MAXIM MAX6680, MAX6681 Technical data

General Description

The MAX6680/MAX6681 are precise, two-channel digi­tal thermometers. Each accurately measures the tem­perature of its own die and one remote PN junction and
reports the temperature on a 2-wire serial interface. The
remote junction can be a diode-connected transistor
like the low-cost NPN type 2N3904 or PNP type
2N3906. The remote junction can also be a common­collector PNP, such as a substrate PNP of a micro­processor.

The MAX6680/MAX6681 include pin-programmable
default temperature thresholds for the OVERT output,
which provides fail-safe clock throttling or system shut­down. In addition, the devices are pin programmable to
select whether the OVERT output responds to either the
local, remote, or both temperatures.

The 2-wire serial interface accepts standard System
Management Bus (SMBus)™ commands such as Write
Byte, Read Byte, Send Byte, and Receive Byte to read
the temperature data and program the alarm thresholds
and conversion rate. The MAX6680/MAX6681 can func­tion autonomously with a programmable conversion
rate, which allows the control of supply current and
temperature update rate to match system needs. For
conversion rates of 4Hz or less, the remote sensor tem­perature can be represented in extended mode as 10
bits + sign with a resolution of 0.125°C. When the con­version rate is 8Hz, output data is 7 bits + sign with a
resolution of 1°C. The MAX6680/MAX6681 also include
an SMBus timeout feature to enhance system reliability.

The MAX6681 is an upgrade to the MAX6654. The
MAX6680/MAX6681 remote accuracy is ±1°C with no
calibration needed. They are available in a 16-pin
QSOP package and operate throughout the -55°C to
+125°C temperature range.

Applications

Features

♦ Two Alarm Outputs: ALERT and OVERT
♦ Pin-Programmable Threshold for OVERT Limit
♦ Programmable Under/Overtemperature ALERT

Limit

♦ Dual Channel: Measures Remote and Local

Temperature

♦ 11-Bit, 0.125°C Resolution for Remote Temperature

Measurements

♦ High Accuracy ±1°C (max) from +60°C to +100°C

(Remote)

♦ No Calibration Required

♦ SMBus/I

2

C™-Compatible Interface

♦ SMBus Timeout Prevents SMBus Lockup

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

________________________________________________________________ Maxim Integrated Products 1

Typical Operating Circuit

Ordering Information

19-2305; Rev 1; 1/05

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.

PART TEMP RANGE PIN-PACKAGE

MAX6680MEE -55°C to +125°C 16 QSOP

MAX6681MEE -55°C to +125°C 16 QSOP

SMBus is a trademark of Intel Corp.

I

2

C is a trademark of Philips Corp.

Pin Configurations appear at end of data sheet.

Desktop Computers

Notebook
Computers

Servers

Thin Clients

Workstations

0.1µF

200Ω

3.3V

MICROPROCESSOR

2200pF

V

DXP

DXN

SENS_SEL

INT_SEL

ADD0

ADD1

CC

STBY

MAX6680
MAX6681

SMBDATA

SMBCLK

ALERT

RESET

OVERT

CRIT1CRIT0GND

10kΩ
EACH

DATA

CLOCK

INTERRUPT
TO µP

TO SYSTEM
SHUTDOWN

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Typical Operating Circuit, VCC= 3.0V to 5.5V, TA= -25°C to +125°C, unless otherwise specified. Typical values are at V

CC

= 3.3V and TA= +25°C.)

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.

