MAXIM MAX1968

19-2447; Rev 0; 4/02
KIT
ATION
EVALU
E
L
B
A
AVAIL
Power Drivers for Peltier TEC Modules
The MAX1968/MAX1969 are highly integrated and costeffective, high-efficiency, switch-mode drivers for Peltier
thermoelectric cooler (TEC) modules. Both devices utilize direct current control to eliminate current surges in
the TEC. On-chip FETs minimize external components
while providing high efficiency. A 500kHz/1MHz switching frequency and a unique ripple cancellation scheme
reduce component size and noise.
The MAX1968 operates from a single supply and provides 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 thermallyenhanced TSSOP-EP package with exposed metal pad
minimizes operating junction temperature. An evaluation kit is available to speed designs.
Features
♦ Direct Current Control Prevents TEC Current
Surges
♦ On-Chip Power MOSFETs
♦ High-Efficiency Switch-Mode Design
♦ Ripple Cancellation for Low Noise
♦ No Dead-Zone or Hunting at Low-Output Current
♦ Adjustable TEC Voltage Limit
♦ Separately Adjustable Heating and Cooling
Current Limits
♦ ITEC Output Monitors TEC Current
♦ 1% Accurate Voltage Reference
♦ 500kHz/1MHz Switching Frequency
♦ ±3A Output Current (MAX1968)
♦ 6A Output Current (MAX1969)
♦ Thermally Enhanced TSSOP-EP Package
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX1968EUI
PART
-40°C to +85°C
28 TSSOP-EP*
MAX1969EUI
-40°C to +85°C
28 TSSOP-EP*
*EP = exposed paddle
Applications
Typical Operating Circuit
Fiber Optic Laser Modules
WDM, DWDM Laser Diode Temperature Control
Fiber Optic Network Equipment
EDFA Optical Amplifiers
3V TO
TEC
CURRENT- 5.5V
CONTROL
SIGNAL
Telecom Fiber Interfaces
ATE
Biotech Lab Equipment
CTLI
VDD
PVDD1
PVDD2
PGND1
PGND2
COMP
MAX1968
LX2
GND
LX1
OS2
OS2
CS
TEC
Pin Configuration and Functional Diagram appear at end
of datasheet.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX1968/MAX1969
General Description
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
ABSOLUTE MAXIMUM RATINGS
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
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.
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 = 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.)
PARAMETER
Input Supply Range
SYMBOL
CONDITIONS
VDD
VDD = 5V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968)
Output Voltage Range
Maximum TEC
Current
Reference Voltage
Reference Load
Regulation
VOUT
ITEC(MAX)
VREF
∆VREF
VDD = 3V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968)
PFET On-Resistance
RDS(ON-P)
NFET Leakage
2
ILEAK(N)
UNITS
3.0
5.5
V
-4.3
+4.3
4.3
V
-2.3
+2.3
2.3
MAX1968
±3
MAX1969
6
VDD = 3V to 5.5V, IREF = 150µA
1.485
VDD = 3V to 5.5V, IREF = +10µA to -1mA
A
1.500
1.515
V
1.2
5
mV
160
VMAXI_ = VREF
140
150
VMAXI_ = VREF/3
40
50
60
VMAXI_ = VREF
140
150
160
VMAXI_ = VREF/3
40
50
60
50
150
250
VDD = 5V, I = 0.5A
0.04
0.07
VDD = 3V, I = 0.5A
0.06
0.08
VDD = 5V, I = 0.5A
0.06
0.10
VDD = 3V, I = 0.5A
0.09
0.12
VLX = VDD = 5V, TA = +25°C
0.02
10
VLX = VDD = 5V, TA = +85°C
1
Switch-Fault Reset
Voltage
RDS(ON-N)
MAX
VDD = 3V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969)
VOS1 > VCS
NFET On-Resistance
TYP
VDD = 5V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969)
VOS1 < VCS
Current-Sense
Threshold Accuracy
MIN
_______________________________________________________________________________________
mV
mV
Ω
Ω
µA
