MAX1978, MAX1979

Add to my manuals
21 Pages

advertisement

MAX1978, MAX1979 | Manualzz

19-2490; Rev 1; 2/07

Integrated Temperature

Controllers for Peltier Modules

General Description

The MAX1978/MAX1979 are the smallest, safest, most accurate complete single-chip temperature controllers for

Peltier thermoelectric cooler (TEC) modules. On-chip power

FETs and thermal control-loop circuitry minimize external components while maintaining high efficiency. Selectable

500kHz/1MHz switching frequency and a unique ripple-cancellation scheme optimize component size and efficiency while reducing noise. Switching speeds of internal

MOSFETs are optimized to reduce noise and EMI. An ultralow-drift chopper amplifier maintains ±0.001°C temperature stability. Output current, rather than voltage, is directly controlled to eliminate current surges. Individual heating and cooling current and voltage limits provide the highest level of

TEC protection.

The MAX1978 operates from a single supply and provides bipolar ±3A output by biasing the TEC between the outputs of two synchronous buck regulators. True bipolar operation controls temperature without “dead zones” or other nonlinearities at low load currents. The control system does not hunt when the set point is very close to the natural operating point, where only a small amount of heating or cooling is needed. An analog control signal precisely sets the TEC current. The MAX1979 provides unipolar output up to 6A.

A chopper-stabilized instrumentation amplifier and a highprecision integrator amplifier are supplied to create a proportional-integral (PI) or proportional-integral-derivative (PID) controller. The instrumentation amplifier can interface to an external NTC or PTC thermistor, thermocouple, or semiconductor temperature sensor. Analog outputs are provided to monitor TEC temperature and current. In addition, separate overtemperature and undertemperature outputs indicate when the TEC temperature is out of range. An on-chip voltage reference provides bias for a thermistor bridge.

The MAX1978/MAX1979 are available in a low-profile

48-lead thin QFN-EP package and is specified over the

-40°C to +85°C temperature range. The thermally enhanced QFN-EP package with exposed metal pad minimizes operating junction temperature. An evaluation kit is available to speed designs.

Applications

Fiber Optic Laser Modules

WDM, DWDM Laser-Diode Temperature Control

Fiber Optic Network Equipment

EDFA Optical Amplifiers

Telecom Fiber Interfaces

ATE

Typical Operating Circuit appears at end of data sheet.

Features

Smallest, Safest, Most Accurate Complete

Single-Chip Controller

On-Chip Power MOSFETS—No External FETs

Circuit Footprint < 0.93in

2

Circuit Height < 3mm

Temperature Stability to 0.001°C

Integrated Precision Integrator and Chopper

Stabilized Op Amps

Accurate, Independent Heating and Cooling

Current Limits

Eliminates Surges By Directly Controlling

TEC Current

Adjustable Differential TEC Voltage Limit

Low-Ripple and Low-Noise Design

TEC Current Monitor

Temperature Monitor

Over- and Undertemperature Alarm

Bipolar ±3A Output Current (MAX1978)

Unipolar +6A Output Current (MAX1979)

Ordering Information

PART T EM P R A N G E PIN-PACKAGE PK G CO D E

MAX1978ETM - 40

° C to + 85° C 48 Thin QFN-EP*

T4877-6

MAX1979ETM - 40

° C to + 85° C 48 Thin QFN-EP*

T4877-6

*EP = Exposed paddle.

Pin Configuration

TOP VIEW

7

8

5

6

3

4

1

2

9

10

11

12

OS2

N.C.

PGND2

LX2

PGND2

LX2

PV

DD

2

N.C.

LX2

PV

DD

2

SHDN

OT

MAX1978

MAX1979

FREQ

N.C.

PGND1

LX1

PGND1

LX1

PV

DD

1

N.C.

LX1

PV

DD

1

GND

GND

32

31

30

29

36

35

34

33

28

27

26

25

QFN-EP

*ELECTRICALLY CONNECTED TO THE UNDERSIDE METAL SLUG.

NOTE: GND IS CONNECTED TO THE UNDERSIDE METAL SLUG.

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Integrated Temperature

Controllers for Peltier Modules

ABSOLUTE MAXIMUM RATINGS

V

DD to GND ..............................................................-0.3V to +6V

SHDN, MAXV, MAXIP, MAXIN,

CTLI, OT, UT to GND............................................-0.3V to +6V

FREQ, COMP, OS1, OS2, CS, REF, ITEC, AIN+, AIN-,

AOUT, INT-, INTOUT, BFB+, BFB-, FB+, FB-,

DIFOUT to GND......................................-0.3V to (V

DD

+ 0.3V)

PV

DD

1, PV

DD

2 to V

DD

...........................................-0.3V to +0.3V

PV

DD

1, PV

DD

2 to GND...............................-0.3V to (V

DD

+ 0.3V)

PGND1, PGND2 to GND .......................................-0.3V to +0.3V

COMP, REF, ITEC, OT, UT, INTOUT, DIFOUT,

BFB-, BFB+, AOUT Short to GND .............................Indefinite

Peak LX Current (MAX1978) (Note 1).................................±4.5A

Peak LX Current (MAX1979) (Note 1)....................................+9A

Continuous Power Dissipation (T

A

= +70°C)

48-Lead Thin QFN-EP

(derate 26.3mW/°C above +70°C) (Note 2) .................2.105W

Operating Temperature Ranges

MAX1978ETM ..................................................-40°C to +85°C

MAX1979ETM ..................................................-40°C to +85°C

Maximum Junction Temperature .....................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Note 1: LX has internal clamp diodes to PGND and PV

DD

. Applications that forward bias these diodes should not exceed the IC’s package power dissipation limits.

Note 2: Solder underside metal slug to PC board ground plane.

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V

DD

= PV

DD

1 = PV

DD

2 =

SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T

A

unless otherwise noted. Typical values at T

A

= +25°C.)

