MAX1668MEE+ - Hytronics - Datasheet.Directory

________________General Description

The MAX1668/MAX1805/MAX1989 are precise multi-

channel digital thermometers that report the tempera-

ture of all remote sensors and their own packages. The

remote sensors are diode-connected transistors—typi-

cally low-cost, easily mounted 2N3904 NPN types—that

replace conventional thermistors or thermocouples.

Remote accuracy is ±3°C for multiple transistor manu-

facturers, with no calibration needed. The remote chan-

nels can also measure the die temperature of other ICs,

such as microprocessors, that contain an on-chip,

diode-connected transistor.

The 2-wire serial interface accepts standard system

management bus (SMBus™) write byte, read byte, send

byte, and receive byte commands to program the alarm

thresholds and to read temperature data. The data for-

mat is 7 bits plus sign, with each bit corresponding to

1°C, in two’s-complement format.

The MAX1668/MAX1805/MAX1989 are available in

small, 16-pin QSOP surface-mount packages. The

MAX1989 is also available in a 16-pin TSSOP.

________________________Applications

____________________________Features

♦Multichannel

4 Remote, 1 Local (MAX1668/MAX1989)

2 Remote, 1 Local (MAX1805)

♦No Calibration Required

♦SMBus 2-Wire Serial Interface

♦Programmable Under/Overtemperature Alarms

♦Supports SMBus Alert Response

♦Accuracy

±2°C (+60°C to +100°C, Local)

±3°C (-40°C to +125°C, Local)

±3°C (+60°C to +100°C, Remote)

♦3µA (typ) Standby Supply Current

♦700µA (max) Supply Current

♦Small, 16-Pin QSOP/TSSOP Packages

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

________________________________________________________________ Maxim Integrated Products 1

SMBCLK

ADD0 ADD1

VCC STBY

GND

ALERT

SMBDATA

DXP1

DXP4

DXN4

INTERRUPT

TO µC

3V TO 5.5V

200Ω

0.1µF

CLOCK

10kΩ EACH

DATA

DXN1

2200pF

DIODE-CONNECTED TRANSISTOR

MAX1668

MAX1805

MAX1989

Pin Configuration

DXP1 GND

STBY

SMBCLK

SMBDATA

ALERT

ADD0

ADD1

VCC

TOP VIEW

MAX1668

MAX1805

MAX1989

QSOP/TSSOP

DXN1

DXP2

(N.C.) DXN3

DXN2

(N.C.) DXP3

(N.C.) DXP4

( ) ARE FOR MAX1805.

(N.C.) DXN4

Typical Operating Circuit

19-1766; Rev 2; 5/03

PART

MAX1668MEE -55°C to +125°C

TEMP RANGE PIN-PACKAGE

16 QSOP

_______________Ordering Information

SMBus is a trademark of Intel Corp. †Pg

MAX1805MEE -55°C to +125°C 16 QSOP

Desktop and Notebook

Computers

LAN Servers

Industrial Controls

Central-Office Telecom

Equipment

Test and Measurement

Multichip Modules

MAX1989MEE -55°C to +125°C 16 QSOP

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.

MAX1989MUE -55°C to +125°C 16 TSSOP

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA= 0°C to +125°C, unless otherwise noted.)

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

DXP_, ADD_, STBY to GND........................-0.3V to (VCC + 0.3V)

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

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

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

DXN_ Current......................................................................±1mA

Continuous Power Dissipation (TA= +70°C)

QSOP (derate 8.30mW/°C above +70°C)....................667mW

TSSOP (derate 9.40mW/°C above +70°C) ..................755mW

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

DXP_ forced to 1.5VRemote-Diode Source Current

Low level (POR state)

Configuration byte =

X0XXXX10, high level

Configuration byte =

X0XXXX01, high level

High level (POR state)

71013

200

DXN_ Source Voltage 0.7 V

Hardware or software standby,

SMBCLK at 10kHz

SMBus static

TA = 0°C to +85°C

TA = +60°C to +100°C

Average measured over 4s; logic inputs forced

VCC or GND

Temperature Error, Local Diode

(Notes 1, 2) -3.5 +3.5 °C

-2.5 +2.5

Including long-term drift

Temperature Error, Remote Diode

(Notes 2, 3) -5 +5 °C

-3 +3

TR = -55°C to +125°C

TR = +60°C to +100°C

PARAMETER MIN TYP MAX UNITS

Undervoltage Lockout Hysteresis 50 mV

Undervoltage Lockout Threshold 2.60 2.8 2.95 V

Supply Voltage Range 3.0 5.5 V

Initial Temperature Error,

Local Diode (Note 2) -3 +3 °C

Power-On Reset (POR) Threshold 1.3 1.8 2.3 V

POR Threshold Hysteresis 50 mV

310

Standby Supply Current

512

µA

Temperature Resolution (Note 1) 8Bits

-2 +2

Average Operating Supply Current 400 700 µA

Conversion Time 260 320 380 ms

70 100 130

µA

Address Pin Bias Current 160 µA

CONDITIONS

VCC input, disables A/D conversion, rising edge

TA = 0°C to +125°C

VCC, falling edge

From stop bit to conversion complete (all channels)

Logic inputs

forced to VCC

or GND

ADD0, ADD1; momentary upon power-on reset

Monotonicity guaranteed

TA = +60°C to +100°C

ADC AND POWER SUPPLY

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +3.3V, STBY = VCC, configuration byte = X0XXXX00, TA= 0°C to +125°C, unless otherwise noted.)

STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V

tHIGH, 90% to 90% points

tLOW, 10% to 10% points

(Note 4)

SMBCLK, SMBDATA

Logic inputs forced to VCC or GND

ALERT forced to 5.5V

STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V

ALERT, SMBDATA forced to 0.4V

CONDITIONS

µs4SMBCLK Clock High Time

µs4.7SMBCLK Clock Low Time

kHzDC 100SMBus Clock Frequency

pF5SMBus Input Capacitance

µA-1 +1Logic Input Current

µA1

ALERT Output High Leakage

Current

V2.2Logic Input High Voltage

V0.8Logic Input Low Voltage

mA6Logic Output Low Sink Current

UNITSMIN TYP MAXPARAMETER

tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK

tSU:STO, 90% of SMBCLK to 10% of SMBDATA

tHD:STA, 10% of SMBDATA to 90% of SMBCLK

tSU:STA, 90% to 90% points

ns250

SMBus Data Valid to SMBCLK

Rising-Edge Time

µs4SMBus Stop-Condition Setup Time

µs4SMBus Start-Condition Hold Time

ns250

SMBus Repeated Start-Condition

Setup Time

µs4.7SMBus Start-Condition Setup Time

nsSMBus Data-Hold Time

Master clocking in data µs1

SMBCLK Falling Edge to SMBus

Data-Valid Time

SMBus INTERFACE

ELECTRICAL CHARACTERISTICS

(VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)

CONDITIONS

Monotonicity guaranteed

TA= +60°C to +100°C

Bits8Temperature Resolution

-2 +2

TR= +60°C to +100°C

TA= -55°C to +125°C °C

-3 +3

Initial Temperature Error,

Local Diode (Note 2)

V4.5 5.5Supply-Voltage Range

From stop bit to conversion complete (both channels) ms260 380Conversion Time

-3 +3

TR= -55°C to +125°C °C

UNITSMIN TYP MAX

-5 +5

PARAMETER

Temperature Error, Remote Diode

(Notes 2, 3)

ADC AND POWER SUPPLY

tHD:DAT, slave receive (Note 5) 0

MAX1668/1805 toc03

FREQUENCY (MHz)

TEMPERATURE ERROR (°C)

TEMPERATURE ERROR

vs. SUPPLY NOISE FREQUENCY

100mVP-P

0.1 1 10 100

WITH VCC 0.1µF CAPACITOR REMOVED

2200pF BETWEEN DXN_ AND DXP_

250mVP-P

-20

1 10 100

TEMPERATURE ERROR

vs. PC BOARD RESISTANCE

-10

MAX1668/1805 toc01

LEAKAGE RESISTANCE (MΩ)

TEMPERATURE ERROR (°C)

PATH = DXP_ TO GND

PATH = DXP_ TO VCC (5V)

-2

-1

-50 -10-30 1030507090110

TEMPERATURE ERROR

vs. TEMPERATURE

MAX1668/1805 toc02

TEMPERATURE (°C)

TEMPERATURE ERROR (°C)

NPN (CMPT3904)

PNP (CMPT3906)

INTERNAL

Typical Operating Characteristics

(Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.)

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)

Note 1: Guaranteed by design, but not production tested.

Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1668/MAX1805/

MAX1989 device temperature is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization

error plus the +0.5°C offset used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to

+100°C temperature range. See Table 2.

Note 3: A remote diode is any diode-connected transistor from Table 1. TRis the junction temperature of the remote diode. See the

Remote-Diode Selection section for remote-diode forward-voltage requirements.

Note 4: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it

violates the 10kHz minimum clock frequency and SMBus specifications, and can monopolize the bus.

Note 5: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of

SMBCLK’s falling edge tHD:DAT.

Note 6: Specifications from -55°C to +125°C are guaranteed by design, not production tested.

CONDITIONS UNITSMIN TYP MAXPARAMETER

STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V

Logic Input High Voltage V2.4

ALERT forced to 5.5V µA1

ALERT Output High Leakage

Current

Logic inputs forced to VCC or GND µA-2 +2Logic Input Current

ALERT, SMBDATA forced to 0.4V mA6Logic Output Low Sink Current

STBY, SMBCLK, SMBDATA; VCC = 4.5V to 5.5V V0.8Logic Input Low Voltage

SMBus INTERFACE

100

120

140

160

012345

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1668/1805 toc07

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

STBY = GND

ADD0 = ADD1 = HIGH-Z

ADD0 = ADD1 = GND

100

125

-2 20468

RESPONSE TO THERMAL SHOCK

MAX1668/1805 toc08

TIME (s)

TEMPERATURE (°C)

16 QSOP IMMERSED IN

+115°C FLUORINERT BATH

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

_______________________________________________________________________________________ 5

0.1 1 1000

TEMPERATURE ERROR

vs. COMMON-MODE NOISE FREQUENCY

MAX1668/1805 toc04

FREQUENCY (MHz)

TEMPERATURE ERROR (°C)

10 100

0.6

0.4

0.2

0.8

1.0

1.2

1.4

1.6

1.8

2.0

SQUARE-WAVE AC-COUPLED INTO DXN

2200pF BETWEEN DXN_ AND DXP_

100mVP-P

50mVP-P

Typical Operating Characteristics (continued)

(Typical Operating Circuit, VCC = +5V, STBY = VCC, configuration byte = X0XXXX00, TA = +25°C, unless otherwise noted.)

