ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 54

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7468
Local = CYL = Bits <5:3> of Calibration Control Register 2
(Address = 0x37).
Remote 2 = CYR2 = Bits <7:6> of Calibration Control Register 2
and Bit 0 of Calibration Control Register 1 (Address = 0x36).
Table 16. Cycle Bit Assignments
Code
000
001
010
011
100
101
110
111
Care should be taken when choosing the cycle time. A long
cycle time means that T
has very fast temperature transients, the dynamic T
loop will always be lagging. If you choose a cycle time that is too
fast, the full benefit of changing T
would need 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 71 shows the steps taken during the short cycle.
Figure 72 shows the steps taken during the long cycle.
The following examples illustrate some of the circumstances
that might cause T
Normal Operation—No T
1.
2.
MEASUREMENT
MEASUREMENT
TEMPERATURE
TEMPERATURE
TEMPERATURE
OPERATING
PREVIOUS
CURRENT
T1 (n – 1)
POINT
T1(n)
OP1
If measured temperature never exceeds the programmed
operating point minus the hysteresis temperature, then
T
If measured temperature never drops below the low
temperature limit, then T
MIN
Short Cycle
8 cycles
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
is not adjusted, that is, remains at its current setting.
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
MIN
IS T1(n) – T1(n – 1)
Figure 71. Short Cycle Steps
MONITORING
to increase, decrease, or stay the same.
(OP1 – HYS)
CYCLES
≤ 0.25°C
IS T1(n) >
WAIT n
MIN
Duration
(sec)
1
2
4
8
16
32
64
128
YES
NO
is updated less often. If your system
MIN
MIN
Adjustment
NO
YES
is not adjusted.
MIN
Long Cycle
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
2048 cycles
might not be realized and
DECREASE T
DECREASE T
DECREASE T
FOR CONSTANT)
DO NOTHING
DO NOTHING
COOLING OF
(SYSTEM IS
MIN
MIN
MIN
MIN
BY 1°C
BY 2°C
BY 4°C
control
Duration
(sec)
2
4
8
16
32
64
128
256
Rev. A | Page 54 of 84
Figure 73. Temperature Between Operating Point and Low Temperature Limit
Because neither the operating point minus the hysteresis
temperature nor the low temperature limit has been exceeded,
the T
determined by the fixed T
automatic fan speed control mode.
Operating Point Exceeded—T
When the measured temperature is below the operating point
temperature minus the hysteresis, T
Once the temperature exceeds the operating temperature minus
the hysteresis (OP − Hyst), T
during the short cycle (see Figure 71). The rate at which T
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 T
2°C. Decreasing T
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
T
erature in the desired operating zone without changing T
The long cycle makes no change to T
MEASUREMENT
TEMPERATURE
TEMPERATURE
MIN
THERM LIMIT
OPERATING
OPERATING
HIGH TEMP
LOW TEMP
CURRENT
does not decrease. This allows small changes in temp-
POINT
MIN
T1(n)
OP1
POINT
LIMIT
LIMIT
T
value is not adjusted, and the fan runs at a speed
MIN
IS T1(n) < LOW TEMP LIMIT
ACTUAL
T
TEMP
HYSTERESIS
MIN
MIN
< HIGH TEMP LIMIT
IS T1(n) > OP1
MONITORING
Figure 72. Long Cycle Steps
T1(n) > T
T
has the effect of increasing the fan speed,
MIN
WAIT 2n
CYCLES
AND
AND
AND
< OP1
MIN
NO
NO
MIN
MIN
and T
starts to decrease. This occurs
YES
MIN
RANGE
MIN
Reduced
MIN
YES
remains the same.
in the temperature
values defined in the
DECREASE T
MIN
T
INCREASE
MIN
CHANGE
DO NOT
BY 1°C
is reduced by
BY 1°C
MIN
MIN
MIN
.