User Manual
308 of 562
V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Fan support
Table 80
Fan PWM operating mode selection
fan_mode
Fan operating mode
0
Duty-cycle mode
1
Current mode
13.1.1
Duty-cycle mode
In duty-cycle mode, the user directly programs the PWM duty cycle through one of the following methods:
•
Register
fan_duty
programs the duty-cycle output in fractional duty cycle
o
fan_duty[7:0] = 0
➔
0/256 = 0.0 percent
o
fan_duty[7:0] = 1
➔
1/256 = 0.390625 percent
o
fan_duty[7:0] = 254
➔
254/256 = 99.21875 percent
o
fan_duty[7:0] = 255
➔
overrides to 100 percent
•
PMBus command FAN_COMMAND_x programs the duty-cycle output in fractional duty cycle of FANx, where
X = 1, 2
o
FAN_COMMAND_x = C000h
➔
0/256 = 0.0 percent
o
FAN_COMMAND_x = C001h
➔
1/256 = 0.390625 percent
o
FAN_COMMAND_x = C0FEh
➔
254/256 = 99.21875 percent
o
FAN_COMMAND_x = C0FFh
➔
overrides to 100 percent
FAN_CONFIG_1_2[6] = 0 is required for FAN1 and FAN_CONFIG_1_2[6 ] = 0 is required for FAN2.
13.1.2
Current mode
In current mode, the PWM duty cycle is computed as the ratio of the output current to the maximum fan current
defined by register
fan_imax
. The following registers:
•
fan_imin
•
fan_duty_min
are provided to give additional control of the current to duty-cycle response as shown in
and
. It should be noted that one or both of these registers may be set to 0.
Figure 96
Current mode duty cycle with fan_duty_min less than or equal to (fan_imin/fan_imax)
1.0
0.0
fan_duty_min
fan_imax
fan_imin
I
OUT
(A)
du
ty
c
yc
le
