Rainbow-electronics MAX6684 Bedienungsanleitung PDF herunterladen (Seite 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

, from FC+ to FC- (Figure 1).

Fan-Failure Detector with Integrated

Power Switch

4 _______________________________________________________________________________________

FC-

BLANK

NOISE

CURRENT-SENSE AND

CURRENT-LIMITING

CIRCUIT

OFF

FC+

LATCH

COMP

8.2kHz 8Hz

OSCILLATOR

FAULT-

DETECTION

DELAY

SENSE

GND PGND

FAIL

FAN

70mV

MAX6684

Figure 1. MAX6684 Functional Diagram

NORMAL

FAN OPERATION

UNDERCURRENT*

NORMAL

CURRENT

OVERCURRENT

NO THERMAL

SHUTDOWN

THERMAL

SHUTDOWN

OVERCURRENT

*INVALID COMMUTATION CURRENT

NOTE: A THERMAL SHUTDOWN CONDITION OVERIDES ALL OTHER CONDITIONS,

IMMEDIATELY SHUTTING THE FAN OFF AND SIGNALING FAIL.

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

1 2 3 4 5 6 7

Power Switch 1

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