= 0°C to +85°C,

PARAMETER

Input Supply Range

SYMBOL

V

DD

CONDITIONS MIN

3.0

TYP MAX

5.5

UNITS

V

Output Voltage Range

Maximum TEC Current

Reference Voltage

Reference Load Regulation

Current-Sense Threshold

NFET On-Resistance

PFET On-Resistance

NFET Leakage

V

OUT

I

TEC(MAX)

V

REF

∆V

REF

R

DS(ON-N)

R

DS(ON-P)

I

LEAK(N)

V

DD

= 5V, I

TEC

= 0 to ±3A,

V

OUT

= V

OS1

- V

OS2

(MAX1978)

V

DD

= 5V, I

TEC

= 0 to 6A,

V

OUT

= V

OS1

(MAX1979)

V

DD

= 3V, I

TEC

= 0 to ±3A,

V

OUT

= V

OS1

- V

OS2

(MAX1978)

V

DD

= 3V, I

TEC

= 0 to 6A,

V

OUT

= V

OS1

(MAX1979)

MAX1978

MAX1979

V

DD

= 3V to 5.5V, I

REF

= 150µA

V

DD

= 3V to 5.5V, I

REF

= +10µA to -1mA

V

MAXI_

= V

REF

V

OS1

< V

CS

V

MAXI_

= V

REF

/3

V

OS1

> V

CS

V

MAXI_

= V

REF

V

MAXI_

= V

REF

/3

V

DD

= 5V, I = 0.5A

V

DD

= 3V, I = 0.5A

V

DD

= 5V, I = 0.5A

V

DD

= 3V, I = 0.5A

V

LX

= V

DD

= 5V, T

A

= +25

°C

V

LX

= V

DD

= 5V, T

A

= +85

°C

-4.3

-2.3

1.485

135

40

135

40

+4.3

4.3

+2.3

2.3

1.2

150

50

150

50

0.04

0.06

0.06

0.09

0.02

1

±3

6

1.500

1.515

5

160

60

160

60

0.07

0.08

0.10

0.12

10

V

A

V mV mV

µA

2 _______________________________________________________________________________________

Integrated Temperature

Controllers for Peltier Modules

ELECTRICAL CHARACTERISTICS (continued)

(V

DD

= PV

DD

1 = PV

DD

2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T

A

= 0°C to +85°C, unless otherwise noted. Typical values at T

A

= +25°C.)

PARAMETER

PFET Leakage

No-Load Supply Current

Shutdown Supply Current

Thermal Shutdown

UVLO Threshold

Switching Frequency Internal

Oscillator

OS1, OS2, CS Input Current

SHDN, FREQ Input Current

SYMBOL

I

LEAK(P)

CONDITIONS

V

LX

= 0, T

A

= +25

°C

V

LX

= 0, T

A

= +85

°C

I

DD(NO

V

DD

= 5V

LOAD)

V

DD

= 3.3V

I

DD-SD

SHDN = GND, V

DD

T

S H U TD OWN

Hysteresis = 15

°C

= 5V (Note 3)

V

UVLO

V

DD

rising

V

DD

falling

FREQ = GND f

SW-INT

FREQ=V

DD

I

OS1

, I

OS2

,

I

CS

0 or V

DD

I

SHDN

,

I

FREQ

0 or V

DD

MIN

2.4

2.25

450

800

-100

-5

TYP

0.02

1

30

15

2

165

2.6

2.5

500

1000

MAX

10

50

30

3

2.8

2.75

650

1200

+100

+5

UNITS

µA mA mA

°C

V kHz

µA

µA

SHDN, FREQ Input Low Voltage

V

IL

V

DD

= 3V to 5.5V

0.25

×

V

DD

V

SHDN, FREQ Input High Voltage

V

IH

V

DD

= 3V to 5.5V

0.75

×

V

DD

V

MAXV Threshold Accuracy

MAXV, MAXIP, MAXIN

Input Bias Current

CTLI Gain

CTLI Input Resistance

Error Amp Transconductance

ITEC Accuracy

ITEC Load Regulation

V

MAXV

= V

REF

✕ 0.67,

V

OS1

to V

OS2

= ±4V, V

DD

= 5V

V

MAXV

= V

REF

✕ 0.33,

V

OS1

to V

OS2

= ±2V, V

DD

= 3V

I

MAXV-BIAS

,

I

MAXI_-BIAS

A

CTLI

R

CTLI g m

V

MAXV

= V

MAXI_

= 0.1V or 1.5V

V

CTLI

= 0.5V to 2.5V (Note 4)

1M

Ω terminated at REF

∆V

ITEC

V

OS1

to V

CS

= +100mV or -100mV

V

OS1

to V

CS

= +100mV or -100mV,

I

ITEC

= ±10µA

-1

-2

-0.1

9.5

0.5

50

-10

-0.1

10

1.0

100

+1

+2

+0.1

10.5

2.0

175

+10

+0.1

%

µA

V/V

M

µS

%

%

Instrumentation Amp Input Bias

Current

Instrumentation Amp Offset

Voltage

Instrumentation Amp Offset-

Voltage Drift with Temperature

Instrumentation Amp Preset

Gain

I

DIF-BIAS

V

DIF-OS

A

DIF

V

DD

= 3V to 5.5V

V

DD

= 3V to 5.5V

R

LOAD

= 10k

Ω to REF

-10

-200

45

0

+20

0.1

50

+10

+200

55 nA

µV

µV/°C

V/V

_______________________________________________________________________________________ 3

Integrated Temperature

Controllers for Peltier Modules

ELECTRICAL CHARACTERISTICS (continued)

(V

DD

= PV

DD

1 = PV

DD

2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T

A

= 0°C to +85°C, unless otherwise noted. Typical values at T

A

= +25°C.)

PARAMETER

Integrator Amp Open-Loop Gain

Integrator Amp Gain Bandwidth

SYMBOL CONDITIONS

A

OL-INT

R

LOAD

= 10k

Ω to REF

Integrator Amp CMRR CMRR

INT

Integrator Amp Input Bias Current I

INT-BIAS

V

DD

= 3V to 5.5V

Integrator Amp Voltage Offset V

INT-OS

GBW

INT

V

DD

= 3V to 5.5V

Undedicated Chopper Amp

Open-Loop Gain

A

OL-AIN

R

LOAD

= 10k

Ω to REF

Undedicated Chopper Amp

CMRR

CMRR

AIN

Undedicated Chopper Amp Input

Bias Current

Undedicated Chopper Amp

Offset Voltage

I

AIN-BIAS

V

AIN-OS

V

V

DD

DD

= 3V to 5.5V

= 3V to 5.5V

Undedicated Chopper Amp Gain

Bandwidth

Undedicated Chopper Amp

Output Ripple

BFB_ Buffer Error

UT and OT Leakage Current

UT and OT Output Low Voltage

UT Trip Threshold

OT Trip Threshold

GBW

V

I

RIPPLE

LEAK

V

AIN

OL

A = 5

MIN

-3

-10

-200

TYP

120

100

+0.1

100

120

85

0

+10

100

20

MAX

1

+3

+10

+200

C

L OA D

< 100p F -200 0 +200

V

UT

= V

OT

= 5.5V 1

Sinking 4mA

FB+ - FB- (see Typical Application Circuit)

