Max 1617 Amee

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________________General Description

The M AX1617A (patents pending) is a precise digital ther-

mometer that reports the temperature of both a remote

sensor and its own package. The remote sensor is a

diode-connected transistor typically a low-cost, easily

mounted 2N3904 NPN type that replaces conventional

thermistors or thermocouples. Remote accuracy is 3C

for multiple transistor manufacturers, with no calibration

needed. T he remote channel can also measure the die

temperature of other IC s, such as microprocessors, that

contain an on-chip, diode-connected transistor.

T he 2-wire serial interface accepts standard System

M anagement Bus (SM Bus) Write Byte, Read Byte, Send

Byte, and Receive Byte commands to program the alarm

thresholds and to read temperature data. The data formatis 7 bits plus sign, with each bit corresponding to 1C, in

twos complement format. M easurements can be done

automatically and autonomously, with the conversion rate

programmed by the user or programmed to operate in a

single-shot mode. T he adjustable rate allows the user to

control the supply-current drain.

The M AX1617A is nearly identical to the popular MAX1617,

but has improved SM Bus timing specifications, improved

bus collision immunity, software manufacturer and device

identification available via the serial interface, and a power-

on reset function that can force a reset of the slave address

via the serial interface.

________________________ApplicationsD esk top and N otebook C entral O ffice

C omputers Telecom Equipment

Smart B attery Packs T est and Measurement

LAN Servers M ultichip M odules

Industrial C ontrols

____________________________Features

o Two Channels: Measures Both Remote and Local

Temperatures

o No Calibration Required

o SMBus 2-Wire Serial Interface

o Programmable Under/Overtemperature Alarms

o Supports SMBus Alert Response

o Supports Manufacturer and Device ID Codes

o Accuracy

2C (+60C to +100C, local)3C (-40C to +125C, local)

3C (+60C to +100C, remote)

o 3A (typ) Standby Supply Current

o 70A (max) Supply Current in Auto-Convert Mode

o +3V to +5.5V Supply Range

o Small 16-Pin QSOP Package

MAX1617A

Remote/Local Temperature Sensorwith SMBus Serial Interface

________________________________________________________________Maxim Integrated Products 1

MAX1617A

SMBCLK

ADD0 ADD1

VCC STBY

GND

ALERT

SMBDATA

DXP

DXN INTERRUPTTO C

3V TO 5.5V

2000.1F

CLOCK

10k EACH

DATA

2N3904 2200pF

___________________Pin Configuration

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

N.C. N.C.

STBY

SMBCLK

N.C.

SMBDATA

ALERT

ADD0

N.C.

TOP VIEW

MAX1617A

QSOP

VCC

DXP

ADD1

DXN

N.C.

GND

GND

Typical Operating Circuit

19-4508; R ev 0; 1/99

PART*

M AX1617AM EE -55C to +125C

TEMP. RANGE PIN-PACKAGE

16 Q SOP

EVALUATION

KITMANUA

L

FOLLOWSDA

TASHEET

Ordering Information

SM Bus is a registered trademark of Intel Corp.

*U .S. and foreign patents pending.

Patents Pending

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.

For small orders, phone 1-800-835-8769.

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MAX1617A


2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS(VC C = + 3.3V, TA = 0C to +85C, unless otherwise noted.)

Stresses beyond those listed under A bsolute M aximum R atings 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.

VC C to G ND ..............................................................-0.3V to +6V

D XP, A DD _ to G ND ....................................-0.3V to (V C C + 0.3V)

D XN to G ND ..........................................................-0.3V to +0.8V

SMBCLK , SM BDATA , ALERT, STBYto G ND ...........-0.3V to +6VSMBDATA , ALERTC urrent.... ..... ...... ...... ...... ...... -1mA to + 50mAD XN C urrent....................... ................................................1mA

ESD Protection (SM BC LK , SMB DA TA ,

ALERT, H uman Body M odel) ......................................... 4000VESD Protection (other pins, Human B ody M odel) ...... ...... ..2000V

C ontinuous Power D issipation ( TA = +70C)

Q SO P (derate 8.30mW/C above + 70C) .....................667mW

O perating Temperature Range ..... ...... ...... ..... ...-55C to + 125C

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

Storage Temperature Range ...... ..... ...... ...... ..... .-65C to +165C

Lead T emperature (soldering, 10sec) ...... ..... ...... ...... ..... .+ 300C

TA = + 60C to +100C

M onotonicity guaranteed

ADD0, A DD1; momentary upon power-on reset

DXP forced to 1.5V

Logic inputs

forced to VC C

or G ND

Auto-convert mode

From stop bi t to conversion complete (both channels)

VC C , falling edge

TA = 0C to + 85C

VC C input, disables A/D conversion, rising edge

Auto-convert mode, average

measured over 4sec. Logic

inputs forced to VC C or G ND.

