MAXIM MAX6678 User Manual

General Description

The MAX6678 monitors its own temperature and the
temperatures of two external diode-connected transis­tors, which typically reside on the die of a CPU or other
integrated circuit. The device reports temperature values
in digital form using a 2-wire serial interface. The
MAX6678 provides a programmable alarm output to gen­erate interrupts, throttle signals, or overtemperature shut­down signals.

The 2-wire serial interface accepts standard System
Management Bus (SMBus)™write byte, read byte, send
byte, and receive byte commands to read the tempera­ture data and program the alarm thresholds. The tem­perature data controls a PWM output signal to adjust
the speed of a cooling fan, thereby minimizing noise
when the system is running cool, but providing maxi­mum cooling when power dissipation increases.

Five GPIO pins provide additional flexibility. The GPIO
power-up states are set by connecting the GPIO preset
inputs to ground or VCC.

The MAX6678 is available in a 20-pin QSOP package
and a 5mm x 5mm thin QFN package. It operates from

3.0V to 5.5V and consumes just 500µA of supply current.

Applications

Desktop Computers
Notebook Computers
Workstations
Servers
Networking Equipment

Features

♦ Two Thermal-Diode Inputs

♦ Local Temperature Sensor

♦ Five GPIO Input/Outputs

♦ Two PWM Outputs for Fan Drive (Open Drain; May

Be Pulled Up to +5V)

♦ Programmable Fan-Control Characteristics

♦ Automatic Fan Spin-Up Ensures Fan Start

♦ Controlled Rate of Change Ensures Unobtrusive

Fan-Speed Adjustments

♦ 1°C Remote Temperature Accuracy (+60°C to

+145°C)

♦ Temperature Monitoring Begins at POR for Fail-

Safe System Protection

♦ OT Output for Throttling or Shutdown

♦ Four Versions Available, Each with a Different

Address

♦ 5mm x 5mm TQFN Package

MAX6678

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

________________________________________________________________ Maxim Integrated Products 1

Pin Configurations

Ordering Information

19-3306; Rev 0; 5/04

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.

*EP = Exposed paddle.

SMBus is a trademark of Intel Corp.

Pin Configurations continued at end of data sheet.

Typical Operating Circuit appears at end of data sheet.

CC

PRESET3

PWMOUT2

V

MAX6678

GND

DXP2

PWMOUT116GPIO0

10

PRESET2

PRESET1

OT

15

GPIO1

14

GPIO2

13

12

GPIO3

11

PRESET0

TOP VIEW

SMBDATA

SMBCLK

GPIO4

PRESET4

20 19 18 17

1

2

3

4

*CONNECT EXPOSED

5DXP1

PADDLE TO GND

6789

DXN

5mm x 5mm THIN QFN

PART TEMP RANGE

MAX6678AEP90 -40°C to +125°C 20 QSOP 1001000

MAX6678AEP92 -40°C to +125°C 20 QSOP 1001001

MAX6678AEP94 -40°C to +125°C 20 QSOP 1001010

MAX6678AEP96 -40°C to +125°C 20 QSOP 1001011

MAX6678ATP90 -40°C to +125°C

MAX6678ATP92 -40°C to +125°C

MAX6678ATP94 -40°C to +125°C

MAX6678ATP96 -40°C to +125°C

PIN­PACKAGE

20 Thin
QFN-EP*

20 Thin
QFN-EP*

20 Thin
QFN-EP*

20 Thin
QFN-EP*

SMBus

ADDRESS

1001000

1001001

1001010

1001011

MAX6678

2-Channel Temperature Monitor with Dual Automatic
PWM Fan-Speed Controller and Five GPIOs

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V, 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.

