General Description

The MAX6681 evaluation system (EV system) consists of a
MAX6681 evaluation kit (EV kit) and a companion Maxim
system management bus (SMBus)TM interface board.

The MAX6681 EV kit is an assembled and tested PC
board that demonstrates the MAX6681 temperature
sensor. The MAX6681 monitors its temperature and the
junction temperature of an external diode-connected
transistor. It converts the temperature to 8-bit or 11-bit
2-wire serial data. (

Note:

11-bit resolution is for the

external sensor only.)

The MAX6681 EV kit includes the external diode-con-
nected transistor (a 2N3906 transistor) soldered to the
board, but removable. The board can then be connect-
ed through a twisted pair to a remote diode close to
your system.

The Maxim SMBus interface board (MAXSMBUS)
allows an IBM-compatible PC to use its parallel port to
emulate an Intel SMBus 2-wire interface. Windows®
95/98/2000-compatible software provides a user-friend-
ly interface to exercise the features of the MAX6681.
The program is menu driven and offers a graphic inter-
face with control buttons and status display. (

Note:

Windows 2000 requires the installation of a driver; refer
to Win2000.pdf or Win2000.txt located on the diskette.)

Order the MAX6681EVSYS for a complete IBM
PC-based evaluation of the MAX6681. Order the
MAX6681EVKIT if you already have an SMBus interface.

Features

Measure and Display Temperature of the
MAX6681 and a Remote Sensor

Programmable Alarms and Configuration

CTM/SMBus Compatible

Easy-to-Use Menu-Driven Software

Assembled and Tested

Include Windows 95/98/2000-Compatible
Software and Demo PC Board

Evaluate: MAX6681

MAX6681 Evaluation System/Evaluation Kit

________________________________________________________________ Maxim Integrated Products

DESIGNATION

QTY

DESCRIPTION

0.1µF, 16V X7R ceramic capacitor
Taiyo Yuden EMK107BJ104KA
Murata GRM188R71C104KA01
TDK C1608X7R1C104K
TDK C1608X7R1E104K

2200pF, 50V X7R ceramic capacitor

2 x 10 right-angle female receptacle
Adam Technologies RS2R-20G
SamTec SSW-110-02-S-D-RA

JU1JU4, JU6,

JU8

3-pin headers

JU5, JU7

2-pin headers

JU9

Not installed

2N3906 PNP transistor
Central Semiconductor CMPT3906
Diodes Inc. MMBT3906
General Semiconductor MMBT3906

10k

±5% resistor

SW1

Slide switch

MAX6681MEE

None

Shunts

MAX6681EVKIT Component List

Ordering Information

19-2430; Rev 0; 4/02

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.

PART

TEMP

RANGE

INTERFACE

TYPE

MAX6681EVKIT

0°C to +70°C

Not included

MAX6681EVSYS

0°C to +70°C

MAXSMBUS

The MAX6681 EV kit software is provided with the
MAX6681EVKIT. However, the MAXSMBUS board is required to
interface the EV kit to the computer when using the software.

SMBus is a trademark of Intel Corp.

Windows is a registered trademark of Microsoft Corp.

C is a trademark of Philips Corp.

PART

QTY

DESCRIPTION

MAX6681EVKIT

MAX6681 evaluation kit

MAXSMBUS

SMBus interface board

MAX6681EVSYS Component List

Evaluate: MAX6681

Quick Start

Required Equipment

Before you begin, the following equipment is needed:

· A computer running Windows 95, 98, or 2000. (

Note:

Windows 2000 requires the installation of a driver;
refer to Win2000.pdf or Win2000.txt located on the
diskette.)

· A parallel printer port (this is a 25-pin socket on the

back of the computer)

· A standard 25-pin, straight-through, male-to-female

cable (printer extension cable) to connect the com-
puter's parallel port to the Maxim SMBus interface
board

· A DC power supply capable of supplying any volt-

age between 7V and 20V at 100mA

Procedure

1) Carefully connect the boards by aligning the 20-pin

connector of the MAX6681 EV kit with the 20-pin
header of the MAXSMBUS interface board. Gently
press them together.

2) Make sure switch SW1 on the MAX6681 EV kit is in

the OFF position.