Power Drivers for Peltier TEC Modules
(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
PFET Leakage
ILEAK(P)
No Load Supply
Current
IDD
(NO LOAD)
Shutdown Supply
Current
IDD-SD
Thermal Shutdown
TYP
MAX
VLX = 0, TA = +25°C
CONDITIONS
MIN
0.02
10
VLX = 0, TA = +85°C
1
VDD = 5V
32
100
VDD = 3.3V
20
30
VDD = 5V (Note 2)
2
3
TSHUTDOWN Hysteresis = 15°C
UNITS
µA
mA
mA
°C
+165
VDD rising
2.4
2.6
2.8
VDD falling
2.25
2.5
2.75
FREQ = GND
400
550
650
kHz
UVLO Threshold
VUVLO
Switching Frequency
Internal Oscillator
fSW-INT
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
MAXV Threshold
Accuracy
MAXV, MAXIP, MAXIN
Input Bias Current
IMAXV-BIAS,
IMAXI_-BIAS
VDD x
0.75
V
V
VMAXV = VREF x 0.67, VOS1 to VOS2 =
±4V, VDD = 5V
-2
+2
%
VMAXV = VREF x 0.33, VOS1 to VOS2 =
±2V, VDD = 3V
-2
+2
%
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
50
100
175
µA/V
Error-Amp
Transconductance
gm
ITEC Accuracy
VOS1 to VCS = +100mV or -100mV
-10
+10
%
ITEC Load Regulation
VOS1 to VCS = +100mV or -100mV,
IITEC = ±10µA
-0.1
+0.1
%
∆VITEC
_______________________________________________________________________________________
3
MAX1968/MAX1969
ELECTRICAL CHARACTERISTICS (continued)
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
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
Input Supply Range
SYMBOL
CONDITIONS
VDD
VDD = 5V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968)
Output Voltage Range
Maximum TEC
Current
Reference Voltage
Reference Load
Regulation
VOUT
ITEC(MAX)
VREF
∆VREF
VDD = 3V, ITEC = 0 to ±3A,
VOUT = VOS1 - VOS2 (MAX1968)
4
PFET On-Resistance
RDS(ON-P)
UNITS
5.5
V
-4.3
+4.3
4.3
V
-2.3
+2.3
2.3
MAX1968
±3
MAX1969
6
VDD = 3V to 5.5V, IREF = 150µA
1.475
VMAXI_ = VREF
V
5
mV
135
165
VMAXI_ = VREF / 3
35
65
VMAXI_ = VREF
135
165
VMAXI_ = VREF / 3
35
65
50
250
VDD = 5V, I = 0.5A
0.07
VDD = 3V, I = 0.5A
0.08
VDD = 5V, I = 0.5A
0.07
VDD = 3V, I = 0.5A
0.12
VLX = VDD = 5V, TA = +25°C
10
VLX = VDD = 5V, TA = -40°C
10
VLX = 0, TA = +25°C
10
VLX = 0, TA = -40°C
10
IDD(NO
VDD = 5V
100
LOAD)
VDD = 3.3V
30
Shutdown Supply
Current
IDD-SD
SHDN = GND, VDD = 5V (Note 2)
3
UVLO Threshold
VUVLO
Switching-Frequency
Internal Oscillator
fSW-INT
NFET Leakage
ILEAK(N)
PFET Leakage
ILEAK(P)
No Load Supply
Current
A
1.515
VDD = 3V to 5.5V, IREF = +10µA to -1mA
Switch-Fault Reset
Voltage
RDS(ON-N)
TYP
VDD = 3V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969)
VOS1 > VCS
NFET On-Resistance
MAX
3.0
VDD = 5V, ITEC = 0 to 6A,
VOUT = VOS1 (MAX1969)
VOS1 < VCS
Current-Sense
Threshold Accuracy
MIN
VDD rising
2.4
2.8
VDD falling
2.25
2.75
FREQ = GND
400
650
_______________________________________________________________________________________
mV
mV
Ω
Ω
µA
µA
mA
mA
V
kHz
Power Drivers for Peltier TEC Modules
(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
SHDN, FREQ Input
High Voltage
VIH
VDD = 3V to 5.5V
VDD x
0.25
V
VMAXV = VREF x 0.67, VOS1 to VOS2 =
±4V, VDD = 5V
MAXV Threshold
Accuracy
VDD x
0.75
-2
+2
%
-0.1
+0.1
µA
VMAXV = VREF x 0.33, VOS1 to VOS2 =
±2V, VDD = 3V
MAXV, MAXIP, MAXIN
Input Bias Current
IMAXV-BIAS,
IMAXI_-BIAS
VMAXV = VMAXI_ = 0.1V or 1.5V
CTLI Gain Accuracy
ACTLI
VCTLI = 0.5V to 2.5V (Note 3)
9.5
10.5
V/V
CTLI Input Resistance
RCTLI
1MΩ terminated at REF
0.5
2.0
MΩ
50
175
µA/V
-10
+10
%
Error-Amp
Transconductance
gm
ITEC Accuracy
VOS1 to VCS = +100mV or -100mV
Note 2: Includes power FET leakage.
