Rainbow Electronics MAX6684 - Manual (Page 4)

MAX6684
Detailed Description
The MAX6684 detects fan failure in brushless DC fans.
This device is especially well suited for critical systems
where no fan control is desired. No software is neces-
sary to control the MAX6684.
Fan-Failure Detection
Fan failure is determined based on the fan current
observed at SENSE. The current observed at SENSE is
converted to a voltage, V
FAN , and highpass filtered by
the capacitor, C F , from FC+ to FC- (Figure 1).
Fan-Failure Detector with Integrated
Power Switch
4 _______________________________________________________________________________________
FC-
BLANK
NOISE
S Q
R
CURRENT-SENSE AND
CURRENT-LIMITING
CIRCUIT OFF
FC+
LATCH
COMP
8.2kHz 8Hz
OSCILLATOR
FAULT-
DETECTION
DELAY
V CC
SENSE
GND PGND
FAIL
VFAN
70mV
C F
MAX6684
Figure 1. MAX6684 Functional Diagram
NORMAL
FAN OPERATION
UNDERCURRENT*
UNDERCURRENT*
NORMAL
CURRENT
OVERCURRENT
NO THERMAL
SHUTDOWN
THERMAL
SHUTDOWN
OVERCURRENT
OVERCURRENT
OVERCURRENT
OVERCURRENT
*INVALID COMMUTATION CURRENT
NOTE: A THERMAL SHUTDOWN CONDITION OVERIDES ALL OTHER CONDITIONS,
IMMEDIATELY SHUTTING THE FAN OFF AND SIGNALING FAIL.
THERMAL SHUTDOWN
THERMAL SHUTDOWN
NORMAL
CURRENT
FAN ON,
FAIL HIGH
2ms DELAY
FAN ON,
FAIL LOW
FAN OFF,
FAIL LOW
2ms DELAY
1s DELAY 60ms DELAY
NORMAL
CURRENT
Figure 2. MAX6684 State Diagram