MAX6660AEE ,Remote-Junction Temperature-Controlled Fan-Speed Regulator with SMBus InterfaceELECTRICAL CHARACTERISTICS(V = +3V to +5.5V, V = +12V, T = -40°C to +125°C, unless otherwise specif ..
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MAX6660AEE
Remote-Junction Temperature-Controlled Fan-Speed Regulator with SMBus Interface
General DescriptionThe MAX6660 is a remote temperature sensor and fan-
speed regulator that provides a complete fan-control
solution. The remote temperature sensor is typically a
common-collector PNP, such as a substrate PNP of a
microprocessor, or a diode-connected transistor, typi-
cally a low-cost, easily mounted 2N3904 NPN type or
2N3906 PNP type.
The device also incorporates a closed-loop fan con-
troller that regulates fan speed with tachometer feed-
back. The MAX6660 compares temperature data to a
fan threshold temperature and gain setting, both pro-
grammed over the SMBus™ by the user. The result is
automatic fan control that is proportional to the remote-
junction temperature. The temperature feedback loop
can be broken at any time for system control over the
speed of the fan.
Fan speed is voltage controlled as opposed to PWM
controlled, greatly reducing acoustic noise and maxi-
mizing fan reliability. An on-chip power device drives
fans rated up to 250mA.
Temperature data is updated every 0.25s and is read-
able at any time over the SMBus interface. The
MAX6660 is accurate to 1°C (max) when the remote
junction is between +60°C to +100°C. Data is formatted
as a 10-bit + sign word with 0.125°C resolution.
The MAX6660 is specified for -40°C to +125°C and is
available in a 16-pin QSOP package.
ApplicationsNotebooks
Telecom Systems
Industrial Control Systems
Servers
Workstations
FeaturesIntegrated Thermal Sensing and Fan-Regulation
SolutionProgrammable Fan Threshold Temperature Programmable Temperature Range for Full-Scale
Fan SpeedAccurate Closed-Loop Fan-Speed RegulationOn-Chip Power Device Drives Fans Rated
Up to 250mAProgrammable Under/Overtemperature AlarmsSMBus 2-Wire Serial Interface with Timeout
(Cannot “Lock Up” the SMBus)Supports SMBus Alert ResponseACPI Compatible, Including OVERTSystem
Shutdown Function±1°C (+60°C to +100°C) Thermal-Sensing AccuracyMAX6660EVKIT Available
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface19-2225; Rev 1; 5/06
Pin Configuration appears at end of data sheet.SMBus is a trademark of Intel Corp.
1μF
5kΩ
FAN
+12V
2200pF
PENTIUM
SMBCLK
SMBDATA
ALERT
OVERT
CLOCK
DATA
INTERUPT
TO μP
TO SYSTEM
SHUTDOWN
VFAN
ADD1ADD0PGND
0.1μF
+3V TO +5.5V
50Ω
VCCSTBY
TACH IN
FAN
DXP
DXN
AGND
10kΩ
EACH
MAX6660
ypical Operating Circuit
PARTTEMP RANGEPIN-
PACKAGE
PKG
CODEMAX6660AEE-40°C to +125°C16 QSOPE16-5
Ordering Information
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +3V to +5.5V, VVFAN= +12V, TA= -40°C to +125°C, unless otherwise specified. Typical values are at VCC= +3.3V and = +25°C.) (Note 1)
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.
(All voltages referenced to GND.)