CONDITIONS

A160Address P in Bias Current

V0.7D XN Source Voltage

A8 10 12

80 100 120Remote-D iode Source C urrent

%-25 25C onversion Rate Timing Error

ms94 125 156C onversion Ti me

A

120 180

35 70

Average O perating Supply Current

-2 2

Bits8Temperature Resolution (Note 1)

A

4

Standby Supply C urrent

3 10

mV50PO R Threshold H ysteresis

V1.0 1.7 2.5Power-O n Reset Threshold

C-3 3

Initial Temperature Error,

Local Diode ( Note 2)

V3.0 5.5Supply-Voltage Range

V2.60 2.80 2.95U ndervoltage Lockout ThresholdmV50U ndervoltage Lockout Hysteresis

UNITSMIN TYP MAXPARAMETER

TR = + 60C to +100C

TR = -55C to +125C

-3 3C

-5 5

Temperature Error, R emote Diode

(Notes 2 and 3)

Including long-term drift-2.5 2.5

C-3.5 3.5

Temperature Error, Local Di ode

(Notes 1 and 2)

0.25 conv/sec

2.0 conv/sec

TA = + 60C to +100C

TA = 0C to + 85C

High level

Low level

ADC AND POWER SUPPLY

SM Bus static

H ardware or software standby,

SM BCLK at 10kHz

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MAX1617A


_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)(VC C = + 3.3V, TA = 0C to +85C, unless otherwise noted.)

STBY, SMBCLK , SMBDATA; VC C = 3V to 5.5V

tH I G H , 90% to 90% points

tLO W, 10% to 10% points

(N ote 4)

SMBCLK , SM BDATA

Logic inputs forced to VC C or G ND

ALERTforced to 5.5V

STBY, SMBCLK , SMBDATA; VC C = 3V to 5.5V

ALERT, SM BD AT A forced to 0.4V

CONDITIONS

s4SM BC LK C lock High Time

s4.7SM BC LK C lock Low Time

kH zD C 100SM Bus C lock Frequency

pF5SM Bus Input C apacitance

A-1 1Logic Input C urrent

A1ALERTO utput Hi gh Leakage

C urrent

V2.2Logic Input High Voltage

V0.8Logic Input Low Voltage

mA6Logic O utput Low Sink C urrent

UNITSMIN TYP MAXPARAMETER

tSU:DAT , 10% or 90% of SMB DA TA to 10% of SM BCLK

tSU:STO , 90% of SM BCLK to 10% of SMB DA TA

tHD:STA , 10% of SM BDA TA to 90% of SMB CLK

tSU:STA , 90% to 90% points

ns250SM Bus Data Valid to SM BC LK

R ising-Edge T ime

s4SM Bus Stop-C ondition Setup Time

s4SM Bus Start-C ondition H old Ti me

ns500SM Bus Repeated Start-C ondition

Setup Ti me

s4.7SM Bus Start-C ondition Setup T ime

tHD:DAT (N ote 5) s0SM Bus Data-Hold Time

M aster clocking in data s1SM BC LK Falling Edge to SM Bus

D ata-Valid T ime

SMBus INTERFACE

ELECTRICAL CHARACTERISTICS(VC C = +3.3V, TA = -55C to +125C, unless otherwise noted. ) (Note 6)

CONDITIONS

M onotonici ty guaranteed

TA = + 60C to +100C

Bits8Temperature Resolution (Note 1)

-2 2

TR = + 60C to +100C

TA = -55C to +125CC

-3 3

Initia l Temperature Error,

Local Diode ( Note 2)

V3.0 5.5Supply-Voltage Range

From stop bi t to conversion complete (both channels)

Auto-convert mode

ms94 125 156C onversion Time

%-25 25C onversion Rate Timing Error

-3 3

TR = -55C to +125CC

UNITSMIN TYP MAX

-5 5

PARAMETER

Temperature Error, R emote Diode

(Notes 2 and 3)

ADC AND POWER SUPPLY

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0

6

3

9

12

50 5k 500k50k 5M500 50M

TEM PERATURE ERROR vs.

POWER-SUPPLY NOISE FREQUENCY

MAX1617ATOC04

FREQUENCY ( Hz)

TEMPERATUREERROR(C)

VIN = SQUARE WAVE APPLIED TOVCC WITH NO 0.1F VCC CAPACITOR

VIN = 250mVp-pREMOTE DIODE

VIN = 250mVp-pLOCAL DIODE

VIN = 100mVp-pREMOTE DIODE

-2 0

-1 0

0

10

20

1 10 303 100

TEM PERATURE ERROR

vs. PC BOARD RESISTANCE

MAX1617ATOC01

LEAKAGE RESISTANCE (M)

TEMPERATUREERROR(C)

PATH = DXP TO VCC (5V)

PATH = DXP TO GND

-2

-1

0

1

2

-50 50 1000 150

TEM PERATURE ERROR

vs. REMOTE-DIODE TEMPERATURE

MAX1617ATOC02

TEMPERATURE (C)

TEMPERATUREERROR(C)

SAMSUNG KST3904

MOTOROLA MMBT3904

ZETEX FMMT3904

RANDOMSAMPLES

__________________________________________Typical Operating Characteristics( TA = + 25C , unless otherwise noted.)

MAX1617A


4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)(VC C = + 3.3V, TA = -55C to +125C, unless otherwise noted. ) (Note 6)

Note 1: G uaranteed but not 100% tested.

Note 2: Q uantization error is not included in specifications for temperature accuracy. For example, if the M AX1617A device temper-ature is exactly + 66.7C , the A DC may report + 66C , + 67C , or +68C (due to the quantization error plus the + 1/2C offset

used for rounding up) and still be within the guaranteed 1C error limits for the +60C to +100C temperature range

(Table 2).

Note 3: A remote diode is any diode-connected transistor from T able 1. TR is the junction temperature of the remote diode. SeeRemote D iode Selectionfor remote diode forward voltage requirements.

Note 4: The SM Bus logic block is a static design that works with clock frequencies down to DC . While slow operation is possible, i tviolates the 10kH z minimum clock frequency and SM Bus specifications, and may 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) ofSM BC LK s falling edge.