TEMPERATURE ERROR

vs. DXP_ TO DXN_ CAPACITANCE

MAX16681805 toc05

DXP_ TO DXN_ CAPACITANCE (nF)

TEMPERATURE ERROR (°C)

-10

-6

-8

-2

-4

0203010 40 50 60

STANDBY SUPPLY CURRENT

vs. CLOCK FREQUENCY

MAX1668/1805 toc06

SMBCLK FREQUENCY (kHz)

SUPPLY CURRENT (µA)

1 10 100 1000

STBY = GND

VCC = 5V

VCC = 3.3V

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

6 _______________________________________________________________________________________

_______________Detailed Description

The MAX1668/MAX1805/MAX1989 are temperature

sensors designed to work in conjunction with an exter-

nal microcontroller (µC) or other intelligence in thermo-

static, process-control, or monitoring applications. The

µC is typically a power-management or keyboard con-

troller, generating SMBus serial commands by “bit-

banging” general-purpose input-output (GPIO) pins or

through a dedicated SMBus interface block.

These devices are essentially 8-bit serial analog-to-digi-

tal converters (ADCs) with sophisticated front ends.

However, the MAX1668/MAX1805/MAX1989 also contain

a switched current source, a multiplexer, an ADC, an

SMBus interface, and associated control logic (Figure 1).

In the MAX1668 and MAX1989, temperature data from

the ADC is loaded into five data registers, where it is

automatically compared with data previously stored in

10 over/undertemperature alarm registers. In the

MAX1805, temperature data from the ADC is loaded into

three data registers, where it is automatically compared

with data previously stored in six over/undertemperature

alarm registers.

ADC and Multiplexer

The ADC is an averaging type that integrates over a

64ms period (each channel, typical), with excellent

noise rejection.

The multiplexer automatically steers bias currents

through the remote and local diodes, measures their

forward voltages, and computes their temperatures.

Each channel is automatically converted once the con-

version process has started. If any one of the channels

is not used, the device still performs measurements on

these channels, and the user can ignore the results of

the unused channel. If any remote-diode channel is

unused, connect DXP_ to DXN_ rather than leaving the

pins open.

The DXN_ input is biased at 0.65V above ground by an

internal diode to set up the A/D inputs for a differential

measurement. The worst-case DXP_ to DXN_ differential

input voltage range is 0.25V to 0.95V.

Excess resistance in series with the remote diode caus-

es about +0.5°C error per ohm. Likewise, 200µV of offset

voltage forced on DXP_ to DXN_ causes about 1°C error.

MAX1668/

MAX1989

FUNCTION

1, 3, 5, 7 DXP_

Combined Current Source and A/D Positive Input for Remote-Diode 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.

12 ALERT SMBus Alert (Interrupt) Output, Open Drain

11 ADD0 SMBus Slave Address Select Pin

10 ADD1

SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up.

Excess capacitance (>50pF) at the address pins when floating can cause address-

recognition problems.

15 STBY Hardware Standby Input. Temperature and comparison threshold data are retained in

standby mode. Low = standby mode, high = operate mode.

14 SMBCLK SMBus Serial-Clock Input

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

1, 3

Pin Description

NAMEMAX1805

2, 4, 6, 8 DXN_ Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode volt-

age above ground.

2, 4

9 VCC Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ωseries

resistor is recommended but not required for additional noise filtering.

16 GND Ground16

—N.C. No Connection. Not internally connected. Can be used for PC board trace routing.5–8

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

_______________________________________________________________________________________ 7

Figure 1. MAX1668/MAX1805/MAX1989 Functional Diagram

DXP4

DXP3

DXP2

DXP1

DXN4

DXN3

DXN2

DXN1

LOCAL

CURRENT

SOURCES

MUX

DIODE

FAULT

ADC CONTROL

LOGIC SMBus

ADDRESS

DECODER

STBY ADD ADD1

SMBDATA

SMBCLK

ALERT

DIGITAL COMPARATORS

ALERT RESPONSE

CONFIGURATION BYTE

ADDRESS REGISTER

STATUS BYTE REGISTERS

1 AND 2

COMMAND BYTE REGISTER

TEMPERATURE DATA REGISTERS

HIGH LIMITS REGISTERS

LOW LIMITS REGISTERS

ALERT MASK

NOTE: DOTTED LINES ARE FOR MAX1668 AND MAX1989.