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

OT, SMBDATA, SMBCLK, PWMOUT_,

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

DXP_ to GND ..........................................-0.3V to + (V

CC

+ 0.3V)

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

PRESET_ to GND ....................................-0.3V to + (V

CC

+ 0.3V)

SMBDATA, OT, PWMOUT_ Current....................-1mA to +50mA

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

ESD Protection (all pins, Human Body Model) ..................2000V

Continuous Power Dissipation (T

A

= +70°C)

20-Pin QSOP (derate 9.1mW/°C above +70°C).......... 727mW

20-Pin TQFN (derate 34.5mW/°C above +70°C) .......2759mW

Operating Temperature Range .........................-40°C to +125°C

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

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

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

Operating Supply Voltage Range V

Operating Current I

External Temperature Error,
V

CC

Internal Temperature Error VCC = +3.3V

Temperature Resolution

Conversion Time 200 250 300 ms

PWM Frequency Tolerance (Note 1) -20 +20 %

Remote-Diode Sourcing Current

DXN Source Voltage 0.7 V

DIGITAL INPUTS AND OUTPUTS

Output Low Voltage (Sink Current)
(OT, GPIO_, SMBDATA, PWMOUT_)

Output High Leakage Current
(OT, GPIO_, SMBDATA, PWMOUT_)

Logic-Low Input Voltage (SMBDATA,
SMBCLK, PRESET_, GPIO_)

Logic-High Input Voltage (SMBDATA,
SMBCLK, PRESET_, GPIO_)

Input Leakage Current 1µA

Input Capacitance C

SMBus TIMING

Serial Clock Frequency f

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

CC

Interface inactive, ADC active 0.5 1 mA

S

+25°C ≤ TR ≤ +125°C,
T

= 60°C

A

= 3.3V

V

OL

I

OH

V

IL

V

IH

IN

SCLK

VCC = 3.3V

High level 80 100 120

Low level 8 10 12

I

= 6mA 0.4 V

OUT

VCC = 3V to 3.6V 0.8

VCC = 3.6V to 5.5V 0.8

VCC = 3V to 3.6V 2.1

VCC = 3.6V to 5.5V 2.1

0°C ≤ T
+25°C ≤ T

0°C ≤ T
0°C ≤ T

+25°C ≤ TR ≤ +100°C ±2.5

0°C ≤ T

≤ +145°C,

R

≤ +100°C

A

≤ +145°C,

R

≤ +125°C

A

≤ +125°C ±4

A

+3.0 +5.5 V

±1

±3

±4

1°C

8 Bits

1µA

5pF

100 kHz

°C

°C

µA

V

V

MAX6678

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V, TA= +25°C.)

Note 1: Deviation from programmed value in Table 6.

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

400

440

520

480

560

600

3.0 4.03.5 4.5 5.0 5.5

OPERATING SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6678 toc02

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

-4

-2

-3

0

-1

1

2

050

7525100

125 150

REMOTE TEMPERATURE ERROR

vs. REMOTE-DIODE TEMPERATURE

MAX6678 toc03

TEMPERATURE (°C)

TEMPERATURE ERROR (

°

C)

FAIRCHILD 2N3906

Clock Low Period t

Clock High Period t

Bus Free Time Between Stop and
Start Conditions

SMBus Start Condition Setup Time t

Start Condition Hold Time t

Stop Condition Setup Time t

Data Setup Time t

Data Hold Time t

SMBus Fall Time t

SMBus Rise Time t

SMBus Timeout t

Startup Time After POR t

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LOW

HIGH

t

BUF

SU:STA

HD:STO

SU:STO

SU:DAT

HD:DAT

TIMEOUT

POR

10% to 10% 4 µs

90% to 90% 4.7 µs

4.7 µs

90% of SMBCLK to 90% of SMBDATA 4.7 µs

10% of SMBDATA to 10% of SMBCLK 4 µs

90% of SMBCLK to 10% of SMBDATA 4 µs

10% of SMBDATA to 10% of SMBCLK 250 ns

10% of SMBCLK to 10% of SMBDATA 300 ns

F

R

29 37 55 ms

300 ns

1000 ns

500 ms

MAX6678

2-Channel Temperature Monitor with Dual Automatic
PWM Fan-Speed Controller and Five GPIOs

4 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

-3

-1

-2

1

0

2

3

05025 75 100 125

LOCAL TEMPERATURE ERROR

vs. DIE TEMPERATURE

MAX6678 toc04

TEMPERATURE (°C)

TEMPERATURE ERROR (

°

C)

-1.5

0

-0.5

-1.0

1.0

0.5

1.5

2.0

0.01 10.1 10 100 1000

REMOTE TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6678 toc05

FREQUENCY (kHz)

TEMPERATURE ERROR (

°

C)

VIN = 250mV

P-P

SQUARE WAVE APPLIED

TO V

CC

WITH NO BYPASS CAPACITOR

-2.5

-1.0

-1.5

-2.0

0

-0.5

0.5

1.0

0.01 10.1 10 100 1000

LOCAL TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6678 toc06

FREQUENCY (kHz)