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

CONDITIONS UNITSMIN TYP MAXPARAMETER

STBY, SM BCLK , SMBDATA2.2

Logic Input H igh Voltage V2.4

STBY, SMBCLK , SMBDATA; VC C = 3V to 5.5V V0.8Logic Input Low Voltage

ALERTforced to 5.5V A1ALERTO utput Hi gh Leakage

C urrent

Logic inputs forced to VC C or G ND A-2 2Logic Input C urrent

VC C = 3V

VC C = 5.5V

ALERT, SM BD AT A forced to 0.4V mA6Logic O utput Low Sink C urrent

SMBus INTERFACE

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MAX1617A


_______________________________________________________________________________________ 5

0

10

20

30

50 5k 500k50k 5M500 50M


COMM ON-M ODE NOISE FREQUENCY

MAX1617ATOC05

FREQUENCY ( Hz)

TEMPERATUREERROR(C)

VIN = SQUARE WAVEAC COUPLED TO DXN

VIN = 100mVp-p

VIN = 50mVp-p

VIN = 25mVp-p

-5

5

0

10

50 5k 500k50k 5M500 50M


DIFFERENTI AL-M ODE NOISE FREQUENCY

MAX1617ATOC06

FREQUENCY ( Hz)

TEMPERATUREERROR(C)

VIN = 10m Vp-p SQUARE WAVEAPPLIED TO DXP-DXN

0

10

20

0 40 60 8020 100


DXPDXN CAPACITANCE

MAX1617ATOC07

DXPDXN CAPACITANCE (nF)

TEMPERATUREERROR(C)

VCC = 5V

0

100

400

200

300

500

0 10.0625 40.25 20.125 0.5 8

OPERATING SUPPLY CURRENT

vs. CONVERSION RATE

M

AX1617ATOC10

CONVERSION RATE (Hz)

SUPPLYCUR

RENT(A)

VCC = 5VAVERAGED M EASUREMENTS

0

5

15

25

10

20

30

35

1k 100k10k 1000k

STANDBY SUPPLY CURRENT

vs. CLOCK FREQUENCY

MAX1617ATOC08

SM BCLK FREQUENCY (Hz)

SU

PPLYCURRENT(A)

VCC = 5V

VCC = 3.3V

SMBCLK ISDRIVEN RAIL-TO-RAIL

0

3

60

6

20

100

0 31 42 5

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1617ATOC09

SUPPLY VOLTAGE (V)

SUPPLYCURRENT(A)

ADD0, ADD1= GND

ADD0, ADD1= HIGH-Z

0

25

100

50

75

125

-2 80 42 6 10

RESPONSE TO THERMAL SHOCK

MAX1617ATOC11

TIME (sec)

TEMPERATURE(C)

16- QSOP IMM ERSEDIN +115C FLUORINERT BATH

____________________________Typical Operating Characteristics (continued)(TA = + 25C, unless otherwise noted.)

-5

0

5

50 5k 500k50k 5M500 50M


DIFFERENTI AL-M ODE NOISE FREQUENCY

MAX1617ATOC03

FREQUENCY ( Hz)

TEMPERATUREERROR(C)

VIN = 3mVp- p SQUARE WAVEAPPLIED TO DXP-DXN

Rail-to Rai l is a registered trademark of Ni ppon M otorola, Ltd.

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MAX1617A


6 _______________________________________________________________________________________

Pin Description

General DescriptionT he M A X1617A ( patents pending) is a temperature

sensor designed to work in conjunction with an external

microcontroller (C ) or other intelligence in thermostat-

ic, process-control, or monitoring applications. The C

is typically a power-management or keyboard con-

troller, g enerating SM Bus serial commands by b it-

banging general-purpose input/output (G PIO ) pins or

via a dedicated SM Bus interface block.

Essentially an 8-bit serial analog-to-digital converter

(AD C ) with a sophisticated front end, the M AX1617A

contains a switched current source, a multiplexer, an

AD C , an SM Bus interface, and associated control logic

(Figure 1) . T emperature data from the AD C is loadedinto two data registers, where it is automatically com-

pared with data previously stored in four over/under-

temperature alarm registers.

ADC and MultiplexerThe AD C is an averaging type that integrates over a

60ms 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.

Both channels are automatically converted once the

conversion process has started, either in free-running

or single-shot mode. If one of the two channels is not

used, the device still performs both measurements, and

the user can simply ignore the results of the unused

channel. I f the remote diode channel is unused, tie DXPto DX N rather than leaving the pins open.

The DX N input is biased at 0.65V above ground by an

internal diod e to set up the analog-to-dig ital ( A /D)

inputs for a differential measurement. The worst-case

D XP DXN differential input voltage range is 0.25V to

0.95V.

SM Bus Serial-Data Input/O utput, O pen DrainSMBDATA12

SM Bus Serial-C lock InputSMBCLK14

H ardware Standby Input. T emperature and comparison threshold data are retained in standby mode.

Low = standby mode, high = operate mode.STBY15

SM Bus Add ress Select Pi n (Table 8). A DD0 and AD D 1 are sampled upon power-up. Excess capacitance(> 50pF) at the address pins when floating may cause address-recognition problems.

ADD16

G roundG N D7, 8

SM Bus Slave Address Select Pi nADD010

SM Bus Alert (interrupt) O utput, O pen DrainALERT11

C ombined C urrent Sink and A /D N egative Input. D XN is normally biased to a diode voltage above

ground.DXN4

C ombined C urrent Source and A /D P ositive Input for Remote-D iode C hannel. Do not leave DX P floating;

tie DXP to DX N if no remote diode is used. P lace a 2200pF capacitor between DX P and D XN for noise fil-

tering.