FB+ - FB- (see Typical Application Circuit)

50

-20

20

150

µV

µA mV mV mV

UNITS

dB dB nA mV kHz dB dB nA

µV kHz mV

4 _______________________________________________________________________________________

Integrated Temperature

Controllers for Peltier Modules

ELECTRICAL CHARACTERISTICS

(V

DD

= PV

DD

1 = PV

DD

2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T

A

= -40°C to +85°C, unless otherwise noted.) (Note 5)

PARAMETER

Input Supply Range

Output Voltage Range

Maximum TEC Current

Reference Voltage

Reference Load Regulation

Current-Sense Threshold

No-Load Supply Current

Shutdown Supply Current

UVLO Threshold

Switching Frequency Internal

Oscillator

OS1, OS2, CS Input Current

SHDN, FREQ Input Current

SYMBOL CONDITIONS

V

DD

V

DD

= 5V, I

TEC

= 0 to ±3A,

V

OUT

= V

OS1

-V

OS2

(MAX1978)

I

I

I f

DD(NO

LOAD)

DD-SD

V

V

OUT

TEC(MAX)

V

∆V

REF

REF

UVLO

SW-INT

V

DD

= 5V, I

TEC

= 0 to 6A,

V

OUT

= V

OS1

(MAX1979)

V

DD

= 3V, I

TEC

= 0 to ±3A,

V

OUT

= V

OS1

- V

OS2

(MAX1978)

V

DD

= 3V, I

TEC

= 0 to 6A,

V

OUT

= V

OS1

(MAX1979)

MAX1978

MAX1979

V

DD

= 3V to 5.5V, I

REF

= 150µA

V

DD

= 3V to 5.5V,

I

REF

= 10µA to -1mA

V

V

OS1

OS1

< V

> V

CS

CS

V

MAXI_

= V

REF

V

MAXI_

= V

REF

/3

V

MAXI_

= V

REF

V

MAXI_

= V

REF

/3

V

DD

= 5V

V

DD

= 3.3V

SHDN = GND, V

DD

= 5V (Note 3)

V

DD

rising

V

DD

falling

FREQ = GND

FREQ = V

DD

I

OS1

, I

OS2

,

I

CS

I

SHDN

,

I

F REQ

0 or V

DD

0 or V

DD

MIN

3

-4.3

-2.3

1.475

135

40

135

40

2.4

2.25

450

800

-100

-5

MAX UNITS

5.5

V

+4.3

4.3

+2.3

2.3

±3

6

1.515

5

160

60

160

60

50

30

3

2.8

2.75

650

1200

+100

+5

V

A

V mV mV mA mA

V kHz

µA

µA

SHDN, FREQ Input Low Voltage

V

IL

V

DD

= 3V to 5.5V

0.25 ✕

V

DD

V

SHDN, FREQ Input High Voltage

V

IH

V

DD

= 3V to 5.5V

0.75 ✕

V

DD

V

_______________________________________________________________________________________ 5

Integrated Temperature

Controllers for Peltier Modules

ELECTRICAL CHARACTERISTICS (continued)

(V

DD

= PV

DD

1 = PV

DD

2 = SHDN = 5V, FREQ = GND, CTLI = FB+ = FB- = MAXV = MAXIP = MAXIN = REF, T

A

= -40°C to +85°C, unless otherwise noted.) (Note 5)

PARAMETER MIN MAX UNITS

MAXV Threshold Accuracy

MAXV, MAXIP, MAXIN

Input Bias Current

CTLI Gain

CTLI Input Resistance

Error Amp Transconductance

SYMBOL CONDITIONS

V

MAXV

= V

REF

✕ 0.67,

V

OS1

to V

OS2

= ±4V, V

DD

= 5V

V

MAXV

= V

REF

0.33, V

OS1

to V

OS2

= ±2V,

V

DD

= 3V

I

MAXV-BIAS

,

I

MAXI_-BIAS

A

CTLI

R

CTLI g m

V

MAXV

= V

MAXI_

= 0.1V or 1.5V

V

CTLI

= 0.5V to 2.5V (Note 4)

1M

Ω terminated at REF

-1

-2

-0.1

9.5

0.5

50

+1

+2

+0.1

10.5

2.0

175

%

µA

V/V

M

µS

ITEC Accuracy V

OS1

to V

CS

= +100mV or -100mV -10 +10 %

ITEC Load Regulation

∆V

ITEC

V

OS1

to V

CS

= +100mV or

-100mV, I

ITEC

= ±10µA

-0.125

+0.125

Instrumentation Amp

Input Bias Current

Instrumentation Amp

Offset Voltage

I

DIF-BIAS

V

DIF-OS

V

DD

= 3V to 5.5V

-10

-200

+10

+200

Instrumentation Amp

Preset Gain

Integrator Amp Input Bias Current I

INT-BIAS

V

DD

= 3V to 5.5V

Integrator Amp Voltage Offset V

INT-OS

V

DD

= 3V to 5.5V

Undedicated Chopper Amp Input

Bias Current

I

A

DIF

AIN-BIAS

R

V

LOAD

DD

= 10k

Ω to REF

= 3V to 5.5V

Undedicated Chopper Amp

Offset Voltage

BFB_ Buffer Error

UT and OT Leakage Current

UT and OT Output Low Voltage

V

I

AIN-OS

LEAK

V

OL

V

C

V

DD

LOAD

UT

= 3V to 5.5V

< 100pF

= V

OT

Sinking 4mA

45

-3

-10

-200

-200

55

1

+3

+10

+200

+200

= 5.5V 1

150

% nA

µV

V/V nA mV nA

µV

µV

µA mV

Note 3: Includes power FET leakage.

Note 4: CTLI gain is defined as:

A

CTLI

=

(

(

V

CTLI

V

REF

V

OSI

V

CS

)

)

Note 5: Specifications to -40°C are guaranteed by design, not production tested.

6 _______________________________________________________________________________________

Integrated Temperature

Controllers for Peltier Modules

Typical Operating Characteristics

(V

DD

= 5V, V

CTLI

= 1V, V

FREQ

= GND, RTEC = 1

Ω, circuit of Figure 1, T

A

= +25°C, unless otherwise noted.)