TEMPERATURE ERROR (

°

C)

VIN = 250mV

P-P

SQUARE WAVE APPLIED

TO V

CC

WITH NO BYPASS CAPACITOR

0

1.4

1.2

1.0

0.8

0.6

0.4

0.2

1.8

1.6

2.0

0.01 10.1 10 100 1000

REMOTE TEMPERATURE ERROR

vs. COMMON-MODE NOISE FREQUENCY

MAX6678 toc07

FREQUENCY (kHz)

TEMPERATURE ERROR (

°

C)

VIN = AC-COUPLED TO DXP AND DXN
V

IN

= 100mV

P-P

SQUARE WAVE

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.9

0.8

1.0

0.01 10.1 10 100 1000

REMOTE TEMPERATURE ERROR

vs. DIFFERENTIAL NOISE FREQUENCY

MAX6678 toc08

FREQUENCY (kHz)

TEMPERATURE ERROR (

°

C)

VIN = AC-COUPLED TO DXP
V

IN

= 100mV

P-P

SQUARE WAVE

-6

-3

-5

-4

-1

-2

1

0

2

0.1 1 10 100

TEMPERATURE ERROR

vs. DXP-DXN CAPACITANCE

MAX6678 toc09

DXP-DXN CAPACITANCE (nF)

TEMPERATURE ERROR (

°

C)

TA = +25°C

30

31

33

32

34

35

-40 10 35-15 60 11085

PWMOUT FREQUENCY

vs. DIE TEMPERATURE

MAX6678 toc10

TEMPERATURE (°C)

PWMOUT FREQUENCY (Hz)

30

31

33

32

34

35

3.0 4.03.5 4.5 5.0 5.5

PWMOUT FREQUENCY
vs. SUPPLY VOLTAGE

MAX6678 toc11

SUPPLY VOLTAGE (V)

PWMOUT FREQUENCY (Hz)

0

100

300

200

400

500

0101552025303540

GPIO OUTPUT VOLTAGE

vs. GPIO SINK CURRENT

MAX6678 toc12

GPIO SINK CURRENT (mA)

GPIO OUTPUT VOLTAGE (mV)

Detailed Description

The MAX6678 temperature sensor and fan controller
accurately measures the temperature of either two
remote pn junctions or one remote pn junction and its
own die. The device reports temperature values in digi­tal form using a 2-wire serial interface. The remote pn
junction is typically the emitter-base junction of a com­mon-collector pnp on a CPU, FPGA, or ASIC. The
MAX6678 operates from supply voltages of 3.0V to

5.5V and consumes 500µA (typ) of supply current. The
temperature data controls a PWM output signal to
adjust the speed of a cooling fan. The device also fea­tures an overtemperature alarm output to generate
interrupts, throttle signals, or shutdown signals.

Five GPIO input/outputs provide additional flexibility.
The GPIO power-up states are set by connecting the
GPIO preset inputs to ground or V

CC

.

MAX6678

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

_______________________________________________________________________________________ 5

Pin Description

Block Diagram

PIN

THIN QFN QSOP

13 SMBDATA

24 SMBCLK

3, 12, 13,

14, 16

4, 9, 10,

11, 20

5, 7 7, 9 DXP1, DXP2

68 DXN

810 GND Ground. Connect to a clean ground reference.

15 17 OT

17, 19 1, 19

18 20 V

5, 14, 15,

16, 18

2, 6, 11,

12, 13

NAME DESCRIPTION

SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V,
regardless of V

SMBus Serial-Clock Input. Can be pulled up to 5.5V, regardless of V
circuit when V

GPIO0–GPIO4

PRESET0–PRESET4 GPIO Preset Inputs. Connect to GND or V

PWMOUT1,

PWMOUT2

CC

Active-Low, Open-Drain GPIO Pins. Can be pulled up to 5.5V, regardless of

. Open circuit when VCC = 0.

V

CC

Combined Current Source and A/D Positive Input for Remote Diode. Connect to
anode of remote-diode-connected temperature-sensing transistor. Do not leave
floating; connect to DXN if no remote diode is used. Place a 2200pF capacitor
between DXP_ and DXN for noise filtering.