DXP3

PIN

Supply Voltage Input, 3V to 5.5V. Bypass to G N D with a 0.1F capacitor. A 200 series resistor is recom-

mended but not required for additional noise filtering.VC C2

N o Connection. N ot internally connected. M ay be used for PC board trace routing.N .C .1, 5, 9,

13, 16

FUNCTIONNAME

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MAX1617A


_______________________________________________________________________________________ 7

Figure 1. Functional Diagram

REMOTE

MUX

LOCAL

REMOTETEMPERATURE

DATAREGISTER

HIGH-TEMPERATURETHRESHOLD

(REMOTETHIGH)

LOW-TEMPERATURETHRESHOLD

(REMOTETLOW)

DIGITALCOMPARATOR

(REMOTE)

LOCALTEMPERATURE

DATAREGISTER

HIGH-TEMPERATURETHRESHOLD

(LOCALTHIGH)

LOW-TEMPERATURETHRESHOLD

(LOCALTLOW)

DIGITALCOMPARATOR

(LOCAL)

COMMANDBYTE

(INDEX)REGISTER

SMBDATA

SMBCLK

ADDRESS

DECODER

READ

WRITE

CONTROL

LOGIC

SM

BUS

ADD1

ADD0

STBY

STATUSBYTEREGISTER

CONFIGURATION

BYTEREGISTER

CONVERSIONRATE

REGISTER

ALERTRESPONSE

ADDRESSREGISTER

SELECTEDVIA

SLAVEADD=0001100

ADC

+

DIODE

FAULT

DXP

DXN

GND

VCC

- + -

+ -

88

8

8

8

8

8

8

2

7

ALERT

Q

S

R

MAX1617A

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Excess resistance in series with the remote diode caus-

es about +1/2C error per ohm. L ikewise, 200V of off-set voltage forced on DXPDXN causes about 1C error.

A/D Conversion SequenceIf a Start command is written (or generated automatical-

ly in the free-running auto-convert mode), both channels

are converted, and the results of both measurements

are available after the end of conversion. A BU SY status

bit in the status byte shows that the device is actually

performing a new conversion; however, even if the ADC

is busy, the results of the previous conversion are

always available.

Remote-Diode SelectionTemperature accuracy depends on having a good-qual-

ity, diode-connected small-signal transistor. A ccuracyhas been experimentally verified for all of the devices

listed in Table 1. The M AX1617A can also directly mea-

sure the die temperature of C PUs and other integrated

circuits having on-board temperature-sensing diodes.

The transistor must be a small-signal type with a rela-

tively high forward voltage; otherwise, the A /D input

voltage range can be violated. The forward voltage

must be greater than 0.25V at 10A ; check to ensure

this is true at the highest expected temperature. The

forward voltage must be less than 0.95V at 100A;

check to ensure this is true at the lowest expected tem-

perature. Large power transistors dont work at all. A lso

ensure that the base resistance is less than 100. T ight

specifications for forward-current gain ( + 50 to + 150, forexample) indicate that the manufacturer has good

process controls and that the devices have consistent

VBE characteristics.

For heatsink mounting, the 500-32BT 02-000 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., M ilford, M A , 508-478-6000).

Thermal Mass and Self-HeatingThermal mass can seriously degrade the M AX1617As

effective accuracy. The thermal time constant of the

Q SO P-16 pack age is about 140sec in still air. For the

M AX1617A junction temperature to settle to within +1Cafter a sudden + 100C change requires about five time

constants or 12 minutes. The use of smaller packages

for remote sensors, such as SO T23s, improves the situ-

ation. 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 auto-converting at the

fastest rate and simultaneously sinking maximum cur-

rent at the ALERToutput. For example, at an 8Hz rateand with ALERT sinking 1mA , the typical power dissi-pation is VC C 450A plus 0.4V 1mA. Package thetaJ-A is about 150C/W, so with VC C = 5V and no copper

PC board heatsinking, the resulting temperature rise is:

dT = 2.7mW 150C/W = 0.4C

Even with these contrived circumstances, it is difficult

to introduce significant self-heating errors.

ADC Noise FilteringThe AD C is an integrating type with inherently good

noise rejection, especially of low-frequency signals

such as 60Hz/120Hz power-supply hum. M icropower

operation places constraints on high-frequency noise

rejection; therefore, careful PC board layout and proper

external noise filtering are required for high-accuracy

remote measurements in electrically noisy environ-

ments.

H igh-frequency EM I is best filtered at D XP and D XN

with an external 2200pF capacitor. This value can be

increased to about 3300pF (max), including cable

capacitance. H igher capacitance than 3300pF intro-

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

rent source.

Nearly all noise sources tested cause the AD C measure-

ments to be higher than the actual temperature, typically

by +1C to +10C , depending on the frequency and

amplitude (see Typical O perating C haracteristics) .

MAX1617A


8 _______________________________________________________________________________________

CM PT3904C entral Semiconductor (USA )

M M BT3904M otorola (U SA)

M M BT3904

SST3904Rohm Semiconductor (Japan)

K ST3904-TFSamsung (K orea)

FM M T3904C T-NDZetex (England)

MANUFACTURER MODEL NUMBER

SM BT 3904Siemens (G ermany)

Table 1. Remote-Sensor TransistorManufacturers

Note: Transistors must be diode-connected (base shorted tocollector).