Note 3: CTLI Gain is defined as:
ACTLI =
(VCTLI − VREF )
VOS1 − VCS
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
5
MAX1968/MAX1969
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. TEC CURRENT
VDD = 3.3V
EFFICIENCY vs. TEC CURRENT
VDD = 5V
80
FREQ = 500kHz
80
70
EFFICIENCY (%)
70
MAX1968 toc03
MAX1968 toc02
FREQ = 500kHz
OUTPUT VOLTAGE RIPPLE
90
MAX1968 toc01
90
EFFICIENCY (%)
60
50
40
30
60
VOS2
100mV/div
AC-COUPLED
50
VOS1
100mV/div
AC-COUPLED
40
30
20
20
RLOAD = 1Ω
10
RLOAD = 0.85Ω
10
0
0
0
1
0
3
2
VDD RIPPLE
1
3
2
400ns/div
TEC CURRENT (A)
TEC CURRENT (A)
TEC CURRENT vs. CTLI VOLTAGE
TEC CURRENT RIPPLE
MAX1968 toc04
MAX1968 toc06
MAX1968 toc05
VCTLI
1V/div
0V
VDD
100mV/div
AC-COUPLED
ITEC
2mA/div
ITEC
1A/div
0A
DC CURRENT = 1A
200ns/div
ZERO-CROSSING TEC CURRENT
vs. CTLI VOLTAGE
ITEC vs. TEMPERATURE
VITEC vs. TEC CURRENT
1.014
MAX1968 toc08
3.0
2.5
1.012
1.010
TEC CURRENT (A)
1.5V
2.0
ITEC
500mA/div
0A
1.5
1.0
MAX1968 toc09
MAX1968 toc07
VCTLI
100mV/div
20ms/div
400ns/div
VITEC (V)
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
1.008
1.006
1.004
1.002
1.000
0.998
0.5
FREQ = 500kHz
VCTLI = 1.9V
RTEC = 1Ω
0.996
0.994
0
1ms/div
-3
-1
1
TEC CURRENT (A)
6
3
-40
-20
0
20
40
TEMPERATURE (°C)
_______________________________________________________________________________________
60
80
Power Drivers for Peltier TEC Modules
SWITCHING FREQUENCY CHANGE
vs. VDD
590
570
550
530
510
490
470
450
25
20
15
10
5
-20
0
20
40
60
80
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
3.0
3.5
4.0
4.5
5.5
5.0
3.0
3.5
4.0
4.5
5.0
TEMPERATURE (°C)
VDD (V)
VDD (V)
REFERENCE VOLTAGE CHANGE
vs. TEMPERATURE
REFERENCE LOAD REGULATION
VDD = 3.3V
REFERENCE LOAD REGULATION
VDD = 5V
-1
-2
-3
-4
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
SINK
-1.2
SOURCE
-20
0
20
40
60
0
-0.2
-0.4
-0.6
-0.8
-0.2
0
0.2
0.4
0.6
0.8
1.0
SOURCE
VSHDN
5V/div
1.5V
0V
0
0.2
0.4
0.6
VDD STEP RESPONSE
MAX1968 toc17
MAX1968 toc16
-0.2
0.8
1.0
LOAD CURRENT (mA)
CTLI STEP RESPONSE
STARTUP AND SHUTDOWN WAVEFORMS
SINK
-0.4
LOAD CURRENT (mA)
TEMPERATURE (°C)
IDD
200mA/div
0.2
-1.2
-0.4
80
0.4
-1.0
-1.4
-5
5.5
0.6
REFERENCE VOLTAGE CHANGE (mV)
0
MAX1968 toc14
1
0.6
REFERENCE VOLTAGE CHANGE (mV)
MAX1968 toc13
2
-40
MAX1968 toc12
30
1.0
0
-40
REFERENCE VOLTAGE CHANGE (mV)
FREQ = 500kHz
MAX1968 toc15
610
35
MAX1968 toc11
FREQ = 500kHz
VCTLI = 1.5V
RTEC = 1Ω
SWITCHING FREQUENCY CHANGE (kHz)
SWITCHING FREQUENCY (kHz)
630
MAX1968 toc10
650
REFERENCE VOLTAGE CHANGE
vs. VDD
REFERENCE VOLTAGE CHANGE (mV)
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX1968 toc18
VDD
2V/div
VCTLI
1V/div
0V
0A
0A
ITEC
500mA/div
ITEC
2A/div
ITEC
20mA/div
1A
0A
VCTLI = 2V
2ms/div
1ms/div
10ms/div
_______________________________________________________________________________________
7
MAX1968/MAX1969
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
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RLOAD = 1Ω, circuit of Figure 1, TA = +25°C, unless otherwise noted.)
