MAX6684ESA+ Maxim Integrated Products, MAX6684ESA+ Datasheet - Page 6

• Manufacturer Part Number: MAX6684ESA+
• Description: IC DETECTOR FAN FAIL 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Fan Failure Detectorr

Specifications of MAX6684ESA+

• Applications: Fan Controller
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 3.4 mA
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The FAIL output is an active-low, open-drain alarm.
Three fan-failure modes are possible (see the Fan-
Failure Detection section).
Drive OFF low to turn off power to the fan. If OFF is tied
high or floating, the MAX6684 is enabled.
This device can be used with fans that require operat-
ing voltages up to 24V and supply currents up to
250mA. See the Fan-Failure Detection section regard-
ing fan-current waveform issues.
Figures 6 and 7 show two ways to increase the current
capability of the MAX6684. In Figure 6, a parallel exter-
nal resistance between SENSE and PGND is used to
increase current capability. This method eliminates the
fan-control functionality normally associated with the
MAX6684 OFF pin. Select the external resistor, R1,
such that approximately 100mA flows across the inter-
nal R
Figure 7 also shows how to use an external current-
boost PNP bipolar transistor to increase the current
capability of the MAX6684. This method preserves the
fan-control functionality of the OFF pin. A 6Ω R
allows approximately 100mA of the fan current to flow
through the MAX6684.
The MAX6684 is not compatible with fans designed for
use with external PWM fan controllers.
Fan-Failure Detector with Integrated
Power Switch
Figure 6. Increased Current Capability Using External
Resistance
6
_______________________________________________________________________________________
DSON
of the MAX6684, which is typically 1Ω.
C
F
Applications Information
OFF
FC+
FC-
GND
MAX6684
3.3V
V
CC
PGND
SENSE
FAIL
Fan Compatibility
10kΩ
12V
FAIL Output
R1
BOOST
OFF
Because fan-current waveforms can vary substantially
from one given fan make or model to another, validate
the performance of the MAX6684 with the intended fan.
It is possible to encounter fans where the MAX6684 is
limited to detecting locked-rotor conditions only,
because of the nature of the fan-current waveform. In
cases where fan-speed detection does not seem to be
working properly (although locked-rotor detection is tak-
ing place), adding a 100µF capacitor across the fan
may solve the problem.
When the MAX6684 is used with fans that include
locked-rotor protection, the FAIL output is active when
the rotor locks, and toggles each time the locked-rotor
protection built into the fan attempts a restart, over a
timeframe typically measured in seconds. Toggling
should be considered an indication of fan failure; con-
versely, a fan is functioning properly only when FAIL is
constantly inactive.
A ceramic or mylar capacitor, C
to FC+. The capacitor blocks the DC component of the
signal, allowing the MAX6684 to monitor the AC current
consumption of the fan. See the Minimum Speed and
Locked-Rotor Detection section for more information.
The effects of noise can be minimized by placing a 1µF
ceramic bypass capacitor close to the device’s supply pin.
Figure 7. Increased Current Capability Using PNP Transistor
C
F
OFF
FC+
FC-
GND
Power Supply and Bypassing
MAX6684
3.3V
V
CC
SENSE
PGND
FAIL
Fan-Specific Concerns
Capacitor Selection
F
10kΩ
, is required from FC-
R
BOOST
12V