50

40

30

20

10

0

0

90

80

70

60

EFFICIENCY vs. TEC CURRENT

V

DD

= 5V

R

TEC

= 1.1

0.5

1.0

1.5

TEC CURRENT (A)

2.0

2.5

80

70

60

50

40

30

20

10

0

0

EFFICIENCY vs. TEC CURRENT

V

DD

= 3.3V

R

TEC

= 0.855

0.5

1.0

1.5

TEC CURRENT (A)

2.0

2.5

V

OS2

100mV/div

AC-COUPLED

V

OS1

100mV/div

AC-COUPLED

V

OS1

- V

OS1

50mV/div

OUTPUT-VOLTAGE

RIPPLE WAVEFORMS

400ns/div

INPUT SUPPLY RIPPLE

V

DD

20mV/div

AC-COUPLED

TEC CURRENT vs. CTLI VOLTAGE

V

CTLI

200mV/div

-0V

-0A

V

CTLI

1V/div

I

TEC

2A/div

I

TEC

500mA/div

ZERO-CROSSING TEC CURRENT

1.5V

0A

200ns/div

20ms/div 1ms/div

V

ITEC

vs. TEC CURRENT

1.0

0.5

0

-3

3.0

2.5

2.0

1.5

-2 -1 0 1

TEC CURRENT (A)

2 3

1.010

1.005

1.000

TEC CURRENT vs. TEMPERATURE

0.995

0.990

-40 -20 0 20

I

TEC

R

= 1A

SENSE

= 0.68

40

TEMPERATURE (

°C)

60 80

SWITCHING FREQUENCY vs. TEMPERATURE

508

506

504

502

500

498

496

494

492

-40

V

CTLI

R

TEC

= 1.5V

= 1

-20 0 20 40

TEMPERATURE (

°C)

60 80

_______________________________________________________________________________________

7

Integrated Temperature

Controllers for Peltier Modules

Typical Operating Characteristics (continued)

(V

DD

= 5V, V

CTLI

= 1V, V

FREQ

= GND, RTEC = 1

Ω, circuit of Figure 1, T

A

= +25°C, unless otherwise noted.)

0

-5

-10

-15

-20

10

5

-25

-30

-35

3.0

SWITCHING FREQUENCY CHANGE vs. INPUT SUPPLY

3.5

4.0

V

DD

(V)

4.5

5.0

5.5

REFERENCE LOAD REGULATION

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

SINK SOURCE

-1.0

-0.4

-0.2

0 0.2

0.4

0.6

REFERENCE LOAD CURRENT (mA)

0.8

1.0

1.0

0.5

0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

3.0

REFERENCE VOLTAGE CHANGE vs. INPUT SUPPLY

3.5

4.0

V

DD

(V)

4.5

5.0

5.5

ATO VOLTAGE vs. THERMISTOR TEMPERATURE

2.0

1.5

1.0

0.5

0

-10

4.5

4.0

3.5

3.0

2.5

NTC, 10k

Ω THERMISTOR

CIRCUIT IN FIGURES 1 AND 2

0 10 20 30 40

THERMISTOR TEMPERATURE (

°C)

50 60

REFERENCE VOLTAGE CHANGE vs. TEMPERATURE

3

2

1

0

-1

-2

-3

-4

-40 -20 0 20 40

TEMPERATURE (

°C)

60 80

V

SHDN

5V/div

STARTUP AND SHUTDOWN WAVEFORMS

I

TEC

500mA/div

I

DD

200mA/div

100

µs/div

CTLI STEP RESPONSE INPUT SUPPLY STEP RESPONSE

THERMAL STABILITY,

COOLING MODE

V

CTLI

1V/div

1.5V

V

DD

2V/div

0V

TEMPERATURE

0.001

°C/div

I

TEC

1A/div

0A

I

TEC

20mA/div

1A

I

T

TEC

A

= +25

°C

= +45

°C

1ms/div 10ms/div

8 _______________________________________________________________________________________

4s/div

Integrated Temperature

Controllers for Peltier Modules

Typical Operating Characteristics (continued)

(V

DD

= 5V, V

CTLI

= 1V, V

FREQ

= GND, RTEC = 1

Ω, circuit of Figure 1, T

A

= +25°C, unless otherwise noted.)

THERMAL STABILITY,

ROOM TEMPERATURE

THERMAL STABILITY,

HEATING MODE

TEMPERATURE ERROR vs. AMBIENT TEMPERATURE

0.03

0.02

0.01

TEMPERATURE

0.001

°C/div

TEMPERATURE

0.001

°C/div

0

-0.01

I

T

TEC

A

= +25

°C

= +25

°C

T

T

TEC

A

= +25

°C

= +5

°C

-0.02

4s/div 4s/div

-0.03

-20 -10 0 10 20 30 40

AMBIENT TEMPERATURE (

°C)

50

Pin Description

PIN

1

NAME

OS2

FUNCTION

Output Sense 2. OS2 senses one side of the differential TEC voltage. OS2 is a sense point, not a power output.

2, 8, 29,

35

N.C.

Not Internally Connected

3, 5

4, 6, 9

7, 10

11

12

13

PGND2

Power Ground 2. Internal synchronous rectifier ground connections. Connect all PGND pins together at power ground plane.

Inductor 2 Connection. Connect all LX2 pins together. Connect LX2 to LX1 when using the MAX1979.

LX2

PV

DD

2

Power 2 Inputs. Must be same voltage as V

DD

. Connect all PV

DD

2 inputs together at the V

DD

power plane.

Bypass to PGND2 with a 10µF ceramic capacitor.

SHDN

Shutdown Control Input. Active-low shutdown control.

OT

Over-Temperature Alarm. Open-drain output pulls low if temperature feedback rises 20mV

(typically +1.5°C) above the set-point voltage.

UT

Under-Temperature Alarm. Open-drain output pulls low if temperature feedback falls 20mV

(typically +1.5°C) below the set-point voltage.

INTOUT Integrator Amp Output. Normally connected to CTLI.

INTIntegrator Amp Inverting Input. Normally connected to DIFOUT through thermal-compensation network.

14

15

16, 25,

26, 42, 43

17

18

19

20

21

22

GND Analog Ground. Connect all GND pins to analog ground plane.

DIFOUT Chopper-Stabilized Instrumentation Amp Output. Differential gain is 50 ✕ (FB+ - FB-).

FBChopper-Stabilized Instrumentation Amp Inverting Input. Connect to thermistor bridge.

FB+ Chopper-Stabilized Instrumentation Amp Noninverting Input. Connect to thermistor bridge.

BFBChopper-Stabilized Buffered FB- Output. Used to monitor thermistor bridge voltage.

BFB+ Chopper-Stabilized Buffered FB+ Output. Used to monitor thermistor bridge voltage.

