Table 32. mfr_fan_config (continued) – Rainbow Electronics MAX34441 User Manual
Page 47
PMBus 5-Channel Power-Supply Manager
and Intelligent Fan Controller
MAX34441
47
Table 32. MFR_FAN_CONFIG (continued)
Note: It is recommended that the fan be disabled prior to changing MFR_FAN_CONFIG.
BIT
BIT NAME
MEANING
7:5
RAMP[2:0]
The RAMP bits select how fast the device ramps the PWM from one duty cycle to another (either up
or down). In PWM mode, the following table always applies. In RPM mode, the fan speed is read
either every 200ms or 1000ms and when the reported fan speed is within 20% of the target speed,
the maximum allowed PWM duty cycle change is set to 1%. In RPM mode, the PWM duty cycle is
not changed as long as the fan is within Q5% of the target speed.
RAMP2
RAMP1
RAMP0
PWM DUTY
CYCLE UPDATE
RATE (ms)
MAX PWM DUTY
CYCLE CHANGE
ALLOWED (%)
TIME TO RAMP
FROM 40% TO
100% PWM DUTY
CYCLE (seconds)
0
0
0
1000
1
60
0
0
1
1000
2
30
0
1
0
1000
3
20
0
1
1
200
1
12
1
0
0
200
2
6
1
0
1
200
3
4
1
1
0
200
4
3
1
1
1
200
5
2.4
4
0
This bit always returns a 0.
3
ROTOR_HI_LO
Determines if a locked rotor indication is active low or active high. This bit is ignored if
ROTOR = 0.
0 = ROTOR is active low (TACH input is low if the rotor stops).
1 = ROTOR is active high (TACH input is high if the rotor stops).
2
ROTOR
The ROTOR bit selects if the fan does not have a tachometer but rather a stalled (or locked)
rotor output.
ROTOR
FAN OUTPUT
MAX34441 CONFIGURATION
0
Tachometer
TACH input expects fan RPM
1
Stalled/locked rotor
detect
TACH input expects locked rotor signal. The polarity is
selected with the ROTOR_HI_LO bit (also set
MFR_FAN_FAULT_LIMIT = 0001h).
1:0
SPIN[1:0]
The SPIN bits determine how the device spins up (or starts) the fan from a dead stop. To over-
come the initial mechanical fan inertia, the device can be programmed to drive the fan at 100%
duty cycle until a programmable number of fan revolutions (cumulative count) is detected or a
locked rotor signal is negated. The device allows a 2s startup period during which the fan speed
monitors are disabled. If after 2s the fan does not respond, the PWM output remains at 100%
duty cycle (if TACHO = 0) or goes to 0% duty cycle (if TACHO = 1).
SPIN1
SPIN0
SPIN-UP RELAXATION CRITERIA
0
0
Automatic spin-up disabled
0
1
Two revolutions or locked rotor negated
1
0
Four revolutions or locked rotor negated
1
1
Eight revolutions or locked rotor negated