ADT7473_11 ONSEMI [ON Semiconductor], ADT7473_11 Datasheet - Page 46

• Manufacturer Part Number: ADT7473_11
• Description: dbCOOL Remote Thermal Monitor and Fan Control
• Manufacturer: ONSEMI [ON Semiconductor]

Short Cycle and Long Cycle
short cycle and a long 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 register locations:
Remote 1 = CYR1 = Bits [2:0] of Dynamic T
Register 2 (0x37).
Local = CYL = Bits [5:3] of Dynamic T
(0x37).
Remote 2 = CYR2 = Bits [7:6] of Dynamic T
Register 2 (0x37) and Bit 0 of Dynamic T
Register 1 (0x36).
long cycle time means that T
your system has very fast temperature transients, the
dynamic T
is chosen that is too fast, the full benefit of changing T
might not be 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.
MEASUREMENT
MEASUREMENT
Table 15. Cycle Bit Assignments
TEMPERATURE
TEMPERATURE
TEMPERATURE
Code
000
001
010
100
101
The ADT7473/ADT7473−1 implements two loops: a
011
110
111
Care should be taken when choosing the cycle time. A
Figure 68 shows the steps taken during the short cycle.
OPERATING
PREVIOUS
CURRENT
T1 (n − 1)
POINT
T1(n)
OP1
8 cycles
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
Short Cycle
MIN
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
Figure 68. Short Cycle Steps
control loop is always lagging. If a cycle time
IS T1(n) − T1(n − 1)
MONITORING
(OP1 − HYS)
CYCLES
≤ 0.255C
IS T1(n) >
WAIT n
1 sec
2 sec
4 sec
8 sec
16 sec
32 sec
64 sec
128 sec
YES
NO
Secs
MIN
NO
YES
is updated less often. If
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
2048 cycles
Long Cycle
MIN
DECREASE T
DECREASE T
DECREASE T
Control Register 2
FOR CONSTANT)
COOLING OFF
DO NOTHING
DO NOTHING
(SYSTEM IS
MIN
MIN
MIN
MIN
MIN
MIN
2 sec
4 sec
8 sec
16 sec
32 sec
64 sec
128 sec
256 sec
Control
Control
Control
Secs
BY 15C
BY 25C
BY 45C
http://onsemi.com
MIN
46
circumstances that might cause T
or stay the same.
Example 1: Normal Operation—No T
•
•
temperature nor the low temperature limit has been
exceeded, the T
a speed determined by the fixed T
defined in the automatic fan speed control mode.
Example 2: Operating Point Exceeded—T
point temperature minus the hysteresis, T
same.
minus the hysteresis (OP − Hyst), T
This occurs during the short cycle (see Figure 68). The rate
MEASUREMENT
TEMPERATURE
TEMPERATURE
THERM LIMIT
Figure 69 shows the steps taken during the long cycle.
The following examples illustrate some of the
Because neither the operating point minus the hysteresis
When the measured temperature is below the operating
Once the temperature exceeds the operating temperature
If measured temperature never exceeds the
programmed operating point minus the hysteresis
temperature, then T
remains at its current setting.
If measured temperature never drops below the low
temperature limit, then T
OPERATING
OPERATING
Figure 70. Temperature Between Operating Point
HIGH TEMP
LOW TEMP
CURRENT
POINT
T1(n)
OP1
POINT
LIMIT
LIMIT
T
MIN
Figure 69. Long Cycle Steps
and Low Temperature Limit
IS T1(n) < LOW TEMP LIMIT
ACTUAL
MIN
T
TEMP
HYSTERESIS
MIN
< HIGH TEMP LIMIT
IS T1(n) > OP1
MONITORING
value is not adjusted, and the fan runs at
T1(n) > T
T
CYCLES
MIN
WAIT 2n
MIN
AND
AND
AND
< OP1
NO
NO
MIN
is not adjusted; that is, it
MIN
YES
is not adjusted.
MIN
MIN
YES
MIN
to increase, decrease,
MIN
and T
starts to decrease.
DECREASE T
MIN
Adjustment
T
INCREASE
MIN
MIN
CHANGE
DO NOT
RANGE
BY 15C
remains the
BY 15C
Reduced
MIN
values