National Semiconductor (USA)

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PC Board Layout

1) Place the M A X1617A as close as practical to theremote diode. In a noisy environment, such as a

computer motherboard, this distance can be 4 in. to

8 in. (typical) or more as long as the worst noise

sources (such as CRTs, clock generators, memory

buses, and ISA /PC I buses) are avoided.

2) Do not route the DXPD XN lines next to the deflec-

tion coils of a C R T . A lso, do not route the traces

across a fast memory bus, which can easily intro-

duce + 30C error, even with good f i ltering.

O therwise, most noise sources are fairly benign.

3) Route the DX P and D XN traces in parallel and in

close proximity to each other, away from any high-

voltage traces such as +12VDC

. Leakage currents

from P C board contamination must be dealt with

carefully, since a 20M leakage path from DXP to

ground causes about +1C error.

4) C onnect guard traces to G ND on either side of the

DXPDXN 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 DX P and the D XN paths have matching

thermocouples. In general, PC board-induced ther-

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

der thermocouple exhibi ts 3V/C , and i t takesabout 200V of voltage error at D XPDXN to cause

a + 1C measurement error. So, most parasitic ther-

mocouple errors are swamped out.

7) U se wide traces. N arrow ones are more inductive

and tend to pick up radiated noise. The 10 mil

widths and spacings recommended in Figure 2

aren t absolutely necessary (as they offer only a

minor improvement in leakage and noise), but try to

use them where practical.

8) K eep in mind that copper cant be used as an EM I

shield, and only ferrous materials, such as steel, work

well. Placing a copper ground plane between the

DXP-DXN traces and traces carrying high-frequencynoise signals does not help reduce EM I.

PC Board Layout Checklist Place the MAX1617A close to a remote diode.

K eep traces away from high voltages (+ 12V bus) .

K eep traces away from fast data buses and CRTs.

U se recommended trace widths and spacings.

Place a ground plane under the traces.

U se guard traces flanking DX P and DXN and con-

necting to G ND .

P lace the noise filter and the 0.1F VC C bypasscapacitors close to the M AX1617A.

A dd a 200 resistor in series with VC C for best noise

filtering (see Typical O perating C ircuit) .

Twisted Pair and Shielded CablesFor remote-sensor distances longer than 8 in., or in par-

ticularly noisy environments, a twisted pair is recom-

mended. Its practical length is 6 feet to 12 feet (typical)

before noise becomes a problem, as tested in a noisy

electronics laboratory. For longer distances, the best

solution is a shielded twisted pair like that used for audio

microphones. For example, the Belden 8451 works well

for distances up to 100 feet in a noisy environment.

C onnect the twisted pair to DX P and D XN and the shieldto G ND , and leave the shields remote end unterminated.

Excess capacitance at DX_ limits practical remote sen-

sor distances (see Typical O perating C haracteristics) .

For very long cable runs, the cables parasitic capaci-

tance often provides noise filtering, so the 2200pF

capacitor can often be removed or reduced in value.

C able resistance also affects remote-sensor accuracy;

1 series resistance introduces about +1/2C error.

Low-Power Standby ModeStandby mode disables the ADC and reduces the sup-

ply-current dra in to less than 10A . E nter standby

mode by forcing the STBYpin low or via the RU N/STO P

bit i n the configuration byte register. H ardware andsoftware standby modes behave almost identically: all

data is retained in memory, and the SM B interface is

alive and listening for reads and writes. The only differ-

ence is that in hardware standby mode, the one-shot

command does not initiate a conversion.

Standby mode is not a shutdown mode. With activity on

the SM Bus, extra supply current is drawn (see Typical

O perating C haracteristics). In software standby mode,

MAX1617A


_______________________________________________________________________________________ 9

MINIMUM

10 MILS

10 MILS

10 MILS

10 MILS

GND

DXN

DXP

GND

Figure 2. Recommended DXP /DXN P C T races

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the M AX1617A can be forced to perform A/D conver-

sions via the one-shot command, despite the RU N/STO Pbit being high.

Activate hardware standby mode by forcing the STBYpin low. In a notebook computer, this line may be con-

nected to the system SUST AT# suspend-state signal.

TheSTBYpin low state overrides any software conversioncommand. If a hardware or software standby command is

received while a conversion is in progress, the conversion

cycle is truncated, and the data from that conversion is not

latched into either temperature reading register. The previ-

ous data is not changed and remains available.

Supply-current drain during the 125ms conversion peri-

od is always about 450A. Slowing down the conver-

sion rate reduces the average supply current (seeT ypical O perating C haracteristics). Between conver-

sions, the instantaneous supply current is about 25A

due to the current consumed by the conversion rate

timer. In standby mode, supply current drops to about

3A . A t 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 100A,

depending on AD D 0 and A D D 1 settings.

SMBus Digital Interface

From a software perspective, the M AX1617A appears asa set of byte-wide registers that contain temperature

data, alarm threshold values, or control bits. A standard

SM Bus 2-wire serial interface is used to read tempera-

ture data and write control bits and alarm threshold data.

Each A/D channel within the device responds to the

same SM Bus slave address for normal reads and writes.

The M AX1617A employs four standard SM Bus protocols:

Write Byte, R ead B yte, Send Byte, and R eceive Byte

(Figure 3). T he shorter R eceive B yte protocol allows

quicker transfers, provided that the correct data register

was previously selected by a Read B yte instruction. U se

caution with the shorter protocols in multi-master systems,

since a second master could overwrite the command

byte without informing the first master.

