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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.