3) Verify that there is no shunt installed on JU7.

4) Verify that the shunt on JU8 is connected across

pins 1 and 2.

5) Connect a cable from the computer's parallel port

to the MAXSMBus interface board. Use a straight-
through 25-pin female-to-male cable. To avoid
damaging the EV kit or your computer, do not use a
25-pin SCSI port or any other connector that is
physically similar to the 25-pin parallel printer port.

6) Install the software by running the INSTALL.EXE

program. The install program copies the files and
creates icons for them in the Windows 95/98/2000
Start menu. An uninstall program is included with
the software. Click on the UNINSTALL icon to

remove the EV kit software from the hard drive.

not turn on the power until all connections are
made.

7) Connect the 7V to 20V power supply to the pads

labeled POS9 and GND1 on the SMBus interface
board.

8) Turn on the power supply.

9) Turn on the EV kit by moving SW1 to the ON position.

10) Start the MAX6681 program by opening its icon in

the Start menu.

11) Wait until the program automatically detects the

address of the MAX6681 and displays the user-
interface panel (Figure 1).

Detailed Description

User-Interface Panel

The user interface is easy to operate; use the mouse, or
press the Tab and arrow keys to navigate. The check-
boxes, edit fields, and radio buttons correspond to bits
in the MAX6681 registers. Clicking on them generates
the correct SMBus command and updates the registers.

Note:

Words in boldface are user-selectable features in

the software.

Temperature

The MAX6681 monitors its own temperature and the
temperature of an external sensor. The internal sensor
has 8-bit resolution, which results in temperature reso-
lution of 1°C/LSB. The external sensor is capable of
either 8-bit or 11-bit (extended) resolution; see the
Configuration section for enabling extended resolution.
Extended resolution results in temperature resolution of
0.125°C/LSB.

Read the temperatures by clicking on the

Read Temp

buttons (Figure 1). The temperature is shown to the
right of the buttons.

The MAX6681 has high, low, and critical limit registers.
Temperature exceeding either the high or low limit regis-

MAX6681 Evaluation System/Evaluation Kit

_______________________________________________________________________________________

SUPPLIER

PHONE

FAX

WEBSITE

Central Semiconductor

631-435-1110

631-435-1824

www.centralsemi.com

Diodes Inc.

805-446-4800

805-381-3899

www.diodes.com

General Semiconductor

760-804-9258

760-804-9259

www.gensemi.com

Murata

770-436-1300

770-436-3030

www.murata.com

Taiyo Yuden

800-348-2496

847-925-0899

www.t-yuden.com

TDK

847-803-6100

847-390-4405

www.component.tdk.com

Component Suppliers

Note:

Please indicate you are using the MAX6681 when contacting these suppliers.

ters generates an alert interrupt. Exceeding the critical
limit generates an over-temperature (

OVERT) alarm.

Read the high, low, and critical limits by clicking on the

Read High

Read Low

, or

Read Critical

buttons,

respectively (Figure 1). The value (in Celsius) is shown
to the right of the button. Change the high, low, and
critical temperature limits by entering the value (in
Celsius) into the appropriate edit field. Pressing Enter,
after typing in the new value, updates the internal regis-
ter.

Note:

Writing to the critical limit registers overrides

the values set by the CRIT0 and CRIT1 pins; see the
Jumpers JU3 and JU4 section.

The MAX6681 includes hysteresis on the over-tempera-
ture alarm to prevent the

OVERT pin from oscillating. The

hysteresis sets the amount the temperature must
decrease from the critical limit to deassert the

OVERT pin.

Read the hysteresis register by clicking on the

Read

Hysteresis

button (Figure 1). The value (in Celsius) is

shown to the right of the button.

Change the hysteresis by entering the value (in
Celsius) into the edit field. Pressing Enter, after typing
in the new value, updates the internal register.

The MAX6681 also includes programmable offset for
the external temperature. Due to manufacturing toler-
ances of the external sensor, the temperature can be
off by a few degrees Celsius. The programmable offset
compensates for this variation.

There are two registers for the external offset. One sets
the fractional portion of the offset and the other sets the
integer portion.

Read the offset by clicking on the appropriate

Read

button (Figure 1). The value (in Celsius) is shown to the
right of the button.