Combined Remote-Diode Cathode Input. Connect cathode of the remote-diode­connected transistor to DXN.

Active-Low, Open-Drain Over-Temperature Output. Typically used for system
shutdown or clock throttling. Can be pulled up to 5.5V regardless of V
circuit when V

Open-Drain Output to Power Transistor Driving Fan. Connect to the gate of a
MOSFET or base of a transistor. PWMOUT_ requires a pullup resistor. The
pullup resistor can be connected to a supply voltage as high as 5.5V,
regardless of the MAX6678’s supply voltage.

Power-Supply Input. 3.3V nominal. Bypass VCC to GND with 0.1µF capacitor.

. Open circuit when VCC = 0.

CC

= 0.

CC

= 0.

CC

. Open

CC

to set POR value of GPIO0–GPIO4.

CC

. Open

CC

DXP1

DXN

DXP2

SMBDATA

SMBCLK

V

CC

TEMPERATURE

PROCESSING

BLOCK

PWM

GENERATOR

BLOCK

PWMOUT1
PWMOUT2

OT

GPIO0

GPIO4

PRESET0

PRESET4

SMBus

INTERFACE

AND

REGISTERS

LOGIC

MAX6678

GND

MAX6678

SMBus Digital Interface

From a software perspective, the MAX6678 appears as a
set of byte-wide registers. This device uses a standard
SMBus 2-wire/I2C-compatible serial interface to access
the internal registers. The MAX6678 has four different
slave addresses available; therefore, a maximum of four
MAX6678 devices can share the same bus.

The MAX6678 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figures 1, 2, and 3). The shorter receive byte protocol
allows quicker transfers, provided that the correct data
register was previously selected by a read byte instruc­tion. Use caution with the shorter protocols in multimaster
systems, since a second master could overwrite the
command byte without informing the first master.

Temperature data can be read from registers 00h and
01h. The temperature data format for these registers is
8 bits, with the LSB representing 1°C (Table 1) and the
MSB representing +128°C. The MSB is transmitted first.
All values below 0°C clip to 00h.

Table 2 details the register address and function, whether
they can be read or written to, and the power-on reset
(POR) state. See Tables 2–6 for all other register functions
and the Register Descriptions section.

Temperature Reading

The MAX6678 contains two external temperature mea­surement inputs to measure the die temperature of CPUs
or other ICs having on-chip temperature-sensing diodes,
or discrete diode-connected transistors as shown in the
Typical Operating Circuits. For best accuracy, the dis­crete diode-connected transistor should be a small-signal
device with its collector and base connected together.
The on-chip ADC converts the sensed temperature and
outputs the temperature data in the format shown in Table

1. Temperature channel 2 can be used to measure either
a remote thermal diode or the internal temperature of the
MAX6678. Bit D1 of register 02h (Table 2) selects local or
remote sensing for temperature channel 2 (1 = local). The
temperature measurement resolution is 1°C for both local
and remote temperatures. The temperature accuracy is
within ±1°C for remote temperature measurements from
+60°C to +100°C.

2-Channel Temperature Monitor with Dual Automatic
PWM Fan-Speed Controller and Five GPIOs

6 _______________________________________________________________________________________

Write Byte Format

Read Byte Format

Send Byte Format

Receive Byte Format

Slave address: equiva­lent to chip-select line of
a 3-wire interface

Command byte: selects which
register you are writing to

Data byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)

Slave address: equivalent
to chip-select line

Command byte: selects
which register you are
reading from

Slave address: repeated
due to change in data­flow direction

Data byte: reads from
the register set by the
command byte

Command byte: sends com­mand with no data, usually
used for one-shot command

Data byte: reads data from
the register commanded
by the last read byte or
write byte transmission;
also used for SMBus alert
response return address

S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged

Figure 1. SMBus Protocols

S ADDRESS RD ACK DATA /// P

— 7 bits — — 8 bits — —

WRS ACK COMMAND ACK P

— — — 8 bits — —

ADDRESS

7 bits

P

1

ACK

—

DATA

8 bits

ACK

—

COMMAND

8 bits

ACK

—

WR

—

ADDRESS

7 bits

S

—

S ADDRESS WR ACK COMMAND ACK S ADDRESS

7 bits——8 bits——7 bits—

RD—ACK—DATA

8 bits

///

—

P

—