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C-compatible interface, Step-by-step part selection and software setup – Rainbow Electronics MAX6651 User Manual

Page 16

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Temperature Monitoring and Fan Control

The circuit shown in

Figure 10

provides complete tem-

perature monitoring and fan control. The MAX1617A (a
remote/local temperature serial interface with SMBus)
monitors temperature with a diode-connected transis-
tor. Based on the temperature readings provided by
the MAX1617A, the µC can adjust the fan speed pro-
portionally with temperature. Connecting the

ALERT

output of the MAX1617A to the

FULL ON input of the

MAX6650/MAX6651 (see the General-Purpose Input/
Output
section) allows the fan to turn on fully if the
MAX1617A detects an overtemperature condition.

MAX6501 Hardware Fail-Safe

Figure 11

shows an application using a MAX6501 as a

hardware fail-safe. The MAX6650 has its GPIO1 config-
ured as

FULL ON input. The MAX6501 TOVER pin goes

low whenever its temperature goes above a preset value.
This pulls the

FULL ON pin (GPIO1) low, forcing the fan to

spin at its maximum speed.

Figure 12

shows the use of

multiple MAX6501s. The MAX6501 has an open-drain
output, allowing multiple devices to be wire ORed to the

FULL ON input. This configuration allows fail-safe moni-
toring of multiple locations around the system.

Hot-Swap Application

Hot swapping of a fan can be detected using the circuit
in

Figure 13

where GPIO2 is configured to generate an

alert whenever it is pulled low. As long as the fan card
is connected, GPIO2 is high. However, when the fan
card is removed, a 2.2k

Ω resistor pulls GPIO2 low,

causing an interrupt. This signals to the system that a
hot swap is occurring.

Step-by-Step Part Selection

and Software Setup

Determining the Fan System Topology

The MAX6650/MAX6651 support three fan system
topologies. These are single fan control, parallel fan
control, and synchronized fan control.

Single Fan Control

The simplest configuration is a single MAX6650 for
each fan. If two or more fans are required per system,
then additional MAX6650 controllers are used (one per
fan). The advantage of this configuration is the ability to
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

MAX6650/MAX6651

Fan-Speed Regulators and Monitors
with SMBus/I

2

C-Compatible Interface

16

______________________________________________________________________________________

MAX6550

GPIO1

MAX6550

GPIO1

MAX6550

GPIO1

FAN

1

FAN

2

FAN

3

MAX6550

GPIO1

FAN

4

GPIO0

GPIO0

GPIO0

GPIO0

ALERT

FULL ON

ALERT

ALERT

ALERT

FULL ON

FULL ON

FULL ON

TO INT PIN

ON NC

Figure 9. N+1 Application