MAX6684ESA Maxim Integrated Products, MAX6684ESA Datasheet - Page 5

• Manufacturer Part Number: MAX6684ESA
• Description: Board Mount Temperature Sensors
• Manufacturer: Maxim Integrated Products

Specifications of MAX6684ESA

• Package / Case: SOIC-8 Narrow
• Digital Output - Bus Interface: Serial (2-Wire)
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Output Type: Analog
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Fan failure is signaled if the AC component of I
less than 35mA
at least 1s (Figure 2). The fan remains powered during
undercurrent failures.
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 C
Because of the complexity of fan-current waveforms,
the value of C
must be verified by bench testing. The guidelines of
Figure 3. MAX6684 Commutation Fault Timing Diagram
Figure 4. Current Fluctuation and Commutation Frequency
Diagram
ƒ
100Hz
FAIL
80
70
60
50
40
30
20
10
0
0
F
P-P
CURRENT COMMUTATION FREQUENCY (Hz)
vs. COMMUTATION FREQUENCY
has to be arrived at empirically and
_______________________________________________________________________________________
and remains out of specification for
CURRENT FLUCTUATION
100
Undercurrent (AC Component)
t
FAIL HIGH
FAIL LOW
FD
Fan-Failure Detector with Integrated
200
Locked-Rotor Detection
Minimum Speed and
300
400
FAN
F
is
.
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.
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.
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.
Figure 5. Test Circuit Demonstrates Failure Frequency as a
Function of the Value of C
*35mA
50mA TO 300mA DC COMPONENT
P-P
SINE-WAVE AC COMPONENT
C
F
OFF
FC+
FC-
GND
MAX6684
3.3V
V
CC
Power Switch
SENSE
PGND
F
FAIL
APPROXIMATE FAILURE FREQUENCIES:
Overcurrent Protection
10kΩ
C
C
C
GENERATOR*
F
F
F
FUNCTION
= 0.033µF < 25Hz
= 0.01µF < 86Hz
= 0.003µF < 250Hz
Thermal Shutdown
5