VCC...........................................................................-0.3V to +6V

DXP.............................................................-0.3V to (V

CC

+ 0.3V)

DXN ......................................................................-0.3V to +0.8V

SMBCLK, SMBDATA, ALERT, OVERT .....................-0.3V to +6V

RESET, INT_SEL, STBY, ADD0, ADD1.....................-0.3V to +6V

CRIT1, CRIT0, SENS_SEL ........................................-0.3V to +6V

SMBDATA, ALERT, OVERT, Current ..................-1mA to +50mA

DXN Current ......................................................................±1mA

Continuous Power Dissipation (T

A

= +70°C)

16-Pin QSOP (derate 8.3mW/°C above +70°C) ..........664mW

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

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

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

Average Operating Current
(Note 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Resolution,
Legacy Mode

Temperature Resolution,
Extended Mode

TRJ = +60°C to +100°C, VCC = 3.3V -1.0 +1.0

TRJ = +50°C to +120°C, VCC = 3.3V -2.0 +2.0Rem ote Tem p er atur e E r r or ( N ote 1)

= -55°C to +125°C, VCC = 3.3V -3.0 +3.0

T

RJ

TA = +60°C to +100°C, VCC = 3.3V -1.5 +1.5

Local Temperature Error

Line Regulation 3.0V ≤ VCC ≤ 5.5V 0.2 0.6 m°C/V

Supply Voltage Range V

Undervoltage Lockout Threshold UVLO Falling edge of VCC disables ADC 2.60 2.80 2.95 V

Undervoltage Lockout Hysteresis 90

Power-On Reset (POR)
Threshold

POR Threshold Hysteresis 90 mV

Conversion Time

Standby Supply Current SMBus static 3 10 µA

Operating Current During conversion 0.55 1.0 mA

DXP and DXN Leakage Current In standby mode 2 µA

Remote-Diode Source Current I

TA = 0°C to +125°C, VCC = 3.3V -3.0 +3.0

= -55°C to +125°C, VCC = 3.3V (Note 2) -5.0 +5.0

T

A

CC

, falling edge 1.5 2.0 2.5 V

V

CC

Legacy 62.5

Extended 125

0.25 conversions/s 35 70

2 conversions/s 120 180

High level 80 100 120

RJ

Low level 8 10 12

1°C

8 Bits

0.125 °C

11 Bits

3.0 5.5 V

°C

°C

mV

ms

µA

µA

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Typical Operating Circuit, VCC= 3.0V to 5.5V, TA= -25°C to +125°C, unless otherwise specified. Typical values are at V

CC

= 3.3V and TA= +25°C.)

Note 1: T

A

= +25°C to +85°C.

Note 2: If both the local and the remote junction are below T

A

= -20°C, then VCC> 3.15V.

Note 3: Conversions done in extended mode. For legacy mode, current is approximately half.
Note 4: Timing specifications guaranteed by design.
Note 5: The serial interface resets when SMBCLK or SMBDATA is low for more than t

TIMEOUT

.

Note 6: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge.

CRIT0, CRIT1, ADD0, ADD1, RESET, INT_SEL, SENS_SEL

Logic Input Low Voltage V

Logic Input High Voltage V

Input Leakage Current I

(ALERT, OVERT)

SMBus INTERFACE (SMBCLK, SMBDATA, STBY)

SMBus-COMPATIBLE TIMING (Note 5)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IL

