Datasheet

independently control each fan. The disadvantage is
cost, size, and complexity.
For single fan control, use the MAX6650 (unless addi-
tional GPIOs are needed).
Parallel Fan Control
If multiple fans are required but independent control is
not, then a single MAX6650/MAX6651 connected to
two or more fans in parallel may make sense (Figure 7).
The obvious advantage is simplicity, size, and cost
savings. If all the fans connected in parallel are the
same type, they will tend to run at similar speeds.
However, if one or more of the fans are wearing out,
speed mismatches can occur. The MAX6651 allows the
system to monitor up to four fans, ensuring any signifi-
cant speed mismatches can be detected.
For parallel fan control while monitoring up to four fan
speeds, select the MAX6651.
Fan-Speed Regulators and Monitors
with SMBus/I
2
C-Compatible Interface
18 Maxim Integrated
MAX6650/MAX6651
MAX6650
V
CC
SCL
10kΩ
SDA
GPIO0
OUT
ADD
GND
FB
TACH0
V
CC
3V TO 5.5V
V
FAN
5V OR 12V
C
COMP
10μF
SMBus/I
2
C
INTERFACE
GPIO1
FULL ON
ALERT
FAN
MAX6501
TOVER
Figure 11. MAX6501 Hardware Fail-Safe
MAX6650
V
CC
SCL
10kΩ
SDA
GPIO0
OUT
ADD
GND
FB
TACH0
V
CC
3V TO 5.5V
V
FAN
5V OR 12V
C
COMP
10μF
SMBus/I
2
C
INTERFACE
GPIO1
FULL ON
ALERT
FAN
MAX6501
TOVER
MAX6501
TOVER
MAX6501
TOVER
Figure 12. MAX6501 Hardware Fail-Safe