Change the offset by entering the value (in Celsius) into
the edit fields. The fractional portion of the offset must
be in decimal format. Pressing Enter, after typing in the
new value, updates the internal register.

Configuration

The configuration register has several functions. Figure
2 shows the checkboxes that configure the register.
Each checkbox corresponds to a bit in the register:

Mask Alert

disables the

ALERT interrupt.

STOP

places the MAX6681 in software standby

mode.

Extended Resolution

increases the measurement of

the external sensor to 11 bits, giving it a resolution of
0.125°C.

Note:

Extended resolution only applies for

conversion rates of 4Hz or less.

Extended Range

extends the temperature range of

the external and internal sensor to -64°C.

Disable SMBus Timeout

disables the SMBus time-

out feature, as well as the alert response.

RESET

provides a software reset from the SMBus

master. The MAX6681 returns to its power-on reset
(POR) values.

Note:

The MAX6681 does not resam-

ple the address or critical limit pins (ADD0, ADD1,
CRIT0, and CRIT1) on software reset.

Read the configuration register by clicking on the

Read

Configuration

button (Figure 2).

Conversion Rate

The conversion rate sets the number of temperature
samples the MAX6681 takes per second.

Note:

The EV

kit software reads the MAX6681 a maximum of two
times a second (2Hz). Read the conversion rate regis-
ter by clicking on the

Read Conversion Rate

button

(Figure 3). Change the conversion rate by clicking on
the radio button next to the desired frequency.

Status

The Status box displays the critical and fault conditions
that occur. It also displays BUSY if the MAX6681 is per-
forming a conversion at the time that the status is read.

The critical and fault conditions are Internal Hot Limit,
Internal Cold Limit, External Hot Limit, External Cold
Limit, Diode Open, Internal Critical Limit, and External
Critical Limit. These conditions indicate that the temper-
ature has exceeded one of the limits. Diode Open indi-
cates that the external diode is open.

Read the status by clicking on the

Read Status

button.

Alert

The message ALERT appears in the Alert box when an
interrupt condition occurs unless the configuration reg-
ister is set to mask the alert. The cause of the interrupt
is shown in the status box. To clear the interrupt, first
eliminate the condition that caused it and then click on

Read Alert

Automatic Read

The program polls the device for new temperature and
status data a maximum of two times a second (2Hz). To
disable the polling of data, uncheck the

Automatic

Read

checkbox.

Data Logging

Check the

Data Logging

checkbox to activate data

logging. Data logging saves temperature, voltage, and
status data to a text file that includes a time/date stamp
next to each data point. If Automatic Read is enabled,
data is sampled at 2Hz; however, the data is logged to

Evaluate: MAX6681

MAX6681 Evaluation System/Evaluation Kit

_______________________________________________________________________________________

the file only if the temperature or status changes. This
slows the growth of the data-logging file. When
Automatic Read is disabled, the data is logged each
time the

Read All

button is clicked. To stop data log-

ging, uncheck the

Data Logging

checkbox.

Simple SMBus Commands

There are two methods for communicating with the
MAX6681: through the normal user-interface panel or
through the SMBus commands available by clicking the

MAXSMBus..

button. A display pops up that allows the

SMBus protocols, such as Read Byte and Write Byte, to
be executed. To stop normal user-interface execution
so that it does not override the manually set values, turn
off the update timer by unchecking the

Automatic

Read

checkbox.

The SMBus dialog boxes accept numeric data in bina-
ry, decimal, or hexadecimal. Hexadecimal numbers
should be prefixed by $ or 0x. Binary numbers must be
exactly eight digits.

Note:

In places where the slave

address asks for an 8-bit value, it must be the 7-bit
slave address of the MAX6681 as determined by the
addresses pins (ADD0 and ADD1) with the last bit set
to 1 for a read operation and a zero for a write.

Switch SW1

The slide switch, SW1, provides a means to force a
reset. This switch disables power to the device.

Jumpers JU1 and JU2

Jumpers JU1 and JU2 set the MAX6681 address. The
default address is 1001 110Y (ADD0 and ADD1 =
VCC); see Table 1 for a complete list of addresses. The
address is determined at POR and hardware RESET
only. The MAX6681 must undergo a power down or
hardware reset for a new address to become effective.