VCC, ADD0, ADD1, SMBDATA,
SMBCLK, ALERT, OVERT...................................-0.3V to +6V
VFAN, TACH IN, FAN .............................................-0.3V to +16V
DXP, GAIN..................................................-0.3V to (VCC+ 0.3V)
DXN.............................................................................-0.3V to 1V
SMBDATA, ALERT, OVERTCurrent ...................-1mA to +50mA
DXN Current ......................................................................±1mA
FAN Out Current ..............................................................500mA
ESD Protection (Human Body Model)................................2000V
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)..........667mW
Operating Temperature Range........................-40°C to +125°C
Junction Temperature .....................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYM B O L CONDITIONSMINTYPMAXUNITS
ADC AND POWER SUPPLYVCC Supply VoltageVCC3.05.5V
VFAN Supply VoltageVVFAN4.513.5V
Operating Supply CurrentICCFan off250500µA
Shutdown Supply CurrentISHDNShutdown310µA
0.125°CTemperature Resolution11Bits
TRJ = +60°C to +100°C-1+1
TRJ = +25°C to +125°C-3+3Temperature Error (Note 2)TETA = +85°C,
VCC = +3.3V
TRJ = -40°C to +125°C-5+5
Internal Reference Frequency
Accuracy+25-25%
Temperature Conversion Time0.25s
Conversion Rate Timing Error-25+25%
Undervoltage Lockout ThresholdVUVLOVCC falling2.502.803.00V
Undervoltage Lockout Threshold
HysteresisVHYST90mV
Power-On-Reset (POR)
Threshold (VCC)VCC rising1.42.02.5V
POR Threshold Hysteresis90mV
High level80100120Remote-Junction Source CurrentIRJLow level81012µA
DXN Source VoltageVDXN0.7V
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Note 1:Junction Temperature = TA. This implies zero dissipation in pass transistor (no load, or fan turned off).
Note 2:TRJ, Remote Temperature accuracy is guaranteed by design, not production tested.
Note 3:Guaranteed by design. Not production tested.
Note 4:The MAX6660 includes an SMBus timeout, which resets the interface whenever SMBCLK or SMBDATA has been low for
greater than 25ms. This feature can be disabled by setting bit 2 of the Fan Gain register at 16h/1Bh to a 1. When the timeout
is disabled, the minimum clock frequency is DC.
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.
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3V to +5.5V, VVFAN= +12V, TA= -40°C to +125°C, unless otherwise specified. Typical values are at VCC= +3.3V and = +25°C.) (Note 1)
PARAMETERSYM B O L CONDITIONSMINTYPMAXUNITSTach Input Transition LevelVVFAN = 12V10.5V
Tach Input HysteresisVFAN = 12V190mV
Current-Sense Tach Threshold20mA
Current-Sense Tach Hysteresis0.3mA
Fan Output Current250mA
Fan Output Current Limit (Note 3)320410mA
Fan Output On-ResistanceRONF250mA load4Ω
SMBus INTERFACE: SMBDATA, ALERT, STBY, OVERTLogic Input Low VoltageVILVCC = +3.0V to +5.5V0.8V
VCC = +3.0V2.2Logic Input High VoltageVIHVCC = +5.5V2.6V
Input Leakage CurrentI_leakVIN = GND or VCC-2+2µA
Output Low Sink CurrentIOLVOL = 0.4V6mA
Input CapacitanceCin5pF
Output High Leakage CurrentVOH = 5.5V1µA
Serial Clock FrequencyfSCL(Note 4)0100kHz
Bus Free Time Between Stop
and Start ConditionstBUF4.7µs
Start Condition Setup Time4.7µs
Repeat Start Condition Setup
TimetSU:STA90% to 90%50µs
Start Condition Hold TimetHD:STA10% of SMBDATA to 90% of SMBCLK4µs
Stop Condition Setup TimetSU:STO90% of SMBCLK to 10% of SMBDATA4µs
Clock Low TimetLOW10% to 10%4.7µs
Clock High TimetHIGH90% to 90%4µs
Data Setup TimetSU:DAT90% of SMBDATA to 10% of SMBCLK250ns
Data Hold TimetHD:DAT(Note 5)0µs
Receive SMBCLK/SMBDATA
Rise TimetR1µs
Receive SMBCLK/SMBDATA
Fall TimetF300ns
SMBus TimeouttTIMEOUTSMBDATA and SMBCLK time low for reset
of serial interface2540ms
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus InterfaceTEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX6660 toc01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (
°C)
PATH = DXP TO GND
PATH = DXP TO VCC (+5V)
MAX6660 toc02
TEMPERATURE (°C)
TEMPERATURE ERROR (
°C)
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE110010k1M101k100k10M100M
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCYMAX6660 toc03
FREQUENCY (Hz)
TEMPERATURE ERROR (
°C)
VIN = 100mVp-p
VIN = SQUARE WAVE APPLIED TO VCC
WITH NO 0.1μF VCC CAPACITOR
VIN = 250mVp-p
MAX6660 toc04
FREQUENCY (Hz)
TEMPERATURE ERROR (
110100M1M10M1001k10k100k
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY VIN = 50mVp-p
VIN = SQUARE WAVE
AC-COUPLED TO DXN
VIN = 100mVp-p
VIN = 25mVp-p
MAX6660 toc05
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCEMAX6660 toc06
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6660 toc07
SUPPLY VOLTAGE (V)
AVERAGE SUPPLY CURRENT (
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
Typical Operating Characteristics
(VCC= +3.3V, TA= +25°C, unless otherwise noted.)
