x RSENSE = VCS -V
OS1
when ITEC < 0.
The MAX1969 controls the TEC current in one direction
(unipolar current flow from OS1 to CS). Set the maxi-
mum unipolar TEC current by applying a voltage to
MAXIN. Connect MAXIP to MAXIN. The equation for
setting MAXIN is the same for the MAX1968 and
MAX1969.
Take care not to exceed the positive or negative cur-
rent limit on the TEC. Refer to the manufacturer’s data
sheet for these limits.
Setting MAX TEC Voltage
Apply a voltage to the MAXV pin to control the maxi-
mum differential TEC voltage. MAXV can vary from 0 to
REF. The voltage across the TEC is four times VMAXV
and can be positive or negative:
|VOS1 - VOS2| = 4 x VMAXV
Set VMAXV with a resistor-divider between REF and
GND using resistors from 10kΩto 100kΩ. VMAXV can
vary from 0 to REF.
Control Inputs/Outputs
Output Current Control
The voltage at CTLI directly sets the TEC current. CTLI
is typically driven from the output of a temperature con-
trol loop. For the purposes of the following equations, it
is assumed that positive TEC current is cooling (see
Figure 1). The transfer function relating current through
the TEC (ITEC) and VCTLI is given by:
ITEC = (VCTLI - VREF)/(10 x RSENSE)
where VREF is 1.50V and:
ITEC = (VOS1 - VCS)/RSENSE
CTLI is centered around REF (1.50V). ITEC is zero when
CTLI = 1.50V. When VCTLI > 1.50V the MAX1968 is
cooling. Current flow is from OS2 to OS1. The voltages
on the pins relate as follows:
VOS2 > VOS1 > VCS
The opposite applies when heating. When VCTLI <
1.50V current flows from OS1 to OS2:
VOS2 < VOS1 < VCS
Shutdown Control
The MAX1968/MAX1969 can be placed in a power-sav-
ing shutdown mode by driving SHDN low. When the
MAX1968/MAX1969 are shut down, the TEC is off (OS1
and OS2 decay to GND) and supply current is reduced
to 2mA (typ).
ITEC Output
ITEC is a status output that provides a voltage proportion-
al to the actual TEC current. ITEC = REF when TEC cur-
rent is zero. The transfer function for the ITEC output is:
VITEC = 1.50 + 8 x (VOS1 - VCS)
Use ITEC to monitor the cooling or heating current
through the TEC. The maximum capacitance that ITEC
can drive is 100pF.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
______________________________________________________________________________________ 13
OS2
OS1
CS
LX1
LX2
COMP
ITEC
GNDCTLI
50mΩ
100kΩ50kΩ
100kΩ
100kΩ
1μF
1μF
1μF
1μF
1μF
1μF
VDD
PVDD1
PVDD2
PGND1
PGND2
REF
MAXIP
FREQ
MAXIN
MAXV
MAX1968
3V TO
5.5V
TO REF
NTC
THERMISTOR
0.01μF
10kΩ
RTHERM
3.3μH
SHDN
3.3μH
10μF
ON
OFF
VDD
U3A
U3B
510kΩ
100kΩ10kΩ
U2
TO REF
10μF0.022μF
240kΩ
10kΩ
TEMPERATURE
SET POINT*
*SEE FIGURE 2
FOR TEMPERATURE
SET POINT SET BY A DAC
0.1μF
0.1μF
VDD 10kΩ
1μF
MAX4477
MAX4477
MAX4475
Figure 1. Typical Application Circuit for MAX1968. Circuit is configured for both cooling and heating with an NTC thermistor. Current
flowing from OS2 to OS1 is cooling.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
14 ______________________________________________________________________________________
VDD LX1
LX2
GND
3V TO
5.5V
PVDD1
PVDD2
PGND1
PGND2
REF
MAXIP
MAXIN
MAXV
CS
OS1
OS2
SHDN
ITEC
COMP
FREQ
CTLI
ON
OFF
MAX1969
TO REF
VDD
U3A
U3B
U2
to REF
510k
Ω
100kΩ10kΩ
1μF
50k
Ω
100k
Ω
2.5μH
25mΩ
100k
Ω
100k
Ω
4.7μF
10μF
RTHERM
10kΩ
0.01μF
0.1μF
10k
Ω
1μF
VDD
240k
Ω
TEMPERATURE
SET POINT*
*SEE FIGURE 1 FOR TEMPERATURE
SET POINT SET BY A POTENTIOMETER
DAC
VDD
DAC
INPUTS
1μF
1μF
1μF
0.1μF
0.022μF
10μF
MAX4475
MAX4477
MAX4477
MAX5144
NTC
THERMISTOR
Figure 2. Typical Application Circuit for MAX1969. MAXIN sets the maximum TEC current. Circuit configured for cooling with NTC
thermistor. Current always flows from CS to OS2.
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
______________________________________________________________________________________ 15
Applications Information
The MAX1968/MAX1969 typically drive a thermoelectric
cooler inside a thermal control loop. TEC drive polarity
and power are regulated based on temperature informa-
tion read from a thermistor, or other temperature-mea-
suring device to maintain a stable control temperature.
Temperature stability of 0.01°C can be achieved with
carefully selected external components.
There are numerous ways to implement the thermal
loop. Figures 1 and 2 show a design that employs preci-
sion op amps, along with a DAC or potentiometer to set
the control temperature. The loop may also be imple-
mented digitally, using a precision A/D to read the ther-
mistor or other temperature sensor, a microcontroller to
implement the control algorithm, and a DAC (or filtered
PWM signal) to send the appropriate signal to the
MAX1968/MAX1969 CTLI input. Regardless of the form
taken by the thermal control circuitry, all designs are
similar in that they read temperature, compare it to a
set-point signal, and then send an error-correcting sig-
nal to the MAX1968/MAX1969 that moves the tempera-
ture in the appropriate direction.
Pin Configuration
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
MAXV
MAXIP
MAXIN
COMP
PGND1
LX1
OS1
PGND1
LX1
PVDD1
LX1
PVDD1
SHDN
CS
OS2
ITEC
FREQ
PVDD2
LX2
PVDD2
LX2
PGND2
LX2
PGND2
REF
CTLI
GND
VDD
TSSOP-EP
TOP VIEW
MAX1968
MAX1969
NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.
Revision History
Pages changed at Rev 2: 1, 9, 15, 16
Chip Information
TRANSISTOR COUNT: 2959
PROCESS: BiCMOS
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
TSSOP 4.4mm BODY.EPS
E11
21-0108
PACKAGE OUTLINE, TSSOP, 4.40 MM BODY,
EXPOSED PAD
XX XX
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.)