The temperature data format is 7 bits plus sign in twos

complement form for each channel, with each data bit rep-

resenting 1C (Table 2), transmitted M SB first. M easure-

ments are offset by + 1/2C to minimize internal rounding

errors; for example, + 99.6C is reported as +100C.

MAX1617A


10 ______________________________________________________________________________________

ACK

7 bits

ADDRESS ACKWR

8 bits

DATA ACK

1

P

8 bits

S COMMAND

Write Byte Format

Read Byte Format

Send Byte Format Receive Byte Format

Slave A ddress: equiva-lent to chip-select line of

a 3-wire interface

C ommand Byte: selects whichregister you are writing to

D ata Byte: data goes into the registerset by the command byte (to set

thresholds, configuration masks, and

sampling rate)

ACK

7 bits

ADDRESS ACKWR S ACK

8 bits

DATA

7 bits

ADDRESS RD

8 bits

/// PS COMMAND

Slave A ddress: equiva-

lent to chip-select line

C ommand B yte: 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

C ommand B yte: sends com-

mand with no data, usually

used for one-shot command

Data Byte: reads data from

the register commanded

by the last Read B yte or

Write Byte transmission;

also used for SM Bus A lert

Response return addressS = Start condition Shaded = Slave transmission

P = Stop condition /// = Not acknowledged

Figure 3. SM Bus Protocols

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Alarm Threshold RegistersFour registers store alarm threshold data, with high-

temperature (TH I GH ) and low-temperature (TLO W) reg-

isters for each A/D channel. I f either mea sured

temperature equals or exceeds the corresponding

alarm threshold value, an ALERT interrupt is asserted.

The power-on-reset (P O R ) state of both TH I GH registers

is full scale (0111 1111, or +127C ) . T he PO R state of

both TLO W registers is 1100 1001 or -55C .

Diode Fault AlarmThere is a continuity fault detector at DXP that detects

whether the remote diode has an open-circuit condi-

tion. A t 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 D XP rises

above VC C - 1V (typical) due to the diode current

source, a fault is detected. N ote that the diode fault

isnt checked until a conversion is initiated, so immedi-

ately after power-on reset the status byte indicates no

fault is present, even if the diode path is broken.

If the remote channel is shorted (D XP to DXN or DX P to

G ND) , the AD C reads 0000 0000 so as not to trip either

the T H I G H or T LO W alarms at their PO R settings. In

applications that are never subjected to 0C in normal

operation, a 0000 0000 result can be checked to indi-

cate a fault condition in which DXP is accidentally short

circuited. Simi larly, i f DXP is short circuited to VC C , the

ADC reads +127C for both remote and local channels,

and the device alarms.

ALERTInterruptsThe ALERT interrupt output signal is latched and canonly be cleared by reading the Alert Response address.

Interrupts are generated in response to THIGH and TLO Wcomparisons and when the remote diode is disconnect-

ed ( for continuity fault detection) . T he interrupt does not

halt automatic conversions; new temperature data con-

tinues to be avai lable over the SM Bus interface after

ALERTis asserted. The interrupt output pin is open-drainso that devices can share a common interrupt line. The

interrupt rate can never exceed the conversion rate.

The interface responds to the SM Bus Alert Response

address, an interrupt pointer return-address feature

(see A lert Response Addresssection). Prior to taking

corrective action, always check to ensure that an inter-

rupt is valid by reading the current temperature.

Alert Response Address

The SM Bus A lert Response interrupt pointer providesquick fault identification for simple slave devices that

lack the complex, expensive logic needed to be a bus

master. U pon receiving an ALERT interrupt signal, thehost master can broadcast a Receive Byte transmission

to the A lert 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

(T able 3).

MAX1617A


______________________________________________________________________________________ 11

DIGITAL OUTPUTDATA BITS

0 111 1111+ 127+ 127.00

0 111 1111

0 111 1110+ 126+ 126.00

+ 127+ 126.50

0 001 1001

0 000 0001+ 1+ 0.50

0 000 0000

0 000 000000.00

ROUNDEDTEMP.

(C)

TEMP.(C)

0+ 0.25

+ 25+ 25.25

0 000 0000

0 000 00000-0.50

1 111 1111

1 111 1111-1-1.00

-1-0.75

1 110 0111

1 110 0110-26-25.50

1 100 1001

1 100 1001-55-55.00

0-0.25

-55-54.75

-25-25.00

1 011 1111

1 011 1111-65-70.00

-65-65.00

Table 2. Data Format (Twos Complement) Table 3. Read Format for Alert ResponseAddress (0001100)

ADD66

Provide the current M AX1617A

slave address that was latched at

PO R ( Table 8)

FUNCTION

ADD55

ADD44

ADD33

ADD22

ADD11

ADD77

(MSB)

1

0

(LSB) Logic 1

BIT NAME

SIGN MSB LSB

0 111 1111+ 127+ 130.00

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The A lert Response can activate several di fferent slave

devices simultaneously, similar to the I2C G eneral

C all. I f more than one slave attempts to respond, bus

arbitration rules apply, and the device with the lower

address code wins. The losing device does not gener-

ate an acknowledge and continues to hold the ALERTline low until serviced ( implies that the host interrupt

input is level-sensitive). Successful reading of the alert

response address clears the interrupt latch.

Command Byte FunctionsThe 8-bit command byte register (Table 4) is the master

index that points to the various other registers within the

M AX1617A . T he registers PO R state is 0000 0000, sothat a Receive B yte transmission ( a protocol that lacks

the command byte) that occurs immediately after PO R

returns the current local temperature data.