IH

LEAK

Output Low Sink Current VOL = 0.4V 1 mA

Output High Leakage Current VOH = 5.5V 1 µA

Logic Input Low Voltage V

Logic Input High Voltage V

Input Leakage Current I

Output Low Sink Current I

Input Capacitance C

Serial Clock Frequency (Note 5) f

Bus Free Time Between STOP
and START Condition

START Condition Setup Time 4.7 µs

Repeat START Condition Setup
Time

START Condition Hold Time t

STOP Condition Setup Time t

Clock Low Period t

Clock High Period t

Data Setup Time (Note 6) t

Receive SCL/SDA Rise Time t

Receive SCL/SDA Fall Time t

Pulse Width of Spike Suppressed t

SMBus Timeout (Note 5) SMBDATA low period for interface reset 25 37 45 ms

IL

IH

LEAK

OL

IN

SCL

t

BUF

t

SU:STA

HD:STA

SU:STO

LOW

HIGH

HD:DAT

R

F

SP

VCC = 3.0V 2.2

VCC = 5.5V 2.4

VIN = GND or V

VOL = 0.6V 6 mA

90% to 90% 50 ns

10% of SMBDATA to 90% of SMBCLK 4 µs

90% of SMDCLK to 90% of SMBDATA 4 µs

10% to 10% 4.7 µs

90% to 90% 4 µs

CC

2.4 V

-1 +1 µA

5pF

4.7 µs

250 ns

050ns

0.8 V

0.8 V

±2 µA

100 kHz

1µs

300 ns

V

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface

4 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

MAX6680/81 toc01

SUPPLY VOLTAGE (V)

STANDBY SUPPLY CURRENT (µA)

5.04.54.03.5

1

2

3

4

5

6

7

8

9

10

0

3.0 5.5

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6680/81 toc02

CONVERSION RATE (Hz)

OPERATING SUPPLY CURRENT (µA)

8.0000

4.0000

2.0000

1.0000

0.5000

0.2500

0.1250

100

200

300

400

500

600

0

0.0625

AVERAGE OPERATING SUPPLY CURRENT

vs. CONVERSION RATE

8Hz IS 1°C
RESOLUTION

MAX6680/81 toc03

TEMPERATURE (°C)

TEMPERATURE ERROR (°C)

1251007550250-25

-2

-1

0

1

2

3

-3

-50 150

TEMPERATURE ERROR

vs. REMOTE-DIODE TEMPERATURE

MAX6680/81 toc04

TEMPERATURE (°C)

TEMPERATURE ERROR (°C)

100500

-2

-1

0

1

2

3

-3

-50 150

LOCAL TEMPERATURE ERROR

vs. DIE TEMPERATURE

MAX6680/81 toc05

FREQUENCY (Hz)

TEMPERATURE ERROR (°C)

1M10k100

0

0.2

0.4

0.6

0.8

1.0

1.2

-0.2
110M100k1k10 100M

TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

VIN = 100mV SQUARE WAVE
APPLIED TO V

CC

WITH NO

0.1µF V

CC

CAPACITOR

LOCAL
DIODE

REMOTE
DIODE

MAX6680/81 toc06

FREQUENCY (Hz)

TEMPERATURE ERROR (°C)

10M1M100k10k1k10010

-1

0

1

2

3

4

5

-2
1 100M

TEMPERATURE ERROR

vs. COMMON-MODE NOISE FREQUENCY

VIN = 100mV

P-P

SQUARE WAVE

AC-COUPLED TO DXN

MAX6680/81 toc07

FREQUENCY (Hz)

TEMPERATURE ERROR (°C)

10M1M100k10k1k

0

1

2

3

-1

100 100M

TEMPERATURE ERROR

vs. DIFFERENTIAL NOISE FREQUENCY

VIN = 10mV

P-P

SQUARE WAVE

APPLIED TO DXP-DXN

MAX6680/81 toc08

DXP-DXN CAPACITANCE (nF)

TEMPERATURE ERROR (°C)

908070605040302010

-4

-3

-2

-1

0

1

-5
0100

TEMPERATURE ERROR

vs. DXP-DXN CAPACITANCE

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

_______________________________________________________________________________________ 5

Pin Description

PIN

MAX6680 MAX6681

12V

2, 5 1, 5

3 3 DXP

44DXN

6 6 ADD1

7 7 RESET

8 8 GND Ground
99OVERT Overtemperature Active-Low Output. Open drain.

10 10 ADD0 SMBus Slave Address Select Pin (see ADD1).
11 11 ALERT SMBus Alert (Interrupt) Active-Low Output. Open drain.

12 12 SMBDATA SMBus Serial-Data Input/Output, Open Drain

13 13 INT_SEL

14 14 SMBCLK SMBus Serial-Clock Input

15 15 STBY

16 16 SENS_SEL

NAME FUNCTION

Supply Voltage Input, 3V to 5.5V. Bypass VCC to GND with a 0.1µF capacitor.