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
PINNAMEFUNCTIONVFANFan Drive Power-Supply Input. 4.5V to 13.5V.
2VCCSupply Voltage Input. +3V to +5.5V. Bypass VCC to ground with a 0.1µF capacitor.DXPInput: Remote-Junction Anode. Place a 2200pF capacitor between DXP and DXN for noise filtering.DXNInput: Remote-Junction Cathode. DXN is internally biased to a diode voltage above ground.FANOpen-Drain Output to Fan Low Side. Connect a minimum 1µF capacitor between FAN and VFAN.ADD1SMBus Address Select Pin. ADD0 and ADD1 are sampled upon power-up.PGNDPower GroundAGNDAnalog GroundOVERTOvertemperature Shutdown Output. Active-low output (programmable for active high if desired). Open drain.ADD0SMBus Slave Address Select Pin. ADD0 and ADD1 are sampled upon power-up.ALERTSMBus Alert (Interrupt) Output. Open-drain, active-low output.SMBDATASMBus Serial Data Input/Output. Open drain.GAINGain Control. Connect an external resistor from GAIN to VCC to reduce the gain of the current-sense mode.SMBCLKSMBus Clock Line from Controller. This line tolerates inputs up to VCC even if MAX6660 is not powered.STBYHardware Standby Input. Drive STBY low to reduce supply current. Temperature and comparison
data are retained in standby mode.TACH INFan Tachometer Input. Tolerates voltages up to VFAN.
Detailed DescriptionThe MAX6660 is a remote temperature sensor and fan
controller with an SMBus interface. The MAX6660 con-
verts the temperature of a remote-junction temperature
sensor to a 10-bit + sign digital word. The remote tem-
perature sensor can be a diode-connected transistor,
such as a 2N3906, or the type normally found on the
substrate of many processors’ ICs. The temperature
information is provided to the fan-speed regulator and
is read over the SMBus interface. The temperature
data, through the SMBus, can be read as a 10-bit +
sign two’s complement word with a 0.125°C resolution
(LSB) and is updated every 0.25s.
The MAX6660 incorporates a closed-loop fan controller
that regulates fan speed with tachometer feedback. The
temperature information is compared to a threshold and
range setting, which enables the MAX6660 to automati-
cally set fan speed proportional to temperature. Full con-
trol of these modes is available, including being able to
open either the thermal control loop or the fan control
loop. Figure 1 shows a simplified block diagram.
ADC The ADC is an averaging type that integrates over a
60ms period with excellent noise rejection. A bias cur-
rent is steered through the remote diode, where the for-
ward voltage is measured, and the temperature is com-
puted. The DXN pin is the cathode of the remote diode
and is biased at 0.65V above ground by an internal
diode to set up the ADC inputs for a differential mea-
surement. The worst-case DXP-DXN differential input
voltage range is 0.25V to 0.95V. Excess resistance in
series with the remote diode causes about +1/2°C error
per ohm. Likewise, 200mV of offset voltage forced on
DXP-DXN causes approximately 1°C error.
A/D Conversion SequenceA conversion sequence is initiated every 250ms in the
free-running autoconvert mode (bit 6 = 0 in the
Configuration register) or immediately by writing a One-
Shot command. The result of the new measurement is
available after the end of conversion. The results of the
previous conversion sequence are still available when
the ADC is converting.
