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REV. 0

ADM1029

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FAN-RELATED REGISTERS

Table IX is a list of registers on the ADM1029 that are specific

to fan speed measurement and control:

Table IX. Fan-Specific Registers

Address

Description

0x02

Fans Supported By Controller

0x03

Fans Supported In System

0x07

Set Fan x Alarm Speed

0x08

Set Fan x Hot-Plug Speed

0x09

Set Fan x Full Speed

0x10

Fan 1 Status

0x11

Fan 2 Status

0x18

Fan 1 Fault Action

0x19

Fan 2 Fault Action

0x20

Fan 1 Event Mask

0x21

Fan 2 Event Mask

0x48

Local Temp Cooling Action

0x49

Remote 1 Cooling Action

0x4A

Remote 2 Cooling Action

0x60

Fan 1 Minimum/Alarm Speed

0x61

Fan 2 Minimum/Alarm Speed

0x68

Fan 1 Configuration

0x69

Fan 2 Configuration

0x70

Fan 1 Tach Value

0x71

Fan 2 Tach Value

0x78

Fan 1 Tach High Limit

0x79

Fan 2 Tach High Limit

FAN CONFIGURATION REGISTERS

Registers 0x68 and 0x69 are the Fan 1 and Fan 2 Configuration

Registers. These allow the PWM output frequencies to be selected

for each fan. The default PWM drive frequency is 250 Hz. Bits

<7:6> adjust the fan tach oscillator frequency for fan tach mea-

surements. Bits <3:0> allow the Hot Plug PWM duty cycle value

for each fan to be programmed.

Figures 16 and 17 show how to configure the fans to handle

thermal or fault events.

Table VIII. Resistor Ratios for Setting TMIN and Number of Fans Installed Using TMIN/INSTALL Pin (Pin 18)

3 MSBs

Ideal Ratio

Actual

Error

Fans

of ADC

R2/(R1 + R2)

(k )(k )

R2/(R1 + R2)

(%)

TMIN

Installed

111

N/A

Disabled

110

0.8125

0.82

0.75

°C2

101

0.6875

0.6812

–0.63

°C2

100

0.5625

0.5556

–0.69

°C2

011

0.4375

0.4444

0.69

°C1

010

0.3125

0.3188

0.63

°C1

001

0.1875

0.18

–0.75

°C1

000

N/A

Disabled

In this case, since the Minimum Duty Cycle is the default 33%,

the equation for TMAX reduces to:

TMAX = TMIN + ((Max DC – Min DC)

× T

RANGE/10)

TMAX = TMIN + ((15 – 5)

× TRANGE/10)

TMAX = TMIN + (10

× TRANGE/10)

TMAX = TMIN + TRANGE

ENABLING AUTOMATIC FAN SPEED CONTROL USING

TMIN/INSTALL PIN (PIN 18)

Automatic fan control can also be enabled in hardware by Pin

18 (TMIN/INSTALL). This is an 8-level input with multiple

functions, which is sampled only at power-up.

If only one fan is installed, the voltage on Pin 18 should be kept

at less than VCC/2, which clears Bit 1 of register 03h. Within this

voltage range, four voltage levels define the minimum temperature

at which the fan will operate in automatic speed control mode.

If two fans are installed, the voltage on Pin 18 should be between

VCC/2 and VCC, which sets Bit 1 of register 03h. Within this

voltage range, four voltage levels define the minimum temperature

at which the fans will operate in automatic speed control mode.

Resistor values for setting the voltage on Pin 18 are given in

Table VIII. If automatic fan speed control is not used, Pin 18 can

simply be strapped to ground (one fan) or VCC (two fans),

depending on how many fans are installed. Under this condi-

tion, the fans will run full speed until the device is written to by

software to change fan speed.

When automatic fan speed control is enabled at power-up by

the TMIN/INSTALL pin, Bit 4 of the Configuration register is

set to enable monitoring, and Bits 0 and 1 of all Temp. Cooling

Action Registers are set, so any temperature channel will auto-

matically control all fans that are installed.

Note: if automatic fan speed control is enabled and an event

occurs that would cause a fan to go to alarm or hot-plug speed

(e.g., temperature fault), that event will override the automatic

fan speed control. If the event affects only one fan, the other fan

will remain under automatic control.

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