Rainbow Electronics 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

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 0; 1/02

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-PACKAGE

MAX6691MUB -55°C to +125°C 10 µMAX

TOP VIEW

T1

1

T2

2

T3

3

4

5

MAX6691

µMAX

10

V

CC

I/O

9

N.C.

8

GNDT4

7

R+R-

6

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.

V

CC

to 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)

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)

T

Supply Voltage Range V

Supply Current I

Sleep-Mode Supply Current I

Input Leakage Current I

Reference Voltage Output V

Reference Load Regulation 0 < I

Reference Supply Rejection 0.2 %

Logic Input Low Voltage V

Logic Input High Voltage V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

HIGH/TLOW

Accuracy V

STANDBY

LEAKAGE

REXT

CC

CC

REF

IL

IH

TA = +25°C, VCC = 3.3V 0.5

TA = T

During conversion, no load 300 600 µA

I

REF

to T

MIN

= 1mA, TA = +25°C 1.19 1.24 1.32 V

< 2mA 0.1 0.2 %

REF

MAX

3.0 5.5 V

3.5 10 µA

✕

0.7
V

CC

1.0

1.0 µA

✕

0.3
V

CC

% FS

V

V

Glitch Immunity on I/O Input 500 ns

Conversion Time t

Nominal Pulse Width t

Start Pulse Width t

Data Ready Pulse Width t

Error Pulse Width t

Rise Time t

Fall Time t

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

CONV

LOW

START

READY

ERROR

RISE

FALL

CL = 15pF, RL = 10kΩ 600 ns

CL = 15pF, RL = 10kΩ 600 ns

86 102 156 ms

4.0 4.9 7.5 ms

5µs

103 122 188 µs

103 122 188 µs

MAX6691

Four-Channel Thermistor Temperature-to-Pulse-

Width Converter

_______________________________________________________________________________________ 3

__________________________________________Typical Operating Characteristics

(VCC= 5V, R

EXT

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

Pin Description

4.5

4.0

3.5

3.0

SLEEP-MODE SUPPLY CURRENT (µA)

2.5

3.0 5.5

PIN NAME FUNCTION

1 T1 Thermistor 1. Connect to external thermistor 1.

SLEEP-MODE SUPPLY CURRENT

vs. SUPPLY VOLTAGE

5.04.54.03.5

SUPPLY VOLTAGE (V)

1.0

MAX6691 toc01

0.5

0

FULL-SCALE ERROR (%)

LOW

/T

-0.5

HIGH

T

-1.0

vs. POWER-SUPPLY NOISE FREQUENCY

025

T

HIGH/TLOW

VIN = SQUARE WAVE
APPLIED TO V
NO VCC BYPASS
CAPACITOR

= 250mV

V

IN

POWER-SUPPLY NOISE FREQUENCY (MHz)

WITH

CC

P-P

VCC = 5.0V

ERROR

VCC = 3.3V

T

HIGH/TLOW

ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

1.0
VIN = SQUARE WAVE

APPLIED TO V

MAX6691 toc02

2015105

NO VCC BYPASS
CAPACITOR

0.5

= 250mV

V

IN

0

FULL-SCALE ERROR (%)

TA = +85°C

LOW

/T

-0.5

HIGH

T

-1.0
025

POWER-SUPPLY NOISE FREQUENCY (MHz)

CC

P-P

TA = +25°C

WITH

TA = -55°C

TA = +125°C

2015105

MAX6691 toc03

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

6 R+ Reference Voltage Output. Connect R

between R- and R+.

EXT

between R- and R+.

EXT

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

10 V

CC

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

CC

.