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19-2490; Rev 0; 7/02
KIT ATION EVALU ABLE AVAIL
Integrated Temperature Controllers for Peltier Modules
General Description Features
o Smallest, Safest, Most Accurate Complete Single-Chip Controller o On-Chip Power MOSFETS--No External FETs o Circuit Footprint < 0.93in2 o Circuit Height < 3mm o Temperature Stability to 0.001C o Integrated Precision Integrator and Chopper Stabilized Op Amps o Accurate, Independent Heating and Cooling Current Limits o Eliminates Surges By Directly Controlling TEC Current o Adjustable Differential TEC Voltage Limit o Low-Ripple and Low-Noise Design o o o o TEC Current Monitor Temperature Monitor Over- and Undertemperature Alarm Bipolar 3A Output Current (MAX1978)
MAX1978/MAX1979
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 0.001C 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 -40C to +85C temperature range. The thermally enhanced QFN-EP package with exposed metal pad minimizes operating junction temperature. An evaluation kit is available to speed designs.
o Unipolar +6A Output Current (MAX1979)
Ordering Information
PART MAX1978ETM MAX1979ETM *EP = Exposed pad. TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 48 Thin QFN-EP* 48 Thin QFN-EP
Pin Configuration
MAXV MAXIN CTLI VDD GND GND
48 47 46
CS REF
45
44
43
42
41
40
39
38
37 36 35 34 33 32 31 30 29 28 27 26 25
ITEC
OS1
TOP VIEW
MAXIP COMP
OS2 N.C. PGND2 LX2 PGND2 LX2 PVDD2 N.C. LX2 PVDD2 SHDN OT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
FREQ N.C. PGND1 LX1 PGND1 LX1 PVDD1 N.C. LX1 PVDD1 GND GND
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.
MAX1978 MAX1979
INTGND DIFOUT FBFB+
BFBBFB+
INTOUT
QFN-EP
*ELECTRICALLY CONNECTED TO THE UNDERSIDE METAL SLUG. NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.
________________________________________________________________ Maxim Integrated Products
AIN+ AINAOUT
UT
1
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Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
ABSOLUTE MAXIMUM RATINGS
VDD 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 (VDD + 0.3V) PVDD1, PVDD2 to VDD ...........................................-0.3V to +0.3V PVDD1, PVDD2 to GND...............................-0.3V to (VDD + 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 (TA = +70C) 48-Lead Thin QFN-EP (derate 26.3mW/C above +70C) (Note 2) .................2.105W Operating Temperature Ranges MAX1978ETM ..................................................-40C to +85C MAX1979ETM ..................................................-40C to +85C Maximum Junction Temperature .....................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: LX has internal clamp diodes to PGND and PVDD. Applications that forward bias these diodes should not exceed the IC's package power dissipation limits. Note 2: Solder underside metal slug to 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
(VDD = PVDD1 = PVDD2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0C to +85C, unless otherwise noted. Typical values at TA = +25C.)
PARAMETER Input Supply Range SYMBOL VDD VDD = 5V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1978) VDD = 5V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1979) VDD = 3V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1978) VDD = 3V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1979) Maximum TEC Current Reference Voltage Reference Load Regulation ITEC(MAX) VREF VREF MAX1978 MAX1979 VDD = 3V to 5.5V, IREF = 150A VDD = 3V to 5.5V, IREF = +10A to -1mA VOS1 < VCS Current-Sense Threshold VOS1 > VCS NFET On-Resistance PFET On-Resistance NFET Leakage RDS(ON-N) RDS(ON-P) ILEAK(N) VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VDD = 5V, I = 0.5A VDD = 3V, I = 0.5A VLX = VDD = 5V, TA = +25C VLX = VDD = 5V, TA = +85C VMAXI_ = VREF VMAXI_ = VREF/3 VMAXI_ = VREF VMAXI_ = VREF/3 135 40 135 40 1.485 1.500 1.2 150 50 150 50 0.04 0.06 0.06 0.09 0.02 1 -2.3 CONDITIONS MIN 3.0 -4.3 TYP MAX 5.5 +4.3 4.3 V +2.3 2.3 3 6 1.515 5 160 60 160 60 0.07 0.08 0.10 0.12 10 A mV A V mV UNITS V
Output Voltage Range
VOUT
2
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Integrated Temperature Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0C to +85C, unless otherwise noted. Typical values at TA = +25C.)