Remote-Diode SelectionTemperature accuracy depends on having a good-
quality, diode-connected small-signal transistor.
Accuracy has been experimentally verified for all
devices listed in Table 1. The MAX6660 can also direct-
Pin Description
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus InterfaceFAN
FAN
TACH IN
VFAN
FAN-SPEED
REGULATOR
MUXDXP
DXN
THIGH
TLOW
CONFIGURATION
FAN COUNT DIVISOR
(FC)
FAN SPEED LIMIT
(FS)
FAN GAIN (FG)
TFAN (FT)
FAN CONVERSION
RATE (FCR)
MODE (M)
FAN LIMIT (FL)
FAN-SPEED CONTROL
(FSC)
STATUS
THYSTCOMPARAT0R
TMAX
THERMAL OPEN/
CLOSED LOOP
FAN OPEN/
CLOSED LOOP
FAN
CONTROL
CIRCUIT
REMOTE DATA
TEMPERATURE
REGISTERS
SMBCLK
SMBDATA
ADD0
ADD1
ADC
CENTRAL
LOGIC
SMBus
INTERFACE
ADDRESS
DECODER
OVERT
ALERT
Figure 1. MAX6660 Block Diagram
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interfacely measure the die temperature of CPUs and other ICs
that have 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
range could 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 volt-
age must be less than 0.95V at 100µA. Check to ensure
that this is true at the lowest expected temperature.
Large power transistors, power diodes, or small-signal
diodes must not be used. Also, ensure that the base
resistance is less than 100Ω. Tight specifications for
forward current gain (50 < β<150, for example) indi-
cate that the manufacturer has good process controls
and that the devices have consistent VBE characteris-
tics. Bits 5–2 of the Mode register can be used to
adjust the ADC gain to achieve accurate temperature
measurements with diodes not included in the recom-
mended list or to individually calibrate the MAX6660 for
use in specific control systems.
Thermal Mass and Self-HeatingWhen measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtu-
ally no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, smaller packages (e.g., a SOT23) yield the best
thermal response times. Take care to account for ther-
mal 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.
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 operation
places constraints on high-frequency noise rejection;
therefore, careful PC board layout and proper external
noise filtering are required for high-accuracy remote mea-
surements 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. Capacitance higher than 3300pF intro-
duces errors due to rise time of the switched current
source. Nearly all noise sources tested cause the ADC
measurements to be higher than the actual tempera-
ture, typically by +1°C to +10°C, depending on the fre-
quency and amplitude.
PC Board LayoutFollow these guidelines to reduce the measurement
error of the temperature sensors:
1) Place the MAX6660 as close as is practical to the
remote diode. In noisy environments, such as a
computer motherboard, this distance can be 4in to
8in (typ). This length can be increased if the worst
noise sources are avoided. Noise sources include
CRTs, clock generators, memory buses, and
ISA/PCI buses.
2) Do not route the DXP-DXN lines next to the deflec-
tion coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily intro-
duce +30°C error, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any high-
er voltage traces, such as +12VDC. Leakage cur-
rents from PC board contamination must be dealt
with carefully since a 20MΩleakage path from
DXP to ground causes about +1°C error. If high-
voltage traces are unavoidable, connect guard
traces to GND on either side of the DXP-DXN
traces (Figure 2).
4) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.
5) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. A copper-solder thermocouple
exhibits 3µV/°C, and it takes about 200µV of voltage
error at DXP-DXN to cause a +1°C measurement
error. Adding a few thermocouples causes a negligi-
ble error.
6) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10mil widths
and spacings that are recommended in Figure 2 are
not absolutely necessary, as they offer only a minor
MANUFACTURERMODEL NO.Central Semiconductor (USA)2N3904, 2N3906
Fairchild Semiconductor (USA)2N3904, 2N3906
Rohm Semiconductor (Japan)SST3904
Samsung (Korea)KST3904-TF
Siemens (Germany)SMBT3904
Zetex (England)FMMT3904CT-ND
Table 1. Remote-Sensor Transistor
Note:Transistors must be diode connected (base shorted to
collector).
