Additional Adc Functions For Temperature Measurement - Analog Devices dBCool ADT7473 Manual

ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7473 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value r
it is necessary to t ake a very fast measurement. Setting Bit 4 of
Configuration Register 2 (0x73) turns averaging off.
Table 10. Conversion Time with Averaging Disabled
Channel
Voltage Channel
Remote 1 Temperature
Remote 2 Temper ture a
Local Temperature
Table 11. Conversion Time with Averaging Enabled
Channel
Voltage Channels
Remote Temperature
Local Temperature
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places the
ADT7473 into single-channel ADC conversion mode. In
mode, the ADT7473 can be made to read a single tempera
channel only. The appropriate ADC channel is selected by
writing to Bits [7:5] of the TACH1 minimum high byte register
(0x55).
Table 12. Programming Single-Channel ADC Mode for
Temperatures
Bits [7:5] Register 0x55
101
110
111
Configuration Register 2 (0x73)
Bit 4 = 1, averaging off
Bit 6 = 1, single-channel convert mode
TACH1 Minim um High Byte Register (0x55)
Bits [7:5] select ADC channel for single-channel convert mode.
egister. Sometimes
Measurement Time
0.7 ms
7 ms
7 ms
1.3 ms
Measureme nt Time
11 ms
39 ms
12 ms
Channel Selected
Remote 1 temperature
Local temperature
Remote 2 temperature
Overtemperature Events
Overtemperature even
be detected and dealt with automatically in automatic fan sp
control mode. Register 0x6A to Register 0x6C are the THERM
limits. When a temperature exceeds its THERM limit, all PWM
outputs run at 100% duty cycle or the maximum PWM duty
cycle (Register 0x38, Register 0x39, and Register 0x3A) if Bi
of Configuration Register 4 (0x7D) is set. The fans remain
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 (0x78), Bit 2. The
hysteresis value for that THERM limit is the value programmed
into the hysteresis registers (Register 0x6D and Register 0x6E
The default hysteresis value is 4°C.
THERM LIMIT
TEMPERATURE
FANS
this
ture
Rev. A | Page 19 of 76
ts on any of the temperature channels can
HYSTERESIS (°C)
100%
Figure 25. THERM Limit Operation
ADT7473
eed
t 3
).