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 SHDN, FREQ Input Low Voltage SHDN, FREQ Input High Voltage SYMBOL ILEAK(P) IDD(NO
LOAD)
MAX1978/MAX1979
CONDITIONS VLX = 0, TA = +25C VLX = 0, TA = +85C VDD = 5V VDD = 3.3V SHDN = GND, VDD = 5V (Note 3) VDD rising VDD falling FREQ = GND FREQ=VDD 0 or VDD 0 or VDD VDD = 3V to 5.5V VDD = 3V to 5.5V VMAXV = VREF 0.67, VOS1 to VOS2 = 4V, VDD = 5V VMAXV = VREF 0.33, VOS1 to VOS2 = 2V, VDD = 3V
MIN
TYP 0.02 1 30 15 2 165
MAX 10 50 30 3 2.8 2.75 650 1200 +100 +5 0.25 x VDD
UNITS A mA mA C V kHz A A V V
IDD-SD
TSHUTDOWN Hysteresis = 15C VUVLO fSW-INT IOS1, IOS2, ICS ISHDN, IFREQ VIL VIH 2.4 2.25 450 800 -100 -5
2.6 2.5 500 1000
0.75 x VDD -1 -2 -0.1 9.5 0.5 50 -10 -0.1 -10 0 +20 0.1 45 50 55 10 1.0 100 +1
MAXV Threshold Accuracy
% +2 +0.1 10.5 2.0 175 +10 +0.1 +10 +200 A V/V M S % % nA V V/C V/V
MAXV, MAXIP, MAXIN Input Bias Current CTLI Gain CTLI Input Resistance Error Amp Transconductance ITEC Accuracy ITEC Load Regulation Instrumentation Amp Input Bias Current Instrumentation Amp Offset Voltage Instrumentation Amp OffsetVoltage Drift with Temperature Instrumentation Amp Preset Gain
IMAXV-BIAS, VMAXV = VMAXI_ = 0.1V or 1.5V IMAXI_-BIAS ACTLI RCTLI gm VOS1 to VCS = +100mV or -100mV VITEC IDIF-BIAS VDIF-OS VDD = 3V to 5.5V VDD = 3V to 5.5V ADIF RLOAD = 10k to REF VOS1 to VCS = +100mV or -100mV, IITEC = 10A VCTLI = 0.5V to 2.5V (Note 4) 1M terminated at REF
-200
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3
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = 0C to +85C, unless otherwise noted. Typical values at TA = +25C.)
PARAMETER Integrator Amp Open-Loop Gain Integrator Amp CMRR Integrator Amp Input Bias Current Integrator Amp Voltage Offset Integrator Amp Gain Bandwidth Undedicated Chopper Amp Open-Loop Gain Undedicated Chopper Amp CMRR Undedicated Chopper Amp Input Bias Current Undedicated Chopper Amp Offset Voltage 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 ILEAK VOL SYMBOL AOL-INT CMRRINT IINT-BIAS VINT-OS GBWINT AOL-AIN CMRRAIN IAIN-BIAS VAIN-OS GBWAIN VRIPPLE A=5 CLOAD < 100pF V UT = V OT = 5.5V Sinking 4mA FB+ - FB- (see Typical Application Circuit) FB+ - FB- (see Typical Application Circuit) 50 -20 20 -200 VDD = 3V to 5.5V VDD = 3V to 5.5V -10 -200 RLOAD = 10k to REF VDD = 3V to 5.5V VDD = 3V to 5.5V -3 +0.1 100 120 85 0 +10 100 20 0 +200 1 150 +10 +200 CONDITIONS RLOAD = 10k to REF MIN TYP 120 100 1 +3 MAX UNITS dB dB nA mV kHz dB dB nA V kHz mV V A mV mV mV
4
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Integrated Temperature Controllers for Peltier Modules
ELECTRICAL CHARACTERISTICS
(VDD = PVDD1 = PVDD2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = -40C to +85C, unless otherwise noted.) (Note 5)