The one-shot command immediately forces a new conver-

sion cycle to begin. In software standby mode

(RUN/STO P bit = high), a new conversion is begun, after

which the device returns to standby mode. If a conversion

is in progress when a one-shot command is received, the

command is ignored. If a one-shot command is received

in auto-convert mode (R UN/STO P bit = low) between con-

versions, a new conversion begins, the conversion rate

timer is reset, and the next automatic conversion takes

place after a full delay elapses.

Configuration Byte FunctionsThe configuration byte register (Table 5) is used to

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

ware standby mode. The lower six bits are internally set

to (XX1111), making them dont care bits. Write zeros

to these bits. This registers contents can be read back

over the serial interface.

Status Byte FunctionsThe status byte register (Table 6) indicates which (if

any) temperature thresholds have been exceeded. This

byte also indicates whether or not the AD C is convert-

ing and whether there is an open circuit in the remote

diode D XP DXN path. A fter PO R , the normal state of all

the flag bits is zero, assuming none of the alarm condi-

tions are present. The status byte is cleared by any

MAX1617A


12 ______________________________________________________________________________________

Table 4. Command-Byte Bit Assignments

*If the device is in hardware standby mode at PO R , both temperature registers read 0C .

Read remote temperature: returns latest temperatureRRTE 01h

00h

COMMAND

0000 0000*

0000 0000*

POR STATE

Read configuration byteRC L 03h

02h

0000 0000

N /A R ead status byte ( flags, busy signal)RSL

Read local TH I G H limitRLHN 05h

Read local temperature: returns latest temperatureRLTS

04h

0111 1111

0000 0010

Read remote TH I G H limitRRHI 07h

06h

0111 1111

1100 1001 Read local TLO W limitRLLI

Read conversion rate byte

REGISTER

RC RA

Write configuration b yteWC A 09h

08h

N /A

1100 1001

FUNCTION

Write local TH I G H limitWLHO 0Bh

0Ah

N /A

N /A Write conversion rate byteWCRW

Write remote TH I G H limitWRHA 0D h

Read remote TLO W limitRRLS

0C h

N /A

N /A

O ne-shot command ( use send-byte format)O SHT 0Fh

0Eh

N /A

N /A Write remote TLO W limitWRLN

Write local TLO W limitWLLM

Write software PO RSPO R FC h N /A

Read device ID codeD EVID FFh

FEh

00000001

0100 1101 R ead manufacturer I D codeMF G I D

I2C is a trademark of Phillips C orp.

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successful read of the status byte, unless the fault per-

sists. N ote that the ALERT interrupt latch is not auto-matically cleared when the status flag bit is cleared.

When auto-converting, if the T H I GH and TLO W limits are

close together, its possible for both high-temp and low-

temp status bits to be set, depending on the amount of

time between status read operations (especially when

converting at the fastest rate). In these circumstances,

its best not to rely on the status bits to indicate rever-

sals in long-term temperature changes and instead use

a current temperature reading to establish the trend

direction.

Conversion Rate ByteThe conversion rate register (Table 7) programs the time

interval between conversions in free-running auto-convert

mode. This variable rate control reduces the supply cur-

rent in portable-equipment applications. The conversion

rate bytes PO R state is 02h (0.25Hz) . T he M AX1617A

looks only at the 3 LSB bits of this register, so the upper 5

bits are dont care bits, which should be set to zero. The

conversion rate tolerance is 25% at any rate setting.

Valid A/D conversion results for both channels are avail-

able one total conversion time (125ms nominal, 156msmaximum) after initiating a conversion, whether conver-

sion is initiated via the RU N/STO P bit, hardware STBYpin, one-shot command, or initial power-up. C hanging the

conversion rate can also affect the delay until new results

are available (Table 8).

Manufacturer and Device ID CodesTwo RO M registers provide manufacturer and device ID

codes (T able 4). Reading the manufacturer ID returns

4Dh, which is the ASC II code M ( for M axim). R eading

the device I D returns 01h, indicating a M A X1617A

device. I f R EA D WO R D 16-bit SM Bus protocol is

employed ( rather than the 8-bit READ BY TE) , the least

significant byte contains the data and the most signifi-

cant byte contains 00h in both cases.

Slave AddressesThe M AX1617A appears to the SM Bus as one device

having a common address for both AD C channels. The

device address can be set to one of nine different val-

ues by pin-strapping A D D 0 and AD D 1 so that more

than one M AX1617A can reside on the same bus with-

out address conflicts (Table 9).

MAX1617A


______________________________________________________________________________________ 13

RUN /

STOP6 0

0

PORSTATE

Standby mode control

bit. If high, the device

immediately stops con-

verting and enters stand-

by mode. If low, the

device converts in ei ther

one-shot or timer mode.

M asks allALERT inter-rupts when high.

FUNCTION

RFU50 0 Reserved for future use

MAS K7 (M SB)

BIT NAME

Table 5. Configuration-Byte BitAssignments

Table 7. Conversion-Rate Control Byte

Table 6. Status-Byte Bit Assignments

*These flags stay high until cleared by PO R , or until the status

byte register is read.

LHIGH*6A high indi cates that the local high-

temperature alarm has activated.

A high indicates that the ADC is busy

converting.

FUNCTION

LLOW*5A high indicates that the local low-


RH I GH *4A high indi cates that the remote high-


RLO W*3 A high indicates that the remote low-temperature alarm has activated.

