MAX6664AEE+T Maxim Integrated Products, MAX6664AEE+T Datasheet - Page 13

• Manufacturer Part Number: MAX6664AEE+T
• Description: IC TEMP MON FAN CNTRL 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6664AEE+T

• Function: Fan Control, Temp Monitor
• Topology: ADC, Multiplexer, Register Bank, Tachometer
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Full Temp Accuracy: +/- 1 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Digital Output - Number Of Bits: 11 bit
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 5 shows a schematic using a current-sensing
resistor and a coupling capacitor to derive the
tachometer information from the power-supply current
of a 2-wire fan. This circuit allows the speed of a 2-wire
fan to be measured even though the fan has no
tachometer signal output. The sensing resistor,
R
voltage and this voltage is AC-coupled into the
TACH/AIN input through coupling capacitor C1. The
value of R
on the fan, and the value of the coupling capacitor C1
is 0.01µF. When using this method, set bit 2 of configu-
ration register 1 to 1.
The FAN_FAULT output is used to indicate fan slow
down or failure. POR disables the FAN_FAULT output
on the MAX6653/MAX6663. POR enables FAN_FAULT
output on the MAX6664. If FAN_FAULT is not enabled,
writing a logic 1 to bit 4 of configuration register 1 (00h)
enables the FAN_FAULT output pin. Either under-
speed or stalled fans are detected as fan faults.
FAN_FAULT is asserted low only when five consecutive
interrupts are generated by the MAX6653/MAX6663/
MAX6664s’ INT due to fan faults. The MAX6653/
MAX6664 apply 100% duty cycle for the duration of the
spin-up time once an INT is asserted. The MAX6663
goes to 100% duty cycle for the duration of the spin-up
time once INT is asserted and status register 1 is read.
Fan-fault detection works by comparing the value of the
fan tachometer high-limit register (10h) with the value of
the fan-speed reading register (08h), which contains the
value of the most recent fan-speed measurement. Note
that the value of the fan-speed reading register (08h)
must exceed the value of the fan tachometer high limit
(10h) by 1 in order to qualify as a fault. The fault gener-
ates an interrupt signal by asserting the INT output, but
does not cause the FAN_FAULT output to assert until five
consecutive failures have been detected. The fan runs at
100% duty cycle when five consecutive failures have
been detected, whether FAN_FAULT is enabled or not.
As an example of the function of the fan-fault detection,
assume a fan is stalled or under speed. The MAX6663 ini-
tially indicates the failure by generating an interrupt on the
INT pin. The fan fault bit (bit 1) of interrupt status register
1 (02h) is also set to 1. Once the processor has acknowl-
edged the INT by reading status register 1, the INT is
cleared. PWM_OUT is then brought high for a 2s (fan
SENSE
, converts the fan commutation pulses into a
SENSE
is on the order of 1Ω to 5Ω, depending
______________________________________________________________________________________
Fan-Fault Detection
Temperature Monitors and
spin-up default, Table 12) spin-up period to restart the
fan. Subsequent fan failures cause INT to be reasserted
and PWM_OUT to be brought high (following a status
register 1 read) for a spin-up period each time to restart
the fan. Once the fifth tachometer failure occurs, the
FAN_FAULT is asserted to indicate a critical fan failure.
A MAX6653/MAX6664 example is somewhat simpler.
Again assume the fan is stalled or under speed. The
MAX6653/MAX6664 initially indicate the failure by gener-
ating an interrupt on the INT pin. The fan fault bit of the
interrupt status register is set to 1. PWM_OUT goes high
for the programmed spin-up time (2s default) to restart
the fan. Each subsequent fan failure causes another spin-
up. Once the fifth tachometer failure occurs, the
FAN_FAULT output is asserted (if enabled) and the PWM
output is driven to 100%.
When the FAN_FAULT output is disabled (register 00h,
bit 4), spin-ups are still attempted whenever the tach
count is greater than the value in the fan tachometer
high-limit register (10h). If fan faults and their associat-
ed spin-ups are not desired, the fan tachometer high-
limit register (10h) to FF. This prevents the tach count
from ever exceeding the limit and faults are not detect-
ed. Simply disabling the tachometer input (register 01h,
bit 2) leaves the fan fault function enabled and can
result in fan faults.
Figure 5. Using the MAX6653/MAX6663/MAX6664 with a
2-Wire Fan
PWM Fan Controllers
MAX6653
MAX6663
MAX6664
PWM_OUT
TACH/AIN
3.3V
100Ω
(TYP)
C1
2Ω
5V
N
NDT3055L
R
SENSE
2-WIRE
FAN
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