PARAMETER Input Supply Range SYMBOL VDD VDD = 5V, ITEC = 0 to 3A, VOUT = VOS1 -VOS2 (MAX1978) VDD = 5V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1979) VDD = 3V, ITEC = 0 to 3A, VOUT = VOS1 - VOS2 (MAX1978) VDD = 3V, ITEC = 0 to 6A, VOUT = VOS1 (MAX1979) Maximum TEC Current Reference Voltage Reference Load Regulation ITEC(MAX) VREF VREF MAX1978 MAX1979 VDD = 3V to 5.5V, IREF = 150A VDD = 3V to 5.5V, IREF = 10A to -1mA VOS1 < VCS Current-Sense Threshold VOS1 > VCS No-Load Supply Current Shutdown Supply Current UVLO Threshold Switching Frequency Internal Oscillator OS1, OS2, CS Input Current SHDN, FREQ Input Current SHDN, FREQ Input Low Voltage SHDN, FREQ Input High Voltage IDD(NO
LOAD)
MAX1978/MAX1979
CONDITIONS
MIN 3 -4.3
MAX 5.5 +4.3 4.3
UNITS V
Output Voltage Range
VOUT
V -2.3 +2.3 2.3 3 6 1.475 1.515 5 A V mV
VMAXI_ = VREF VMAXI_ = VREF/3 VMAXI_ = VREF VMAXI_ = VREF/3
135 40 135 40
160 60 160 60 50 30 3 mA mA V kHz A A V V mV
VDD = 5V VDD = 3.3V SHDN = GND, VDD = 5V (Note 3) VDD rising VDD falling FREQ = GND FREQ = VDD 2.4 2.25 450 800 -100 -5
IDD-SD VUVLO fSW-INT
2.8 2.75 650 1200 +100 +5 0.25 VDD
IOS1, IOS2, 0 or VDD ICS I SHDN, I FREQ VIL VIH 0 or VDD VDD = 3V to 5.5V VDD = 3V to 5.5V
0.75 VDD
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5
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD1 = PVDD2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, TA = -40C to +85C, unless otherwise noted.) (Note 5)
PARAMETER SYMBOL CONDITIONS VMAXV = VREF 0.67, VOS1 to VOS2 = 4V, VDD = 5V VMAXV = VREF 0.33, VOS1 to VOS2 = 2V, VDD = 3V MAXV, MAXIP, MAXIN Input Bias Current CTLI Gain CTLI Input Resistance Error Amp Transconductance ITEC Accuracy ITEC Load Regulation Instrumentation Amp Input Bias Current Instrumentation Amp Offset Voltage Instrumentation Amp Preset Gain Integrator Amp Input Bias Current Integrator Amp Voltage Offset Undedicated Chopper Amp Input Bias Current Undedicated Chopper Amp Offset Voltage BFB_ Buffer Error UT and OT Leakage Current UT and OT Output Low Voltage ILEAK VOL VITEC IDIF-BIAS VDIF-OS ADIF IINT-BIAS VINT-OS IAIN-BIAS VAIN-OS VDD = 3V to 5.5V RLOAD = 10k to REF VDD = 3V to 5.5V VDD = 3V to 5.5V VDD = 3V to 5.5V VDD = 3V to 5.5V CLOAD < 100pF V UT = V OT = 5.5V Sinking 4mA -3 -10 -200 -200 IMAXV-BIAS, VMAXV = VMAXI_ = 0.1V or 1.5V IMAXI_-BIAS ACTLI RCTLI gm VOS1 to VCS = +100mV or -100mV VOS1 to VCS = +100mV or -100mV, IITEC = 10A VCTLI = 0.5V to 2.5V (Note 4) 1M terminated at REF MIN -1 -2 -0.1 9.5 0.5 50 -10 -0.125 -10 -200 45 MAX +1 % +2 +0.1 10.5 2.0 175 +10 +0.125 +10 +200 55 1 +3 +10 +200 +200 1 150 A V/V M S % % nA V V/V nA mV nA V V A mV UNITS
MAXV Threshold Accuracy
Note 3: Includes power FET leakage. Note 4: CTLI gain is defined as:
A CTLI = (VCTLI -VREF )
(VOSI -VCS )
Note 5: Specifications to -40C are guaranteed by design, not production tested.
