ADT7462ACPZ-R7 datasheet(43/81 Pages) ONSEMI

43 / 81 page

ADT7462

http://onsemi.com

Table 25. Cycle Bit Assignments

Code

Short

Cycle

Duration

Long Cycle

Duration

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 a system has

very fast temperature transients, the dynamic TMIN control

loop is always lagging. If a cycle time that is too short is

chosen, the full benefit of changing TMIN is not realized and

TMIN 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 68 shows the steps taken during the short cycle.

Figure 68. Short Cycle Steps

IS T1(n) − T1(n − 1) = 0.5 − 0.755C

IS T1(n) − T1(n − 1) = 1.0 − 1.755C

IS T1(n) − T1(n − 1) > 2.05C

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 15C

DECREASE TMIN BY 25C

DECREASE TMIN BY 45C

Figure 69 shows the steps taken during the long cycle.

Figure 69. Long Cycle Steps

WAIT 2n

MONITORING

CYCLES

IS T1(n) < LOW TEMP LIMIT

AND

TMIN < HIGH TEMP LIMIT

AND

TMIN < OP1

AND

T1(n) > TMIN

IS T1(n) > OP1

YES

INCREASE

TMIN BY 15C

YES

DECREASE TMIN

BY 15C

CURRENT

TEMPERATURE

MEASUREMENT

T1(n)

OPERATING

POINT

TEMPERATURE

OP1

DO NOT

CHANGE

The following examples illustrate some of the

circumstances that may cause TMIN to increase, decrease, or

stay the same.

Example 1: Normal Operation, No TMIN Adjustment

1. If the measured temperature never exceeds the

programmed operating point minus the hysteresis

temperature, TMIN is not adjusted; that is, it

remains at its current setting.

2. If the measured temperature never drops below the

low temperature limit, TMIN is not adjusted.

TMIN

THERM LIMIT

OPERATING

POINT

HIGH TEMP

LIMIT

LOW TEMP

LIMIT

ACTUAL

TEMP

HYSTERESIS

Figure 70. Temperature Between the Operating Point

and the Low Temperature Limit

Because neither the operating point minus the hysteresis

temperature nor the low temperature limit has been

exceeded, the TMIN value is not adjusted, and the fan runs at

a speed determined by the fixed TMIN and TRANGE values

defined in the automatic fan speed control mode.

Example 2: Operating Point Exceeded, TMIN Reduced

When the measured temperature is below the operating

point temperature minus the hysteresis, TMIN remains the

same. Once the temperature exceeds the operating

temperature minus the hysteresis (OP − Hyst), TMIN starts

to decrease as illustrated in Figure 71. This occurs during the

short cycle (see Figure 68). The rate at which TMIN

decreases depends on the programmed value of n. It also

depends on how much the temperature has increased

between this monitoring cycle and the last monitoring cycle;

that is, if the temperature has increased by 1

°C, then TMIN

is reduced by 2

°C. Decreasing TMIN has the effect of

increasing the fan speed, thus providing more cooling to the

system.

If the temperature is slowly increasing only in the range

(OP − Hyst), that is,

≤0.25°C per short monitoring cycle,

then TMIN does not decrease. This allows small changes in

temperature in the desired operating zone without changing

TMIN. The long cycle makes no change to TMIN in the

temperature range (OP − Hyst), because the temperature has

not exceeded the operating temperature.

When the temperature exceeds the operating temperature,

the long cycle causes TMIN to be reduced by 1°C every long

cycle while the temperature remains above the operating

temperature. This takes place in addition to the decrease in

TMIN that would occur due to the short cycle. In Figure 70,

because the temperature is increasing at a rate

≤0.25°C per

short cycle, no reduction in TMIN takes place during the

short cycle.

ADT7462ACPZ-R7 数据表(PDF) 43 Page - ON Semiconductor

ADT7462ACPZ-R7 数据表(HTML) 43 Page - ON Semiconductor

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

数据表下载

链接网址

ADT7462ACPZ-R7 数据表(PDF) 43 Page - ON Semiconductor

ADT7462ACPZ-R7 数据表(HTML) 43 Page - ON Semiconductor

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

数据表 下载

链接网址

数据表下载