MAX6660AEE [MAXIM]
Remote-Junction Temperature-Controlled Fan-Speed Regulator with SMBus Interface; 远端结温控制的风扇转速调节器，带有SMBus接口
| 型号： | MAX6660AEE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Remote-Junction Temperature-Controlled Fan-Speed Regulator with SMBus Interface |
| 文件： | 总21页 (文件大小：204K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2225; Rev 0; 10/01
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
General Description
Features
The 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.
♦ Integrated Thermal Sensing and Fan-Regulation
Solution
♦ Programmable Fan Threshold Temperature
♦ Programmable Temperature Range for Full-Scale
Fan Speed
♦ Accurate Closed-Loop Fan-Speed Regulation
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.
♦ On-Chip Power Device Drives Fans Rated
Up to 250mA
♦ Programmable Under/Overtemperature Alarms
♦ SMBus 2-Wire Serial Interface with Timeout
(Cannot “Lock Up” the SMBus)
♦ Supports SMBus Alert Response
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.
♦ ACPI Compatible, Including OVERT System
Shutdown Function
♦ ±±1C (ꢀ+01C to ꢀ±001C) Thermal-Sensing Accuracy
♦ MAX+++0EVKIT Available
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.
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX6660AEE
-40°C to +125°C
16 QSOP
The MAX6660 is specified for -40°C to +125°C and is
available in a 16-pin QSOP package.
Typical Operating Circuit
Applications
+3V TO +5.5V
PC
0.1µF
50Ω
Notebooks
10kΩ
EACH
Telecom Systems
Industrial Control Systems
Servers
+12V
5kΩ
VFAN
V
CC
STBY
Workstations
FAN
TACH IN
CLOCK
DATA
SMBCLK
SMBDATA
ALERT
1µF
MAX6660
FAN
DXP
SMBus is a trademark of Intel Corp.
INTERUPT
TO µP
2200pF
DXN
TO SYSTEM
SHUTDOWN
OVERT
PENTIUM
AGND
Pin Configuration appears at end of data sheet.
ADD0
ADD1 PGND
________________________________________________________________ Maxim Integrated Products
±
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.
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND
FAN Out Current ..............................................................500mA
ESD Protection (Human Body Model)................................2000V
V , ADD0, ADD1, SMBDATA,
CC
SMBCLK, ALERT, OVERT ...................................-0.3V to +6V
, TACH IN, FAN .............................................-0.3V to +16V
Continuous Power Dissipation (T = +70°C)
A
V
FAN
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
DXP, GAIN..................................................-0.3V to (V
+ 0.3V)
CC
DXN.............................................................................-0.3V to 1V
SMBDATA, ALERT, OVERT Current ...................-1mA to +50mA
DXN Current ...................................................................... 1mA
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.
ELECTRICAL CHARACTERISTICS
(V
= +3V to +5.5V, V
= +12V, T = -40°C to +125°C, unless otherwise specified. Typical values are at V
= +3.3V and
CC
VFAN
A
CC
T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ADC AND POWER SUPPLY
V
V
Supply Voltage
V
3.0
4.5
5.5
13.5
500
10
V
V
CC
CC
Supply Voltage
V
VFAN
FAN
Operating Supply Current
Shutdown Supply Current
I
Fan off
250
3
µA
µA
°C
Bits
CC
I
Shutdown
SHDN
0.125
11
Temperature Resolution
T
RJ
T
RJ
T
RJ
= +60°C to +100°C
= +25°C to +125°C
= -40°C to +125°C
-1
-3
-5
+1
+3
+5
T = +85°C,
A
Temperature Error (Note 2)
T
E
°C
V
= +3.3V
CC
Internal Reference Frequency
Accuracy
+25
-25
%
Temperature Conversion Time
Conversion Rate Timing Error
Undervoltage Lockout Threshold
0.25
s
%
V
-25
+25
3.00
V
V
V
falling
rising
2.50
2.80
90
UVLO
CC
CC
Undervoltage Lockout Threshold
Hysteresis
V
mV
HYST
Power-On-Reset (POR)
1.4
2.0
2.5
V
mV
µA
V
Threshold (V )
CC
POR Threshold Hysteresis
Remote-Junction Source Current
DXN Source Voltage
90
100
10
High level
Low level
80
8
120
12
I
RJ
V
0.7
DXN
2
_______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(V
= +3V to +5.5V, V
= +12V, T = -40°C to +125°C, unless otherwise specified. Typical values are at V
= +3.3V and
CC
VFAN
A
CC
T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
10.5
190
20
MAX
UNITS
V
Tach Input Transition Level
Tach Input Hysteresis
V
V
= 12V
= 12V
VFAN
mV
mA
mA
mA
mA
Ω
FAN
Current-Sense Tach Threshold
Current-Sense Tach Hysteresis
Fan Output Current
0.3
250
Fan Output Current Limit (Note 3)
Fan Output On-Resistance
320
4
410
0.8
+2
R
ONF
250mA load
SMBus INTERFACE: SMBDATA, ALERT, STBY, OVERT
Logic Input Low Voltage
V
V
V
V
V
V
= +3.0V to +5.5V
V
V
IL
CC
CC
CC
= +3.0V
= +5.5V
2.2
2.6
-2
Logic Input High Voltage
V
IH
Input Leakage Current
Output Low Sink Current
Input Capacitance
I_leak
= GND or V
= 0.4V
µA
mA
pF
IN
CC
I
6
OL
OL
C
5
in
Output High Leakage Current
Serial Clock Frequency
V
= 5.5V
1
µA
OH
f
(Note 4)
0
100
kHz
SCL
Bus Free Time Between Stop
and Start Conditions
t
4.7
4.7
50
µs
µs
µs
BUF
Start Condition Setup Time
Repeat Start Condition Setup
Time
t
t
90% to 90%
SU:STA
Start Condition Hold Time
Stop Condition Setup Time
Clock Low Time
10% of SMBDATA to 90% of SMBCLK
90% of SMBCLK to 10% of SMBDATA
10% to 10%
4
4
µs
µs
µs
µs
ns
µs
HD:STA
SU:STO
t
t
4.7
4
LOW
Clock High Time
t
90% to 90%
HIGH
Data Setup Time
t
90% of SMBDATA to 10% of SMBCLK
(Note 5)
250
0
SU:DAT
HD:DAT
Data Hold Time
t
Receive SMBCLK/SMBDATA
Rise Time
t
1
µs
ns
R
Receive SMBCLK/SMBDATA
Fall Time
t
300
40
F
SMBDATA and SMBCLK time low for reset
of serial interface
SMBus Timeout
t
25
ms
TIMEOUT
Note ±: Junction Temperature = T . This implies zero dissipation in pass transistor (no load, or fan turned off).