6
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Integrated Temperature Controllers for Peltier Modules
Typical Operating Characteristics
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. TEC CURRENT VDD = 5V
MAX1978 toc01
MAX1978/MAX1979
EFFICIENCY vs. TEC CURRENT VDD = 3.3V
MAX1978 toc02
OUTPUT-VOLTAGE RIPPLE WAVEFORMS
VOS2 100mV/div AC-COUPLED
MAX1978 toc03
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0 0.5 1.0 1.5 2.0 RTEC = 1.1
80 70 60 EFFICIENCY (%) 50 40 30 20 RTEC = 0.855 10 0
VOS1 100mV/div AC-COUPLED
VOS1 - VOS1 50mV/div
2.5
0
0.5
1.0
1.5
2.0
2.5
400ns/div
TEC CURRENT (A)
TEC CURRENT (A)
INPUT SUPPLY RIPPLE
MAX1978 toc04
TEC CURRENT vs. CTLI VOLTAGE
MAX1978 toc05
ZERO-CROSSING TEC CURRENT
VCTLI 200mV/div
MAX1978 toc06
1.5V VDD 20mV/div AC-COUPLED VCTLI 1V/div -0V -0A ITEC 2A/div ITEC 500mA/div
0A
200ns/div
20ms/div
1ms/div
VITEC vs. TEC CURRENT
MAX1978 toc07
TEC CURRENT vs. TEMPERATURE
MAX1978 toc08
SWITCHING FREQUENCY vs. TEMPERATURE
506 SWITCHING FREQUENCY (kHz) 504 502 500 498 496 494 492 -40 VCTLI = 1.5V RTEC = 1 -20 0 20 40 60 80
MAX1978 toc09
3.0 2.5 2.0 VITEC (V) 1.5 1.0
1.010
508
1.005 ITEC (A)
1.000
0.995 0.5 0 -3 -2 -1 0 1 2 3 TEC CURRENT (A) 0.990 -40 -20 0 20 40 60 80 TEMPERATURE (C) ITEC = 1A RSENSE = 0.68
TEMPERATURE (C)
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7
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.)
SWITCHING FREQUENCY CHANGE vs. INPUT SUPPLY
SWITCHING FREQUENCY CHANGE (kHz) REFERENCE VOLTAGE CHANGE (mV) 5 0 -5 -10 -15 -20 -25 -30 -35 3.0 3.5 4.0 4.5 5.0 5.5 VDD (V)
MAX1978 toc10
REFERENCE VOLTAGE CHANGE vs. INPUT SUPPLY
MAX1978 toc11
REFERENCE VOLTAGE CHANGE vs. TEMPERATURE
REFERENCE VOLTAGE CHANGE (mV)
MAX1978 toc12
10
1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 3.0 3.5 4.0 4.5 5.0
3 2 1 0 -1 -2 -3 -4
5.5
-40
-20
0
20
40
60
80
VDD (V)
TEMPERATURE (C)
REFERENCE LOAD REGULATION
MAX1978 toc13
ATO VOLTAGE vs. THERMISTOR TEMPERATURE
MAX1978 toc14
STARTUP AND SHUTDOWN WAVEFORMS
VSHDN 5V/div
MAX1978 toc15
0.6 REFERENCE VOLTAGE CHANGE (mV) 0.4 0.2
4.5 4.0 3.5 ATO VOLTAGE (V) 3.0 2.5 2.0 1.5 1.0 0.5 0 NTC, 10k THERMISTOR CIRCUIT IN FIGURES 1 AND 2
0 -0.2 -0.4 -0.6 -0.8 -1.0 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 REFERENCE LOAD CURRENT (mA) SINK SOURCE
ITEC 500mA/div
IDD 200mA/div -10 0 10 20 30 40 50 60 100s/div
THERMISTOR TEMPERATURE (C)
CTLI STEP RESPONSE
MAX1978 toc16
INPUT SUPPLY STEP RESPONSE
VDD 2V/div
MAX1978 toc17
THERMAL STABILITY, COOLING MODE
MAX1978 toc18
VCTLI 1V/div
1.5V TEMPERATURE 0.001C/div
ITEC 1A/div 0A
ITEC 20mA/div
0V
1A
ITEC = +25C TA = +45C
1ms/div
10ms/div
4s/div
8
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Integrated Temperature Controllers for Peltier Modules
Typical Operating Characteristics (continued)
(VDD = 5V, VCTLI = 1V, VFREQ = GND, RTEC = 1, circuit of Figure 1, TA = +25C, unless otherwise noted.)
