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PDF MAX6684 Data sheet ( Hoja de datos )
| Número de pieza | MAX6684 | |
| Descripción | Fan-Failure Detector with Integrated Power Switch | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2306; Rev 0; 1/02
Fan-Failure Detector with Integrated
Power Switch
General Description
The MAX6684 is an integrated fan-failure detector that
detects when a fan exhibits excessive underspeed or a
locked rotor. This device is especially well suited for criti-
cal systems where no fan control, or simple on/off control
is desired. The MAX6684 detects fan failure by evaluat-
ing fluctuations in current at the low side of the fan; no
tachometer signal is necessary. The output of the device,
FAIL, is an active-low, open-drain alarm. The MAX6684
can also be used to switch the fan on or off, based on
the state of a logic-level input, OFF. This device can be
used with fans rated at up to 24V and 250mA. The
MAX6684 is available in an 8-pin SO package, and is
specified for operation from -40°C to +85°C.
Features
o Dedicated Fan-Failure Detector
o Works with Ordinary 2-Wire Fans
o No Fan Tachometer Output Required
o No Software Development Required
o No Analog Circuit Design Required
o Logic-Level Fan Driver Control
o Works with Fans Rated Up to 24V/250mA
Desktop PCs
Notebooks
Networking Equipment
Telecommunications
Industrial Applications
Applications
PART
MAX6684ESA
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
8 SO
Typical Operating Circuit
3.3V
VCC
OFF
MAX6684
FC+ FAIL
1µF 0.1µF
FC-
GND
SENSE
PGND
12V
10kΩ
0.1µF
Pin Configuration
TOP VIEW
SENSE 1
FAIL 2
GND 3
FC- 4
MAX6684
8 PGND
7 OFF
6 VCC
5 FC+
SO
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
Fan-Failure Detector with Integrated
Power Switch
100Hz
ƒ
FAIL
tFD
Figure 3. MAX6684 Commutation Fault Timing Diagram
3.3V
VCC
OFF
MAX6684
FC+ FAIL
CF
FC-
GND
SENSE
PGND
10kΩ
FUNCTION
GENERATOR*
CURRENT FLUCTUATION
vs. COMMUTATION FREQUENCY
80
70
60 FAIL HIGH
50
40
30 FAIL LOW
20
10
0
0 100 200 300 400
CURRENT COMMUTATION FREQUENCY (Hz)
Figure 4. Current Fluctuation and Commutation Frequency
Diagram
Undercurrent (AC Component)
Fan failure is signaled if the AC component of IFAN is
less than 35mAP-P and remains out of specification for
at least 1s (Figure 2). The fan remains powered during
undercurrent failures.
Minimum Speed and
Locked-Rotor Detection
The MAX6684 asserts FAIL if the fan-current fluctuation
frequency is below 25Hz, which corresponds to a fan
speed of approximately 700rpm. The fan remains pow-
ered during a locked rotor or an under-speed failure
condition (Figures 3 and 4).
The MAX6684 can be designed to detect fan failure
below intended speeds by varying the value of CF.
Because of the complexity of fan-current waveforms,
the value of CF has to be arrived at empirically and
must be verified by bench testing. The guidelines of
*35mAP-P SINE-WAVE AC COMPONENT
50mA TO 300mA DC COMPONENT
APPROXIMATE FAILURE FREQUENCIES:
CF = 0.033µF < 25Hz
CF = 0.01µF < 86Hz
CF = 0.003µF < 250Hz
Figure 5. Test Circuit Demonstrates Failure Frequency as a
Function of the Value of CF
Figure 5 are only appropriate for the test signals used
and do not represent all possible fan waveforms. They
are to illustrate the ability of the MAX6684 to discrimi-
nate failure due to low fan speed. As a rule, failure typi-
cally occurs when the amplitude measured at pin 4 of
the MAX6684 drops below 70mV.
Overcurrent Protection
If an overcurrent condition begins and continues for 2ms,
fan failure is signaled for 60ms. During this 60ms period,
the power to the fan is turned off. If the part does not enter
thermal shutdown and the overcurrent condition contin-
ues, power to the fan is turned on every 62ms for 2ms
(see Overcurrent Operation in Typical Operating Char-
acteristics). Once the overcurrent condition is removed,
the fan is powered continuously. A 0.1µF capacitor
between SENSE and PGND prevents the internal DMOS
switch from being damaged by back EMF current.
Thermal Shutdown
A die temperature in excess of +160°C initiates thermal
shutdown. In thermal shutdown, the MAX6684 shuts off
the fan and the FAIL output asserts. While in thermal
shutdown, the MAX6684 monitors the die temperature.
Once the die has cooled to below +145°C, the MAX6684
exits thermal shutdown and power is returned to the fan.
A thermal shutdown fault condition has precedence over
all other failure modes. While the MAX6684 die is over
temperature, power is not cycled to the fan, as occurs
during overcurrent failure.
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet MAX6684.PDF ] | |
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