ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 20

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

ADT7467
Temperature Measurement Limit Registers
High and low limit registers are associated with each
temperature measurement channel. Exceeding the programmed
high or low limit sets the appropriate status bit and 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 ADT7467
It is important to note that temperature can be read from the
ADT7467 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 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. Then all temperature reading
registers freeze until all temperature reading registers are read.
This prevents updating of an MSB reading while its two LSBs
are read and vice versa.
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7467 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings are made internally, the results of which are averaged
and then placed into the value register. Sometimes it is necessary
to perform 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 Channel
Remote Temperature 1
Remote Temperature 2
Local Temperature
Table 10. Conversion Time with Averaging Enabled
Channel
Voltage Channels
Remote Temperature
Local Temperature
Measurement Time
11 ms
39 ms
12 ms
Measurement Time
0.7 ms
7 ms
7 ms
1.3 ms
Rev. A | Page 20 of 80
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADT7467 into single-channel ADC conversion mode. In this
mode, users can read a single temperature 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 a temperature channel can be
automatically detected and dealt with in automatic fan speed
control mode. Reg. 0x6A to Reg. 0x6C contain 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, Reg. 0x3A); therefore, fans run
at the fastest speed allowed and continue 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%
HYSTERESIS (°C)