THERMAL STABILITY, ROOM TEMPERATURE
MAX1978 toc19
MAX1978/MAX1979
THERMAL STABILITY, HEATING MODE
MAX1978 toc20
TEMPERATURE ERROR vs. AMBIENT TEMPERATURE
MAX1978 toc21
0.03 0.02 TEMPERATURE ERROR (C) 0.01 0 -0.01 -0.02 -0.03
TEMPERATURE 0.001C/div
TEMPERATURE 0.001C/div
ITEC = +25C TA = +25C
TTEC = +25C TA = +5C
4s/div
4s/div
-20
-10
0
10
20
30
40
50
AMBIENT TEMPERATURE (C)
Pin Description
PIN 1 2, 8, 29, 35 3, 5 4, 6, 9 7, 10 11 12 13 14 15 16, 25, 26, 42, 43 17 18 19 20 21 22 NAME OS2 N.C. PGND2 LX2 PVDD2 SHDN OT UT FUNCTION Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power output. Not Internally Connected 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. Power 2 Inputs. Must be same voltage as VDD. Connect all PVDD2 inputs together at the VDD power plane. Bypass to PGND2 with a 10F ceramic capacitor. Shutdown Control Input. Active-low shutdown control. Under-Temperature Alarm. Open-drain output pulls low if temperature feedback falls 20mV (typically +1.5C) below the set-point voltage. Under-Temperature Alarm. Open-drain output pulls low if temperature feedback falls 20mV (typically +1.5C) below the set-point voltage. Integrator Amp Inverting Input. Normally connected to DIFOUT through thermal-compensation network. Analog Ground. Connect all GND pins to analog ground plane.
INTOUT Integrator Amp Output. Normally connected to CTLI. INTGND
DIFOUT Chopper-Stabilized Instrumentation Amp Output. Differential gain is 50 (FB+ - FB-). FBFB+ BFBBFB+ AIN+ Chopper-Stabilized Instrumentation Amp Inverting Input. Connect to thermistor bridge. Chopper-Stabilized Instrumentation Amp Noninverting Input. Connect to thermistor bridge. Chopper-Stabilized Buffered FB- Output. Used to monitor thermistor bridge voltage. Chopper-Stabilized Buffered FB+ Output. Used to monitor thermistor bridge voltage. Undedicated Chopper-Stabilized Amplifier Noninverting Input
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9
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
Pin Description (continued)
PIN 23 24 27, 30 28, 31, 33 32, 34 36 37 38 39 40 41 44 45 46 47 48 NAME AINAOUT PVDD1 LX1 PGND1 FREQ ITEC COMP MAXIP MAXIN MAXV VDD CTLI REF CS OS1 FUNCTION Undedicated Chopper-Stabilized Amplifier Inverting Input Undedicated Chopper-Stabilized Amplifier Output Power 1 Inputs. Must be same voltage as VDD. Connect all PVDD1 inputs together at the VDD power plane. Bypass to PGND1 with a 10F ceramic capacitor. Inductor 1 Connection. Connect all LX1 pins together. Connect LX1 to LX2 when using the MAX1979. Power Ground 1. Internal synchronous-rectifier ground connections. Connect all PGND pins together at power ground plane. Switching-Frequency Select. Low = 500kHz, high = 1MHz. TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC currentsense resistor. VITEC = 1.50V + (VOS1 - VCS) 8. Current-Control Loop Compensation. For most designs, connect a 10nF capacitor from COMP to GND. Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV / RSENSE. Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit -150mV / RSENSE. Connect MAXIN to GND when using the MAX1979. 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 VMAXV. Analog Supply Voltage Input. Bypass to GND with a 10F ceramic capacitor. 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. ITEC = (VOS1 - VCS) / RSENSE = (VCTLI - 1.50) / (10 RSENSE). When (VCLTI - VREF) > 0, VOS2 > VOS1 > VCS. 1.5V Reference Voltage Output. Bypass REF to GND with a 1F ceramic capacitor. 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 for the MAX1978. The MAX1979 TEC current is unipolar. Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power output.
10
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Integrated Temperature Controllers for Peltier Modules
Functional Diagram
ON OFF SHDN REF 1.5V REFERENCE FREQ VDD PVDD1 3V TO 5.5V
MAX1978/MAX1979
MAXV
MAX VTEC = VMAXV x 4
LX1
MAXIP
MAX ITEC = (VMAXIP/ VREF) x (0.15V/RSENSE) PGND1 MAX ITEC = (VMAXIN/ VREF) x (0.15V/RSENSE) PWM CONTROL AND GATE DRIVE
MAXIN
CS RSENSE
CS ITEC
OS1
OS1 REF
OS2
CTLI COMP
PVDD2 VDD
LX2 GND
MAX1978
OT REF + 1V 50R PGND2
UT 50R REF - 1V R
R REF
REF
BFB-
BFB+ INTOUT INTAINAOUT AIN+ DIFOUT FB+ FB-
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11
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
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 0.001C. 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.
