MAXIM MAX6691 User Manual

General Description

The MAX6691 four-channel thermistor temperature-to­pulse-width converter measures the temperatures of up
to four thermistors and converts them to a series of out­put pulses whose widths are related to the thermistors’
temperatures. Each of the four thermistors and an
external fixed resistor (R

EXT

) form a voltage-divider that
is driven by the MAX6691’s internal voltage reference
(V

REF

). V

REF

and the voltage across R

EXT

are mea-

sured and converted to a pulse.

The MAX6691 has a single open-drain I/O pin that can
be readily connected to a variety of microcontrollers.
The microcontroller initiates a conversion by pulling the
I/O pin low and releasing it. When conversion is done,
the MAX6691 signals the end of conversion by pulling
the I/O pin low once again. The pulse corresponding to
the first thermistor is sent immediately after the release
of the I/O pin.

The on-chip power-management circuitry reduces the
average thermistor current to minimize errors due to
thermistor self-heating. Between conversions, the
MAX6691 falls into a 10µA (max) sleep mode, where
the voltage reference is disabled and the supply cur­rent is at its minimum.

The MAX6691 is available in a 10-pin µMAX package
and is specified from -55°C to +125°C temperature
range.

Applications

HVAC

Home Appliances

Medical Devices

Features

♦ Simple Single-Wire Interface

♦ Measures Up to Four Thermistor Temperatures

♦ Low-Average Thermistor Current Minimizes Self-

Heating Errors

♦ Internal Voltage Reference Isolates Thermistor

from Power-Supply Noise

♦ Accommodates Any Thermistor Temperature

Range

MAX6691

Four-Channel Thermistor Temperature-to-Pulse-

Width Converter

________________________________________________________________ Maxim Integrated Products 1

1

2

3

4

5

10

9

8

7

6

V

CC

I/O

N.C.

GNDT4

T3

T2

T1

MAX6691

µMAX

TOP VIEW

R+R-

Pin Configuration

1

2

3

4

5

10

9

8

7

6

V

CC

I/O

N.C.

GND

T4

T3

T2

T1

MAX6691

TOP VIEW

R+

R-

T4

T3

T2

T1

MICRO-

CONTROLLER

10kΩ

V

CC

R

EXT

Typical Application Circuit

19-2304; Rev 1; 2/07

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.

Ordering Information

PART

TEMP RANGE

PIN-

PKG

CODE

MAX6691MUB

10 µMAX

U10-2

PACKAGE

-55°C to +125°C

MAX6691

Four-Channel Thermistor Temperature-to-Pulse­Width Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

Note 1: Specification limits over temperature are guaranteed by design, not production tested.

VCCto GND...........................................................-0.3V to +6.0V

All Other Pins to GND.................................-0.3V to (V

CC

+ 0.3V)

I/O, R+, R-, T1–T4 Current................................................±20mA

ESD Protection (Human Body Model) .............................±2000V

Continuous Power Dissipation (T

A

= +70°C)

10-Pin µMAX (derate 5.6mW/°C above +70°C) ........444.4mW

Operating Temperature Range .........................-55°C to +125°C

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

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

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

ELECTRICAL CHARACTERISTICS

(VCC= 3.0V to 5.5V, TA= -55°C to +125°C, unless otherwise noted. Typical values are specified at VCC= 3.3V and TA= +25°C.) (Note1)

PARAMETER

CONDITIONS

UNITS

TA = +25°C, VCC = 3.3V 0.5

T

HIGH/TLOW

Accuracy V

REXT

TA = T

MIN

to T

MAX

1.0

% FS

Supply Voltage Range V

CC

3.0 5.5 V

Supply Current I

CC

During conversion, no load

µA

Sleep-Mode Supply Current

3.5 10 µA

Input Leakage Current

1.0 µA

Reference Voltage Output V

REF

I

REF

= 1mA, TA = +25°C

V

Reference Load Regulation 0 < I

REF

< 2mA 0.1 0.2 %

Reference Supply Rejection 0.2 %

Logic Input Low Voltage V

IL

0.3

✕

V

Logic Input High Voltage V

IH

0.7

✕

V

TIMING CHARACTERISTICS

(VCC= 3.0V to 5.5V, TA= -55°C to +125°C, unless otherwise noted. Typical values are specified at VCC= 3.3V and TA= +25°C.)
(Figure 1) (Note1)

PARAMETER

CONDITIONS

UNITS

Glitch Immunity on I/O Input

ns

Conversion Time t

CONV

86

ms

Nominal Pulse Width t

LOW

4.0 4.9 7.5 ms

Start Pulse Width t

START

5µs

Data Ready Pulse Width t

READY

µs

Error Pulse Width t

ERROR

µs

Rise Time t

RISE

CL = 15pF, RL = 10kΩ

ns

Fall Time t

FALL

CL = 15pF, RL = 10kΩ

ns

SYMBOL

I

STANDBY

I

LEAKAGE

MIN TYP MAX

300 600

1.19 1.24 1.32

V

CC

SYMBOL

MIN TYP MAX

103 122 188

103 122 188

500

102 156

600

600

V

CC

MAX6691

Four-Channel Thermistor Temperature-to-Pulse-

Width Converter

_______________________________________________________________________________________ 3

SLEEP-MODE SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6691 toc01

SUPPLY VOLTAGE (V)

SLEEP-MODE SUPPLY CURRENT (µA)

5.04.54.03.5

3.0

3.5

4.0

4.5

2.5

3.0 5.5

T

HIGH/TLOW

ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6691 toc02

POWER-SUPPLY NOISE FREQUENCY (MHz)

T

HIGH

/T

LOW

FULL-SCALE ERROR (%)

2015105

-0.5

0

0.5

1.0

-1.0
025

VCC = 5.0V

VCC = 3.3V

VIN = SQUARE WAVE
APPLIED TO V

CC

WITH
NO VCC BYPASS
CAPACITOR
V

IN

= 250mV

P-P

T

HIGH/TLOW

ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6691 toc03

POWER-SUPPLY NOISE FREQUENCY (MHz)

T

HIGH

/T

LOW

FULL-SCALE ERROR (%)

2015105

-0.5

0

0.5

1.0

-1.0
025

TA = +25°C

TA = -55°C

TA = +85°C

TA = +125°C

VIN = SQUARE WAVE
APPLIED TO V

CC

WITH
NO VCC BYPASS
CAPACITOR
V

IN

= 250mV

P-P

__________________________________________Typical Operating Characteristics

(VCC= 5V, R

EXT

= 7.5kΩ, RTH= 12.5kΩ, TA= +25°C, unless otherwise noted.)

PIN NAME FUNCTION

1 T1 Thermistor 1. Connect to external thermistor 1.

2 T2 Thermistor 2. Connect to external thermistor 2.

3 T3 Thermistor 3. Connect to external thermistor 3.

4 T4 Thermistor 4. Connect to external thermistor 4.

5 R- External Resistor Low Side. Connect R

EXT

between R- and R+.

6 R+ Reference Voltage Output. Connect R

EXT

between R- and R+.

7 GND Ground. Ground connection for MAX6691 and ground return for external thermistor(s).

8 N.C. No Connection. Do not make a connection to this pin.

9 I/O I/O Connection to Microcontroller. Connect a 10kΩ pullup resistor from I/O pin to V

CC

.

10 V

CC

Supply Voltage. Bypass VCC to GND with a capacitor of at least 0.1µF.

Pin Description