CC

CRIT1,

CRIT0

A 200Ω series resistor is recommended, but not required for additional noise
filtering. See the Typical Operating Circuit.

Hardware-Programmable Default Alarm Threshold for OVERT Limits. Use Table
4 to set default temperatures.

Combined Remote-Diode Current Source and A/D Positive Input for Remote­Diode Channel. DO NOT LEAVE DXP FLOATING; connect DXP to DXN if no
remote diode is used. Place a 2200pF capacitor between DXP and DXN for
noise filtering.

Combined Remote-Diode Current Sink and A/D Negative Input. DXN is
internally biased to one diode drop above ground.

SMBus Address Select Pin (Table 9). ADD0 and ADD1 are sampled upon
power-up. Excess capacitance (>50pF) at the address pins when floating may
cause address-recognition problems.

Reset Input. Drive RESET high to set all registers to their default values (POR
state). Drive RESET low or leave floating for normal operation.

Input. Connect high or leave floating to conform to the standard SMBus ALERT
protocol. See the
comparator mode, where ALERT is asserted whenever any of the temperature
conditions is violated by the remote sensor. In this mode, ALERT can only be
deasserted by the condition returning within the temperature limits by enabling
the mask bit in the Configuration register.

Input. Hardware Standby. Connect to ground to place in device in standby.
Supply current drops below 10µA and all registers’ data are maintained.

Input. Selects which temperature sensor (local, remote, or both) activates
OVERT.

High = Remote, Low = Local, Open = Local and Remote

ALERT

Interrupts section. Connect to GND to invoke

MAX6680/MAX6681

Detailed Description

The MAX6680/MAX6681 are temperature sensors designed
to work in conjunction with a microprocessor or other
intelligence in thermostatic, process-control, or monitoring
applications. Communication with the MAX6680/MAX6681
occurs through the SMBus serial interface and dedicated
alert pin. The overtemperature alarm OVERT is asserted if
the software or hardware programmed temperature thresh­olds are exceeded. OVERT can be connected to a fan,
system shutdown, or other thermal management circuitry.

The MAX6680/MAX6681 convert temperatures at a pro­grammed rate or a single conversion. Legacy mode
conversions have a 1°C resolution. Legacy resolution
represents temperature as 7 bits + sign bit and allows
for faster autonomous conversion rates at 8Hz. The
remote diode temperature can also be represented in
extended-resolution mode. Extended resolution repre-

sents temperature as 10 bits + sign bit and is available
for autonomous conversions that are 4Hz or slower and
single-shot conversions.

The MAX6680/MAX66681 default low-temperature mea­surement limit is 0 °C. The device temperature measure­ment can be placed in extended temperature range by
setting bit 3 of the Configuration register to 1. In extend­ed temperature range, the remote and local temperature
measurement range is extended down to -64°C.

ADC and Multiplexer

The averaging ADC integrates over a 60ms period
(each channel, typically, in the 7-bit + sign “legacy”
mode). Using an averaging ADC attains excellent noise
rejection.

The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward volt-

±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface

6 _______________________________________________________________________________________

Figure 1. MAX6680/MAX6681 Functional Diagram

V

DXP

DXN

CC

RESET

CIRCUITRY

RESET

MUX

REMOTE

LOCAL

ADC

MAX6680
MAX6681

2

CONTROL

LOGIC

SENS_SEL

STBY

INT_SEL

DIODE

ALERT

FAULT

S

Q

R

OVERT

S

Q

R

CRIT0

CRIT1

SMBus

REGISTER BANK

COMMAND BYTE

REMOTE TEMPERATURE

LOCAL TEMPERATURE

ALERT THRESHOLD

ALERT RESPONSE ADDRESS

OVERT THRESHOLD (EXT)
OVERT THRESHOLD (INT)

8

READ

8

WRITE

7

ADDRESS
DECODER

SMBDATA

SMBCLK

ADD0

ADD1