AIN+ Undedicated Chopper-Stabilized Amplifier Noninverting Input

_______________________________________________________________________________________ 9

Integrated Temperature

Controllers for Peltier Modules

Pin Description (continued)

PIN

23

24

27, 30

28, 31, 33

32, 34

36

37

38

39

40

41

44

45

46

47

48

EP

NAME FUNCTION

AINUndedicated Chopper-Stabilized Amplifier Inverting Input

AOUT Undedicated Chopper-Stabilized Amplifier Output

PV

DD

LX1

1

Power 1 Inputs. Must be same voltage as V

DD

. Connect all PV

DD

1 inputs together at the V

DD

power plane.

Bypass to PGND1 with a 10µF ceramic capacitor.

Inductor 1 Connection. Connect all LX1 pins together. Connect LX1 to LX2 when using the MAX1979.

PGND1

Power Ground 1. Internal synchronous-rectifier ground connections. Connect all PGND pins together at power ground plane.

FREQ Switching-Frequency Select. Low = 500kHz, high = 1MHz.

ITEC

MAXIN

TEC Current Monitor Output. The ITEC output voltage is a function of the voltage across the TEC currentsense resistor. V

ITEC

= 1.50V + (V

OS1

- V

CS

) ✕ 8.

COMP Current-Control Loop Compensation. For most designs, connect a 10nF capacitor from COMP to GND.

MAXIP Maximum Positive TEC Current. Connect MAXIP to REF to set default positive current limit +150mV / R

SENSE

.

Maximum Negative TEC Current. Connect MAXIN to REF to set default negative current limit

-150mV / R

SENSE

. Connect MAXIN to GND when using the MAX1979.

MAXV

Maximum Bipolar TEC Voltage. Connect an external resistive divider from REF to GND to set the maximum voltage across the TEC. The maximum TEC voltage is 4 ✕ V

MAXV

.

V

DD

Analog Supply Voltage Input. Bypass to GND with a 10µF ceramic capacitor.

CTLI

TEC Current-Control Input. Sets differential current into the TEC. Center point is 1.50V (no TEC current).

Connect to INTOUT when using the thermal control loop. I

TEC

= (V

OS1

- V

CS

) / R

SENSE

= (V

CTLI

- 1.50) / (10 ✕

R

SENSE

). When (V

CLTI

- V

REF

) > 0, V

OS2

> V

OS1

> V

CS

.

REF 1.5V Reference Voltage Output. Bypass REF to GND with a 1µF ceramic capacitor.

CS

Current-Sense Input. The current through the TEC is monitored between CS and OS1. The maximum TEC current is given by 150mV / R

SENSE

and is bipolar for the MAX1978. The MAX1979 TEC current is unipolar.

OS1

EP

Output Sense 1. OS1 senses one side of the differential TEC voltage. OS1 is a sense point, not a power output.

Exposed Paddle. Solder evenly to the PCB ground plane to maximize thermal performance.

10 ______________________________________________________________________________________

REF

1.5V

REFERENCE

OFF

ON

SHDN

Integrated Temperature

Controllers for Peltier Modules

Functional Diagram

FREQ

V

DD

PV

DD

1

3V TO 5.5V

MAXV MAX V

TEC

V

MAXV

=

x 4

LX1

MAXIP

MAXIN

MAX I

TEC

= (V

MAXIP

/

V

REF

) x (0.15V/R

SENSE

)

MAX I

TEC

= (V

MAXIN

/

V

REF

) x (0.15V/R

SENSE

)

PGND1

CS

ITEC

CTLI

COMP

GND

OT

UT

MAX1978

CS

OS1

REF

REF + 1V

50R

PGND2

R

50R

R

REF

REF - 1V

REF

INTOUT INTAINAOUT AIN+ DIFOUT FB+ FB-

BFB-

BFB+

OS1

OS2

PV

DD

2

LX2

V

DD

R

SENSE

______________________________________________________________________________________ 11

Integrated Temperature

Controllers for Peltier Modules

Detailed Description

Power Stage

The power stage of the MAX1978/MAX1979 thermoelectric cooler (TEC) temperature controllers consists of two switching buck regulators that operate together to directly control TEC current. This configuration creates a differential voltage across the TEC, allowing bidirectional TEC current for controlled cooling and heating. Controlled cooling and heating allow accurate

TEC temperature control within the tight tolerances of laser driver specifications.

The voltage at CTLI directly sets the TEC current. The internal thermal-control loop drives CTLI to regulate

TEC temperature. The on-chip thermal-control circuitry can be configured to achieve temperature control stability of 0.001°C. Figure 1 shows a typical TEC thermalcontrol circuit.

Ripple Cancellation

Switching regulators like those used in the

MAX1978/MAX1979 inherently create ripple voltage on each common-mode output. The regulators in the

MAX1978 switch in phase and provide complementary in-phase duty cycles, so ripple waveforms at the differential TEC output are greatly reduced. This feature suppresses ripple currents and electrical noise at the TEC to prevent interference with the laser diode while minimizing output capacitor filter size.

V

DD

REF

10

µF

10

µF

1

µF

10

µF

THERMISTOR

VOLTAGE

MONITOR

80.6k

REF

69.8k

1%

UNDERTEMP

ALARM

OVERTEMP

ALARM

DC CURRENT

MONITOR

1

µF

105k

1%

0.01

µF

20k

1%

V

DD

COMP

UT

SHDN

PV

DD

1 PV

DD

2

OT

ITEC

MAX1978

REF MAXV MAXIN MAXIP

LX1

CS

OS1

BFB-

AIN-

AOUT

OS2

LX2

AIN+

CTLI

FREQ

GND PGND2 PGND1 INTOUT INT-

FB-

DIFOUT FB+

4.7

µF

3

µH

3

µH

TEC

0.068

1

µF

REF

10k

100k

100k

Ω 10

µF

0.47

µF

20k

0.047

µF

1M

1

µF

THERMAL

FEEDBACK

Figure 1. MAX1978 Typical Application Circuit

12 ______________________________________________________________________________________

Switching Frequency

FREQ sets the switching frequency of the internal oscillator. The oscillator frequency is 500kHz when FREQ =

GND. The oscillator frequency is 1MHz when FREQ =

V

DD

. The 1MHz setting allows minimum inductor and filter-capacitor values. Efficiency is optimized with the

500kHz setting.

Voltage and Current-Limit Settings

The MAX1978 and MAX1979 provide settings to limit the maximum differential TEC voltage. Applying a voltage to MAXV limits the maximum voltage across the

TEC to ±(4 ✕ V

MAXV

).