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interfaceimprovement in leakage and noise over narrow
traces. Use wider traces when practical.
7) Add a 50Ωresistor in series with VCCfor best
noise filtering (see Typical Operating Circuit).
PC Board Layout ChecklistPlace the MAX6660 close to the remote-sense junc-
tion.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 connect-
ing to GND.Place the noise filter and the 0.1µF VCCbypass
capacitors close to the MAX6660.
Twisted-Pair and Shielded CablesUse a twisted-pair cable to connect the remote sensor
for remote-sensor distances longer than 8in or in very
noisy environments. Twisted-pair cable lengths can be
between 6ft and 12ft before noise introduces excessive
errors. 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. At the
device, connect the twisted pair to DXP and DXN and
the shield to GND. Leave the shield unconnected at the
remote sensor.
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy.
For every 1Ωof series resistance, the error is approxi-
mately +1/2°C.
Low-Power Standby ModeStandby mode reduces the supply current to less than
10µA by disabling the ADC, the control loop, and the
fan driver. Enter hardware standby mode by forcing
STBYlow, or enter software standby by setting the
RUN/STOP bit to 1 in the Configuration Byte register.
Hardware and software standbys are very similar; all
data is retained in memory, and the SMB interface is
alive and listening for SMBus commands. The only dif-
ference is that in software standby mode, the one-shot
command initiates a conversion. With hardware stand-
by, the one-shot command is ignored. Activity on the
SMBus causes the device to draw extra supply current.
Driving STBYlow overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the con-
version cycle is interrupted, and the temperature regis-
ters are not updated. The previous data is not changed
and remains available.
SMBus Digital InterfaceFrom a software perspective, the MAX6660 appears as
a set of byte-wide registers that contain temperature
data, alarm threshold values, and control bits. The
device responds to the same SMBus slave address for
access to all functions.
The MAX6660 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figures 3, 4, 5) to program the alarm thresholds, read
the temperature data, and read and write to all fan con-
trol loop registers. The shorter Receive Byte protocol
allows quicker transfers, provided that the correct data
register was previously selected by a Read Byte
instruction. Use caution with the shorter protocols in
multimaster systems, since a second master could
overwrite the command byte without informing the first
master.
Figure 2. Recommended DXP-DXN PC Trace
MINIMUM
10mils
10mils
10mils
10mils
GND
DXN
DXP
GND
TEMP (°C)DIGITAL OUTPUT+1270111 1111 111
+125.000111 1101 000
+250001 1001 000
+0.1250000 0000 0010000 0000 000
-0.1251111 1111 111
-251110 0111 111
-401101 1000111
Table 2. Temperature Data Format (Two’s
Complement)
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus InterfaceFigure 4. SMBus Write Timing Diagram
Figure 5. SMBus Read Timing Diagram
ACK7 bits
ADDRESSACKWR8 bits
DATAACK8 bits
COMMAND
Write Byte Format
Read Byte Format
Send Byte FormatReceive Byte FormatSlave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
ACK7 bits
ADDRESSACKWRSACK8 bits
DATA7 bits
ADDRESSRD8 bits
///PSCOMMANDSlave 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
ACK7 bits
ADDRESSWR8 bits
COMMANDACKPSACK7 bits
ADDRESSRD8 bits
DATA///PSCommand Byte: sends com-
mand with no data, usually
used for one-shot command
Data Byte: reads data from
the register commanded
by the last Read Byte or
Write Byte transmission;
also used for SMBus Alert
Response return address
S = Start conditionShaded = Slave transmission
P = Stop condition/// = Not acknowledged
SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVECDEFGHIJ
SMBDATA
tSU:STAtHD:STA
tLOWtHIGH
tSU:DATM
tSU:STOtBUF
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 = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLEAR PULSE
J = STOP CONDITION, DATA
EXECUTED BY SLAVE
K = NEW START CONDITION
SMBCLKCDEFGHIJK
SMBDATA
tSU:STAtHD:STA
tLOWtHIGH
tSU:DATtHD:DATtSU:STOtBUF
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 M
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
Figure 3. SMBus Protocols
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus InterfaceThe SMBus interface includes a Timeout, which resets
the interface any time the data or clock line is held low
for more than 35ms, ensuring that the MAX6660 can
never “lock” the bus.