THERMAL STABILITY, HEATING
THERMAL STABILITY, COOLING
MAX1968 toc19
TEMPERATURE
0.001°C/div
MAX1968 toc20
TEMPERATURE
0.001°C/div
TTEC = +25°C
TA = +5°C
TTEC = +25°C
TA = +45°C
4s/div
4s/div
THERMAL STABILITY, ROOM TEMPERATURE
MAX1968 toc21
TEMPERATURE
0.001°C/div
TTEC = +25°C
TA = +25°C
4s/div
8
_______________________________________________________________________________________
Power Drivers for Peltier TEC Modules
PIN
NAME
1
VDD
Analog Supply Voltage Input
FUNCTION
2
GND
Analog Ground. Connect to underside metal slug.
3
CTLI
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.
4
REF
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
PVDD2
Power 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 currentsense 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
17
18, 20
SHDN
PVDD1
19, 21, 23
LX1
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 GND.
27
MAXIP
Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV / RSENSE.
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.
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.
Shutdown Control Input. Active-low shutdown control.
Power 1 Inputs. Must be same voltage as VDD. Connect all PVDD1 inputs together at the VDD power plane.
Inductor Connection. Connect all LX1 pins together. For MAX1969, connect all LX1 and LX2 pins together.
_______________________________________________________________________________________
9
MAX1968/MAX1969
Pin Description
Power Drivers for Peltier TEC Modules
MAX1968/MAX1969
Functional Diagram
ON
OFF
SHDN
FREQ
3V TO
5.5V
VDD
REF
MAXV
REF
PVDD1
MAX VTEC =
VMAXV ✕ 4
LX1
MAXIP
MAX ITEC =
(VMAXIP / VREF) ✕
(0.15V / RSENSE)
PGND1
MAXIN
MAX ITEC =
-(VMAXIN / VREF) ✕
(0.15V / RSENSE)
PWM CONTROL
AND
GATE CONTROL
CS
RSENSE
OS1
CS
OS2
ITEC
OS1
PVDD2
VDD
REF
LX2
CTLI
COMP
PGND2
GND
10
MAX1968
______________________________________________________________________________________
Power Drivers for Peltier TEC Modules
Design Procedure
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 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. An external thermal-control loop is typically used to drive CTLI. Figures 1 and 2 show examples of thermal control-loop circuits.
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 switching frequency. For example, 3.3µH and 1µF have a resonance at 87.6kHz, which is adequate for 500kHz
operation
Inductor Selection
f=
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 oscillator. 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 independently controlled. The MAX1969 only controls TEC current 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 reference. 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.
1
2π LC
where:
f = resonant frequency of output filter.
Capacitor Selection
Filter Capacitors
Decouple each power-supply input (V DD , PV DD 1,
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, additional bypassing may be needed to stabilize the input supply. 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 output filter:

R TEC
g  
CCOMP ≥  m  × 
 f   2π × RSENSE 
where:
f = loop frequency, less than or equal to the output filter
resonant frequency
gm = loop transconductance, typically 100µA/V
CCOMP = value of the compensation capacitor
RTEC = TEC series resistance
RSENSE = sense resistor
Setting Voltage and Current Limits
Certain TEC parameters must be considered to guarantee 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.
______________________________________________________________________________________
11
MAX1968/MAX1969
Detailed Description
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
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 / RSENSE 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 VMAXI_. Use resistors in the 10kΩ to 100kΩ range.
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 = CS - OS1
when ITEC < 0.
ITEC x RSENSE = OS1 - CS
when ITEC > 0.
The MAX1969 controls the TEC current in one direction
(unipolar). Set the maximum unipolar TEC current by
applying a voltage to MAXIP. Connect MAXIN to GND.