A/D Conversion Sequence

If a start command is written (or generated automatically

in the free-running autoconvert mode), all channels are

converted, and the results of all measurements are

available after the end of conversion. A BUSY status bit

in the status byte shows that the device is actually per-

forming a new conversion; however, even if the ADC is

busy, the results of the previous conversion are always

available.

Remote-Diode Selection

Temperature accuracy depends on having a good-qual-

ity, diode-connected small-signal transistor. Accuracy

has been experimentally verified for all of the devices

listed in Table 1. The MAX1668/MAX1805/MAX1989 can

also directly measure the die temperature of CPUs and

other ICs having on-board temperature-sensing diodes.

The transistor must be a small-signal type, either NPN

or PNP, with a relatively high forward voltage; other-

wise, the A/D input voltage range can be violated. The

forward voltage must be greater than 0.25V at 10µA;

check to ensure this is true at the highest expected

temperature. The forward voltage must be less than

0.95V at 100µA; check to ensure this is true at the low-

est expected temperature. Large power transistors do

not work at all. Also, ensure that the base resistance is

less than 100Ω. Tight specifications for forward-current

gain (+50 to +150, for example) indicate that the manu-

facturer has good process controls and that the

devices have consistent VBE characteristics.

For heat-sink mounting, the 500-32BT02-000 thermal

sensor from Fenwal Electronics is a good choice. This

device consists of a diode-connected transistor, an

aluminum plate with screw hole, and twisted-pair cable

(Fenwal Inc., Milford, MA, 508-478-6000).

Thermal Mass and Self-Heating

Thermal mass can seriously degrade the MAX1668/

MAX1805/MAX1989s’ effective accuracy. The thermal

time constant of the 16-pin QSOP package is about

140s in still air. For the MAX1668/MAX1805/MAX1989

junction temperature to settle to within +1°C after a

sudden +100°C change requires about five time con-

stants or 12 minutes. The use of smaller packages for

remote sensors, such as SOT23s, improves the situa-

tion. Take care to account for thermal gradients

between the heat source and the sensor, and ensure

that stray air currents across the sensor package do

not interfere with measurement accuracy.

Self-heating does not significantly affect measurement

accuracy. Remote-sensor self-heating due to the diode

current source is negligible. For the local diode, the

worst-case error occurs when sinking maximum current

at the ALERT output. For example, with ALERT sinking

1mA, the typical power dissipation is VCC x 400µA plus

0.4V x 1mA. Package theta J-A is about 150°C/W, so

with VCC = 5V and no copper PC board heat sinking,

the resulting temperature rise is:

dT = 2.4mW x 150°C/W = 0.36°C

Even with these contrived circumstances, it is difficult

to introduce significant self-heating errors.

ADC Noise Filtering

The ADC is an integrating type with inherently good

noise rejection, especially of low-frequency signals such

as 60Hz/120Hz power-supply hum. Micropower opera-

tion places constraints on high-frequency noise rejec-

tion; therefore, careful PC board layout and proper

external noise filtering are required for high-accuracy

remote measurements in electrically noisy environments.

High-frequency EMI is best filtered at DXP_ and DXN_

with an external 2200pF capacitor. This value can be

increased to about 3300pF (max), including cable

capacitance. Higher capacitance than 3300pF intro-

duces errors due to the rise time of the switched cur-

rent source.

Nearly all noise sources tested cause additional error

measurements, typically by +1°C to +10°C, depending

on the frequency and amplitude (see the Typical

Operating Characteristics).

PC Board Layout

1) Place the MAX1668/MAX1805/MAX1989 as close as

practical to the remote diode. In a noisy environment,

such as a computer motherboard, this distance can

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

8 _______________________________________________________________________________________

CMPT3904Central Semiconductor (USA)

MMBT3904Motorola (USA)

MMBT3904

SST3904Rohm Semiconductor (Japan)

KST3904-TFSamsung (Korea)

FMMT3904CT-NDZetex (England)

MANUFACTURER MODEL NO.

SMBT3904Siemens (Germany)

Table 1. Remote-Sensor Transistor

Manufacturers

Note: Transistors must be diode connected (base shorted to

collector).

National Semiconductor (USA)

be 4in to 8in (typ) or more as long as the worst noise

sources (such as CRTs, clock generators, memory

buses, and ISA/PCI buses) are avoided.

2) Do not route the DXP_ to DXN_ lines next to the

deflection coils of a CRT. Also, do not route the

traces across a fast memory bus, which can easily

introduce +30°C error, even with good filtering.

Otherwise, most noise sources are fairly benign.

3) Route the DXP_ and DXN_ traces in parallel and in

close proximity to each other, away from any high-

voltage traces such as +12VDC. Leakage currents

from PC board contamination must be dealt with

carefully, since a 20MΩleakage path from DXP_ to

ground causes about +1°C error.

4) Connect guard traces to GND on either side of the

DXP_ to DXN_ traces (Figure 2). With guard traces

in place, routing near high-voltage traces is no

longer an issue.

5) Route through as few vias and crossunders as possi-

ble to minimize copper/solder thermocouple effects.