REF
VDD
10F 10F
10F
1F
0.01F
VDD COMP
SHDN
PVDD1
PVDD2
REF MAXV MAXIN MAXIP LX1 CS
3H 1F 0.068
UNDERTEMP ALARM OVERTEMP ALARM DC CURRENT MONITOR 20k 1%
UT OT ITEC
OS1
MAX1978
BFBAINAOUT LX2 AIN+ OS2
4.7F
TEC
80.6k THERMISTOR VOLTAGE MONITOR REF 69.8k 1%
1F
3H 1F REF PGND2 PGND1 INTOUT INTFBDIFOUT FB+ 10k 100k 100k 10F 0.47F 20k THERMAL FEEDBACK
105k 1%
CTLI FREQ GND
0.047F
1M
Figure 1. MAX1978 Typical Application Circuit 12 ______________________________________________________________________________________
Integrated Temperature Controllers for Peltier Modules
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 = VDD. The 1MHz setting allows minimum inductor and filter-capacitor values. Efficiency is optimized with the 500kHz setting. derived from, and is synchronized to, the switching frequency of the power stage.
MAX1978/MAX1979
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.
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 VMAXV). 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.
Current Monitor Output
ITEC provides a voltage output proportional to the TEC current, ITEC (see the Functional Diagram): VITEC = 1.5V + 8 (VOS1 - VCS)
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 0.001C can be achieved over a 0C to +50C 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
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 1.5C error.
Reference Output
The MAX1978/MAX1979 include an on-chip 1.5V voltage reference accurate to 1% over temperature. Bypass REF with 1F 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, 0.001C 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 VDD / 2 if some shift in instrumentation amp offset (approximately -50V/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 MAX1978/MAX1979
VDD REF
10F 10F
10F
1F
0.01F
VDD COMP
SHDN
PVDD1
PVDD2
UNDERTEMP ALARM OVERTEMP ALARM DC CURRENT MONITOR 20k 1%
UT OT ITEC
REF MAXV MAXIN MAXIP LX1 LX2 CS
3H 1F 0.03
OS1
MAX1979
BFBAINAOUT
4.7F
TEC
80.6k THERMISTOR VOLTAGE MONITOR REF 69.8k 1%
1F
OS2
AIN+ 105k 1% CTLI FREQ GND PGND2 PGND1 INTOUT INTDIFOUT 10k 100k FBFB+ REF
THERMAL FEEDBACK
100k
10F
0.47F
20k
0.047F
1M
Figure 2. MAX1979 Typical Application Circuit
Buffered Outputs, BFB+ and BFBBFB+ 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.
tional 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.
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-propor14 ______________________________________________________________________________________
Integrated Temperature Controllers for Peltier Modules
REF 69.8k 1% AIN+ AOUT 105k 1%
22F to 100F 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: g 24 x RSENSE CCOMP m x fBW 2 x (RSENSE + RTEC ) where: fBW = unity-gain bandwidth frequency gm = loop transconductance, typically 100A/V CCOMP = value of the compensation capacitor RTEC = TEC series resistance RSENSE = sense resistor
MAX1978/MAX1979
80.6k 1% AIN-
1F
REF
MAX1978 MAX1979
20k 1% BFB10k
x50
FBVSETPOINT FB+
Setting Voltage and Current Limits
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, 3.0H and 1F have a resonance at 92kHz, which is adequate for 500kHz operation. 1 2 LC
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 / 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 10k to 100k range. VMAXI_ is related to ITEC by the following equations: VMAXIP = 10 (ITECP(MAX) RSENSE) VMAXIN = 10 (ITECN(MAX) RSENSE) where ITECP(MAX) is the maximum positive TEC current and ITECN(MAX) is the maximum negative TEC current. Positive TEC current occurs when CS is less than OS1: ITEC RSENSE = CS - OS1 when ITEC < 0. ITEC RSENSE = OS1 - CS when ITEC > 0.
f LC=
where: fLC = resonant frequency of output filter.
Capacitor Selection
Filter Capacitors Decouple each power-supply input (VDD, PVDD1, and PVDD2) with a 10F 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
______________________________________________________________________________________
15
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
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 VMAXV and can be positive or negative.