A
Note 2: T , Remote Temperature accuracy is guaranteed by design, not production tested.
RJ
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.
_______________________________________________________________________________________
3
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Typical Operating Characteristics
(V
= +3.3V, T = +25°C, unless otherwise noted.)
A
CC
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
5
4
20
20
15
10
V
IN
= SQUARE WAVE APPLIED TO V
CC
15
10
WITH NO 0.1µF V CAPACITOR
CC
3
PATH = DXP TO GND
2
5
0
5
0
V
IN
= 250mVp-p
1
0
-5
-5
-10
-15
-20
-25
-30
-1
-2
-3
-4
-5
-10
-15
-20
-25
-30
PATH = DXP TO V (+5V)
CC
V
= 100mVp-p
IN
1
10
100
-50
0
50
100
150
1
10 100 1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE (°C)
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
4.0
3.5
3.0
1
0
V
= SQUARE WAVE
IN
AC-COUPLED TO DXN
-1
-2
-3
-4
-5
-6
-7
-8
2.5
2.0
1.5
1.0
0.5
0
V
= 100mVp-p
IN
V
= 50mVp-p
IN
-0.5
-1.0
-1.5
V
= 25mVp-p
IN
1
10 100 1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
0
10 20 30 40 50 60 70 80 90 100
DXP-DXN CAPACITANCE (nF)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
5
4
3
2
1
0
400
300
200
100
3.0
3.5
4.0
4.5
5.0
5.5
3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
4
_______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Pin Description
PIN
1
NAME
FUNCTION
VFAN
Fan Drive Power-Supply Input. 4.5V to 13.5V.
Supply Voltage Input. +3V to +5.5V. Bypass V
2
V
to ground with a 0.1µF capacitor.
CC
CC
3
DXP
DXN
Input: Remote-Junction Anode. Place a 2200pF capacitor between DXP and DXN for noise filtering.
Input: Remote-Junction Cathode. DXN is internally biased to a diode voltage above ground.
Open-Drain Output to Fan Low Side. Connect a minimum 1µF capacitor between FAN and VFAN.
SMBus Address Select Pin. ADD0 and ADD1 are sampled upon power-up.
Power Ground
4
5
FAN
6
ADD1
7
PGND
AGND
OVERT
ADD0
8
Analog Ground
9
Overtemperature Shutdown Output. Active-low output (programmable for active high if desired). Open drain.
SMBus Slave Address Select Pin. ADD0 and ADD1 are sampled upon power-up.
SMBus Alert (Interrupt) Output. Open-drain, active-low output.
10
11
12
13
14
ALERT
SMBDATA
GAIN
SMBus Serial Data Input/Output. Open drain.
Gain Control. Connect an external resistor from GAIN to V
to reduce the gain of the current-sense mode.
CC
SMBCLK
SMBus Clock Line from Controller. This line tolerates inputs up to V
even if MAX6660 is not powered.
CC
Hardware Standby Input. Drive STBY low to reduce supply current. Temperature and comparison
data are retained in standby mode.
15
16
STBY
TACH IN
Fan Tachometer Input. Tolerates voltages up to VFAN.
rent is steered through the remote diode, where the for-
ward voltage is measured, and the temperature is com-
Detailed Description
The 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.
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 Sequence
A 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.
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.
Remote-Diode Selection
Temperature 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-
ADC
The ADC is an averaging type that integrates over a
60ms period with excellent noise rejection. A bias cur-
_______________________________________________________________________________________
5
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
VFAN
TACH IN
FAN-SPEED
REGULATOR
FAN
FAN
N
REGISTERS
T
MAX
DXP
DXN
MUX
ADC
T
COMPARAT0R
HYST
OVERT
ALERT
REMOTE DATA
TEMPERATURE
CENTRAL
LOGIC
T
HIGH
SMBCLK
SMBus
INTERFACE
SMBDATA
T
LOW
ADD0
ADD1
ADDRESS
DECODER
CONFIGURATION
THERMAL OPEN/
CLOSED LOOP
FAN
CONTROL
CIRCUIT
FAN COUNT DIVISOR
(FC)
FAN OPEN/
CLOSED LOOP
T
(FT)
FAN
FAN GAIN (FG)
FAN SPEED LIMIT
(FS)
FAN LIMIT (FL)
MODE (M)
FAN CONVERSION
RATE (FCR)
FAN-SPEED CONTROL
(FSC)
STATUS
Figure 1. MAX6660 Block Diagram
+
________________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
ly measure the die temperature of CPUs and other ICs
that have on-board temperature-sensing diodes.
Table ±. Remote-Sensor Transistor
MANUFACTURER
MODEL NO.
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.