The equation for setting MAXIP is the same for the
MAX1968 and MAX1969.
Take care not to exceed the positive or negative current 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 maximum 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 10kΩ to 100kΩ. VMAXV can
vary from 0 to REF.
12
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 control loop. For the purposes of the following equations, it
is assumed that positive TEC current is heating.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
heating. Current flow is from OS2 to OS1. The voltages
on the pins relate as follows:
VOS2 > VOS1 > VCS
The opposite applies when cooling. When VCTLI <
1.50V current flows from OS1 to OS2:
VOS2 < VOS1 < VCS
Shutdown Control
The MAX1968/MAX1969 can be placed in a power-saving 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 proportional to the actual TEC current. ITEC = REF when TEC current 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.
______________________________________________________________________________________
Power Drivers for Peltier TEC Modules
MAX1968/MAX1969
3.3µH
3V TO
5.5V
LX1
VDD
1µF
CS
TO REF
1µF
FREQ
10kΩ
50mΩ
MAX1968
OS1
PVDD1
1µF
PGND1
10µF
PVDD2
1µF
PGND2
OS2
REF
LX2
RTHERM
3.3µH
50kΩ
1µF
100kΩ
1µF
MAXIP
COMP
0.01µF
MAXIN
100kΩ
ITEC
ON
MAXV
CTL1
GND
SHDN
OFF
100kΩ
240kΩ
10µF
0.022µF
VDD
VDD
1µF
10kΩ
0.1µF
0.1µF
510kΩ
U3A
MAX4477
U2
TO REF
MAX4475
100kΩ
TEMPERATURE
SET POINT*
10kΩ
10kΩ
U3B
*SEE FIGURE 2
FOR TEMPERATURE
SET POINT SET BY A DAC
MAX4477
Figure 1. Typical Application Circuit for MAX1968
______________________________________________________________________________________
13
MAX1968/MAX1969
Power Drivers for Peltier TEC Modules
3V TO
5.5V
VDD
LX1
TO REF
3.3µH
1µF
CS
1µF
FREQ
10kΩ
25mΩ
PVDD1
OS1
1µF
PGND1
10µF
PVDD2
1µF
RTHERM
PGND2
OS2
MAX1969
LX2
REF
50kΩ
100kΩ
1µF
COMP
MAXIP
0.01µF
MAXIN
100kΩ
ITEC
ON
MAXV
100kΩ
GND
CTLI
10µF
SHDN
OFF
VDD
240kΩ
0.022µF
0.1µF
1 µF
VDD
10kΩ
U3A
0.1µF
U2
510kΩ
MAX4477
to REF
MAX4475
VDD
100kΩ
*SEE FIGURE 1 FOR TEMPERATURE
SET POINT SET BY A POTENTIOMETER
DAC
INPUTS
10kΩ
DAC
MAX5144
TEMPERATURE
SET POINT*
U3B
MAX4477
Figure 2. Typical Application Circuit for MAX1969
14
______________________________________________________________________________________
Power Drivers for Peltier TEC Modules
The MAX1968/MAX1969 typically drive a thermoelectric
cooler inside a thermal control loop. TEC drive polarity
and power are regulated based on temperature information read from a thermistor, or other temperature-measuring device to maintain a stable control temperature.
Temperature stability of 0.01°C can be achieved with
carefully selected external components.
Chip Information
TRANSISTOR COUNT: 2959
PROCESS: BiCMOS
There are numerous ways to implement the thermal
loop. Figures 1 and 2 show a design that employs precision op amps, along with a DAC or potentiometer to set
the control temperature. The loop may also be implemented digitally, using a precision A/D to read the thermistor 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 signal to the MAX1968/MAX1969 that moves the temperature in the appropriate direction.
Pin Configuration
TOP VIEW
VDD 1
28 MAXV
GND 2
27 MAXIP
CTLI 3
26 MAXIN
REF 4
25 COMP
PGND2 5
LX2 6
24 PGND1
MAX1968
MAX1969
PGND2 7
23 LX1
22 PGND1
LX2 8
21 LX1
PVDD2 9
20 PVDD1
LX2 10
19 LX1
PVDD2 11
18 PVDD1
FREQ 12
17 SHDN
ITEC 13
16 CS
OS2 14
15 OS1
TSSOP-EP
NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.
______________________________________________________________________________________
15
MAX1968/MAX1969
Applications Information
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.)
TSSOP, 4.0,EXP PADS.EPS
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.
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