MAX6620ATI MAXIM [Maxim Integrated Products], MAX6620ATI Datasheet - Page 19

• Manufacturer Part Number: MAX6620ATI
• Description: Quad Linear Fan-Speed Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

BIT
7
6
5
4
3
2
1
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
—
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RPM/DAC:
When changing from DAC to RPM mode, if the current RPM value is different from the value selected in
the Fan_ Target TACH Count register, the drive voltage will start from the current value and increment/
decrement toward the desired value at the selected DAC rate-of-change.
Spin-Up:
When the fan drive voltage increases from 0V to a value less than the full-scale drive voltage, it may be
necessary to drive the fan with the full-scale drive voltage for a brief period to ensure that the fan is
spinning before reducing the drive to the selected value.
When spin-up is selected, the fan is driven at the full-scale drive voltage until two tachometer pulses
have been detected or locked rotor has been cleared. A maximum spin-up time is also selectable to
ensure that the spin-up time is not excessive. After two tachometer pulses have been detected, or locked
rotor has been cleared or the spin-up has timed out, the drive voltage goes to the value in the Fan_ Target
Drive Voltage register.
The POR state is set by the state of the SPINUP_START pin at power-up.
Reserved
TACH Input Enable:
Enables TACH input function and fan fault detection (automatically enabled in RPM mode).
TACH/Locked Rotor:
Selects TACH input function as TACH count or locked rotor. In locked rotor mode, the TACH count stops
and assertion of the TACH input indicates that the fan has stopped.
Locked Rotor Polarity:
Reserved
0 = DAC mode. The fan drive voltage is set by the value in the Fan_ Target Drive Voltage register.
1 = RPM mode. The fan drive voltage is adjusted to produce the TACH count value in the Fan_ Target
0 = disabled. When disabled and TACH input is not used, bit 1 and bit 2 are ignored.
1 = enabled
0 = TACH count
1 = locked rotor
0 = low locked rotor. TACH input low in locked rotor mode indicates fan is stopped.
1 = high locked rotor. TACH input high in locked rotor mode indicates fan is stopped.
D6:D5
00
01
10
11
TACH Count register.
Fan_ Configuration Registers (02h, 03h, 04h, 05h)—POR = 0XX0 0000
Quad Linear Fan-Speed Controller
Spin-up until two tachometer pulses or
Spin-up until two tachometer pulses or
Spin-up until two tachometer pulses or
clearing of locked rotor, or 0.5s (max)
clearing of locked rotor, or 1s (max)
clearing of locked rotor, or 2s (max)
FUNCTION
No spin-up
FUNCTION
SPIN_START pin = ground
SPIN_START pin = open
SPIN_START pin = V
POR CONDITION
—
CC
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