Remote Temperature Data RegisterTwo registers, at addresses 00h and 01h, store the
measured temperature data from the remote diode. The
data format for the remote-diode temperature is 10 bit
+ sign, with each bit corresponding to 0.125°C, in two’s
complement format (Table 2). Register 01h contains the
sign bit and the first 7 bits. Bits 7, 6, 5 of Register 00h
are the 3LSBs. If the two registers are not read at the
same time, their contents may be the result of two dif-
ferent temperature measurements leading to erroneous
temperature data. For this reason, a parity bit has been
added to the 00h register. Bit 4 of this is zero if the data
in 00h and 01h are from the same temperature conver-
sion and are 1 if they are not. The remaining bits are
“don’t cares.” When reading temperature data, register
01h must be read first.
Alarm Threshold Registers The MAX6660 provides four alarm threshold registers
that can be programmed with a two’s complement tem-
perature value with each bit corresponding to 1°C. The
registers are THIGH, TLOW, TMAX, and THYST. If the
measured temperature equals or exceeds THIGH, or is
less than TLOW, an ALERTinterrupt is asserted. If the
measured temperature equals or exceeds TMAX, the
OVERToutput is asserted (see Over-Temperature
Output (OVERT)section). If ALERTand OVERTare acti-
vated by the temperature exceeding TMAX, they can
only be deasserted by the temperature dropping below
THYST. The POR state for THIGHis +127°C, for TLOWis -
55°C, for TMAXis +100°C, and for THYSTis +95°C.
Over-Temperature Output (OVERT)The MAX6660 has an over-temperature output (OVERT)
that is set when the remote-diode temperature crosses
the limits set in the TMAXregister. It is always active if
the remote-diode temperature exceeds TMAX. The
OVERTline clears when the temperature drops below
THYST. Bit 1 of the Configuration register can be used
to mask the OVERToutput. Typically, the OVERToutput
is connected to a power-supply shutdown line to turn
system power off. At power-up, OVERTdefaults to
active-low but the polarity can be reversed by setting
bit 5 of the Configuration register.
The OVERTline can be taken active, either by the
MAX6660 or driven by an external source. An external
source can be masked by bit 2 of the Configuration
register. When OVERTis active, the fan loop forces the
fan to full speed and bit 1 of the Status register is set.
Diode Fault AlarmA continuity fault detector at DXP detects an open cir-
cuit between DXP and DXN. If an open or short circuit
exists, register 01h is loaded with 000 0000.
Additionally, if the fault is an open circuit, bit 2 of the
status byte is set to 1 and the ALERT condition is acti-
vated at the end of the conversion. Immediately after
POR, the Status register indicates that no fault is pre-
sent until the end of the first conversion.
ALERT
InterruptsThe ALERTinterrupt output signal is activated (unless it is
masked by bit 7 in the Configuration register) whenever
the remote-diode’s temperature is below TLOWor exceeds
THIGH. A disconnected remote diode (for continuity detec-
tion), a shorted diode, or an active OVERT alsoactivates
the ALERTsignal. The activation of the ALERTsignal sets
the corresponding bits in the Status register. There are two
ways to clear the ALERT: sending the ALERT Response
Address or reading the Status register.
The interrupt does not halt automatic conversions. New
temperature data continues to be available over the
SMBus interface after ALERTis asserted. ALERTis an
active-low open-drain output so that devices can share
a common interrupt line. The interrupt is updated at the
end of each temperature conversion so, after being
cleared, reappears after the next temperature conver-
sion, if the cause of the fault has not been removed.