Central Semiconductor (USA)
Fairchild Semiconductor (USA)
Rohm Semiconductor (Japan)
Samsung (Korea)
2N3904, 2N3906
2N3904, 2N3906
SST3904
KST3904-TF
SMBT3904
Siemens (Germany)
Zetex (England)
FMMT3904CT-ND
Note: Transistors must be diode connected (base shorted to
collector).
PC Board Layout
Follow 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.
Thermal Mass and Self-Heating
When 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.
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 20MΩ leakage 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).
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.
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.
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.
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
_______________________________________________________________________________________
7
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
improvement in leakage and noise over narrow
traces. Use wider traces when practical.
GND
7) Add a 50Ω resistor in series with V
for best
CC
10mils
noise filtering (see Typical Operating Circuit).
10mils
10mils
DXP
PC Board Layout Checklist
• Place the MAX6660 close to the remote-sense junc-
tion.
MINIMUM
10mils
DXN
GND
• 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.
Figure 2. Recommended DXP-DXN PC Trace
• Place the noise filter and the 0.1µF V
capacitors close to the MAX6660.
bypass
CC
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.
Twisted-Pair and Shielded Cables
Use 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.
SMBus Digital Interface
From 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.
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 1Ω of series resistance, the error is approxi-
mately +1/2°C.
Low-Power Standby Mode
Standby 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
STBY low, 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.
Table 2. Temperature Data Format (Two’s
Complement)
TEMP. (°C)
DIGITAL OUTPUT
+127
+125.00
+25
+0.125
0
0111 1111 111
0111 1101 000
0001 1001 000
0000 0000 001
0000 0000 000
1111 1111 111
1110 0111 111
-0.125
-25
Driving STBY low overrides any software conversion
command. If a hardware or software standby command
-40
1101 1000111
8
_______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
DATA
ACK
P
7 bits
8 bits
8 bits
1
Slave 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)
Read Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
S
ADDRESS
RD
ACK
DATA
///
P
7 bits
8 bits
7 bits
8 bits
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
Send Byte Format
Receive Byte Format
S
ADDRESS WR ACK COMMAND ACK
P
S
ADDRESS
RD
ACK DATA
8 bits
///
P
7 bits
8 bits
7 bits
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
Command Byte: sends com-
mand with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
Shaded = Slave transmission
/// = Not acknowledged
Figure 3. SMBus Protocols
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
HD:DAT
HD:STA
SU:STA
SU:DAT
t
t
SU:STO
BUF
A = START CONDITION
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
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
Figure 4. SMBus Write Timing Diagram
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
t
BUF
SU:STA HD:STA
SU:DAT
SU:STO
A = START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
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
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
Figure 5. SMBus Read Timing Diagram
_______________________________________________________________________________________
9
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
The 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.
Diode Fault Alarm
A 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.
Remote Temperature Data Register
Two 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.
ALERT Interrupts
The ALERT interrupt output signal is activated (unless it
is masked by bit 7 in the Configuration register) when-
ever the remote-diode’s temperature is below T
or
LOW
exceeds T
. A disconnected remote diode (for con-
HIGH
tinuity detection), a shorted diode, or an active OVERT
also activates the ALERT signal. The activation of the
ALERT signal sets the corresponding bits in the Status
register. There are two ways to clear the ALERT: send-
ing 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 ALERT is asserted. ALERT is 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.
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 T
, T
, T
, and T
. If the
HYST
HIGH
LOW
MAX
measured temperature equals or exceeds T
, or is
HIGH
less than T
, an ALERT interrupt is asserted. If the
LOW
measured temperature equals or exceeds T
, the
MAX
OVERT output is asserted (see Over-Temperature
By setting bit 0 in the Configuration register to 1, the
Status register can only be cleared by sending the
SMBus Alert Response Address (see Alert Response
Address section). 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 ALERT only once per
crossing of a given temperature threshold. To enable a
new interrupt, the value in the limit register that trig-
gered 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.
Output (OVERT) section). If ALERT and OVERT are acti-
vated by the temperature exceeding T
, they can
MAX
only be deasserted by the temperature dropping below
T
HYST
. The POR state for T
is +127°C, for T
is -
HIGH
LOW
is +95°C.
55°C, for T
is +100°C, and for T
MAX
HYST
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 T
register. It is always active if
MAX
the remote-diode temperature exceeds T
. The
MAX
OVERT line clears when the temperature drops below
. Bit 1 of the Configuration register can be used
T
HYST
Example: The remote temperature reading crosses
to mask the OVERT output. Typically, the OVERT output
is connected to a power-supply shutdown line to turn
system power off. At power-up, OVERT defaults to
active-low but the polarity can be reversed by setting
bit 5 of the Configuration register.
T
, activating ALERT. The host responds to the
HIGH
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
The OVERT line 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 OVERT is active, the fan loop forces the
fan to full speed and bit 1 of the Status register is set.
T
T
. This enables the device to generate a new
interrupt if the alert condition still exists.
HIGH
HIGH
±0 ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
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.
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 (see Slave
Addresses section). Then, any slave device that gener-
ated an interrupt attempts to identify itself by putting its
own address on the bus (Table 3).
Configuration Byte Functions
The Configuration Byte register (Table 5) is used to
mask (disable) the ALERT signal 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 OVERT signal, to mask OVERT out-
put, and to clear the ALERT signal. The MAX6660 has a
write protection feature (bit 4) that prohibits write com-
mands to bits 6–3 of the Configuration register. It also
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
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 ALERT
line 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.
prohibits writes to the T
Conversion Rate registers.
, T
, and Fan
HYST
MAX
Status Byte Functions
The 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, T
and T
,
HIGH
LOW
have been exceeded, and whether there is an open cir-
cuit in the DXP-DXN path. The register also reports the
state of the ALERT and OVERT lines and indicates
when the fan driver is fully on. The final bit in the Status
register indicates when a fan failure has occurred.
Table 3. Read Format for Alert Response
Address
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 ALERT output follows the
status flag bit. Both are cleared when successfully
read, but if the condition still exists, the ALERT is
reasserted at the end of the next conversion.
Command Byte Functions
The 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
BIT
NAME
FUNCTION
7 (MSB)
ADD7
ADD6
ADD5
ADD4
ADD3
ADD2
ADD1
1
The MAX6660 incorporates collision avoidance so that
completely asynchronous operation is allowed between
SMBus operations and temperature conversions.
6
5
4
3
2
1
Provide the current MAX6660
slave address
When autoconverting, if the T
and T
limits are
HIGH
LOW
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.
0 (LSB)
Logic 1
command byte) that occurs immediately after POR
returns the current remote temperature data.
Manufacturer and Device ID Codes
Two 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
One-Shot
The 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
I2C is a trademark of Philips Corp.
______________________________________________________________________________________ ±±
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Table 4. Command-Byte Bit Assignments
REGISTERS
RRL
COMMAND
POR STATE
00000000
FUNCTION
Read Remote Temperature Low Byte (3MSBs)
00h
RRH
01h
00000000
00000000
Read Remote Temperature High Byte (Sign Bit and First 7 Bits)
Read Status Byte
RSL
02h
RCL/WCL
03h/09h
04h/0Ah
10h/12h
11h/13h
07h/0Dh
08h/0Eh
FCh
00000000
Read/Write Configuration Byte
RFCR/WFCR
RTMAX/WTMAX
RTHYST/WTHYST
RTHIGH/WTHIGH
RTLOW/WTLOW
SPOR
00000010
Read/Write Fan-Conversion Rate Byte
01100100 at +100°C
01011111 at +95°C
01111111 at +127°C
11001001 at -55°C
N/A
Read/Write Remote T
Read/Write Remote T
Read/Write Remote T
Read/Write Remote T
Write Software POR
MAX
HYST
HIGH
LOW
OSHT
0Fh
N/A
Write One-Shot Temperature Conversion
Read/Write Fan-Control Threshold Temperature T
Read/Write Fan-Speed Control
RTFAN/WTFAN
RFSC/WFSC
RFG/WFG
RFTC
14h/19h
15h/1Ah
16h/1Bh
17h
00111100 at +60°C
00000000
FAN
10000000
Read/Write Fan Gain
00000000
Read Fan Tachometer Count
RFTCL/WFTCL
RFCD/WFCD
RFS/WFS
18h/1Ch
1Dh/1Eh
1Fh/20h
FAh/FBh
FEh
11111111
Read/Write Fan Tachometer Count Limit (Fan Failure Limit)
Read/Write Fan Count Divisor
00000001
11111111
Read/Write Full-Scale Register
RM/WM
00000000
Read/Write Mode Register
ID Code
01001101
Read Manufacturer ID Code
ID Code
9Dh
00001001
Read Device ID Code
(rather than the 8-bit READ BYTE), the LSB contains the
data and the MSB contains 00h in both cases.
falls below 1.91V (typ, see Electrical Characteristics).
When power is first applied and V
rises above 2.0V
CC
(typ), the logic blocks begin operating, although reads
and writes at V levels below 3.0V are not recom-
Slave Addresses
The MAX6660 can be programmed to have one of nine
different addresses by pin strapping ADD0 and ADD1
so that up to nine MAX6660s can reside on the same
bus without address conflicts. See Table 7 for address
information.
CC
mended. A second V
voltage lockout (UVLO) comparator prevents the ADC
comparator, the ADC under-
CC
from converting until there is sufficient headroom (V
= 2.8V typ).
CC
The SPOR software POR command can force a power-on
reset of the MAX6660 registers through the serial interface.
Use the SEND BYTE protocol with COMMAND = FCh.
The address pin state is 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 MAX6660 also responds to the SMBus Alert
Response slave address (see the Alert Response
Address section).
POR and UVLO
The MAX6660 has a volatile memory. To prevent unreli-
able power-supply conditions from corrupting the data
in memory and causing erratic behavior, a POR voltage
detector monitors V
and clears the memory if V
CC
CC
±2 ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Table 5. Configuration-Byte Bit Assignments
POR
STATE
BIT
NAME
DESCRIPTION
7(MSB)
ALERT Mask
Run/Stop
0
0
0
When set to 1, ALERT is masked from internally generated errors.
When set to 1, the MAX6660 enters low-power standby.
0 provides active low, 1 provides active high.
6
5
OVERT Polarity
When set to 1, Write Protect is in effect for the following applicable registers:
1. Configuration register bits 6, 5, 4, 3
4
Write Protect
0
0
2. T
3. T
register
register
MAX
HYST
4. Fan Conversion Rate register
When set to 1, the thermal loop is open. The Fan Speed Control retains the last
closed-loop value unless overwritten by a bus command (in closed loop, the Fan
Speed Control is read only). If Fan Mode is set to Open Loop by writing a 1 to bit
0 of the Fan Gain register, then this bit is automatically set.
Thermal Closed/
Open Loop
3
When set to 1, an external signal on OVERT is masked from bit 1 of the Status
register.
2
1
OVERT Input Inhibit
0
0
Mask OVERT
Mask the OVERT output from an internally generated overtemperature error.
Output
When 0, reading the Status register clears or sending an Alert Response Request
clears ALERT (if the fault condition is no longer true). When set high, only an Alert
Response Request clears ALERT.
0
ALERT Clear Mode
0
Table +. Status-Byte Bit Assignments
POR
STATE
BIT
NAME
MAX6660 Overheat
ALERT
DESCRIPTION
When high, indicates that the fan driver transistor of the MAX6660 has
overheated (temp > +150°C) and is in thermal shutdown. The fan driver remains
disabled until temperature falls below +140°C.
7 (MSB)
0
When high, indicates ALERT has been activated (pulled low), regardless of
6
5
4
0
0
0
cause (internal or external).
When high, indicates the fan driver is at full scale. Only valid in fan
closed-loop mode (Register FG B170 = 0). Set to high in fan open-loop mode
(Register FG B170 = 1).
Fan Driver Full
Scale
When high, the remote-junction temperature exceeds the temperature in the
Remote High register.
Remote High
When high, the remote-junction temperature is lower than the temperature in the
Remote Low register.
3
2
1
Remote Low
Diode Open
OVERT
0
0
0
When high, the remote-junction diode is open.
When high, indicates that OVERT has been activated, regardless of cause
(internal or external).
When high, indicates the count in the Fan Tachometer Count register is higher
than the limit set in the Fan Tachometer Count Limit register.
0
Fan Failure
0
______________________________________________________________________________________ ±3
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
•
•
•
Interrupt latch is cleared.
Table 7. POR Slave Address Decoding
(ADD0 and ADD±)
ADC begins autoconverting.
Command register is set to 00h to facilitate quick
internal Receive Byte queries.
ADD0
GND
ADD±
GND
ADDRESS
0011 000
0011 001
0011 010
0101 001
0101 010
0101 011
1001 100
1001 101
•
•
T
and T
registers are set to +127°C and
LOW
HIGH
-55°C, respectively.
GND
High-Z
T
and T
are set to +95°C and +100°C,
MAX
GND
V
HYST
respectively.
CC
High-Z
High-Z
High-Z
GND
High-Z
Fan Control
The fan-control function can be divided into the thermal
loop, the fan-speed-regulation loop (fan loop), and the
fan-failure sensor. The thermal loop sets the desired fan
speed based on temperature while the fan-speed-regu-
lation loop uses an internally divided down reference
oscillator to synchronize to and regulate the fan speed.
The fan-speed-regulation loop includes the fan driver
and the tachometer sensor. The fan-failure sensor pro-
vides a FAN FAIL alarm that signals when the fan
tachometer count is greater than the fan tachometer
value, which corresponds to a fan going slower than
the limit. The fan driver is an N-channel, 4Ω, 320mA
V
CC
V
V
V
GND
CC
CC
CC
High-Z
V
1001 110
CC
TEMPDATA
FCR
0.25s TO 16s
MOSFET with a 16V maximum V
whose drain termi-
DS
nal connects to the low side of the fan. The tachometer
sensor (TACH IN) of the MAX6660 is driven from the
tachometer output of the fan and provides the feed-
back signal to the fan-speed-regulation loop for control-
ling the fan speed. For fans without tachometer outputs,
the MAX6660 can generate its own tachometer pulses
by monitoring the commutating current pulses (see
Commutating Current Pulses section).
UPDATE
T
FAN
FSC
Thermal Loop
FG
Thermal Closed Loop
The MAX6660 can be operated in a complete closed-
loop mode, with both the thermal and fan loops closed,
where the remote-diode sensor temperature directly
controls fan speed. Setting bit 3 of the Configuration
register to zero places the MAX6660 in thermal closed
loop (Figure 6). The remote-diode temperature sensor
is updated every 250ms. The value is stored in a tem-
porary register (TEMPDATA) and compared to the pro-
4/5/6 BITS
FAN CONTROL
DRIVER CIRCUIT
grammed temperature values in the T
, T
,
LOW
HIGH
T
, T
, and T
registers to produce the error
HYST MAX
outputs OVERT and ALERT.
FAN
Figure 6. MAX6660 Thermal Loop
The Fan Conversion Rate (FCR) register (Table 8) can
be programmed to update the TEMPDATA every 0.25s
Power-up defaults include:
±4 ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
to 16s and stores the data in an update register
(UPDATE). This enables control over timing of the ther-
mal feedback loop to optimize stability.
from fan off to full fan speed. If bits 6 and 5 are set to
01, the thermal control loop has a control range of 16°C
with 32 temperature steps from fan off to full fan speed.
If bits 6 and 5 are set to 00, the thermal control loop
has a control range of 8°C with 16 temperature steps
from fan off to full fan speed.
The Fan Threshold (T ) register value is subtracted
FAN
from the UPDATE register value. If UPDATE exceeds
temperature, then the Fan-Speed Control (FSC)
T
FAN
register (Table 9) stores the excess temperature in the
form of a 7-bit word with an LSB of 0.5°C for bits 4–0,
Thermal Open Loop
Setting bit 3 of the Configuration register (Table 5) to 1
places the MAX6660 in thermal open loop. In thermal
open-loop mode, the FSC register is read/write and con-
with bit 5 = 16°C. If the difference between the T
FAN
and UPDATE registers is higher than 32°C, then bit 6 is
set to 1, along with bits 5–1. In thermal closed loop, the
Fan Speed Control register is READ ONLY.
tains the 7-bit result of UPDATE subtracted from T
.
FAN
In fan open loop, the FSC register programs fan voltage
with acceptable values from 0 to 64 (40h). For example,
in fan open-loop mode, 0 corresponds to zero output
and 40h corresponds to full fan voltage, for example
(11.3V, typ). Proportional control is available over the 0
to 63 (3Fh) range with 64 (40h) forcing unconditional
full speed. In fan closed-loop mode, 0 corresponds to
zero fan speed and 10h corresponds to 100% fan
speed, when the FG register is set to 4 bits, 20h at 5
bits, and 3Fh at 6 bits.
The Fan Gain (FG) register (Table 10) determines the
number of bits used in the Fan-Speed Control register.
This gain can be set to 4, 5, or 6. If bits 6 and 5 are set
to 10, all 6 bits of TEMPDATA are used directly to pro-
gram the speed of the fan so that the thermal loop has
a control range of +32°C with 64 temperature steps
Table 8. Fan Conversion Update Rate
FAN
UPDATE
RATE (Hz)
SECONDS
BETWEEN
UPDATES
DATA
BINARY
Fan Loop
The fan controller (Figure 7) is based on an up/down
counter where there is a reference clock representing
the desired fan speed counting up, while tachometer
pulses count down. The reference clock frequency is
divided down from the MAX6660 internal clock to a fre-
quency of 8415Hz. This clock frequency is further
divided by the Fan Full-Scale (FS) register (Table 11),
which is limited to values between 127 to 255, for a
00h
01h
02h
03h
04h
05h
00000000
00000001
00000010
00000011
00000100
00000101
0.0625
0.125
0.25
0.5
16
8
4 (POR)
2
1
0.5
1
2
06h
00000110
4
0.25
Table 9. Fan-Speed Control Register (RFSC/W FSC)
REGISTER/
ADDRESS
FSC (±5h = READ, ±Ah = WRITE)
READ/WRITE FAN DAC REGISTER
COMMAND
7
N/A
6
5
4
Data
3
Data
2
Data
1
Data
0
Data
Bit
Overflow Bit
(MSB)
POR State
0
0
0
0
0
0
0
0
Note: In thermal closed-loop mode, the fan DAC is read only and contains the difference between the measured temperature and
the fan threshold temperature. The LSB is 0.5°C and bit 5 is 16°C. If the difference is higher than 32°C, then bit 6 is set to 1,
together with bits 5–0. Bit 6 can be regarded as an overflow bit for differences higher than 32°C. Bit 7 is always zero. The FSC
register can be programmed directly in thermal open mode. In fan closed-loop mode, FSC programs fan speed with accept-
able values from 0 to 10h, when FG is set to 4 bits or 20h when FG is set to 5 bits, or 3F when FG is set to 6 bits. In fan open-
loop mode, FSC programs fan voltage with acceptable values from 0 to 64 (40h). For example, in fan closed-loop mode, zero
corresponds to zero fan speed and 10h corresponds to 100% fan speed. In fan open-loop mode, zero corresponds to zero
volts out and 40h corresponds to full fan voltage (11.3V typ).
______________________________________________________________________________________ ±5
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
range of reference clock full-scale frequencies from
33Hz to 66Hz. A further division is performed to set the
actual desired fan speed. This value appears in the Fan-
Speed Control register in thermal closed-loop mode. If
the thermal loop is open, but the fan-speed control loop
is closed, this value is programmable in the fan DAC.
When in fan open-loop mode (which forces the thermal
loop to open), the FSC register becomes a true DAC,
programming the voltage across the fan from zero to
should be set such that the full-speed fan frequency
divided by the prescalar fall in the 33Hz to 66Hz range.
The (UP/DN) counter has six stages that form the input
of a 6-bit resistive ladder DAC whose voltage is divided
down from V
. This DAC determines the voltage
VFAN
applied to the fan. Internal coding is structured such
that when in fan closed-loop mode (which includes
thermal closed loop) that higher values in the 0 to 32
range correspond to higher fan speeds and greater
voltage across the fan. In fan open-loop mode (which
forces thermal open loop) acceptable values range
from 0 to 63 (3Fh) for proportional control; a value of 64
(40h) commands unconditional full speed.
nearly 12V to V
.
VFAN
The tachometer input (TACH IN) includes a program-
mable (1/2/4/8) prescalar. The divider ratio for the
(1/2/4/8) prescalar is stored in the Fan Count Divisor
(FCD) register (Table 12). In general, the values in FC
Table ±0. Fan Gain Register (RFG/WFG)
REGISTER/
ADDRESS
FG (±+h = READ, ±Bh = WRITE)
COMMAND
READ/WRITE FAN GAIN REGISTER
1
Fan
Feedback
Mode
0
Fan
Driver
Mode
2
7
6
5
Bit
4
x
3
x
SMBus
Timeout
Reserved
Fan Gain
Fan Gain
POR State
1
0
0
x
0
0
Notes:
Bit 7:
Reserved. Always 1. If bit 7 is written to zero, then bits 7, 6, and 5 are set to 100.
Bits 6, 5: Fan gain of the fan loop, where 00 = 8°C with resolution = 4 bits. This means that the fan reaches its full-scale (maximum)
,
speed when there is an 8°C difference between the remote-diode temperature and the value stored in TFAN 01 = 16°C,
with a 5-bit resolution and 10 = 32°C with a 6-bit resolution.
Bits 4, 3: Reserved.
2
Bit 2:
SMBus Timeout. When 1, the SMBus timeout is disabled. This permits full I C compatibility with minimum clock frequency
to DC.
Bit 1:
Bit 0:
Fan feedback mode. When bit 1 is set to 1, the fan loop uses driver current sense rather than tachometer feedback.
Fan Driver Mode. When bit 0 is set to 1, the fan driver is in fan open-loop mode. In this mode, the fan DAC programs the
fan voltage rather than the fan speed. Tachometer feedback is ignored, and the user must consider minimum fan drive and
startup issues. Thermal open loop is automatically set to 1 (see Configuration register). Fan Fail (bit 0 of the Status register)
is set to 1 in this mode and should be ignored.
Table ±±. Fan Full-Scale Register (RFS/WFS)
REGISTER/
ADDRESS
COMMAND
FS (±Fh = READ, 20h = WRITE)
READ/WRITE MAXIMUM TEMPERATURE LIMIT BYTE
7
6
5
4
3
2
1
0
Bit
(MSB)
Data Bit
Data Bit
Data Bit
Data Bit
Data Bit
Data Bit
Data Bit
POR State
1
1
1
1
1
1
1
1
Note: This register determines the maximum reference frequency at the input of the phase detector. It controls a programmable
divider that can be set anywhere between 127 and 255. The value in this register must be set in accordance with the proce-
dure described in the TACH IN section (equivalent to 8415/(Fan Frequency/Fan Count Divisor)). Programmed value below 127
defaults to 127. POR value is 255.
±+ ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Table ±2. Fan Count Divisor Register (RFCD/WFCD)
REGISTER/
FCD (±Dh = READ, ±Eh = WRITE)
ADDRESS
COMMAND
Bit
READ LIMIT/FAILURE REGISTER
7
6
0
5
0
4
0
3
0
2
0
1
0
0
1
POR State
0
Notes: This byte sets the prescalar division ratio for tachometer or current-sense feedback. (This register does not apply to the tach
signal used in the Fan-Speed register). Select this value such that the fan frequency (RPM/60 x number of poles) divided by
the FCD falls in the 33Hz to 66Hz range. See TACH IN section.
Bits 1, 0: 00 = divide by 1, 01 = divide by 2, 10 = divide by 4, 11 = divide by 8.
TEMPDATA
FG
FTC
FTCL
4/5/6
REF FREQUENCY
8415Hz
FS
127/255
1/64
COUNTER
COMPARATOR
TACH IN
FCD
1/2/4/8
FAN OPEN/CLOSED
LOOP
FAN FAIL
UP/DOWN
VFAN
FAN
DAC
N
DRIVER
Figure 7. MAX6660 Fan Loop Functional Diagram
______________________________________________________________________________________ ±7
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Fan Conversion Rate Byte
TACH IN
The TACH IN input connects directly to the tachometer
The FCR register (Table 8) programs the fan’s update
time interval in free-running autonomous mode (RUN/
STOP = 0). The conversion rate byte’s POR state is 02h
(0.25Hz). The MAX6660 uses only the 3LSBs of this
register. The 4MSBs are “don’t cares.” The update rate
tolerance is 25% (max) at any rate setting.
output of a fan. Most commercially available fans have
two tachometer pulses per revolution. The tachometer
input is fully compatible with tachometer signals, which
are pulled up to V
.
VFAN
Commutating Current Pulses
Fan Closed Loop
In the thermal open loop but fan closed-loop mode, the
feedback loop can be broken and the temperature data
read directly. After performing external manipulations,
the result can be injected back into the fan control loop
by writing to the FSC register to control fan speed. Fan
closed-loop mode is selected by setting bit 0 of the FG
to zero.
When a fan does not come equipped with a tachometer
output, the MAX6660 uses commutating generated cur-
rent pulses for speed detection. This mode is entered
by setting the FG register’s bit 1 to 1. An internal cur-
rent pulse is generated whenever a step increase
occurs in the fan current. Connecting an external resis-
tor between the GAIN pin and V
can reduce the sen-
CC
sitivity of current pulses to changes in fan current. In
general, the lower the resistor value, then the lower the
sensitivity, and the fan is easier to turn ON and can use
a smaller external capacitor across its terminals. A suit-
able resistor range is 1kΩ to 5kΩ.
Fan Open Loop
In fan control open-loop mode, selected by setting bit 0
of the FG register to 1, the gain block is bypassed and
the FSC register is used to program the fan voltage
rather than the fan speed. In the fan open-loop mode,
both the temperature feedback loop and fan-speed
control loop are broken, which results in the TACH IN
input becoming disabled. A direct voltage can be
applied after reading the temperature, using the FSC
register, to the fan that provides more flexibility in exter-
nal control algorithms. By selecting fan open-loop
mode, the MAX6660 automatically invokes thermal
open-loop mode.
Fan-Failure Detection
The MAX6660 detects fan failure by comparing the
value in the Fan Tachometer Count (FTC) register, a
READ ONLY register, with a limit stored in the Fan
Tachometer Count Limit (FTCL) register (Table 13). A
counter counts the number of on-chip oscillator pulses
between successive tachometer pulses and loads the
FTC register every time a tachometer pulse arrives. If
the value in FTC is greater than the value in FTCL, a
failure is indicated. In fan closed loop, a flag is activat-
ed when the fan is at full speed.
Fan Driver
The fan driver consists of an amplifier and low-side
Set the Fan Tachometer Limit Byte to:
NMOS device whose drain is connected to FAN and is
the input from the low side of the fan. The FET has a
typical 4Ω on-resistance with a typical 320mA maxi-
mum current limit. The driver has a thermal shutdown
sensor that senses the driver’s temperature. It shuts
down the driver if the temperature exceeds +150°C.
The driver is reactivated once the temperature has
dropped below +140°C.
✕
f = 8415/[N f]
L
where N = fan fail ratio and f = frequency of fan
tachometer.
The factor N is less than 1 and produces a fan failure
indication when the fan should be running at full speed
but is only reaching a factor N of its expected frequen-
cy. The factor N is typically set to 0.75 for all fan
Table±3. Fan Tachometer Count Limit (RFTCL/WFTCL)
REGISTER/
ADDRESS
FL (±8h = READ, ±Ch = WRITE)
READ LIMIT/FAILURE REGISTER
COMMAND
7
BIT
6
1
5
1
4
1
3
1
2
1
1
1
0
1
(MSB)
POR STATE
1
Note: The Fan Limit register is programmed with the maximum speed that is compared against the value in the FS register (Address
17) to produce an error output to the Status register.
±8 ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
speeds except at very low speeds where a fan failure is
indicated by an overflow of the fan speed counter
2) Set the programmable FCD to a value P so that the
above frequency falls in the 33Hz to 66Hz range.
rather than f . The overflow flag cannot be viewed sep-
L
3) Determine the value required for the Fan FS register:
arately in the Status Byte but is ORed with bit 0, the fan
fail bit.
8415
FS =
f
Applications Information
Mode Register
Resistance in series with the remote-sensing junction
causes conversion errors on the order of 0.5°C per ohm.
P
Example: Fan A has a 2500rpm rating:
2500rpm / 60s gives an output of 41.7Hz
41.7Hz x 2 pulses = 83.4Hz
The MAX6660 Mode register gives the ability to elimi-
nate the effects of external series resistance of up to
several hundred ohms on the remote temperature mea-
surement and to adjust the temperature measuring
ADC to suit different types of remote-diode sensor. For
systems using external switches or long cables to con-
nect to the remote sensor, a parasitic resistance can-
cellation mode can be entered by setting Mode register
bit 7 = 1. This mode requires a longer conversion time
and so can only be used for fan conversion rates of
1Hz or slower. Bits 6, 1, and 0 are Reserved. Use bits
5–2 to adjust the ADC gain to achieve accurate temper-
ature measurements with diodes not included in the
recommended list or to individually calibrate the
MAX6660 for use in specific control systems. These
bits adjust gain to set the temperature reading at
+25°C, using two’s complement format reading. Bit 5 is
the sign (1 = increase, 0 = decrease), bit 4 = 2°C shift,
bit 3 = 1°C shift, bit 2 = 1/2°C shift.
The 83.4Hz value is out of the 33Hz to 66Hz decre-
ment/increment range.
4) Set bits in the FC register to divide the signal down
within the 33Hz to 66Hz range. Bits 1, 0 = 10
(divide by 2: P = 2):
83.4 / 2 = 41.7Hz
5) Set the FS register to yield approximately 42Hz:
42 = 8415 / FS (value)
FS (value) = 200
FS register = 11001000
6) In current-sense feedback, a current pulse is gener-
ated whenever there is a step increase in fan cur-
rent. The frequency of pulses is then not only
determined by the fan rpms and the number of
poles, but also by the update rate at which the fan
driver forces an increase in voltage across the fan.
The maximum current pulse frequency is then given
by:
General Programming Techniques
The full-scale range of the fan regulation loop is
designed to accommodate fans operating between the
1000rpm to 8000rpm range of different fans. An on-
chip 8415Hz oscillator is used to generate the 33Hz to
66Hz reference frequency. Choose the prescalar such
that the fan full-speed frequency divided by the
prescalar falls in the 33Hz to 66Hz range. The full-scale
reference frequency is further divided by the value in
the FSC register to the desired fan frequency [read:
speed].
✕
f = f P / (P-1)
C
✕
Where f = {RPM/60} poles and P is the value in FCD.
The value required for the fan FS register is:
FS = 8415 / {f / (P-1)}
The fan speed limit in FCTL should be set to:
✕
f = 8415 / (N f )
L
C
1) Determine the fan’s maximum tachometer frequency:
A value of P = 1 cannot be used in current-sense mode.
RPM
60
f =
x poles
Fan Selection
For closed-loop operation and fan monitoring, the
MAX6660 requires fans with tachometer outputs. A
tachometer output is typically specified as an option on
many fan models from a variety of manufacturers. Verify
Where poles = number of tachometer poles (pulses
per revolution). Most fans are two poles; therefore,
two pulses per revolution.
______________________________________________________________________________________ ±9
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Low-Speed Operation
Table ±4. Fan Manufacturers
Brushless DC fans increase reliability by replacing
mechanical commutation with electronic commutation.
By lowering the voltage across the fan to reduce its
speed, the MAX6660 is also lowering the supply volt-
age for the electronic commutation and tachometer
electronics. If the voltage supplied to the fan is lowered
too far, the internal electronics may no longer function
properly. Some of the following symptoms are possible:
MANUFACTURER
FAN MODEL OPTION
All DC brushless models can be
ordered with optional tachometer
output.
Comair Roton
Tachometer output optional on
some models.
EBM-Papst
NMB
•
•
•
The fan may stop spinning.
All DC brushless models can be
ordered with optional tachometer
output.
The tachometer output may stop generating a signal.
The tachometer output may generate more than two
pulses per revolution.
Panaflo and flat unidirectional
miniature fans can be ordered with
tachometer output.
•
The problems that occur and the supply voltages at
which they occur depend on which fan is used. As
a rule of thumb, 12V fans can be expected to expe-
rience problems somewhere around 1/4 and 1/2
their rated speed.
Panasonic
Sunon
Tachometer output optional on
some models.
the nature of the tachometer output (open collector,
totem pole) and the resultant levels and configure the
connection to the MAX6660. For a fan with an open
drain/collector output, a pullup resistor of typically 5kΩ
must be connected between FAN and VFAN. Note how
many pulses per revolution are generated by the
tachometer output (this varies from model to model and
among manufacturers, though two pulses per revolu-
tion is the most common). Table 14 lists the representa-
tive fan manufacturers and the model they make
available with tachometer outputs.
Chip Information
TRANSISTOR COUNT: 22,142
PROCESS: BiCMOS
Pin Configuration
TOP VIEW
VFAN
1
2
3
4
5
6
7
8
16 TACH IN
15 STBY
V
CC
DXP
DXN
14 SMBCLK
13 GAIN
MAX6660
FAN
12 SMBDATA
11 ALERT
10 ADDO
ADD1
PGND
AGND
9
OVERT
QSOP
20 ______________________________________________________________________________________
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
Package Information
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 ____________________ 2±
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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