EVAL-ADT7470EB Analog Devices Inc, EVAL-ADT7470EB Datasheet - Page 25

• Manufacturer Part Number: EVAL-ADT7470EB
• Description: BOARD EVALUATION FOR ADT7470
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADT7470EB

• Sensor Type: Temperature
• Interface: SMBus (2-Wire/I²C)
• Voltage - Supply: 3 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: ADT7470
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

MANUAL FAN SPEED CONTROL
Manual fan speed control on the ADT7470 allows the user to
control the PWM duty cycle for each fan via the registers. The
ADt7470 powers-up in manual fan control mode, with all
PWM duty cycles set to maximum. The PWM Configuration
registers determine whether the fans are in manual or automatic
fan control mode.
SETTING THE PWM DUTY CYCLE
The ADT7470 allows the duty cycle of any PWM output to be
manually adjusted. This can be useful if users want to change
fan speed in software or want to adjust PWM duty cycle output
for test purposes. The PWM current duty cycle registers
(Register 0x32 to Register 0x35) can be written with 8-bit
values in manual fan speed control mode to manually adjust
the speeds of the cooling fans.
The PWM duty cycle for each output can be set anywhere from
0% to 100%, in steps of 0.39%.
Table 22.Fan Control Mode Configuration
Register/Bit
0x68 Bit[6]
0x68 Bit[7]
0x69 Bit[6]
0x69 Bit[7]
Mnenonic
BHVR2
BHVR1
BHVR4
BHVR3
Description
This bit determines fan behavior for PWM2 output.
0 = Manual mode (PWM2 duty cycle controlled in software).
1 = Fastest speed calculated by all temperatures control PWM2 (automatic fan control mode).
This bit determines fan behavior for PWM1 output.
0 = Manual mode (PWM1 duty cycle controlled in software).
1 = Fastest speed calculated by all temperatures control PWM1 (automatic fan control mode).
This bit determines fan behavior for PWM4 output.
0 = Manual mode (PWM4 duty cycle controlled in software).
1 = Fastest speed calculated by all temperatures control PWM4 (automatic fan control mode).
This bit determines fan behavior for PWM3 output.
0 = Manual mode (PWM3 duty cycle controlled in software).
1 = Fastest speed calculated by all temperatures control PWM3 (automatic fan control mode).
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The value to be programmed into the PWM Current Duty
Cycle registers can be calculated as follows:
Example 1: For a PWM Duty Cycle of 50%
Example 2: For a PWM Duty Cycle of 33%
Table 21. PWM Current Duty Cycle Registers
Register Address
0x32
0x33
0x34
0x35
Value (decimal) = Desired PWM duty cycle/0.39
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex
Description
PWM1 duty cycle
PWM2 duty cycle
PWM3 duty cycle
PWM4 duty cycle
Default
0xFF (100%)
0xFF (100%)
0xFF (100%)
0xFF (100%)
ADT7470