MAX6651 MAXIM [Maxim Integrated Products], MAX6651 Datasheet - Page 12

• Manufacturer Part Number: MAX6651
• Description: Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface
• Manufacturer: MAXIM [Maxim Integrated Products]

Fan-Speed Regulators and Monitors
with SMBus/I
Table 7. Alarm-Enable Register Bit Masks
Table 8. Alarm Status Register Bit Assignments
1 = Alarm condition
Table 9. Tachometer Count-Time Register
(Assumes two pulses per revolution)
The first 6 bits of the Tachometer Count-Time Register
are always zero, and the last 2 bits set the count time
(Table 9). The count time may be determined from the
following equation:
where K
The 0.25 factor has a ±10% uncertainty.
12
1 = Enabled
REGISTER
0000 0000
0000 0001
0000 0010
0000 0011
(K
7 (MSB) to 5
7 (MSB) to 5
VALUE
COUNT
0 (LSB)
______________________________________________________________________________________
0 (LSB)
BIT
BIT
4
3
2
1
4
3
2
1
COUNT
)
t
COUNT
COUNT
is the numerical value of the two 2LSBs.
TIME
0.25
GPIO2 (MAX6651 only)
GPIO2 (MAX6651 only)
0.5
1.0
2.0
(s)
= 0.25s x 2
NAME
GPIO1
GPIO1
TACH
NAME
TACH
MAX
MAX
MIN
MIN
—
FAN SPEED
—
MAXIMUM
(RPS)
512
256
128
64
2
K
C-Compatible Interface
COUNT
RESOLUTION
(Hz/COUNT)
(DEFAULT)
(DEFAULT)
MINIMUM
STATE
STATE
POR
POR
0.25
0.5
0
0
0
0
0
0
2
1
0
0
0
0
0
0
Always 0
GPIO2 Alarm Enable/Disable (MAX6651 only)
GPIO1 Alarm Enable/Disable
Tachometer Overflow Alarm Enable/Disable
Minimum Output Level Alarm Enable/Disable
Maximum Output Level Alarm Enable/Disable
Always 0
GPIO2 Alarm. Set when GPIO2 is low (MAX6651 only).
GPIO1 Alarm. Set when GPIO1 is low.
Tachometer Overflow Alarm
Minimum Output Level Alarm
Maximum Output Level Alarm
Upon power-up, the Tachometer Count Registers reset
to 00h and the Tachometer Count-Time Register sets a
1s integration time.
When using the open-loop mode of operation, the DAC
Register sets the voltage on the low side of the fan. An
internal operational amplifier compares the feedback
voltage (V
DAC, and adjusts the output voltage (V
two input voltages are equal. The voltage at the FB pin
may be determined by the following equation:
and the voltage across the fan is:
where K
and V
limited by the voltage drop across the external MOS-
FET (R
by the fan’s supply voltage (V
REF
ON
DAC
V
FB
V
x I
FAN
= 1.5V. The minimum feedback voltage is
FB
) with the reference voltage set by the 8-bit
FAN
is the numerical value of the DAC Register
= (10 x V
–
), and the maximum voltage is limited



10
90
FUNCTION
Digital-to-Analog Converter
FUNCTION
k
k
+
REF
1






x K
K
256
DAC
DAC
FAN
) / 256
V
). For linear opera-
REF



OUT
) until the