By setting bit 0 in the Configuration register to 1, the
Status register can only be cleared by sending the
SMBus Alert Response Address (seeAlert Response
Addresssection). Prior to taking corrective action, always
check to ensure that an interrupt is valid by reading the
current temperature. To prevent recurring interrupts, the
MAX6660 asserts ALERTonly once per crossing of a
given temperature threshold. To enable a new interrupt,
the value in the limit register that triggered the interrupt
must be rewritten. Other interrupt conditions can be
caused by crossing the opposite temperature threshold,
or a diode fault can still cause an interrupt.
Example: The remote temperature reading crosses
THIGH, activating ALERT. The host responds to the
interrupt and reads the Alert Response Address, clear-
ing the interrupt. The system may also read the status
byte at this time. If the condition persists, the interrupt
reappears. Finally, the host writes a new value to
THIGH. This enables the device to generate a new
THIGHinterrupt if the alert condition still exists.
Alert Response AddressThe SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interfacemaster. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (see Slave
Addressessection). Then, any slave device that gener-
ated 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 ALERTline low
until cleared. (The conditions for clearing an alert vary
depending on the type of slave device.) Successful
completion of the Alert Response protocol clears the
interrupt latch, provided the condition that caused the
alert no longer exists. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
Table 3. Read Format for Alert Response
Address
Command Byte FunctionsThe 8-bit Command Byte register (Table 4) is the mas-
ter index that points to the other registers within the
MAX6660. The register’s POR is 0000 0000, so that a
receive byte transmission (a protocol that lacks the
command byte) that occurs immediately after POR
returns the current remote temperature data.
One-ShotThe one-shot command immediately forces a new conver-
sion cycle to begin. In software standby mode
(RUN/STOP 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 between
conversions, in autoconvert mode (RUN/STOP bit = low),
a new conversion begins immediately.
Configuration Byte FunctionsThe Configuration Byte register (Table 5) is used to
mask (disable) the ALERTsignal to place the device in
software standby mode, to change the polarity of
OVERT, to set MAX6660 to thermal open/closed-loop
mode, to inhibit the OVERTsignal, to mask OVERTout-
put, and to clear the ALERTsignal. The MAX6660 has a
write protection feature (bit 4) that prohibits write com-
mands to bits 6–3 of the Configuration register. It also
prohibits writes to the TMAX, THYST, and Fan
Conversion Rate registers.
Status Byte FunctionsThe status byte (Table 6) reports several fault condi-
tions. It indicates when the fan driver transistor of the
MAX6660 has overheated and/or is thermal shutdown,
when the temperature thresholds, TLOWand THIGH,
have been exceeded, and whether there is an open cir-
cuit in the DXP-DXN path. The register also reports the
state of the ALERTand OVERTlines and indicates
when the fan driver is fully on. The final bit in the Status
register indicates when a fan failure has occurred.
After POR, the normal state of the flag bits is zero,
assuming no alert or overtemperature conditions are
present. Bits 2 through 6 of the Status register are
cleared by any successful read of the Status register,
unless the fault persists. The ALERToutput follows the
status flag bit. Both are cleared when successfully
read, but if the condition still exists, the ALERTis
reasserted at the end of the next conversion.
The MAX6660 incorporates collision avoidance so that
completely asynchronous operation is allowed between
SMBus operations and temperature conversions.
When autoconverting, if the THIGHand TLOWlimits are
close together, it is possible for both high-temperature
and low-temperature status bits to be set, depending
on the amount of time between status read operations.
In these circumstances, it is best not to rely on the sta-
tus bits to indicate reversals in long-term temperature
changes. Instead, use a current temperature reading to
establish the trend direction.
Manufacturer and Device ID CodesTwo ROM registers provide manufacturer and device
ID codes. Reading the manufacturer ID returns 4D,
which is the ASCII code M (for Maxim). Reading the
device ID returns 09h, indicating the MAX6660 device.
If READ WORD 16-bit SMBus protocol is employed
(rather than the 8-bit READ BYTE), the LSB contains the
data and the MSB contains 00h in both cases.
BITNAMEFUNCTION7 (MSB)ADD7ADD6ADD5ADD4ADD3ADD2ADD1
Provide the current MAX6660
slave address
0 (LSB)1Logic 1
*Pe
