ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 51

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

STEP 10: HIGH AND LOW LIMITS FOR
TEMPERATURE CHANNELS
If temperature falls below the temperature channel’s low limit,
T
heat up. An interrupt can be generated when the temperature
drops below the low limit.
If temperature increases above the temperature channel’s high
limit, T
system. An interrupt can be generated when the temperature
rises above the high limit.
Programming High and Low Limits
There are six limit registers; a high limit and low limit are
associated with each temperature channel. These 8-bit registers
allow the high and low limit temperatures to be programmed
with 1°C resolution.
Temperature Limit Registers
Reg. 0x4E, Remote 1 temperature low limit = 0x01
Reg. 0x4F, Remote 1 temperature high limit = 0x7F
Reg. 0x50, local temperature low limit = 0x01
Reg. 0x51, local temperature high limit = 0x7F
Reg. 0x52, Remote 2 temperature low limit = 0x01
Reg. 0x53, Remote 2 temperature high limit = 0x7F
How Dynamic T
The basic premise is as follows:
1.
2.
3.
However, the loop operation is not as simple as described in
these steps. A number of conditions govern the situations in
which T
MIN
Set the target temperature for the temperature zone, for
example, the Remote 1 thermal diode. This value is
programmed to the Remote 1 operating temperature
register.
As the temperature in that zone (Remote 1 temperature)
exceeds the operating point temperature, T
and the fan speed increases.
As the temperature drops below the operating point
temperature, T
reduced.
increases. This reduces fan speed, allowing the system to
MIN
MIN
decreases. This increases fan speed to cool down the
can increase or decrease.
MIN
MIN
Control Works
is increased and the fan speed is
MIN
is reduced
Rev. A| Page 51 of 80
Short Cycle and Long Cycle
The ADT7467 implements two loops: a 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 Calibration Control
Register 2 (Address 0x37)
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
fast temperature transients, the dynamic T
lag. If a cycle time is chosen that is too fast, the full benefit of
changing T
upon the next cycle; in effect, it is overshooting. Some calibra-
tion is necessary to identify the most suitable response time.
Figure 70 shows the steps taken during the short cycle.
Figure 71 shows the steps taken during the long cycle.
MEASUREMENT
MEASUREMENT
TEMPERATURE
TEMPERATURE
TEMPERATURE
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
MIN
might not be realized and will need to change
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
Short Cycle
MIN
IS T1(n) – T1(n – 1)
Figure 70. Short Cycle Steps
MONITORING
is updated less often. If a system has very
(OP1 – HYS)
CYCLES
IS T1(n) >
≤ 0.25°C
WAIT n
(1 sec)
(2 sec)
(4 sec)
(8 sec)
(16 sec)
(32 sec)
(64 sec)
(128 sec)
YES
NO
NO
YES
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
2048 cycles
DECREASE T
DECREASE T
DECREASE T
MIN
FOR CONSTANT)
Long Cycle
COOLING OFF
control loop will
DO NOTHING
DO NOTHING
(SYSTEM IS
ADT7467
MIN
MIN
MIN
BY 1°C
BY 2°C
BY 4°C
(2 sec)
(4 sec)
(8 sec)
(16 sec)
(32 sec)
(64 sec)
(128 sec)
(256 sec)