MAX6650_10 MAXIM [Maxim Integrated Products], MAX6650_10 Datasheet - Page 19

• Manufacturer Part Number: MAX6650_10
• Description: Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 13. Hot-Swap Application
For parallel fan control while monitoring only a single
fan, select the MAX6650.
In systems with multiple fans, an audible beat frequency
can sometimes be detected due to fan speed mismatch.
This happens in systems where fans are connected in
parallel or in systems with a MAX6650 controlling each
fan. In parallel fan systems, speed mismatches occur
because no two fans are identical. Slight mechanical
variations or loading differences can result in enough of
a speed mismatch to cause an audible beat.
Even in systems where there is a MAX6650/MAX6651
for each fan, there can still be speed mismatches. This
is primarily due to the oscillator tolerance. The
MAX6650/MAX6651 oscillator tolerance is specified to
be ±10%. In the worst case, this could result in a 20%
(one 10% high, one 10% low) speed mismatch.
The solution is to use a single MAX6651 for each fan,
and configure the parts to use a shared clock. The
shared clock can either be an external system clock or
one of the MAX6651’s internal clocks. If an external
clock is used, its frequency can range from approxi-
mately 50kHz to 500kHz.
Synchronized Fan Control (MAX6651 Only)
INTERFACE
3V TO 5.5V
SMBus/I
______________________________________________________________________________________
V
CC
2
C
with SMBus/I
Fan-Speed Regulators and Monitors
FULL ON
ALERT
V
SCL
SDA
GPIO0
GPIO1
CC
MAX6651
TACH0
GPIO2
2
GND
ADD
OUT
FB
C-Compatible Interface
For synchronized fan control, select the MAX6651.
In more complex systems, a combination of some or all
of the above control types may be needed.
Once the topology is chosen, the next step is to choose
a fan. See the appropriate section.
Enter a zero in bit 3 of the configuration register for a
5V fan and 1 for a 12V fan.
Configuring this bit also adjusts the tachometer input
threshold voltage. This optimizes operation of the
MAX6650/MAX6651 for the operating voltage of the fan
being used.
The MAX6650/MAX6651 have four modes of operation
as determined by bits 5 and 6 of the configuration reg-
ister: full on, full off, open loop, and closed loop.
The full-on mode applies the maximum available volt-
age across the fan, guaranteeing maximum cooling.
Full-on mode can be entered through software or hard-
10kΩ
V
5V OR 12V
ID
2.2kΩ
V
FAN
Setting the Mode of Operation
C
10μF
COMP
HOT-SWAP SECTION
FAN
Choosing a Fan
Combination
Full-On
19