6) When introducing a thermocouple, make sure that

both the DXP_ and the DXN_ paths have matching

thermocouples. In general, PC board-induced ther-

mocouples are not a serious problem. A copper-sol-

der thermocouple exhibits 3µV/°C, and it takes

about 200µV of voltage error at DXP_ to DXN_ to

cause a +1°C measurement error. So, most para-

sitic thermocouple errors are swamped out.

7) Use wide traces. Narrow ones are more inductive

and tend to pick up radiated noise. The 10mil

widths and spacings recommended in Figure 2 are

not absolutely necessary (as they offer only a minor

improvement in leakage and noise), but try to use

them where practical.

8) Copper cannot be used as an EMI shield, and only

ferrous materials such as steel work well. Placing a

copper ground plane between the DXP_ to DXN_

traces and traces carrying high-frequency noise sig-

nals does not help reduce EMI.

PC Board Layout Checklist

• Place the MAX1668/MAX1805/MAX1989 as close as

possible to the remote diodes.

• Keep traces away from high voltages (+12V bus).

• Keep traces away from fast data buses and CRTs.

• Use recommended trace widths and spacings.

• Place a ground plane under the traces.

• Use guard traces flanking DXP_ and DXN_ and con-

necting to GND.

• Place the noise filter and the 0.1µF VCC bypass

capacitors close to the MAX1668/MAX1805/

MAX1989.

• Add a 200Ωresistor in series with VCC for best noise

filtering (see the Typical Operating Circuit).

Twisted-Pair and Shielded Cables

For remote-sensor distances longer than 8in, or in partic-

ularly noisy environments, a twisted pair is recommend-

ed. Its practical length is 6ft to 12ft (typ) before noise

becomes a problem, as tested in a noisy electronics lab-

oratory. For longer distances, the best solution is a

shielded twisted pair like that used for audio micro-

phones. For example, Belden #8451 works well for dis-

tances up to 100ft in a noisy environment. Connect the

twisted pair to DXP_ and DXN_ and the shield to GND,

and leave the shield’s remote end unterminated.

Excess capacitance at DX_ _ limits practical remote-sen-

sor distances (see the Typical Operating Characteristics).

For very long cable runs, the cable’s parasitic capaci-

tance often provides noise filtering, so the 2200pF capac-

itor can often be removed or reduced in value.

Cable resistance also affects remote-sensor accuracy;

1Ωseries resistance introduces about +0.5°C error.

Low-Power Standby Mode

Standby mode disables the ADC and reduces the sup-

ply-current drain to less than 12µA. Enter standby

mode by forcing the STBY pin low or through the

RUN/STOP bit in the configuration byte register.

Hardware and software standby modes behave almost

identically: all data is retained in memory, and the SMB

interface is alive and listening for reads and writes.

Activate hardware standby mode by forcing the STBY

pin low. In a notebook computer, this line can be con-

nected to the system SUSTAT# suspend-state signal.

The STBY pin low state overrides any software conversion

command. If a hardware or software standby command

is received while a conversion is in progress, the conver-

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

_______________________________________________________________________________________ 9

MINIMUM

10mils

GND

DXN_

DXP_

Figure 2. Recommended DXP_/DXN_ PC Traces

sion cycle is truncated, and the data from that conversion

is not latched into either temperature-reading register. The

previous data is not changed and remains available.

In standby mode, supply current drops to about 3µA.

At very low supply voltages (under the power-on-reset

threshold), the supply current is higher due to the

address pin bias currents. It can be as high as 100µA,

depending on ADD0 and ADD1 settings.

SMBus Digital Interface

From a software perspective, the MAX1668/MAX1805/

MAX1989 appear as a set of byte-wide registers that

contain temperature data, alarm threshold values, or

control bits. A standard SMBus 2-wire serial interface is

used to read temperature data and write control bits and

alarm threshold data. Each A/D channel within the

devices responds to the same SMBus slave address for

normal reads and writes.

The MAX1668/MAX1805/MAX1989 employ four standard

SMBus protocols: write byte, read byte, send byte, and

receive byte (Figure 3). The shorter receive byte protocol

allows quicker transfers, provided that the correct data

tion. Use caution with the shorter protocols in multimaster

systems, since a second master could overwrite the com-

mand byte without informing the first master.

The temperature data format is 7 bits plus sign in two’s-com-

plement form for each channel, with each data bit represent-

ing 1°C (Table 2), transmitted MSB first. Measurements are

offset by +0.5°C to minimize internal rounding errors; for

example, +99.6°C is reported as +100°C.

Alarm Threshold Registers

Ten (six for MAX1805) registers store alarm threshold

data, with high-temperature (THIGH) and low-tempera-

ture (TLOW) registers for each A/D channel. If either

measured temperature equals or exceeds the corre-

sponding alarm threshold value, an ALERT interrupt is

asserted.

The power-on-reset (POR) state of all THIGH registers of

the MAX1668 and MAX1805 is full scale (0111 1111, or

+127°C). The POR state of the channel 1 THIGH register

of the MAX1989 is 0110 1110 or +110°C, while all other

channels are at +127°C. The POR state of all TLOW reg-

isters is 1100 1001 or -55°C.