The MAX1978 also limits the maximum positive and negative TEC current. The voltages applied to MAXIP and MAXIN independently set the maximum positive and negative output current limits. The MAX1979 controls TEC current in only one direction, so the maximum current is set only with MAXIP. MAXIN must be connected to GND when using the MAX1979.

Chopper-Stabilized Instrumentation

Amplifier

The MAX1978 and MAX1979 include a chopped input instrumentation amplifier with a fixed gain of 50. An external thermal sensor, typically a thermistor, is connected to one of the amp’s inputs. The other input is connected to a voltage that represents the temperature set point. This set point can be derived from a resistordivider network or DAC. The included instrumentation amplifier provides low offset drift needed to prevent temperature set-point drift with ambient temperature changes. Temperature stability of 0.001°C can be achieved over a 0°C to +50°C ambient temperarure range by using the amplifier as in Figure 1. DIFOUT is the instrumentation amplifier output and is proportional to 50 times the difference between the set-point temperature and the TEC temperature. This difference is commonly referred to as the “error signal”. For best temperature stability, derive the set-point voltage from the same reference that drives the thermistor (usually the MAX1978/MAX1979 REF output). This is called a

“ratiometric” or “bridge” connection. The bridge connection optimizes stability by eliminating REF drift as an error source. Errors at REF are nullified because they affect the thermistor and set point equally.

The instrumentation amplifier utilizes a chopped input scheme to minimize input offset voltage and drift. This generates output ripple at DIFOUT that is equal to the chop frequency. The DIFOUT peak-to-peak ripple amplitude is typically 100mV but has no effect on temperature stability. DIFOUT ripple is filtered by the integrator in the following stage. The chopper frequency is

Integrated Temperature

Controllers for Peltier Modules

derived from, and is synchronized to, the switching frequency of the power stage.

Integrator Amplifier

An on-chip integrator amplifier is provided on the

MAX1978/MAX1979. The noninverting terminal of the amplifier is connected internally to REF. Connect an appropriate network of resistors and capacitors between

DIFOUT and INT-, and connect INTOUT to CTLI for typical operation. CTLI directly controls the TEC current magnitude and polarity. The thermal-control-loop dynamics are set by the integrator input and feedback components. See the Applications Information section for details on thermal-loop compensation.

Current Monitor Output

ITEC provides a voltage output proportional to the TEC current, ITEC (see the Functional Diagram):

V

ITEC

= 1.5V + 8 ✕ (V

OS1

- V

CS

)

Over- and Under-Temperature Alarms

The MAX1978/MAX1979 provide open-drain status outputs that alert a microcontroller when the TEC temperature is over or under the set-point temperature. OT and

UT pull low when V

(FB1+ - FB-) is more than 20mV. For a typical thermistor connection, this translates to approximately 1.5°C error.

Reference Output

The MAX1978/MAX1979 include an on-chip 1.5V voltage reference accurate to 1% over temperature.

Bypass REF with 1µF to GND. REF can be used to bias an external thermistor for temperature sensing as shown in Figures 1 and 2. Note that the 1% accuracy of

REF does not limit the temperature stability achievable with the MAX1978/MAX1979. This is because the thermistor and set-point bridge legs are intended to be driven ratiometrically by the same reference source (REF).

Variations in the bridge-drive voltage then cancel out and do not generate errors. Consequently, 0.001°C stable temperature control is achievable with the

MAX1978/MAX1979 reference.

An external source can be used to bias the thermistor bridge. For best accuracy, the common-mode voltage applied to FB+ and FB- should be kept between 0.5V

and 1V, however the input range can be extended from

0.2V to V

DD

/ 2 if some shift in instrumentation amp offset

(approximately -50µV/V) can be tolerated. This shift remains constant with temperature and does not contribute to set-point drift.

______________________________________________________________________________________ 13

Integrated Temperature

Controllers for Peltier Modules

V

DD

REF

10

µF

10

µF

1

µF

10

µF

THERMISTOR

VOLTAGE

MONITOR

80.6k

REF

69.8k

1%

UNDERTEMP

ALARM

OVERTEMP

ALARM

DC CURRENT

MONITOR

1

µF

0.01

µF

20k

1%

V

DD

COMP

UT

SHDN

PV

DD

1 PV

DD

2

OT

ITEC

MAX1979

REF MAXV MAXIN MAXIP

LX1

LX2

CS

OS1

BFB-

AIN-

AOUT

OS2

4.7

µF

3

µH

105k

1%

AIN+

CTLI

FREQ

GND PGND2 PGND1 INTOUT INTDIFOUT

FB-

FB+

TEC

0.03

REF

10k

100k

Ω 10

µF

0.47

µF

20k

100k

0.047

µF

1M

1

µF

THERMAL

FEEDBACK

Figure 2. MAX1979 Typical Application Circuit

Buffered Outputs, BFB+ and BFB-

BFB+ and BFB- output a buffered version of the voltage that appears on FB+ and FB-, respectively. The buffers are typically used in conjunction with the undedicated chopper amplifier to create a monitor for the thermistor voltage/TEC temperature (Figures 1 and 2). These buffers are unity-gain chopper amplifiers and exhibit output ripple. Each output can be either integrated or filtered to remove the ripple content if necessary.

Undedicated Chopper-Stabilized Amplifier

In addition to the chopper amplifiers at DIFOUT and

BFB_, the MAX1978/MAX1979 include an additional chopper amplifier at AOUT. This amplifier is uncommitted but is intended to provide a temperature-proportional analog output. The thermistor voltage typically is connected to the undedicated chopper amplifier through the included buffers BFB+ and BFB-. Figure 3 shows how to configure the undedicated amplifier as a thermistor voltage monitor. The output voltage at AOUT is not precisely linear, because the thermistor is not linear. AOUT is also chopper stabilized and exhibits output ripple and can be either integrated or filtered to remove the ripple content if necessary.

14 ______________________________________________________________________________________

x50

MAX1978

MAX1979

AIN+

AOUT

AIN-

BFB-

FB-

FB+

REF

69.8k

1%

105k

1%

80.6k

1%

20k

1%

V

SETPOINT

Integrated Temperature

Controllers for Peltier Modules

1

µF

REF

10k

Figure 3. Thermistor Voltage Monitor

Design Procedure

Inductor Selection

Small surface-mount inductors are ideal for use with the

MAX1978/MAX1979. Select the output inductors so that the LC resonant frequency of the inductance and the output capacitance is less than 1/5 the selected switching frequency. For example, 3.0µH and 1µF have a resonance at 92kHz, which is adequate for 500kHz operation.