FBFBREF CREF
MAX1978 MAX1979
FB+
VTHERMISTOR VSETPOINT
|VOS1 - VOS2| = 4 VMAXV Use resistors from 10k to 100k to form a voltagedivider to set VMAXV. 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.
MAX1978 MAX1979
REF CREF VTHERMISTOR
FB+
DAC VSETPOINT
DIGITAL INPUT
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 CINTOUT. 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:
C3
ITEC = (VCTLI - VREF) / (10 RSENSE)
C1
R1 INT-
R3
C2
DIFOUT
R2
INTOUT
where VREF is 1.50V and ITEC = (VOS1 - VCS) / RSENSE VCTLI is centered around REF (1.50V). ITEC is zero when VCTLI = 1.50V. When VCTLI > 1.50V, the MAX1978 is heating. Current flow is from OS2 to OS1. The voltages are: VOS2 > VOS1 > VCS
REF
Figure 4. Proportional Integral Derivative Controller 16
when VCTLI < 1.50V, current flows from OS1 to OS2: VOS2 < VOS1 < VCS
______________________________________________________________________________________
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 (VOS1 and VOS2 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: VITEC = 1.50 + 8 (VOS1 - VCS) Use ITEC to monitor the cooling or heating current through the TEC. The maximum capacitance that ITEC can drive is 100pF. grator 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 = 10F. Resistor R3 then sets the zero at 0.16Hz using the following equation: fz1 = 1 2 x C2 x R3
MAX1978/MAX1979
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 0.001C 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 inte-
This yields a value of R3 = 99.47k. For our example, use 100k. 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. C1 = A 1 + 2 x R3 x fC C2
______________________________________________________________________________________
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. fC = The desired crossover frequency, 1.5Hz in this example. C1 is found to be 0.58F; use 0.47F. 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 x 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: 1 fz2 = 2 x C1x R2 where fz2 is the second zero. R2 is calculated to be 1.1M; use 1M. 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: fp1 = 1 2 x C1x R1
MAX1978/MAX1979
Resistor R1 is found to be 22k, use 20k 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: fp2 = 1 2 x C3 x R3
where C3 is found to be 0.05F, use 0.047F. 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.
Chip Information
TRANSISTOR COUNT: 6023 PROCESS: BiCMOS
TEC GAIN AND PHASE
40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 0.001 0.01 0.1 1 10 90 45 0 -45 -90 -135 -180 100 PHASE (DEGREES) 80 70 60 50 40 30 20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 0.001
COMPENSATED TEC GAIN AND PHASE
90 45 0 -45 -90 -135 -180 100 PHASE (DEGREES)
GAIN (dB)
GAIN (dB)
0.01
0.1
1
10
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 6. Bode Plot of a Generic TEC Module
Figure 7. Compensated Thermal-Control Loop Using the TEC Module in Figure 6
18
______________________________________________________________________________________
Integrated Temperature Controllers for Peltier Modules
Typical Operating Circuit
INPUT 3V TO 5.5V VDD PVDD-
MAX1978/MAX1979
LX1 PGND1
ON OFF OVERTEMP ALARM UNDERTEMP ALARM SHDN OT UT BFB-
CS
OS1
MAX1978
OS2 LX2 PGND2
TEC
ITEC = 3A
AIN-
REF
TEMP MONITOR TEC CURRENT MONITOR
AOUT FB+ ITEC AIN+ NTC VOLTAGE LIMIT MAXV MAXIP MAXIN REF FBOPTIONAL DAC DAC
HEATING CURRENT LIMIT COOLING CURRENT LIMIT
______________________________________________________________________________________
19
Integrated Temperature Controllers for Peltier Modules MAX1978/MAX1979
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.)
32, 44, 48L QFN .EPS
E2/2 (NE-1) X e
C L
D2 D D/2 k
C L
b D2/2
E/2
E
E2
k L DETAIL A e (ND-1) X e
C L
C L
L
L
e
e
A1
A2
A
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 32, 44, 48L QFN THIN, 7x7x0.8 mm
DOCUMENT CONTROL NO. REV.
APPROVAL
21-0144
1 2
A
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
** NOTE: T4877-1 IS A CUSTOM 48L PKG. WITH 4 LEADS DEPOPULATED. TOTAL NUMBER OF LEADS ARE 44.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 32, 44, 48L QFN THIN, 7x7x0.8 mm
DOCUMENT CONTROL NO. REV.
APPROVAL
21-0144
2 2
A
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.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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