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

10 ______________________________________________________________________________________

ACK

7 bits

ADDRESS ACKWR

8 bits

DATA ACK

8 bits

SCOMMAND

Write Byte Format

Read Byte Format

Send Byte Format Receive Byte Format

Slave Address: equiva-

lent to chip-select line of

a 3-wire interface

Command Byte: selects which

Data Byte: data goes into the register

set by the command byte (to set

thresholds, configuration masks, and

sampling rate)

ACK

7 bits

ADDRESS ACKWR SACK

8 bits

DATA

7 bits

ADDRESS RD

8 bits

/// PS COMMAND

Slave Address: equiva-

lent to chip-select line

Command Byte: selects

which register you are

reading from

Slave Address: repeated

due to change in data-

flow direction

Data Byte: reads from

the register set by the

command byte

ACK

7 bits

ADDRESS WR

8 bits

COMMAND ACK PS ACK

7 bits

ADDRESS RD

8 bits

DATA /// PS

Command Byte: sends com-

mand with no data

Data Byte: This command only

works immediately following a

Read Byte. Reads data from the

Read Byte; also used for SMBus

Alert Response return address

S = Start condition Shaded = Slave transmission

P = Stop condition /// = Not acknowledged

Figure 3. SMBus Protocols

Diode Fault Alarm

There is a continuity fault detector at DXP_ that detects

whether the remote diode has an open-circuit condi-

tion. At the beginning of each conversion, the diode

fault is checked, and the status byte is updated. This

fault detector is a simple voltage detector; if DXP_ rises

above VCC - 1V (typ) due to the diode current source, a

fault is detected. Note that the diode fault is not

checked until a conversion is initiated, so immediately

after power-on reset, the status byte indicates no fault

is present, even if the diode path is broken.

If any remote channel is shorted (DXP_ to DXN_ or

DXP_ to GND), the ADC reads 0000 0000 so as not to

trip either the THIGH or TLOW alarms at their POR set-

tings. In applications that are never subjected to 0°C in

normal operation, a 0000 0000 result can be checked

to indicate a fault condition in which DXP_ is acciden-

tally short circuited. Similarly, if DXP_ is short circuited

to VCC, the ADC reads +127°C for all remote and local

channels, and the device alarms.

AALLEERRTT

Interrupts

The ALERT interrupt output signal is latched and can

only be cleared by reading the alert response address.

Interrupts are generated in response to THIGH and TLOW

comparisons and when a remote diode is disconnected

(for continuity fault detection). The interrupt does not halt

automatic conversions; new temperature data continues

to be available over the SMBus interface after ALERT is

asserted. The interrupt output pin is open drain so that

devices can share a common interrupt line. The interrupt

rate can never exceed the conversion rate.

The interface responds to the SMBus alert response

address, an interrupt pointer return-address feature

(see Alert Response Address section). Prior to taking

corrective action, always check to ensure that an inter-

rupt is valid by reading the current temperature.

Alert Response Address

The SMBus alert response interrupt pointer provides

quick fault identification for simple slave devices that

lack the complex, expensive logic needed to be a bus

master. Upon receiving an ALERT interrupt signal, the

host master can broadcast a receive byte transmission

to the alert response slave address (0001 100). Then

any slave device that generated an interrupt attempts

to identify itself by putting its own address on the bus

(Table 3).

The alert response can activate several different slave

devices simultaneously, similar to the I2C general call. If

more than one slave attempts to respond, bus arbitra-

tion rules apply, and the device with the lower address

code wins. The losing device does not generate an

acknowledge and continues to hold the ALERT line low

until serviced (implies that the host interrupt input is

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

______________________________________________________________________________________ 11

Table 2. Data Format (Two’s Complement) Table 3. Read Format for Alert Response

Address (0001100)

ADD66Provide the current

MAX1668/MAX1805/MAX1989

slave address that was latched at

POR (Table 8)

FUNCTION

ADD55

ADD44

ADD33

ADD22

ADD11

ADD7

(MSB)

(LSB) Logic 1

BIT NAME

DIGITAL OUTPUT DATA BITS

TEMP

(°C)

ROUNDED

TEMP

(°C) SIGN MSB LSB

+130.00 +127 0 111 1111

+127.00 +127 0 111 1111

+126.50 +127 0 111 1111

+126.00 +126 0 111 1110

+25.25 +25 0 001 1001

+0.50 +1 0 000 0000

+0.25 +0 0 000 0000

+0.00 +0 0 000 0000

-0.25 +0 0 000 0000

-0.50 +0 0 000 0000

-0.75 -1 1 111 1111

-1.00 -1 1 111 1111

-25.00 -25 1 110 0111

-25.50 -25 1 110 0110

-54.75 -55 1 100 1001

-55.00 -55 1 100 1001

-65.00 -65 1 011 1111

-70.00 -65 1 011 1111

level sensitive). Successful reading of the alert

response address clears the interrupt latch.