OPEN*2A high indicates a remote-diode conti-

nuity (open-circuit) fault.

RFU1

BUSY7

(MSB)

Reserved for future use (returns 0)

RFU0

(LSB)Reserved for future use (returns 0)

BIT NAME

0.12501h 33

30

0.2502h 35

0.503h 48

104h 70

205h 128

406h

0.062500h

225

807h 425

RFU08h to

FFh

DATACONVERSION

RATE(Hz)

AVERAGE SUPPLYCURRENT

(A typ, at VCC = 3.3V)

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MAX1617A


14 ______________________________________________________________________________________

The address pin states are checked at PO R and SPO R

only, and the address data stays latched to reduce qui-

escent supply current due to the bias current needed

for high-Z state detection.

T he M A X1617A also responds to the SM Bus A lert

R esponse slave address ( see the A lert Response

Addresssection).

POR and UVLOThe MAX1617A has a volatile memory. To prevent ambig-

uous power-supply conditions from corrupting the data in

memory and causing erratic behavior, a P O R voltage

detector monitors VC C and clears the memory if VC C falls

below 1.7V (typical, see Electrical C haracteristics table).

When power is first applied and VC C rises above 1.75V

(typical), the logic blocks begin operating, although reads

and writes at VC C levels below 3V are not recommended.

A second VC C comparator, the ADC UVLO comparator,

prevents the ADC from converting until there is sufficient

headroom (VC C = 2.8V typical).The SPO R software PO R command can force a power-on

reset of the M AX1617A registers via the serial interface.

Use the SEND BY TE protocol with CO M M AN D = FCh.

This is most commonly used to reconfigure the slave

address of the M AX1617A on the fly, where external

hardware has forced new states at the ADD0 and ADD1

address pins prior to the software PO R. T he new address

takes effect less than 100s after the SPO R transmission

stop condition.

Power-Up Defaults:

Interrupt latch is cleared.

Address select pins are sampled.

ADC begins auto-converting at a 0.25Hz rate.

C omma nd byte is set to 00h to facilitate quick

remote Receive Byte queries.

TH I G H and TLO W registers are set to max and min

limits, respectively.

Table 8. RLTS and RRTE Temp Register Update Timing Chart

n/a ( 0.25H z)

NEW CONVERSION RATE(CHANGED VIA WRITE TO

WCRW)

Power-on resetAuto-C onvert

OPERATING MODE CONVERSION INITIATED BY:

156ms max

TIME UNTIL RLTS AND RRTEARE UPDATED

156ms maxn/a1-shot command, while idling

between automatic conversionsAuto-C onvert

When current conversion is

complete ( 1-shot is ignored)

20sec

n/a

0.0625HzRate timerAuto-C onvert

1-shot command that occurs

during a conversionAuto-C onvert

10sec

5sec

0.125Hz

0.25HzRate timerAuto-C onvert

2.5sec

1.25sec

0.5Hz

1HzRate timerAuto-C onvert

Rate timerAuto-C onvert


625ms

312.5ms

2Hz

4HzRate timerAuto-C onvert

237.5ms

156ms

8Hz

n/aSTBYpinHardware Standby



156ms

156ms

n/a

n/a1-shot commandSoftware Standby

RU N/STO P bitSoftware Standby

Table 9. Slave Address Decoding (ADD0and ADD1)

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

0011 001High-ZG ND0011 000

ADDRESS

0101 001G N DH igh-Z

0011 010VC CG ND

0101 011VC CH igh-Z

0101 010

1001 101High-ZVC C

1001 100

G N DG ND

G N DVC C

High-ZH igh-Z

1001 110VC CVC C

ADD0 ADD1

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MAX1617A


______________________________________________________________________________________ 15

Figure 5. SM Bus Read Timing D iagram

Figure 4. SM Bus Write Timing D iagram

SMBCLK

A B C D E F G H I J K

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tHD:DAT tSU:STO tBUF

A = START CONDITION

B = M SB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA L INE LOW

L M

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = M SB OF DATA CLOCKED INTO SLAVE

H = L SB 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

SMBCLK

A = START CONDITION

B = M SB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

A B C D E F G H I J

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tSU:STO tBUF

K

E = SLAVE PULLS SMBDATA L INE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = M SB OF DATA CLOCKED INTO MASTER

H = L SB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

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MAX1617A


16 ______________________________________________________________________________________

Listing 1. Pseudocode Example

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MAX1617A


______________________________________________________________________________________ 17

Listing 1. Pseudocode Example (continued)

Programming Example:Clock-Throttling Control for CPUs

Listing 1 gives an untested example of pseudocode for

proportional temperature control of Intel mobile C PU s

via a power-management microcontroller. This program

consists of two main parts: an initialization routine and

an interrupt handler. The initialization routine checks for

SM B us communications problems and sets up the

M A X1617A configuration and conversion rate. T he

interrupt handler responds to ALERTsignals by readingthe current temperature and setting a C PU clock duty

factor proportional to that temperature. The relationshipbetween clock duty and temperature is fixed in a look-

up table contained in the microcontroller code.

Note: Thermal management decisions should be madebased on the latest temperature obtained from the

M AX1617A rather than the value of the Status Byte. The

M A X1617A responds very quick ly to changes in its

environment due to its sensitivity and its small thermal

mass. H igh and low alarm conditions can exist in the

Status Byte due to the M A X1617A correctly reporting

environmental changes around it.

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MAX1617A


18 ______________________________________________________________________________________

Listing 1. Pseudocode Example (continued)

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