Jumpers JU3 and JU4

Jumpers JU3 and JU4 set the critical limits for the over-
temperature (

OVERT) feature. The OVERT pin on the

MAX6681 activates when the temperature exceeds the
limits programmed by pins CRIT0 and CRIT1, or by the
values in the critical limit registers. Table 2 lists the
jumper settings and the corresponding critical temper-
ature limits.

Jumper JU5

Jumper JU5 selects the interrupt mode for the

ALERT

pin. To operate the

ALERT pin in comparator mode,

install the shunt on JU5. In this mode, the

ALERT pin

only resets by removing the fault condition or by mask-
ing

ALERT in the configuration register.

To operate the

ALERT pin in the standard SMBus

ALERT mode, remove the shunt from JU5. In this mode,

the

ALERT pin resets once the master reads the Alert

address. Reading the Alert address does not clear the
status register. It still indicates what caused the alert.

Jumper JU6

Jumper JU6 selects which temperature source activates
the

OVERT pin. See Table 3 for the jumper settings.

Jumper JU7

Install a shunt on jumper JU7 to generate a hardware
reset and return the MAX6681 to the POR values.
Remove the shunt for normal operation.

Note:

The

MAX6681 resamples the address and critical limit pins
(ADD0, ADD1, CRIT0, and CRIT1) on hardware reset.

SHUNT

LOCATION

JU1 (ADD0)

JU2 (ADD1)

MAX6681

ADDRESS

2-3

0011 000Y

2-3

Open

0011 001Y

2-3

1-2

0011 010Y

Open

2-3

0101 001Y

Open

0101 010Y

Open

1-2

0101 011Y

1-2

2-3

1001 100Y

1-2

Open

1001 101Y

1-2*

1001 110Y

Table 1. JU1 and JU2 Shunt Settings for
SMBus Address

*Default position

Note:

The first 7 bits shown are the address. Y (bit 0) is the

SMBus read/write bit. This bit is a 1 for a read operation and a
zero for a write.

Evaluate: MAX6681

MAX6681 Evaluation System/Evaluation Kit

_______________________________________________________________________________________

SHUNT

LOCATION

OVER-TEMPERATURE SET

POINT (°C)

JU4 (CRIT1)

JU3 (CRIT0)

REMOTE

LOCAL

2-3

Open

2-3

1-2

Open

2-3

100

Open

105

Open

1-2

110

1-2

2-3

115

100

1-2

Open

120

105

1-2*

125

110

Table 2. JU3 and JU4 Shunt Settings for
the Over-Temperature Critical Limits

*Default position

Jumper JU8

Jumper JU8 controls shutdown on the MAX6681.
Jumper position 1-2 connects the

SHDN pin to VCC,

enabling the MAX6681 for normal operation. Position 2-
3 connects the

SHDN pin to GND, placing the

MAX6681 in shutdown mode.

To drive shutdown with an external signal, remove the
shunt from JU8 and apply the signal to the

SHDN pad.

Jumper JU9

To evaluate the MAX6681 with a different voltage, cut
the trace shorting the two pins of JU9 and apply a volt-
age to the pad labeled VCC.

Evaluate: MAX6681

MAX6681 Evaluation System/Evaluation Kit

_______________________________________________________________________________________

JUMPER

SHUNT

SETTINGS

FUNCTION

Open*

ALERT pin operates in standard SMBus ALERT mode.

JU5

Closed

ALERT pin operates in comparator mode.

1-2*

SENS_SEL pin connected to VCC. The remote sensor activates the

OVERT pin.

2-3

SENS_SEL pin connected to GND. The local sensor on the MAX6681 activates the

OVERT pin.

JU6

Open

SENS_SEL pin open. Both the remote sensor and local sensor on the MAX6681 activate the

OVERT pin.

Open*

Normal operation.

JU7

Closed

Hardware reset. Forces the MAX6681 to reset to the POR values.

1-2*

SHDN = High. MAX6681 enabled.

2-3

SHDN = Low. MAX6681 disabled.

JU8

Open

Drive the

SHDN pad with an external signal.

Table 3. JU5JU8 Shunt Settings

*Default position

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