Command Byte Functions

The 8-bit command byte register (Table 4) is the master

index that points to the various other registers within the

MAX1668/MAX1805/MAX1989. The register’s POR

state is 0000 0000, so that a receive byte transmission

(a protocol that lacks the command byte) that occurs

immediately after POR returns the current local temper-

ature data.

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

12 ______________________________________________________________________________________

Table 4. Command Byte Bit Assignments for MAX1668/MAX1805/MAX1989

*If the device is in hardware standby mode at POR, all temperature registers read 0°C.

**Not available for MAX1805.

RIT 00h 0000 0000* Read local temperature

RET1 01h 0000 0000* Read remote DX1 temperature

RET2 02h 0000 0000* Read remote DX2 temperature

RET3** 03h 0000 0000* Read remote DX3 temperature

RET4** 04h 0000 0000* Read remote DX4 temperature

RS1 05h 0000 0000 Read status byte 1

RS2 06h 0000 0000 Read status byte 2

RC 07h 0000 0000 Read Configuration Byte

RIHL 08h 0111 1111 Read local THIGH limit

RILL 09h 1100 1001 Read local TLOW limit

REHL1 0Ah 0111 1111

(0110 1110) Read remote DX1 THIGH limit (MAX1989)

RELL1 0Bh 1100 1001 Read remote DX1 TLOW limit

REHL2 0Ch 0111 1111 Read remote DX2 THIGH limit

RELL2 0Dh 1100 1001 Read remote DX2 TLOW limit

REHL3** 0Eh 0111 1111 Read remote DX3 THIGH limit

RELL3** 0Fh 1100 1001 Read remote DX3 TLOW limit

REHL4** 10h 0111 1111 Read remote DX4 THIGH limit

RELL4** 11h 1100 1001 Read remote DX4 TLOW limit

WC 12h N/A Write configuration byte

WIHL 13h N/A Write local THIGH limit

WILL 14h N/A Write local TLOW limit

WEHI1 15h N/A Write remote DX1 THIGH limit

WELL1 16h N/A Write remote DX1 TLOW limit

WEHI2 17h N/A Write remote DX2 THIGH limit

WELL2 18h N/A Write remote DX2 TLOW limit

WEHI3** 19h N/A Write remote DX3 THIGH limit

WELL3** 1Ah N/A Write remote DX3 TLOW limit

WEHI4** 1Bh N/A Write remote DX4 THIGH limit

WELL4** 1Ch N/A Write remote DX4 TLOW limit

MFG ID FEh 0100 1101 Read manufacture ID

DEV ID FFh 0000 0011 (0000 0101)

[0000 1011] Read device ID (for MAX1805) [for MAX1989]

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

______________________________________________________________________________________ 13

Manufacturer and Device

ID Codes

Two ROM registers provide manufacturer and device

ID codes. Reading the manufacturer ID returns 4Dh,

which is the ASCII code M (for Maxim). Reading the

device ID returns 03h for MAX1668, 05h for MAX1805,

and 0Bh for MAX1989. If the read word 16-bit SMBus

protocol is employed (rather than the 8-bit Read Byte),

the least significant byte contains the data and the most

significant byte contains 00h in both cases.

Configuration Byte Functions

The configuration byte register (Table 5) is used to

mask (disable) interrupts and to put the device in soft-

ware standby mode.

Status Byte Functions

The two status byte registers (Tables 6 and 7) indicate

which (if any) temperature thresholds have been

exceeded. The first byte also indicates whether the

ADC is converting and whether there is an open circuit

in a remote-diode DXP_ to DXN_ path. After POR, the

normal state of all the flag bits is zero, assuming none

of the alarm conditions are present. The status byte is

cleared by any successful read of the status byte,

unless the fault persists. Note that the ALERT interrupt

latch is not automatically cleared when the status flag

bit is cleared.

When reading the status byte, you must check for inter-

nal bus collisions caused by asynchronous ADC timing,

or else disable the ADC prior to reading the status byte

(through the RUN/STOP bit in the configuration byte).

To check for internal bus collisions, read the status

byte. If the least significant 7 bits are ones, discard the

data and read the status byte again. The status bits

LHIGH, LLOW, RHIGH, and RLOW are refreshed on the

SMBus clock edge immediately following the stop con-

dition, so there is no danger of losing temperature-relat-

ed status data as a result of an internal bus collision.

The OPEN status bit (diode continuity fault) is only

refreshed at the beginning of a conversion, so OPEN

data is lost. The ALERT interrupt latch is independent of

the status byte register, so no false alerts are generated

by an internal bus collision.

If the THIGH and TLOW limits are close together, it’s

possible for both high-temp and low-temp status bits to

be set, depending on the amount of time between sta-

tus read operations (especially when converting at the

fastest rate). In these circumstances, it’s best not to rely

on the status bits to indicate reversals in long-term tem-

perature changes and instead use a current tempera-

ture reading to establish the trend direction.

Conversion Rate

The MAX1668/MAX1805/MAX1989 are continuously

measuring temperature on each channel. The typical

conversion rate is approximately three conversions/s

(for both devices). The resulting data is stored in the

temperature data registers.

