ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 21

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

Temperature Measurement Limit Registers
Each temperature measurement channel is associated with high
and low limit registers. Exceeding the programmed high or low
limit causes the appropriate status bit to be set. Exceeding either
limit can also generate SMBALERT interrupts.
Reg. 0x4E, Remote 1 temperature low limit = 0x01 default
Reg. 0x4F, Remote 1 temperature high limit = 0x7F default
Reg. 0x50, local temperature low limit = 0x01 default
Reg. 0x51, local temperature high limit = 0x7F default
Reg. 0x52, Remote 2 temperature low limit = 0x01 default
Reg. 0x53, Remote 2 temperature high limit = 0x7F default
Reading Temperature from the ADT7468
It is important to note that temperature can be read from the
ADT7468 as an 8-bit value (with 1°C resolution) or as a 10-bit
value (with 0.25°C resolution). If only 1°C resolution is
required, the temperature readings can be read back at any
time and in no particular order.
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution register
(Reg. 0x77) should be read first. This causes all temperature
reading registers to be frozen until all temperature reading
registers have been read from. This prevents an MSB reading
from being updated while its two LSBs are being read and
vice versa.
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7468 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings are made internally and the results are averaged
before being placed into the value register. Sometimes it is
necessary to take a very fast measurement. Setting Bit 4 of
Configuration Register 2 (Reg. 0x73) turns averaging off.
Table 9. Conversion Time with Averaging Disabled
Channel
Voltage Channels
Remote Temperature 1
Remote Temperature 2
Local Temperature
Measurement Time
0.7 ms
7 ms
7 ms
1.3 ms
Rev. A | Page 21 of 84
Table 10. Conversion Time with Averaging Enabled
Channel
Voltage Channels
Remote Temperature
Local Temperature
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places
the ADT7468 into single-channel ADC conversion mode. In
this mode, the ADT7468 can be made to read a single temp-
erature channel only. The appropriate ADC channel is selected
by writing to Bits <7:5> of the TACH1 minimum high byte
register (0x55).
Table 11. Channel Selection
Bits <7:5> Reg. 0x55
101
110
111
Configuration Register 2 (Reg. 0x73)
<4> = 1, averaging off.
<6> = 1, single-channel convert mode.
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> selects ADC channel for single-channel convert mode.
Overtemperature Events
Overtemperature events on any of the temperature channels can
be detected and dealt with automatically in automatic fan speed
control mode. Register 0x6A to Register 0x6C are the THERM
temperature limits. When a temperature exceeds its THERM
temperature limit, all PWM outputs run at the maximum PWM
duty cycle (Reg. 0x38, Reg. 0x39, and Reg. 0x3A). This
effectively runs the fans at the fastest allowed speed. The fans
stay running at this speed until the temperature drops below
THERM minus hysteresis. (This can be disabled by setting the
boost bit in Configuration Register 3, Bit 2, Reg. 0x78.) The
hysteresis value for that THERM temperature limit is the value
programmed into Reg. 0x6D and Reg. 0x6E (hysteresis
registers). The default hysteresis value is 4°C.
THERM LIMIT
FANS
TEMPERATURE
Figure 27. THERM Temperature Limit Operation
Channel Selected
Remote 1 temperature
Local temperature
Remote 2 temperature
100%
Measurement Time
11 ms
39 ms
12 ms
HYSTERESIS (°C)
ADT7468