ADT7462 datasheet(49/92 Pages) AD

49 / 92 page

ADT7462

Rev. 0 | Page 49 of 92

DYNAMIC TMIN CONTROL PROGRAMMING

Because the dynamic TMIN control mode is a basic extension of

the automatic fan control mode, the automatic fan control mode

parameters should be programmed first (see Step 1—Configuring

the MUX through Step 8—Operating Points for Temperature

Channels). Then proceed with dynamic TMIN control mode

programming.

STEP 8—OPERATING POINTS FOR TEMPERATURE

CHANNELS

The operating point for each temperature channel is the optimal

temperature for that thermal zone. The hotter each zone is

allowed to be, the quieter the system, because the fans are not

required to run as fast. The ADT7462 increases or decreases fan

speeds as necessary to maintain the operating point temperature,

allowing for system-to-system variation and removing the need

for worst-case design. If a sensible operating point value is

chosen, any TMIN value can be selected in the system characteri-

zation. If the TMIN value is too low, the fans run sooner than

required, and the temperature is below the operating point. In

response, the ADT7462 increases TMIN to keep the fans off

longer and to allow the temperature zone to get closer to the

operating point. Likewise, too high a TMIN value causes the

operating point to be exceeded, and in turn, the ADT7462

reduces TMIN to turn the fans on sooner to cool the system.

Programming the Operating Point Registers

There are two operating point registers, one for the Remote 1

temperature channel and one for the Remote 2 temperature

channel. These 8-bit registers allow the operating point

temperatures to be programmed with 1°C resolution.

Operating Point Registers

Operating Point Hysteresis Register

The operating point hysteresis register sets the value below the

operating point at which TMIN begins to reduce.

(4°C default)

STEP 9—HIGH AND LOW LIMITS FOR

TEMPERATURE CHANNELS

The low limit defines the temperature at which the TMIN value

starts to be increased, if temperature falls below this value. This

has the net effect of reducing the fan speed, allowing the system

to get hotter. An interrupt can be generated when the tempera-

ture drops below the low limit.

The high limit should be set above the operating point but

below the critical THERM point. An interrupt can be generated

when the temperature rises above the high limit.

How Dynamic TMIN Control Works

The basic premise is as follows:

Set the target temperature for the temperature zone, which

could be, for example, the Remote 1 thermal diode. This value

is programmed to the Remote 1 operating temperature register.

As the temperature in that zone rises toward and exceeds

the operating point temperature minus hysteresis, TMIN is

reduced, and fan speed increases.

As the temperature drops below the low limit value, TMIN is

increased, and the fan speed is reduced.

Short Cycle and Long Cycle

The ADT7462 implements two loops: a short (or decrease)

cycle and a long (or increase) cycle. The short cycle takes place

every n monitoring cycles. The long cycle takes place every 2n

monitoring cycles. The value of n is programmable for each

temperature channel. The bits are located at the following

Dynamic TMIN Control Register 2 (0x0C)

Remote 1 = CYR1 = Bits [2:0]

Remote 2 = CYR2 = Bits [5:3]

Table 29. Cycle Bit Assignments

Code

Short Cycle

Long Cycle

000

8 cycles

1 sec

16 cycles

2 sec

001

16 cycles

2 sec

32 cycles

4 sec

010

32 cycles

4 sec

64 cycles

8 sec

011

64 cycles

8 sec

128 cycles

16 sec

100

128 cycles

16 sec

256 cycles

32 sec

101

256 cycles

32 sec

512 cycles

64 sec

110

512 cycles

64 sec

1024 cycles

128 sec

111

1024 cycles

128 sec

2048 cycles

256 sec

The cycle time must be chosen carefully. A long cycle time

means that TMIN is updated less often. If your system has very

fast temperature transients, the dynamic TMIN control loop is

always lagging. If you choose a cycle time that is too fast, the

full benefit of changing TMIN is not realized and needs to change

again on the next cycle. In effect, it is overshooting. It is necessary

to carry out some calibration to identify the most suitable

response time.

Figure 67 shows the steps taken during the short cycle.

IS T1(n) – T1(n – 1) = 0.5 – 0.75°C

IS T1(n) – T1(n – 1) = 1.0 – 1.75°C

IS T1(n) – T1(n – 1) > 2.0°C

IS T1(n) >

(OP1 – HYS)

YES

IS T1(n) – T1(n – 1)

≤ 0.25°C

DO NOTHING

(SYSTEM

COOLING IS OFF

OR CONSTANT)

YES

DO NOTHING

WAIT n

MONITORING

CYCLES

TEMPERATURE

MEASUREMENT

T1 (n – 1)

CURRENT

TEMPERATURE

MEASUREMENT

T1(n)

OPERATING

POINT

TEMPERATURE

OP1

DECREASE TMIN BY 1°C

DECREASE TMIN BY 2°C

DECREASE TMIN BY 4°C

Figure 67. Short Cycle Steps

ADT7462 Datasheet(PDF) 49 Page - Analog Devices

ADT7462 Datasheet(HTML) 49 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Datasheet Download

Link URL