Slave Addresses

The MAX1668/MAX1805/MAX1989 appear to the

SMBus as one device having a common address for all

ADC channels. The device address can be set to one

of nine different values by pin-strapping ADD0 and

ADD1 so that more than one MAX1668/MAX1805/

MAX1989 can reside on the same bus without address

conflicts (Table 8).

The address pin states are checked at POR only, and

the address data stays latched to reduce quiescent

supply current due to the bias current needed for high-Z

state detection.

The MAX1668/MAX1805/MAX1989 also respond to the

SMBus alert response slave address (see the Alert

Response Address section).

POR and Undervoltage Lockout

The MAX1668/MAX1805/MAX1989 have a volatile

memory. To prevent ambiguous power-supply condi-

tions from corrupting the data in memory and causing

erratic behavior, a POR voltage detector monitors VCC

and clears the memory if VCC falls below 1.8V (typ, see

the Electrical Characteristics table). When power is first

applied and VCC rises above 1.85V (typ), the logic

blocks begin operating, although reads and writes at

VCC levels below 3V are not recommended. A second

VCC comparator, the ADC UVLO comparator, prevents

the ADC from converting until there is sufficient head-

room (VCC = 2.8V typ).

Power-Up Defaults

•Interrupt latch is cleared.

•Address select pins are sampled.

•ADC begins converting.

•Command byte is set to 00h to facilitate quick

remote receive byte queries.

•THIGH and TLOW registers are set to max and min

limits, respectively.

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

14 ______________________________________________________________________________________

Table 5. Configuration Byte Bit Assignments

Table 7. Status Byte 2 Bit Assignments

Table 6. Status Byte Bit 1 Assignments

Note: All flags in this byte stay high until cleared by POR or until the status byte is read.

BIT NAME

POR

FUNCTION

7 (MSB) MASKALL 0 Masks all ALERT interrupts when high.

6 RUN/STOP 0 Standby mode control bit. If high, the device immediately stops converting and

enters standby mode. If low, the device converts.

5 MASK4* 0 Masks remote DX4 interrupts when high.

4 MASK3* 0 Masks remote DX3 interrupts when high.

3 MASK2 0 Masks remote DX2 interrupts when high.

2 MASK1 0 Masks remote DX1 interrupts when high.

0 IBIAS1 0 M ed i um /l ow - b i as contr ol b i t. H i g h = l ow b i as, l ow = m ed i um b i as. IBIAS 0 m ust b e l ow .

1 IBIAS0 0 High-bias control bit. High bias on DXP_ when high. Overrides IBIAS1.

BIT NAME FUNCTION

7 (MSB) BUSY A high indicates that the ADC is busy converting.

6 LHIGH†A high indicates that the local high-temperature alarm has activated.

5 LLOW†A high indicates that the local low-temperature alarm has activated.

4 OPEN†A high indicates one of the remote-diode continuity (open-circuit) faults.

3 ALARM†A high indicates one of the remote-diode channels has over/undertemperature alarm.

2 N/A N/A

1 N/A N/A

0 N/A N/A

BIT NAME FUNCTION

7 (MSB) RLOW1 A high indicates that the DX1 low-temperature alarm has activated.

6 RHIGH1 A high indicates that the DX1 high-temperature alarm has activated.

5 RLOW2 A high indicates that the DX2 low-temperature alarm has activated.

4 RHIGH2 A high indicates that the DX2 high-temperature alarm has activated.

3 RLOW3* A high indicates that the DX3 low-temperature alarm has activated.

2 RHIGH3* A high indicates that the DX3 high-temperature alarm has activated.

1 RLOW4* A high indicates that the DX4 low-temperature alarm has activated.

0 RHIGH4* A high indicates that the DX4 high-temperature alarm has activated.

*Not available for MAX1805.

†These flags stay high until cleared by POR, or until the status byte register is read.

*Not available for MAX1805.

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

______________________________________________________________________________________ 15

Figure 5. SMBus Write Timing Diagram

Figure 4. SMBus Read Timing Diagram

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

AB CD

EFG H

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tSU:STO tBUF

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

SMBCLK

AB CD

EFG H

IJK

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tHD:DAT tSU:STO tBUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

I = SLAVE PULLS SMBDATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO MASTER

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION, DATA EXECUTED BY SLAVE

M = NEW START CONDITION

Table 8. Slave Address Decoding (ADD0

and ADD1)

Note: High-Z means that the pin is left unconnected and floating.

0011 001High-ZGND

0011 000

ADDRESS

0101 001GNDHigh-Z

0011 010VCC

GND

0101 011VCC

High-Z

0101 010

1001 101High-ZVCC

1001 100

GNDGND

GNDVCC

High-ZHigh-Z

1001 110VCC

VCC

ADD0 ADD1

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

16 ______________________________________________________________________________________

QSOP.EPS

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information

go to www.maxim-ic.com/packages.)

MAX1668/MAX1805/MAX1989†

Multichannel Remote/Local

Temperature Sensors

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17

TSSOP4.40mm.EPS

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information

go to www.maxim-ic.com/packages.)