ADT7473 Analog Devices, Inc., ADT7473 Datasheet - Page 50

• Manufacturer Part Number: ADT7473
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7473
STEP 10: HIGH AND LOW LIMITS FOR
TEMPERATURE CHANNELS
T
s
has the net effect of reducing the fan speed, allowing the system
to get hotter. An interrupt can be generated when the temper
ture drops below the low limit.
The high limit defines the temperature a
starts to be reduced, if temperature increases above this value.
This has the net effect of increasing fan speed to cool down the
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
Register 0x4E, Remote 1 Temperature Low Limit = 0x01
Register 0x4F, Remote 1 Temperature High Limit = 0x7F
Register 0x50, Local Temperature Low Limit = 0x01
Register 0x51, L
Reg ster 0x52, Remote 2 Temperature Low Limit = 0x01
Re
How Dynamic T
Th basic premise is as follows:
1.
2.
3.
However, the
these steps. A number of conditions govern the situations in
which T
tarts to be increased, if temperature falls below this value. This
he low limit defines the temperature at which the T
gist
e
i
Set the tar
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 (Remote 1 temperature)
rises toward and exceeds the operating point temperatur
T
As the temperature drops below the operating point
temperature, T
reduced.
er 0x53, Remote 2 Temperature High Limit = 0x7F
MIN
MIN
is reduced, and the fan speed increases.
can increase or decrease.
loop operation is not as simple as described in
get temperature for the temperature zone, which
ocal Temperature High Limit = 0x7F
MIN
MIN
Control Works
is increased, and the fan speed is
t which the T
MIN
MIN
value
value
Rev. A | Page 50 of 76
a-
e,
Short Cycle and Long Cycle
The ADT7473 implements t
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 =
Register 2 (0x37).
Local = CYL = Bits [5:3] f Dynamic T
(0x37).
Remote
Register 2 (0x37) and Bit 0 of Dynamic T
(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 is always lagging. If a cycle time is chosen that is t
the full benefit of changing T
needs to change again on the next cycle; in effect, it is over-
shootin
identify the most suitable response time.
Figure 65 shows the steps taken during the short cycle.
MEASUREMENT
MEASUREMENT
TEMPERATURE
TEMPERATURE
TEMPERATURE
OPERATING
PREVIOUS
CURRENT
T1 (n – 1)
POINT
T1(n)
OP1
g. It is necessary to carry out some calibration to
2 = CYR2 = Bits [7:6] of Dynamic T
8 cycles
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
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) – T1(n – 1)
Bits [2:0] of Dynamic T
Figure 65. Short Cycle Steps
MONITORING
(OP1 – HYS)
CYCLES
IS T1(n) >
≤ 0.25°C
WAIT n
MIN
o
1 sec
2 sec
4 sec
8 sec
16 sec
32 sec
64 sec
128 sec
YES
NO
is updated less often. If your system
wo loops: a short cycle and a long
MIN
NO
might not be realized and
YES
Long Cycle
16 cycles
32 cycles
64 cycles
128 cycles
256 cycles
512 cycles
1024 cycles
2048 cycles
MIN
MIN
DECREASE T
DECREASE T
DECREASE T
Control Re
MIN
MIN
Control Register 1
FOR CONSTANT)
COOLING OFF
DO NOTHING
DO NOTHING
(SYSTEM IS
Control
Control
MIN
MIN
MIN
MIN
2 sec
4 sec
8 sec
16 sec
32 sec
64 sec
128 sec
256 sec
BY 1°C
gister 2
BY 2°C
BY 4°C
oo fast,
control