22µF to 100µF ceramic capacitor between the V

DD power plane and power ground. Insufficient supply bypassing can result in supply bounce and degraded accuracy.

Compensation Capacitor

Include a compensation capacitor to ensure currentpower control-loop stability. Select the capacitor so that the unity-gain bandwidth of the current-control loop is less than or equal to 10% the resonant frequency of the output filter:

C

COMP

 g m

 f

BW



×



2

×

24

R

×

R

SENSE

SENSE

+

R

TEC

)

 where: f

BW

= unity-gain bandwidth frequency g m

= loop transconductance, typically 100µA/V

C

COMP

= value of the compensation capacitor

R

TEC

= TEC series resistance

R

SENSE

= sense resistor

Setting Voltage and Current Limits

Consider TEC parameters to guarantee a robust design. These parameters include maximum positive current, maximum negative current, and the maximum voltage allowed across the TEC. These limits should be used to set MAXIP, MAXIN, and MAXV voltages.

Setting Max Positive and Negative TEC Current

MAXIP and MAXIN set the maximum positive and negative TEC currents, respectively. The default current limit is ±150mV / R

SENSE when MAXIP and MAXIN are connected to REF. To set maximum limits other than the defaults, connect a resistor-divider from REF to GND to set V

MAXI_

. Use resistors in the 10k

Ω to 100kΩ range.

V

MAXI_ is related to ITEC by the following equations:

¡ f

LC

=

2

π

1

LC where: f

LC

= resonant frequency of output filter.

Capacitor Selection

Filter Capacitors

Decouple each power-supply input (V

DD

, PV

DD

1, and

PV

DD

2) with a 10µF ceramic capacitor close to the supply pins. If long supply lines separate the source supply from the MAX1978/MAX1979, or if the source supply has high output impedance, place an additional

V

MAXIP

= 10 (I

TECP(MAX)

✕ R

SENSE

)

V

MAXIN

= 10 (I

TECN(MAX)

✕ R

SENSE

) where I

TECP(MAX) is the maximum positive TEC current and I

TECN(MAX) is the maximum negative TEC current.

Positive TEC current occurs when CS is less than OS1:

I

TEC

✕ R

SENSE

= CS - OS1 when I

TEC

< 0.

I

TEC

R

SENSE

= OS1 - CS when I

TEC

> 0.

______________________________________________________________________________________ 15

Integrated Temperature

Controllers for Peltier Modules

The MAX1979 controls the TEC current in only one direction (unipolar). Set the maximum unipolar TEC current by applying a voltage to MAXIP. Connect MAXIN to

GND when using the MAX1979. The equation for setting MAXIP is the same for the MAX1978 and

MAX1979. Do not exceed the positive or negative current-limit specifications on the TEC. Refer to the TEC manufacturer’s data sheet for these limits.

Setting Max TEC Voltage

Apply a voltage to MAXV to control the maximum differential TEC voltage. MAXV can vary from 0 to REF. The voltage across the TEC is four times V

MAXV and can be positive or negative.

FB-

REF

MAX1978

MAX1979

FB+

C

REF

V

SETPOINT

V

THERMISTOR

|V

OS1

- V

OS2

| = 4

V

MAXV

Use resistors from 10k

Ω to 100kΩ to form a voltagedivider to set V

MAXV

.

Thermal-Control Loop

The MAX1978/MAX1979 provide all the necessary amplifiers needed to create a thermal-control loop.

Typically, the chopper-stabilized instrumentation amplifier generates an error signal and the integrator amplifier is used to create a PID controller. Figure 4 shows an example of a simple PID implementation. The error signal needed to control the loop is generated from the difference between the set point and the thermistor voltage. The desired set-point voltage can be derived from a potentiometer, DAC, or other voltage source.

Figure 5 details the required connections. Connect the output of the PID controller to CTLI. For details, see the

Applications Information section.

FB-

REF

C

REF

MAX1978

MAX1979

FB+

V

SETPOINT

DAC

DIGITAL

INPUT

V

THERMISTOR

Figure 5. The Set Point can be Derived from a Potentiometer or a DAC

Control Inputs/Outputs

TEC Current Control

The voltage at CTLI directly sets the TEC current. CTLI typically is driven from the output of a temperature-control circuit C

INTOUT

. For the purposes of the following equations, it is assumed that positive TEC current is heating.

C3

The transfer function relating current through the TEC

(I

TEC

) and V

CTLI is given by:

I

TEC

= (V

CTLI

- V

REF

) / (10 ✕ R

SENSE

)

C1

R1

INT-

R3

C2 where V

REF is 1.50V

and I

TEC

= (V

OS1

- V

CS

) / R

SENSE

V

CTLI is centered around REF (1.50V). I

TEC is zero when

V

CTLI

= 1.50V. When V

CTLI

> 1.50V, the MAX1978 is heating. Current flow is from OS2 to OS1. The voltages are:

DIFOUT

R2

INTOUT

V

OS2

> V

OS1

> V

CS

REF

Figure 4. Proportional Integral Derivative Controller

when V

CTLI

< 1.50V, current flows from OS1 to OS2:

V

OS2

< V

OS1

< V

CS

16 ______________________________________________________________________________________

Integrated Temperature

Controllers for Peltier Modules

Shutdown Control

Drive SHDN low to place the MAX1978/MAX1979 in a power-saving shutdown mode. When the MAX1978/

MAX1979 are in shutdown, the TEC is off (V

OS1 and

V

OS2 decay to GND) and input supply current lowers to

2mA (typ).

ITEC Output

ITEC is a status output that provides a voltage proportional to the actual TEC current. ITEC = REF when TEC current is zero. The transfer function for the ITEC output:

V

ITEC

= 1.50 + 8 ✕ (V

OS1

- V

CS

)

Use ITEC to monitor the cooling or heating current through the TEC. The maximum capacitance that ITEC can drive is 100pF.

Applications Information

The MAX1978/MAX1979 drive a thermoelectric cooler inside a thermal-control loop. TEC drive polarity and power are regulated to maintain a stable control temperature based on temperature information read from a thermistor, or from other temperature-measuring devices. Carefully selected external components can achieve 0.001°C temperature stability. The MAX1978/

MAX1979 provide precision amplifiers and an integrator amplifier to implement the thermal-control loop

(Figures 1 and 2).

Connecting and Compensating the

Thermal-Control Loop

Typically, the thermal loop consists of an error amplifier and proportional integral derivative controller (PID)

(Figure 4). The thermal response of the TEC module must be understood before compensating the thermal loop. In particular, TECs generally have stronger heating capacity than cooling capacity because of the effects of waste heat. Consider this point when analyzing the TEC response.

