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ADM1029ARQ

Dual PWM Fan Controller and Temperature Monitor for High Availability Systems

Analog Devices 

ADM1029

LAYOUT CONSIDERATIONS

Digital boards can be electrically noisy environments, and care

must be taken to protect the analog inputs from noise, particu-

larly when measuring the very small voltages from a remote diode

sensor. The following precautions should be taken:

1. Place the ADM1029 as close as possible to the remote sens-

ing diode. Provided that the worst noise sources such as

clock generators, data/address buses, and CRTs are avoided,

this distance can be 4 to 8 inches.

2. Route the D+ and D– tracks close together, in parallel, with

grounded guard tracks on each side. Provide a ground plane

under the tracks if possible.

3. Use wide tracks to minimize inductance and reduce noise

pickup. Ten mil track minimum width and spacing is

recommended.

GND

D+

D–

GND

10MIL

10MIL

10MIL

10MIL

10MIL

10MIL

10MIL

Figure 6. Arrangement of Signal Tracks

4. Try to minimize the number of copper/solder joints, which

can cause thermocouple effects. Where copper/solder joints

are used, make sure that they are in both the D+ and D–

path and at the same temperature.

Thermocouple effects should not be a major problem as 1°C

corresponds to about 240 µV, and thermocouple voltages are

about 3 µV/oC of temperature difference. Unless there are two

thermocouples with a big temperature differential between

them, thermocouple voltages should be much less than 200 µV.

5. Place 0.1 µF bypass and 1000 pF input filter capacitors close

to the ADM1029.

6. If the distance to the remote sensor is more than 8 inches,

the use of twisted pair cable is recommended. This will work

up to about 6 to 12 feet.

7. For really long distances (up to 100 feet), use shielded

twisted pair such as Belden #8451 microphone cable. Con-

nect the twisted pair to D+ and D– and the shield to GND

close to the ADM1029. Leave the remote end of the shield

unconnected to avoid ground loops.

Because the measurement technique uses switched current

sources, excessive cable and/or filter capacitance can affect the

measurement. When using long cables, the filter capacitor may

be reduced or removed.

Cable resistance can also introduce errors. 1 Ω series resistance

introduces about 0.5°C error.

TEMPERATURE-RELATED REGISTERS

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

to temperature measurement and control.

Table III. Temperature-Specific Registers

Address

0x06

0x30

0x31

0x32

0x40

0x41

0x42

0x48

0x49

0x4A

0x80

0x81

0x82

0x88

0x89

0x8A

0x90

0x91

0x92

0x98

0x99

0x9A

0xA0

0xA1

0xA2

Description

Temp Devices Installed

Local Temp Offset

Remote 1 Temp Offset

Remote 2 Temp Offset

Local Temp Fault Action

Remote 1 Temp Fault Action

Remote 2 Temp Fault Action

Local Temp Cooling Action

Remote 1 Temp Cooling Action

Remote 2 Temp Cooling Action

Local Temp TMIN

Remote 1 Temp TMIN

Remote 2 Temp TMIN

Local Temp TRANGE/THYST

Remote 1 Temp TRANGE/THYST

Remote 2 Temp TRANGE/THYST

Local Temp High Limit

Remote 1 Temp High Limit

Remote 2 Temp High Limit

Local Temp Low Limit

Remote 1 Temp Low Limit

Remote 2 Temp Low Limit

Local Temp Value

Remote 1 Temp Value

Remote 2 Temp Value

The flowchart in Figure 7 shows how to configure the ADM1029

to measure temperature. It also shows how to configure the

ADM1029’s behavior for out-of-limit temperature measurements.

FAN INTERFACING

The ADM1029 can be interfaced to many types of fan. It can be

used to control the speed of a simple two-wire fan. It can mea-

sure the speed of a fan with a tach output, and it can accept a

logic input from fans with a FAULT output. By means of a

shorting link in the fan connector it can also determine if a fan is

present or not and if fans have been hot-swapped.

The ADM1029 can control or monitor one or two fans. Bits 0

and 1 of the Fans Supported In System Register (03h) tell the

ADM1029 how many fans it should be controlling/monitoring.

In the following descriptions “installed” means that the corre-

sponding bit of register 03h is set and the ADM1029 expects to

see a fan interfaced to it. It does not necessarily mean that the

fan is actually, physically, connected.

If a fan is installed, events such as a fault output and hot-swapping

of the fan can cause INT and CFAULT to be asserted, unless

they are masked for that particular event. If a fan is not installed,

but is still physically connected to the ADM1029, these events will

be ignored with respect to asserting INT or CFAULT, but will

still be reflected in the corresponding Fan Status Register.

Setting Bit 0 indicates that Fan 1 is installed and is set to 1

at power-up by default. Setting Bit 1 indicates that Fan 2 is

installed and depends on the state of Pin 18 (TMIN/INSTALL)

at power-up.

REV. 0

–11–

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