Datasheet

6-Channel Intelligent Fan Controller
MAX31785
29
VOUT_MODE (20h)
The VOUT_MODE command is used to report the data format of the device. The device uses the DIRECT format for all
the voltage-related commands. The value returned is 40h, indicating DIRECT data format. This command is read-only.
If a host attempts to write this command, the CML status bit is asserted. See Table 3 for the m, b, and R values for the
various commands.
VOUT_SCALE_MONITOR (2Ah)
VOUT_SCALE_MONITOR is used in applications where the measured remote voltage is not equal to the voltage at the
ADC input. For example, if the ADC input expects a 1.0V input for a 12V output, VOUT_SCALE_MONITOR = 1.0V/12V
= 0.0833. In applications where the remote voltage is greater than the device input range, the voltage of the remote
supply is sensed through a resistive voltage-divider. The resistive voltage-divider reduces or scales the remote voltage.
The PMBus commands specify the actual remote voltages and not the input voltage to the ADC. To allow the device to
map between the remote voltage (such as 12V) and the voltage at the ADC input, the VOUT_SCALE_MONITOR com-
mand is used. The 2 data bytes are in DIRECT format. This value is dimensionless. For example, if the required scaling
factor is 0.0833, then VOUT_SCALE_MONITOR should be set to 0AABh (2731/32,767 = 0.0833).
Table 12. VOUT_SCALE_MONITOR
USER NOTE: On the device, the full-scale ADC voltage is 1.225V. The scaling factor where a 1.0V ADC input
represents a nominal 100% voltage level is recommended.
FAN_CONFIG_1_2 (3Ah)
The FAN_CONFIG_1_2 command is used in conjunction with MFR_FAN_CONFIG to configure the fan. See the
MFR_FAN_CONFIG (F1h) section for more details on this command. The FAN_CONFIG_1_2 command is described
in Table 13.
Table 13. FAN_CONFIG_1_2 Command Byte
NOMINAL VOLTAGE LEVEL
MONITORED (V)
NOMINAL ADC INPUT VOLTAGE
LEVEL (V) (SEE NOTE)
RESISTIVE VOLTAGE-
DIVIDER RATIO
VOUT_SCALE_MONITOR
VALUE (HEX)
1.2 1.0 0.833 6AAAh
1.5 1.0 0.667 5555h
1.8 1.0 0.555 470Ah
2.5 1.0 0.4 3333h
3.3 1.0 0.303 26C8h
5 1.0 0.2 1999h
12 1.0 0.0833 0AABh
BIT NAME MEANING
7 FAN ENABLE
0 = Fan disabled (PWM forced low).
1 = Fan enabled.
6 RPM/PWM
0 = PWM duty cycle is the fan-controlling parameter.
1 = RPM is the fan-controlling parameter.
5:4 PULSE
00 = 1 Tach pulse per fan revolution.
01 = 2 Tach pulses per fan revolution.
10 = 3 Tach pulses per fan revolution.
11 = 4 Tach pulses per fan revolution.
3:0 0 These bits always return a 0.