Analysis of the TEC using a signal analyzer can ease compensation calculations. Most TECs can be crudely modeled as a two-pole system. The second pole potentially creates an oscillatory condition because of the associated 180° phase shift. A dominant pole compensation scheme is not practical because the crossover frequency (the point of the Bode plot where the gain is zero dB) must be below the TEC’s first pole, often as low as 0.02Hz. This requires an excessively large integrator capacitor and results in slow loop-transient response. A better approach is to use a PID controller, where two additional zeros are used to cancel the TEC and integrator poles. Adequate phase margin can be achieved near the frequency of the TEC’s second pole when using a PID controller. The following is an example of the compensation procedure using a PID controller.

Figure 6 details a two-pole transfer function of a typical

TEC module. This Bode plot can be generated with a signal analyzer driving the CTLI input of the

MAX1978/MAX1979, while plotting the thermistor voltage from the module. For the example module, the two poles are at 0.02Hz and 1Hz.

The first step in compensating the control loop involves selecting components R3 and C2 for highest DC gain.

Film capacitors provide the lowest leakage but can be large. Ceramic capacitors are a good compromise between low leakage and small size. Tantalum and electrolytic capacitors have the highest leakage and generally are not suitable for this application. The integrating capacitor, C2, and R3 (Figure 4) set the first zero (fz1). The specific application dictates where the first zero should be set. Choosing a very low frequency results in a very large value capacitor. Set the first zero frequency to no more than 8 times the frequency of the lowest TEC pole. Setting the frequency more than 8 times the lowest pole results in the phase falling below

-135° and may cause instability in the system. For this example, C2 = 10µF. Resistor R3 then sets the zero at

0.16Hz using the following equation: fz 1

=

1

2

π ×

C 2

×

R 3

This yields a value of R3 = 99.47k

Ω. For our example, use 100k

Ω.

Next, adjust the gain for a crossover frequency for maximum phase margin near the TEC’s second pole. From

Figure 6, the TEC bode plot, approximately 30dB of gain is needed to move the 0dB crossover point up to

1.5Hz. The error amplifier provides a fixed gain of 50, or approximately 34dB. Therefore, the integrator needs to provide -4dB of gain at 1.5Hz. C1 and R3 set the gain at the crossover frequency.

C 1

=

A

1

C 2

+

2

π ×

R 3

× f

C

______________________________________________________________________________________ 17

Integrated Temperature

Controllers for Peltier Modules

where:

A = The gain needed to move the 0dB crossover point up to the desired frequency. In this case, A = -4dB =

0.6.

f

C

= The desired crossover frequency, 1.5Hz in this example.

C1 is found to be 0.58µF; use 0.47µF.

Next, the second TEC pole must be cancelled by adding a zero. Canceling the second TEC pole provides maximum phase margin by adding positive phase to the circuit. Setting a second zero (fz2) to at least 1/5 the crossover frequency (1.5Hz/5 = 0.3Hz), and a pole (fp1) to 5 times the crossover frequency or higher (5

× 1.5Hz = 7.5Hz) ensures good phase margin, while allowing for variation in the location of the TEC’s second pole. Set the zero fz2 to 0.3Hz and calculate R2: fz 2

=

1

2

π ×

C 1

×

R 2 where fz2 is the second zero.

R2 is calculated to be 1.1M

Ω; use 1MΩ.

Now pole fp1 is added at least 5 times the crossover frequency to terminate zero fz2.

Choose fp1 = 15Hz, find R1 using the following equation: fp 1

=

1

2

π ×

C 1

×

R 1

Resistor R1 is found to be 22k

Ω, use 20kΩ

The final step is to terminate the first zero by setting the rolloff frequency with a second pole, fp2. A good choice is 2 times fp1.

Choose fp2 = 30Hz, find C3 using the following equation: fp 2

=

1

2

π ×

C 3

×

R 3 where C3 is found to be 0.05µF, use 0.047µF.

Figure 7 displays the compensated gain and phase plots for the above example.

The example given is a good place to start when compensating the thermal loop. Different TEC modules require individual testing to find their optimal compensation scheme. Other compensation schemes can be used. The above procedure should provide good results for the majority of optical modules.

TEC GAIN AND PHASE

40

30

20

10

0

-10

-20

-30

-40

-50

-60

-70

-80

0.001

0.01

0.1

1

FREQUENCY (Hz)

10

Figure 6. Bode Plot of a Generic TEC Module

90

45

-135

100

-180

0

-45

-90

COMPENSATED

TEC GAIN AND PHASE

50

40

30

20

10

0

-10

80

70

60

-20

-30

-40

-50

-60

-70

-80

0.001

90

45

0

-45

-90

-135

0.01

0.1

1

FREQUENCY (Hz)

10 100

-180

Figure 7. Compensated Thermal-Control Loop Using the TEC

Module in Figure 6

18 ______________________________________________________________________________________

INPUT

3V TO 5.5V

ON

OFF

OVERTEMP ALARM

UNDERTEMP ALARM

TEMP MONITOR

TEC CURRENT MONITOR

VOLTAGE LIMIT

HEATING CURRENT LIMIT

COOLING CURRENT LIMIT

AOUT

ITEC

AIN+

MAXV

MAXIP

MAXIN

REF

Integrated Temperature

Controllers for Peltier Modules

Typical Operating Circuit

V

DD

PV

DD-

SHDN

OT

UT

BFB-

LX1

PGND1

CS

MAX1978

OS1

OS2

LX2

PGND2

TEC

I

TEC

=

±3A

AIN-

REF

FB+

FB-

NTC

OPTIONAL DAC

DAC

TRANSISTOR COUNT: 6023

PROCESS: BiCMOS

Chip Information Revision History

Pages changed at Rev 1: 1, 9, 10, 19, 20, 21

______________________________________________________________________________________ 19

Integrated Temperature Controller for

Peltier Modules

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)

D

D/2

E/2

E

DETAIL A

(NE-1) X e e k e

(ND-1) X e

D2/2

CL

D2 b

L1

L

DETAIL B

L k

CL

CL

E2

E2/2

L e

A1 A2

A

CL e

L

PACKAGE OUTLINE

32, 44, 48, 56L THIN QFN, 7x7x0.8mm

21-0144 E

1

2

20 ______________________________________________________________________________________

Integrated Temperature Controller for

Peltier Modules

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE

32, 44, 48, 56L THIN QFN, 7x7x0.8mm

21-0144 E

2

2

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21

© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

advertisement

Was this manual useful for you? Yes No
Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertisement