MAX6650EUB ,Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible InterfaceApplicationsI C is a trademark of Philips Corp.RAID Desktop ComputersPin Configurations appear at e ..
MAX6650EUB+ ,Fan-Speed Regulators and Monitors with SMBus/I²C-Compatible InterfaceFeatures♦ Closed/Open-Loop Fan-Speed Control for The MAX6650/MAX6651 fan controllers use an25V/12V ..
MAX6650EUB+T ,Fan-Speed Regulators and Monitors with SMBus/I²C-Compatible InterfaceFeatures♦ Closed/Open-Loop Fan-Speed Control for The MAX6650/MAX6651 fan controllers use an25V/12V ..
MAX6650EUB+T ,Fan-Speed Regulators and Monitors with SMBus/I²C-Compatible InterfaceEVALUATION KIT AVAILABLE MAX6650/MAX6651Fan-Speed Regulators and Monitors 2with SMBus/I C-Compatib ..
MAX6651EEE ,Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible InterfaceFeaturesThe MAX6650/MAX6651 fan controllers use an Closed/Open-Loop Fan-Speed Control for 2SMBus™ ..
MAX6651EEE+ ,Fan-Speed Regulators and Monitors with SMBus/I²C-Compatible InterfaceGeneral Description ________
MB3761 ,VOLTAGE DETECTORFUJITSU SEMICONDUCTORDS04-27300-2EDATA SHEETASSPVOLTAGE DETECTORMB3761VOLTAGE DETECTORDesigned for ..
MB3761M , VOLTAGE DETECTOR
MB3761P ,Voltage detectorFUJITSU SEMICONDUCTORDS04-27300-2EDATA SHEETASSPVOLTAGE DETECTORMB3761VOLTAGE DETECTORDesigned for ..
MB3761P ,Voltage detectorFUJITSU SEMICONDUCTORDS04-27300-2EDATA SHEETASSPVOLTAGE DETECTORMB3761VOLTAGE DETECTORDesigned for ..
MB3761PF ,Voltage detectorFUJITSU SEMICONDUCTORDS04-27300-2EDATA SHEETASSPVOLTAGE DETECTORMB3761VOLTAGE DETECTORDesigned for ..
MB3763 ,Bidirectional Motor DriverFEATURES• Motor Drive Current: 150 mA maximum (DC)300 mA maximum (tON = 1 s, Duty = 50 %)• Wide Pow ..
MAX6650EUB-MAX6651EEE
Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface
General DescriptionThe MAX6650/MAX6651 fan controllers use an
SMBus™/I2C™-compatible interface to regulate and mon-
itor the speed of 5VDC/12VDC brushless fans with built-in
tachometers. They automatically force the fan’s tachome-
ter frequency (fan speed) to match a preprogrammed
value in the Fan-Speed Register by using an external
MOSFET or bipolar transistor to linearly regulate the volt-
age across the fan. The MAX6650 regulates the speed of
a single fan by monitoring its tachometer output. The
MAX6651 also regulates the speed of a single fan, but it
contains additional tachometer inputs to monitor up to four
fans and control them as a single unit when they are used
in parallel.
The MAX6650/MAX6651 provide general-purpose
input/output (GPIO) pins that serve as digital inputs,
digital outputs, or various hardware interfaces. Capable
of sinking 10mA, these open-drain inputs/outputs can
drive an LED. To add additional hardware control, con-
figure GPIO1 to fully turn on the fan in case of software
failure. To generate an interrupt when a fault condition
is detected, configure GPIO0 to behave as an active-
low alert output. Synchronize multiple devices by set-
ting GPIO2 (MAX6651 only) as an internal clock output
or an external clock input.
The MAX6650 is available in a space-saving 10-pin
µMAX package, and the MAX6651 is available in a
small 16-pin QSOP package.
________________________ApplicationsRAIDDesktop Computers
ServersNetworking
WorkstationsTelecommunications
____________________________FeaturesClosed/Open-Loop Fan-Speed Control for
5V/12V Fans 2-Wire SMBus/I2C-Compatible InterfaceMonitors Tachometer Output
Single Tachometer (MAX6650)
Up to Four Tachometers (MAX6651) Programmable Alert OutputGPIOsHardware Full-On OverrideSynchronize Multiple FansFour Selectable Slave Addresses3V to 5.5V Supply VoltageSmall Packages
10-Pin µMAX (MAX6650)
16-Pin QSOP (MAX6651)
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface19-1784; Rev 2; 12/01
Ordering InformationSMBus is a trademark of Intel Corp.
I2C is a trademark of Philips Corp.
Typical Operating Circuit
Pin Configurations appear at end of data sheet.
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= 3.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= 5V.)
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.
VCCto GND..............................................................-0.3V to +6V
FB, TACH_ ..........................................................-0.3V to +13.2V
All Other Pins..............................................-0.3V to (VCC+ 0.3V)
Output Voltages..........................................-0.3V to (VCC+ 0.3V)
Maximum Current
Into VCC, GND, VOUT...................................................100mA
Into All Other Pins..........................................................50mA
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C)..........444mW
16-Pin QSOP (derate 8.3mW/°C above +70°C)..........667mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature .....................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
ELECTRICAL CHARACTERISTICS (continued)(VCC= 3.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= 5V.)
TIMING CHARACTERISTICS (VCC= 3.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= 5V.)
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
TIMING CHARACTERISTICS (continued)(VCC= 3.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= 5V.)
Note 1:For proper measurement of VFB, connect OUT and FB as shown in the Typical Operating Circuit.
Note 2:GPIO2, GPIO3, and GPIO4 only in the MAX6651.
Note 3:Note that the transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCL’s
falling edge.
Note 4:CBis the total capacitance of one bus line in pF. Tested with CB= 400pF. Rise and fall times are measured between 0.3 x
VCCand 0.7 x VCC.
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
Detailed DescriptionThe MAX6650/MAX6651 use an SMBus/I2C-Compatible
interface to regulate and monitor the speed of
5VDC/12VDC brush-less fans with built-in open-collec-
tor/drain tachometers. Regulating fan speed propor-
tionally with temperature saves power, increases fan
life, and reduces acoustic noise. Since fan speed is
proportional to the voltage across the fan, the
MAX6650/MAX6651 control the speed by regulating the
voltage on the low side of the fan with an external MOS-
FET or bipolar transistor.
The MAX6650/MAX6651 each contain two internal con-
trol loops. The first loop controls the voltage across the
fan. The internal digital-to-analog converter (DAC) sets
the reference voltage for an internal amplifier (Figure 1),
which then drives the gate of an external N-channel
MOSFET (or the base of a bipolar transistor) to regulate
the voltage on the low side of the fan. As the reference
voltage provided by the DAC changes, the feedback
amplifier automatically adjusts the feedback voltage,
which changes the voltage across the fan.
The second control loop consists of the internal digital
logic that controls the fan’s speed. The MAX6650/
MAX6651 control fan speed by forcing the tachometer
frequency to equal a reference frequency set by the
Fan-Speed Register, the prescaler, and the internal
oscillator (see the Fan-Speed Registersection). When
the tachometer frequency is too high, the value of the
DAC’s input register is increased by the regulator.
Once the DAC voltage increases, the analog control
loop forces the feedback voltage to rise, which reduces
the voltage across the fan. Since fan speed is propor-
tional to the voltage across the fan, the fan slows down.
2-Wire SMBus/I2C-Compatible
Digital InterfaceFrom a software perspective, the MAX6650/MAX6651
appear as a set of byte-wide registers that contain
speed control, tachometer count, alarm conditions, or
configuration bits. These devices use a standard
SMBus/I2C-compatible 2-wire serial interface to access
the internal registers.
Pin Description
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible InterfaceThe MAX6650/MAX6651 employ three standard SMBus
protocols: write byte, read byte, and receive byte
(Figure 2). The shorter protocol (receive) allows quicker
transfers, provided that the correct data register was
previously selected by a write or read byte instruction.
Use caution with the shorter protocol in multimaster
systems, since a second master could overwrite the
command byte without informing the first master.
Slave AddressesThe device address can be set to one of four different
values. Accomplish this by pin-strapping ADD so that
more than one MAX6650/MAX6651 can reside on the
same bus without address conflicts (Table 1).
Figure 1. Block Diagram
Table 1. Slave Address Decoding (ADD)
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible InterfaceFigure 2a. SMBus Protocol: Write Byte Format
Figure 2b. SMBus Protocol: Read Byte Format
Figure 2c. SMBus Protocol: Receive Byte Format
S = Start conditionShaded = Slave transmissionWR = Write = 0
P = Stop conditionACK = Acknowledged = 0RD = Read =1= Not acknowledged = 1
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible InterfaceFigure 3. SMBus Write Timing Diagram
Figure 4. SMBus Read Timing Diagram
Command-Byte FunctionsThe 8-bit Command-Byte Register (Table 2) is the mas-
ter index that points to the various other registers within
MAX6650/MAX6651. The register’s power-on reset
(POR) state is 0000 0000, so that a receive-byte trans-
mission (a protocol that lacks the command byte)
occurring immediately after POR returns the current
speed setting.
Fan-Speed Register In closed-loop mode, the MAX6650/MAX6651 use the
Fan-Speed Register to set the period of the tachometer
signal that controls the fan speed. The Fan-Speed
Register is ignored in all other modes of operation. The
MAX6650/MAX6651 regulate the fan speed by forcing
the tachometer period (tTACH) equal to the scaled reg-
ister value. One revolution of the fan generates two
tachometer pulses, so the required Fan-Speed Register
value (KTACH)may be calculated as:
tTACH= 1 / (2 x Fan Speed)
KTACH= [tTACHx KSCALEx (fCLK/ 128)] - 1
where the fan speed is in rotations per second (RPS),
tTACHis the period of the tachometer signal, fCLKis the
internal oscillator frequency (254kHz ±10%), and
KSCALEis the prescaler value (see Configuration-Byte
Register). Since the fan speed is inversely proportional
to the tachometer period, the Fan-Speed Register value
(KTACH) does not linearly control the fan speed (Table
3). Select the prescaler value so the fan’s full speed is
achieved with a register value of approximately 64
(0100 0000) to optimize speed range and resolution.
The MAX6651 may be controlled by an external oscilla-
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interfacetor that overrides the internal oscillator (see General-
Purpose Input/Output). When using an external oscillator
(fOSC), calculate the Fan-Speed Register value with fCLK
equal to fOSC. Codes above F8h (1111 1000) are
allowed, but will not significantly decrease the frequency.
Configuration-Byte RegisterThe Configuration-Byte Register (Table 4) adjusts the
prescaler, changes the tachometer threshold voltage,
and sets the mode of operation. The three least-signifi-
cant bits configure the prescaler division used to scale
the tachometer period. Select the prescaler value so the
fan’s full speed is achieved with a register value of
approximately 64 (0100 0000) to optimize speed range
and resolution (see the Fan Speed Register section). The
fourth bit selects the fan operating voltage.
The fifth and sixth bits configure the operating mode.
The MAX6650/MAX6651 have four modes of operation:
full-on, full-off (shutdown), closed-loop, and open-loop.
In closed-loop operation, the external microcontroller
(µC) sets the desired speed by writing an 8-bit word to
the Fan-Speed Register (see the Fan-Speed Register
section). The MAX6650/MAX6651 monitor the fan’s
tachometer output and automatically adjust the voltage
Table 2. Command-Byte Assignments
Table 3. Fan Speed *The minimum allowed tachometer period is 1ms.
across the fan until the desired speed is reached. Open-
loop operation allows the µC to regulate fan speed direct-
ly. The µC reads the fan speed from the Tach-
ometer-Count Register. Based on the tachometer
count, the µC decides if the fan speed requires adjust-
ment, and changes the voltage across the fan by writ-
ing an 8-bit word to the DAC Register. Full-on mode
applies the maximum voltage across the fan, forcing it
to spin at full speed. Configuring GPIO1 (see the
General-Purpose Input/Output section) as an active-low
input provides additional hardware control that fully
turns on the fan and overrides all software commands.
General-Purpose Input/OutputThe GPIO pins connect to the drain of the internal N-
channel MOSFET and pullup resistor (Figure 5). When
the N-channel MOSFET is off (Table 5), the pullup resis-
tor provides a logic-level high output. However, with the
MOSFET off, the GPIO may serve as an input pin and
its state is read from the GPIO Status Register (Table
6). The MAX6650/MAX6651 power up with the MOSFET
off, so input signals may be safely connected to the
GPIO pins. When using the GPIO pin as a general-pur-
pose output, change the output by writing to the GPIO
Definition Register.
GPIO0 may be configured as an ALERToutput that will
go low whenever a fault-condition is detected (see the
Alarm-Enable and Status Registers section). GPIO1
may be configured as a FULL ONinput to allow hard-
ware control to fully turn on the fan in case of software
or µC failure. GPIO2 (MAX6651 only) may be config-
ured as an internal clock output or as an external clock
input to allow synchronization of multiple devices.
Alarm-Enable and Status RegistersThe alarms are enabled only when the appropriate bits of
the Alarm-Enable Register are set (Table 7). The maxi-
mum and minimum output level alarms function only
when the device is configured to operate in the closed-
loop mode (see the Configuration-Byte Registersection).
The Alarm Status Register allows the system to deter-
mine which alarm caused the alert output (Table 8).
The set-alarm and alert outputs clear after reading the
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
Table 4. Configuration Byte Register
Alarm Status Register if the condition that caused the
alarm is removed.
TachometerThe Tachometer Count Registers record the number of
pulses on the corresponding tachometer input during the
period defined by the Tachometer Count-Time Register.
The MAX6651 contains three additional tachometer
inputs, which may be used to monitor additional fans. For
accurate control of multiple fans, use identical fans.
The Tachometer Count-Time Register sets the integration
time over which the MAX6650/MAX6651 count tachome-
ter pulses. The devices can count up to 255 (FFh) pulses
during the selected count time. If more than 255 pulses
occur, the IC sets the overflow alarm and the Tachometer
Count Register reports the maximum value of 255. Set
the time register so the count register will not overflow
under worst-case conditions (maximum fan speed) while
maximizing resolution. Calculate the maximum measur-
able fan speed and minimum resolution with the following
equations:
Max Fan Speed (in RPS) = 255 / (2 x tCOUNT)
Min Resolution (in RPS) = 1 / (2 x tCOUNT)
where tCOUNTis the tachometer count time; 1kHz is the
maximum allowable tachometer input frequency for the
MAX6650/MAX6651.
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
Table 5. GPIO Definition Register
Table 6. GPIO Status Register
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible Interface
Table 8. Alarm Status Register Bit Assignments The first 6 bits of the Tachometer Count-Time Register
are always zero, and the last 2 bits set the count time
(Table 9). The count time may be determined from the
following equation:
tCOUNT= 0.25s x 2KCOUNT
where KCOUNTis the numerical value of the two 2LSBs.
The 0.25 factor has a ±10% uncertainty.
Upon power-up, the Tachometer Count Registers reset
to 00h and the Tachometer Count-Time Register sets a
1s integration time.
Digital-to-Analog ConverterWhen using the open-loop mode of operation, the DAC
Register sets the voltage on the low side of the fan. An
internal operational amplifier compares the feedback
voltage (VFB) with the reference voltage set by the 8-bit
DAC, and adjusts the output voltage (VOUT) until the
two input voltages are equal. The voltage at the FB pin
may be determined by the following equation:
VFB= (10 x VREFx KDAC) / 256
and the voltage across the fan is:
where KDACis the numerical value of the DAC Register
and VREF= 1.5V. The minimum feedback voltage is
limited by the voltage drop across the external MOS-
FET (RONx IFAN), and the maximum voltage is limited
by the fan’s supplyvoltage (VFAN). For linear opera-
Table 9. Tachometer Count-Time Register(Assumes two pulses per revolution)
1 = Alarm condition
Table 7. Alarm-Enable Register Bit Masks1 = Enabled
tion, use DAC values between 08h and TB0h(see
Typical Operating Characteristics). When using the
closed-loop mode of operation, the contents of the
DAC Register are ignored. When writing to the DAC,
wait at least 500µs before attempting to read back.
Power-on Reset (POR)The MAX6650/MAX6651 have volatile memory. To pre-
vent ambiguous power-supply conditions from corrupt-
ing the data in the memory and causing erratic
behavior, a POR voltage detector monitors VCCand
clears the memory if VCCfalls below 1.6V. When power
is first applied and VCCrises above 1.6V, the logic
blocks begin operating (though reads and writes at
VCClevels below 3V are not recommended).
Power-up defaults include the following:
• All alarms are disabled.
• Prescale divider is set to 4.
• Fan speed is set in full-on mode.
See Table 2 for the default states of all registers.
Applications Information
MOSFET and Bipolar Transistor
SelectionThe MAX6650/MAX6651 drive an external N-channel
MOSFET that requires five important parameters for
proper selection: gate-to-source conduction threshold,
maximum gate-to-source voltage, drain-to-source
breakdown voltage, current rating, and drain-to-source
on-resistance (RDS(ON)). Gate-to-source conduction
threshold must be compatible with available VCC. The
maximum gate-to-source voltage and the drain-to-
source breakdown voltage rating should both be at
least a few volts higher than the fan supply voltage
(VFAN). Choose a MOSFET with a maximum continuous
drain current rating higher than the maximum fan cur-
rent. RDS(ON)should be as low as practical to maxi-
mize the feedback voltage range. Maximum power
dissipation in the power transistor can be approximat-
ed by P = (VFAN XIFAN(MAX)) / 4. Bipolar power transis-
tors are practical for driving small and midsize fans
(Figure 6). Very-high-current fans may require output
transistor base current greater than the MAX6650’s
50mA drive capability. Bipolar Darlington transistors
will work but have poor saturation characteristics and
could lose up to 2V to 3V of drive voltage.
Resistor SelectionThe tachometer input voltages (VTACH_) and feedback
voltage (VFB) cannot exceed 13.2V (see Absolute
Maximum Ratings). When using a fan powered by a
13.2V or greater supply (VFAN), protect these inputs
from overvoltage conditions with series resistors. The
resistance required to protect these pins may be calcu-
lated from the following equation:
RPROTECT= [(VFAN(MAX)- 13.2V) x RIN] / 13.2V
where VFAN(MAX)is the worst-case maximum supply
voltage used to power the fan and RINis the input
MAX6650/MAX6651
Fan-Speed Regulators and Monitors
with SMBus/I2C-Compatible InterfaceFigure 6. Fan Control with a Bipolar Transistor
